diff --git a/src/lib/client/dune b/src/lib/client/dune
index dace844303..3edced7df5 100644
--- a/src/lib/client/dune
+++ b/src/lib/client/dune
@@ -28,7 +28,8 @@
   logs.browser
   cohttp
   tyxml
-  reactiveData)
+  reactiveData
+  eio)
  (foreign_stubs
   (language c)
   (names eliom_stubs))
diff --git a/src/lib/client/eliommod_dom.ml b/src/lib/client/eliommod_dom.ml
index 54028c8fb9..41f82c9369 100644
--- a/src/lib/client/eliommod_dom.ml
+++ b/src/lib/client/eliommod_dom.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -479,7 +479,7 @@ let fetch_linked_css e =
           let css =
             Eliom_request.http_get href [] Eliom_request.string_result
           in
-          acc @ [e, (e##.media, href, css >|= snd)]
+          acc @ [e, (e##.media, href, snd css)]
     | Dom.Element e ->
         let c = e##.childNodes in
         let acc = ref acc in
@@ -578,26 +578,25 @@ let rewrite_css_url ~prefix css pos =
 let import_re = Regexp.regexp "@import\\s*"
 
 let rec rewrite_css ~max (media, href, css) =
-  Lwt.catch
-    (fun () ->
-       css >>= function
-       | None -> Lwt.return_nil
-       | Some css ->
-           if !Eliom_config.debug_timings
-           then Console.console##(time (Js.string ("rewrite_CSS: " ^ href)));
-           let* imports, css =
-             rewrite_css_import ~max ~prefix:(basedir href) ~media css 0
-           in
-           if !Eliom_config.debug_timings
-           then Console.console##(timeEnd (Js.string ("rewrite_CSS: " ^ href)));
-           Lwt.return (imports @ [media, css]))
-    (fun _ -> Lwt.return [media, Printf.sprintf "@import url(%s);" href])
+  try
+    match css with
+    | None -> []
+    | Some css ->
+        if !Eliom_config.debug_timings
+        then Console.console##(time (Js.string ("rewrite_CSS: " ^ href)));
+        let imports, css =
+          rewrite_css_import ~max ~prefix:(basedir href) ~media css 0
+        in
+        if !Eliom_config.debug_timings
+        then Console.console##(timeEnd (Js.string ("rewrite_CSS: " ^ href)));
+        imports @ [media, css]
+  with _ -> [media, Printf.sprintf "@import url(%s);" href]
 
 and rewrite_css_import ?(charset = "") ~max ~prefix ~media css pos =
   match Regexp.search import_re css pos with
   | None ->
       (* No @import anymore, rewrite url. *)
-      Lwt.return ([], rewrite_css_url ~prefix css pos)
+      [], rewrite_css_url ~prefix css pos
   | Some (i, res) -> (
       (* Found @import rule, try to preload. *)
       let init = String.sub css pos (i - pos) in
@@ -606,45 +605,46 @@ and rewrite_css_import ?(charset = "") ~max ~prefix ~media css pos =
         let i = i + String.length (Regexp.matched_string res) in
         let i, href = parse_url ~prefix css i in
         let i, media' = parse_media css i in
-        let* import =
-          if max = 0
-          then
-            (* Maximum imbrication of @import reached, rewrite url. *)
-            Lwt.return
-              [media, Printf.sprintf "@import url('%s') %s;\n" href media']
-          else if media##.length > 0 && String.length media' > 0
-          then
-            (* TODO combine media if possible...
+        let (imports, css), import =
+          Fiber.pair
+            (fun () -> rewrite_css_import ~charset ~max ~prefix ~media css i)
+            (fun () ->
+               if
+                 (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+                 max = 0
+               then
+                 (* Maximum imbrication of @import reached, rewrite url. *)
+                 [media, Printf.sprintf "@import url('%s') %s;\n" href media']
+               else if media##.length > 0 && String.length media' > 0
+               then
+                 (* TODO combine media if possible...
                in the mean time keep explicit import. *)
-            Lwt.return
-              [media, Printf.sprintf "@import url('%s') %s;\n" href media']
-          else
-            let media =
-              if media##.length > 0 then media else Js.string media'
-            in
-            let css =
-              Eliom_request.http_get href [] Eliom_request.string_result
-            in
-            rewrite_css ~max:(max - 1) (media, href, css >|= snd)
-        and* imports, css =
-          rewrite_css_import ~charset ~max ~prefix ~media css i
+                 [media, Printf.sprintf "@import url('%s') %s;\n" href media']
+               else
+                 let media =
+                   if media##.length > 0 then media else Js.string media'
+                 in
+                 let css =
+                   Eliom_request.http_get href [] Eliom_request.string_result
+                 in
+                 rewrite_css ~max:(max - 1) (media, href, snd css))
         in
-        Lwt.return (import @ imports, css)
+        import @ imports, css
       with
-      | Incorrect_url -> Lwt.return ([], rewrite_css_url ~prefix css pos)
+      | Incorrect_url -> [], rewrite_css_url ~prefix css pos
       | exn ->
           Logs.info ~src:section (fun fmt ->
             fmt
               ("Error while importing css" ^^ "@\n%s")
               (Printexc.to_string exn));
-          Lwt.return ([], rewrite_css_url ~prefix css pos))
+          [], rewrite_css_url ~prefix css pos)
 
 let max_preload_depth = ref 4
 
 let build_style (e, css) =
-  let* css = rewrite_css ~max:!max_preload_depth css in
-  (* lwt css = *)
-  Lwt_list.map_p
+  let css = rewrite_css ~max:!max_preload_depth css in
+  Fiber.List.map
+    (* lwt css = *)
     (fun (media, css) ->
        let style = Dom_html.createStyle Dom_html.document in
        style##._type := Js.string "text/css";
@@ -655,7 +655,7 @@ let build_style (e, css) =
        if Js.Optdef.test styleSheet
        then Js.Unsafe.(set styleSheet (Js.string "cssText") (Js.string css))
        else style##.innerHTML := Js.string css;
-       Lwt.return (e, (style :> Dom.node Js.t)))
+       e, (style :> Dom.node Js.t))
     css
 
 (* IE8 doesn't allow appendChild on noscript-elements *)
@@ -669,7 +669,7 @@ let build_style (e, css) =
 let preload_css (doc : Dom_html.element Js.t) =
   if !Eliom_config.debug_timings
   then Console.console##(time (Js.string "preload_css (fetch+rewrite)"));
-  let* css = Lwt_list.map_p build_style (fetch_linked_css (get_head doc)) in
+  let css = Fiber.List.map build_style (fetch_linked_css (get_head doc)) in
   let css = List.concat css in
   List.iter
     (fun (e, css) ->
@@ -682,8 +682,7 @@ let preload_css (doc : Dom_html.element Js.t) =
              section (fun fmt -> fmt "Unique CSS skipped..."))
     css;
   if !Eliom_config.debug_timings
-  then Console.console##(timeEnd (Js.string "preload_css (fetch+rewrite)"));
-  Lwt.return_unit
+  then Console.console##(timeEnd (Js.string "preload_css (fetch+rewrite)"))
 
 (** Window scrolling *)
 
diff --git a/src/lib/client/eliommod_dom.mli b/src/lib/client/eliommod_dom.mli
index 5286bd8e50..70267dcd90 100644
--- a/src/lib/client/eliommod_dom.mli
+++ b/src/lib/client/eliommod_dom.mli
@@ -71,7 +71,7 @@ val html_document :
 (** Assuming [d] has a body and head element, [html_document d] will
     return the same document as html *)
 
-val preload_css : Dom_html.element Js.t -> unit Lwt.t
+val preload_css : Dom_html.element Js.t -> unit
 (** [preload_css e] downloads every css included in every link
     elements that is a descendant of [e] and replace it and its linked
     css by inline [<style>] elements *)
diff --git a/src/lib/eliom_bus.client.ml b/src/lib/eliom_bus.client.ml
index 2440901be2..c296ea4235 100644
--- a/src/lib/eliom_bus.client.ml
+++ b/src/lib/eliom_bus.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -27,36 +27,16 @@ let section = Logs.Src.create "eliom:bus"
 
 module Ecb = Eliom_comet_base
 
+type 'a consumers = {mutable consumers : ('a option -> unit) list}
+
 type ('a, 'b) t =
   { channel : 'b Ecb.wrapped_channel
-  ; stream : 'b Lwt_stream.t Lazy.t
+  ; consumers : 'b consumers Lazy.t
   ; queue : 'a Queue.t
   ; mutable max_size : int
-  ; write : 'a list -> unit Lwt.t
-  ; mutable waiter : unit -> unit Lwt.t
-  ; mutable last_wait : unit Lwt.t
-  ; mutable original_stream_available : bool
-  ; error_h : 'b option Lwt.t * exn Lwt.u }
-
-(* clone streams such that each clone of the original stream raise the same exceptions *)
-let consume (t, u) s =
-  let t' =
-    Lwt.catch
-      (fun () -> Lwt_stream.iter (fun _ -> ()) s)
-      (fun e ->
-         (match Lwt.state t with Lwt.Sleep -> Lwt.wakeup_exn u e | _ -> ());
-         Lwt.fail e)
-  in
-  Lwt.choose [Lwt.bind t (fun _ -> Lwt.return_unit); t']
-
-let clone_exn (t, u) s =
-  let s' = Lwt_stream.clone s in
-  Lwt_stream.from (fun () ->
-    Lwt.catch
-      (fun () -> Lwt.choose [Lwt_stream.get s'; t])
-      (fun e ->
-         (match Lwt.state t with Lwt.Sleep -> Lwt.wakeup_exn u e | _ -> ());
-         Lwt.fail e))
+  ; write : 'a list -> unit
+  ; mutable waiter : unit -> unit
+  ; mutable last_wait : unit Promise.t }
 
 type ('a, 'att, 'co, 'ext, 'reg) callable_bus_service =
   ( unit
@@ -72,57 +52,47 @@ type ('a, 'att, 'co, 'ext, 'reg) callable_bus_service =
     , Eliom_registration.Action.return )
     Eliom_service.t
 
-let create service channel waiter =
-  let write x =
-    Lwt.catch
-      (fun () ->
-         let* _ =
-           Eliom_client.call_service
-             ~service:(service :> ('a, _, _, _, _) callable_bus_service)
-             () x
-         in
-         Lwt.return_unit)
-      (function
-        | Eliom_request.Failed_request 204 -> Lwt.return_unit
-        | exc -> Lwt.reraise exc)
-  in
-  let error_h =
-    let t, u = Lwt.wait () in
-    ( Lwt.catch
-        (fun () ->
-           let* _ = t in
-           assert false)
-        (fun e -> Lwt.fail e)
-    , u )
-  in
-  let stream =
-    lazy
-      (let stream = Eliom_comet.register channel in
-       (* iterate on the stream to consume messages: avoid memory leak *)
-       let _ = consume error_h stream in
-       stream)
+(** Register a callback in the underlying comet. *)
+let comet_register chan =
+  let t = {consumers = []} in
+  let notify data = List.iter (fun callback -> callback data) t.consumers in
+  let teardown () =
+    let
+        (* Notify that the channel reached its end. Clear the [consumers] list to
+       avoid memory leaks. *)
+          ()
+      =
+      notify None
+    in
+    t.consumers <- []
   in
-  let t =
-    { channel
-    ; stream
-    ; queue = Queue.create ()
-    ; max_size = 20
-    ; write
-    ; waiter
-    ; last_wait = Lwt.return_unit
-    ; original_stream_available = true
-    ; error_h }
-  in
-  (* the comet channel start receiving after the load phase, so the
-     original channel (i.e. without message lost) is only available in
-     the first loading phase. *)
-  let _ =
-    let* () = Eliom_client.wait_load_end () in
-    t.original_stream_available <- false;
-    Lwt.return_unit
+  let _chan =
+    Eliom_comet.register_wrapped chan (function
+      | Some data -> notify (Some data)
+      | None -> teardown ())
   in
   t
 
+let create service channel waiter =
+  let write x =
+    try
+      let _ =
+        Eliom_client.call_service
+          ~service:(service :> ('a, _, _, _, _) callable_bus_service)
+          () x
+      in
+      ()
+    with Eliom_request.Failed_request 204 -> ()
+  in
+  let consumers = lazy (comet_register channel) in
+  { channel
+  ; consumers
+  ; queue = Queue.create ()
+  ; max_size = 20
+  ; write
+  ; waiter
+  ; last_wait = () }
+
 let internal_unwrap ((wrapped_bus : ('a, 'b) Ecb.wrapped_bus), _unwrapper) =
   let waiter () = Js_of_ocaml_lwt.Lwt_js.sleep 0.05 in
   let channel, Eliom_comet_base.Bus_send_service service = wrapped_bus in
@@ -131,28 +101,31 @@ let internal_unwrap ((wrapped_bus : ('a, 'b) Ecb.wrapped_bus), _unwrapper) =
 let () =
   Eliom_unwrap.register_unwrapper Eliom_common.bus_unwrap_id internal_unwrap
 
-let stream t = clone_exn t.error_h (Lazy.force t.stream)
-
-let original_stream t =
-  if Eliom_client_core.in_onload () && t.original_stream_available
-  then stream t
-  else
-    raise_error ~section
-      "original_stream: the original stream is not available anymore"
+let register t callback =
+  let (lazy c) = t.consumers in
+  c.consumers <- callback :: c.consumers
 
 let flush t =
   let l = List.rev (Queue.fold (fun l v -> v :: l) [] t.queue) in
   Queue.clear t.queue; t.write l
 
 let try_flush t =
-  Lwt.cancel t.last_wait;
+  Lwt.cancel
+    (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+    (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+    t.last_wait;
   if Queue.length t.queue >= t.max_size
   then flush t
   else
-    let th = Lwt.protected (t.waiter ()) in
+    let th =
+      Lwt.protected
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        (t.waiter ())
+    in
     t.last_wait <- th;
-    let _ = th >>= fun () -> flush t in
-    Lwt.return_unit
+    let _ = th; flush t in
+    ()
 
 let write t v = Queue.add v t.queue; try_flush t
 let close {channel; _} = Eliom_comet.close channel
@@ -160,6 +133,8 @@ let set_queue_size b s = b.max_size <- s
 
 let set_time_before_flush b t =
   b.waiter <-
-    (if t <= 0. then Lwt.pause else fun () -> Js_of_ocaml_lwt.Lwt_js.sleep t)
+    (if t <= 0.
+     then fun x1 -> Fiber.yield x1
+     else fun () -> Js_of_ocaml_lwt.Lwt_js.sleep t)
 
 let force_link = ()
diff --git a/src/lib/eliom_bus.client.mli b/src/lib/eliom_bus.client.mli
index 06950d8396..d75fc55e27 100644
--- a/src/lib/eliom_bus.client.mli
+++ b/src/lib/eliom_bus.client.mli
@@ -25,21 +25,13 @@
 
 type ('a, 'b) t
 
-val stream : ('a, 'b) t -> 'b Lwt_stream.t
-(** [stream b] returns the stream of data sent to bus [b]. A new
-    stream is created each time this function is called. Some messages
-    from the bus can be lost if they were sent before the call to
-    [stream]. If you need to receive every message, use original stream
-    instead. *)
+val register : ('a, 'b) t -> ('b option -> unit) -> unit
+(** Register a callback that will get called on every messages from the server.
+    Messages received before the call to [register] are lost. The callback is
+    called with [Some data] when receiving a message from the server or with
+    [None] when no more data will be received. *)
 
-val original_stream : ('a, 'b) t -> 'b Lwt_stream.t
-(** [stream b] returns the stream of data sent to bus [b]. A new
-    stream is created each time this function is called. Every
-    messages sent to the bus after the generation of the page are
-    received. This function can be called only in the onload event
-    handler, if called outside, it will raise a Failure. *)
-
-val write : ('a, 'b) t -> 'a -> unit Lwt.t
+val write : ('a, 'b) t -> 'a -> unit
 (** [write b v] send [v] to the bus [b]. Every participant of the bus
     will receive [v], including the sender. *)
 
diff --git a/src/lib/eliom_bus.server.ml b/src/lib/eliom_bus.server.ml
index 6ba8b81e20..e47f630ee2 100644
--- a/src/lib/eliom_bus.server.ml
+++ b/src/lib/eliom_bus.server.ml
@@ -1,5 +1,3 @@
-open Lwt.Syntax
-
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2010
@@ -27,7 +25,7 @@ type ('a, 'b) t =
   ; scope : Eliom_comet.Channel.comet_scope
   ; name : string option
   ; channel : 'b Eliom_comet.Channel.t option
-  ; write : 'a -> unit Lwt.t
+  ; write : 'a -> unit
   ; service : 'a Ecb.bus_send_service
   ; service_registered : bool Eliom_state.volatile_table option
   ; size : int option
@@ -36,7 +34,7 @@ type ('a, 'b) t =
 
 let register_sender scope service write =
   Eliom_registration.Action.register ~scope ~options:`NoReload ~service
-    (fun () x -> Lwt_list.iter_s write x)
+    (fun () x -> List.iter write x)
 
 let internal_wrap (bus : ('a, 'b) t) :
   ('a, 'b) Ecb.wrapped_bus * Eliom_common.unwrapper
@@ -94,8 +92,8 @@ let create_filtered ?scope ?name ?size ~filter typ =
   (*The stream*)
   let stream, push = Lwt_stream.create () in
   let push x =
-    let* y = filter x in
-    push (Some y); Lwt.return_unit
+    let y = filter x in
+    push (Some y)
   in
   let scope =
     match scope with
@@ -144,7 +142,7 @@ let create_filtered ?scope ?name ?size ~filter typ =
   bus
 
 let create ?scope ?name ?size typ =
-  create_filtered ~filter:Lwt.return ?scope ?name ?size typ
+  create_filtered ~filter:(fun x1 -> x1) ?scope ?name ?size typ
 
 let stream bus =
   match bus.scope with `Site -> bus.stream | `Client_process _ -> bus.stream
diff --git a/src/lib/eliom_bus.server.mli b/src/lib/eliom_bus.server.mli
index c7debfed13..0aea9de789 100644
--- a/src/lib/eliom_bus.server.mli
+++ b/src/lib/eliom_bus.server.mli
@@ -56,7 +56,7 @@ val create_filtered :
    ?scope:[< Eliom_comet.Channel.comet_scope]
   -> ?name:string
   -> ?size:int
-  -> filter:('a -> 'b Lwt.t)
+  -> filter:('a -> 'b)
   -> 'a Deriving_Json.t
   -> ('a, 'b) t
 (** Same as [create], but data is filtered through [filter] function
@@ -70,6 +70,6 @@ val stream : ('a, 'b) t -> 'b Lwt_stream.t
     return the same stream. If you want to receive multiple times the
     same data, you should copy the stream with [Lwt_stream.clone] *)
 
-val write : ('a, 'b) t -> 'a -> unit Lwt.t
+val write : ('a, 'b) t -> 'a -> unit
 (** [write b x] sends the value [x] on the bus [b]. Every participant,
     including the server, will receive [x]. *)
diff --git a/src/lib/eliom_client.client.ml b/src/lib/eliom_client.client.ml
index 857a51b63e..b942971569 100644
--- a/src/lib/eliom_client.client.ml
+++ b/src/lib/eliom_client.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -39,8 +39,8 @@ type changepage_event =
   ; origin_id : int
   ; target_id : int option }
 
-let run_lwt_callbacks : 'a -> ('a -> unit Lwt.t) list -> unit Lwt.t =
- fun ev handlers -> Lwt_list.iter_s (fun h -> h ev) handlers
+let run_lwt_callbacks : 'a -> ('a -> unit) list -> unit =
+ fun ev handlers -> List.iter (fun h -> h ev) handlers
 
 let (onload, _, flush_onload, _push_onload) :
   ((unit -> unit) -> unit)
@@ -50,9 +50,9 @@ let (onload, _, flush_onload, _push_onload) :
   =
   Eliom_client_core.create_buffer ()
 
-let ( (onchangepage : (changepage_event -> unit Lwt.t) -> unit)
+let ( (onchangepage : (changepage_event -> unit) -> unit)
     , _
-    , (flush_onchangepage : unit -> (changepage_event -> unit Lwt.t) list)
+    , (flush_onchangepage : unit -> (changepage_event -> unit) list)
     , _ )
   =
   Eliom_client_core.create_buffer ()
@@ -77,8 +77,12 @@ let run_onunload_wrapper set_content cancel =
       set_content ()
 
 let lwt_onload () =
-  let t, u = Lwt.wait () in
-  onload (Lwt.wakeup u);
+  let t, u =
+    Promise.create
+      (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+      ()
+  in
+  onload (fun x1 -> Promise.resolve u x1);
   t
 
 (* == Initialize the client values sent with a request *)
@@ -202,7 +206,7 @@ let form_handler :
       if String.lowercase_ascii (Js.to_string form##._method) = "get"
       then `Form_get
       else `Form_post
-    and f _ = Lwt.return_false in
+    and f _ = false in
     Js.bool
       (Eliom_client_core.raw_form_handler form kind
          (get_element_cookies_info form)
@@ -428,17 +432,16 @@ let scroll_to_fragment ?offset fragment =
         let elem = Dom_html.document##(getElementById (Js.string fragment)) in
         Js.Opt.iter elem scroll_to_element)
 
-let with_progress_cursor : 'a Lwt.t -> 'a Lwt.t =
+let with_progress_cursor : 'a Promise.t -> 'a =
  fun t ->
-  Lwt.catch
-    (fun () ->
-       Dom_html.document##.body##.style##.cursor := Js.string "progress";
-       let* res = t in
-       Dom_html.document##.body##.style##.cursor := Js.string "auto";
-       Lwt.return res)
-    (fun exn ->
-       Dom_html.document##.body##.style##.cursor := Js.string "auto";
-       Lwt.fail exn)
+  try
+    Dom_html.document##.body##.style##.cursor := Js.string "progress";
+    let res = t in
+    Dom_html.document##.body##.style##.cursor := Js.string "auto";
+    res
+  with exn ->
+    Dom_html.document##.body##.style##.cursor := Js.string "auto";
+    raise exn
 
 (* Type for partially unwrapped elt. *)
 type tmp_recontent =
@@ -634,8 +637,7 @@ type page =
   ; mutable previous_page : int option
   ; set_page_status : ?step:React.step -> Page_status_t.t -> unit
   ; mutable dom : Dom_html.bodyElement Js.t option
-  ; mutable reload_function :
-      (unit -> unit -> Eliom_service.result Lwt.t) option }
+  ; mutable reload_function : (unit -> unit -> Eliom_service.result) option }
 
 let string_of_page p =
   Printf.sprintf "%d/%d %s %s %d %b" p.page_unique_id p.page_id.state_index
@@ -696,10 +698,10 @@ let set_active_page p =
 
 (* This key serves as a hook to access the page the currently running code is
    generating. *)
-let this_page : page Lwt.key = Lwt.new_key ()
+let this_page : page Fiber.key = Fiber.create_key ()
 
 let get_this_page () =
-  match Lwt.get this_page with
+  match Fiber.get this_page with
   | Some p -> p
   | None ->
       Logs.debug ~src:section_page (fun fmt -> fmt "No page in context");
@@ -713,7 +715,10 @@ let with_new_page ?state_id ?old_page ~replace () f =
     | None -> None, None
   in
   let page = mk_page ?state_id ?url ?previous_page ~status:Generating () in
-  Lwt.with_value this_page (Some page) f
+  (Stdlib.Option.fold ~none:Fiber.without_binding
+     ~some:(Fun.flip Fiber.with_binding)
+     (Some page))
+    this_page f
 
 module History = struct
   let section = Logs.Src.create "eliom:client:history"
@@ -845,7 +850,7 @@ let update_state () =
 let lock_request_handling = Eliom_request.lock
 let unlock_request_handling = Eliom_request.unlock
 
-type ('a, +'b) server_function = 'a -> 'b Lwt.t
+type ('a, +'b) server_function = 'a -> 'b
 
 let only_replace_body = ref false
 let persist_document_head () = only_replace_body := true
@@ -1006,58 +1011,65 @@ let init () =
         onload_handler := None
     | None -> ());
     Eliom_client_core.set_initial_load ();
-    Lwt.async (fun () ->
-      if !Eliom_config.debug_timings
-      then Console.console##(time (Js.string "onload"));
-      let* () =
-        Eliom_request_info.set_session_info
-          ~uri:
-            (String.concat "/"
-               (Eliom_request_info.get_csp_original_full_path ()))
-          js_data.Eliom_common.ejs_sess_info
-        @@ fun () -> Lwt.return_unit
-      in
-      (* Give the browser the chance to actually display the page NOW *)
-      let* () = Js_of_ocaml_lwt.Lwt_js.sleep 0.001 in
-      (* Ordering matters. See [Eliom_client.set_content] for explanations *)
-      relink_request_nodes Dom_html.document##.documentElement;
-      let root = Dom_html.document##.documentElement in
-      let closure_nodeList, attrib_nodeList =
-        relink_page_but_client_values root
-      in
-      do_request_data js_data.Eliom_common.ejs_request_data;
-      (* XXX One should check that all values have been unwrapped.
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         if !Eliom_config.debug_timings
+         then Console.console##(time (Js.string "onload"));
+         let () =
+           Eliom_request_info.set_session_info
+             ~uri:
+               (String.concat "/"
+                  (Eliom_request_info.get_csp_original_full_path ()))
+             js_data.Eliom_common.ejs_sess_info
+           @@ fun () -> ()
+         in
+         let
+             (* Give the browser the chance to actually display the page NOW *)
+               ()
+           =
+           Js_of_ocaml_lwt.Lwt_js.sleep 0.001
+         in
+         (* Ordering matters. See [Eliom_client.set_content] for explanations *)
+         relink_request_nodes Dom_html.document##.documentElement;
+         let root = Dom_html.document##.documentElement in
+         let closure_nodeList, attrib_nodeList =
+           relink_page_but_client_values root
+         in
+         do_request_data js_data.Eliom_common.ejs_request_data;
+         (* XXX One should check that all values have been unwrapped.
             In fact, client values should be special and all other values
             should be eagerly unwrapped. *)
-      let () =
-        relink_attribs root js_data.Eliom_common.ejs_client_attrib_table
-          attrib_nodeList
-      in
-      let onload_closure_nodes =
-        relink_closure_nodes root js_data.Eliom_common.ejs_event_handler_table
-          closure_nodeList
-      in
-      Eliom_client_core.reset_request_nodes ();
-      Eliommod_dom.add_formdata_hack_onclick_handler ();
-      if not (is_client_app ()) then dom_history_ready := true;
-      let load_callbacks =
-        flush_onload ()
-        @ [onload_closure_nodes; Eliom_client_core.broadcast_load_end]
-      in
-      Lwt_mutex.unlock Eliom_client_core.load_mutex;
-      run_callbacks load_callbacks;
-      if !Eliom_config.debug_timings
-      then Console.console##(timeEnd (Js.string "onload"));
-      Lwt.return_unit);
+         let () =
+           relink_attribs root js_data.Eliom_common.ejs_client_attrib_table
+             attrib_nodeList
+         in
+         let onload_closure_nodes =
+           relink_closure_nodes root
+             js_data.Eliom_common.ejs_event_handler_table closure_nodeList
+         in
+         Eliom_client_core.reset_request_nodes ();
+         Eliommod_dom.add_formdata_hack_onclick_handler ();
+         if not (is_client_app ()) then dom_history_ready := true;
+         let load_callbacks =
+           flush_onload ()
+           @ [onload_closure_nodes; Eliom_client_core.broadcast_load_end]
+         in
+         Eio.Mutex.unlock Eliom_client_core.load_mutex;
+         run_callbacks load_callbacks;
+         if !Eliom_config.debug_timings
+         then Console.console##(timeEnd (Js.string "onload")));
     Js._false
   in
   Logs.debug ~src:section (fun fmt -> fmt "Set load/onload events");
   if Dom_html.document##.readyState = Js.string "complete"
   then
-    Lwt.async @@ fun () ->
-    let* () = Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame () in
-    let _ = onload () in
-    Lwt.return_unit
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         let () = Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame () in
+         let _ = onload () in
+         ())
   else
     onload_handler :=
       Some
@@ -1165,7 +1177,7 @@ let raw_call_service
      Also set with_credentials to true in CORS configuration.
   *)
   let with_credentials = not (Eliom_service.is_external service) in
-  let* uri, content =
+  let uri, content =
     match
       create_request_ ?absolute ?absolute_path ?https ~service ?hostname ?port
         ?fragment ?keep_nl_params ?nl_params ?keep_get_na_params get_params
@@ -1193,8 +1205,8 @@ let raw_call_service
           Eliom_request.string_result
   in
   match content with
-  | None -> Lwt.fail (Eliom_request.Failed_request 204)
-  | Some content -> Lwt.return (uri, content)
+  | None -> raise (Eliom_request.Failed_request 204)
+  | Some content -> uri, content
 
 let call_service
       ?absolute
@@ -1213,12 +1225,12 @@ let call_service
       get_params
       post_params
   =
-  let* _, content =
+  let _, content =
     raw_call_service ?absolute ?absolute_path ?https ~service ?hostname ?port
       ?fragment ?keep_nl_params ?nl_params ?keep_get_na_params ?progress
       ?upload_progress ?override_mime_type get_params post_params
   in
-  Lwt.return content
+  content
 
 (* == Leave an application. *)
 
@@ -1288,7 +1300,7 @@ let unwrap_caml_content content =
   let r : 'a Eliom_runtime.eliom_caml_service_data =
     Eliom_unwrap.unwrap (Url.decode content) 0
   in
-  Lwt.return (r.Eliom_runtime.ecs_data, r.Eliom_runtime.ecs_request_data)
+  r.Eliom_runtime.ecs_data, r.Eliom_runtime.ecs_request_data
 
 let call_ocaml_service
       ?absolute
@@ -1308,22 +1320,22 @@ let call_ocaml_service
       post_params
   =
   Logs.debug ~src:section (fun fmt -> fmt "Call OCaml service");
-  let* _, content =
+  let _, content =
     raw_call_service ?absolute ?absolute_path ?https ~service ?hostname ?port
       ?fragment ?keep_nl_params ?nl_params ?keep_get_na_params ?progress
       ?upload_progress ?override_mime_type get_params post_params
   in
-  let* () = Lwt_mutex.lock Eliom_client_core.load_mutex in
+  let () = Eio.Mutex.lock Eliom_client_core.load_mutex in
   Eliom_client_core.set_loading_phase ();
-  let* content, request_data = unwrap_caml_content content in
+  let content, request_data = unwrap_caml_content content in
   do_request_data request_data;
   Eliom_client_core.reset_request_nodes ();
   let load_callbacks = [Eliom_client_core.broadcast_load_end] in
-  Lwt_mutex.unlock Eliom_client_core.load_mutex;
+  Eio.Mutex.unlock Eliom_client_core.load_mutex;
   run_callbacks load_callbacks;
   match content with
-  | `Success result -> Lwt.return result
-  | `Failure msg -> Lwt.fail (Eliom_client_value.Exception_on_server msg)
+  | `Success result -> result
+  | `Failure msg -> raise (Eliom_client_value.Exception_on_server msg)
 
 (* == Current uri.
 
@@ -1351,9 +1363,11 @@ let set_current_uri, get_current_uri =
     let current_uri = fst (Url.split_fragment uri) in
     (get_this_page ()).url <- current_uri;
     let path, all_get_params = path_and_args_of_uri current_uri in
-    Lwt.async @@ fun () ->
-    Eliom_request_info.update_session_info ~path ~all_get_params
-      ~all_post_params:None (fun () -> Lwt.return_unit)
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         Eliom_request_info.update_session_info ~path ~all_get_params
+           ~all_post_params:None (fun () -> ()))
   in
   let get_current_uri () = (get_this_page ()).url in
   set_current_uri, get_current_uri
@@ -1438,11 +1452,22 @@ module Page_status = struct
     @@ Events.inactive ()
 
   let while_active ?now ?(stop = React.E.never) action =
-    let thread = ref Lwt.return_unit in
+    let thread = ref () in
     onactive ?now ~stop (fun () -> thread := action ());
-    oninactive ~stop (fun () -> Lwt.cancel !thread);
+    oninactive ~stop (fun () ->
+      Lwt.cancel
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        !thread);
     Dom_reference.retain_generic (get_this_page ())
-      ~keep:(React.E.map (fun () -> Lwt.cancel !thread) stop)
+      ~keep:
+        (React.E.map
+           (fun () ->
+              Lwt.cancel
+                (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+                (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+                !thread)
+           stop)
 end
 
 let is_in_cache state_id =
@@ -1534,17 +1559,16 @@ let set_template_content ~replace ~uri ?fragment =
     (match fragment with
     | None -> change_url_string ~replace uri
     | Some fragment -> change_url_string ~replace (uri ^ "#" ^ fragment));
-    let* () = Lwt_mutex.lock Eliom_client_core.load_mutex in
-    let* (), request_data = unwrap_caml_content content in
+    let () = Eio.Mutex.lock Eliom_client_core.load_mutex in
+    let (), request_data = unwrap_caml_content content in
     do_request_data request_data;
     Eliom_client_core.reset_request_nodes ();
     let load_callbacks = flush_onload () in
-    Lwt_mutex.unlock Eliom_client_core.load_mutex;
-    run_callbacks load_callbacks;
-    Lwt.return_unit
-  and cancel () = Lwt.return_unit in
+    Eio.Mutex.unlock Eliom_client_core.load_mutex;
+    run_callbacks load_callbacks
+  and cancel () = () in
   function
-  | None -> Lwt.return_unit
+  | None -> ()
   | Some content -> run_onunload_wrapper (really_set content) cancel
 
 let set_uri ~replace ?fragment uri =
@@ -1578,7 +1602,7 @@ let set_content_local ?offset ?fragment new_page =
   Logs.debug ~src:section_page (fun fmt -> fmt "Set content local");
   let locked = ref true in
   let recover () =
-    if !locked then Lwt_mutex.unlock Eliom_client_core.load_mutex;
+    if !locked then Eio.Mutex.unlock Eliom_client_core.load_mutex;
     if !Eliom_config.debug_timings
     then Console.console##(timeEnd (Js.string "set_content_local"))
   and really_set () =
@@ -1586,12 +1610,10 @@ let set_content_local ?offset ?fragment new_page =
        Otherwise, the browser start to display the page before
        loading the CSS. *)
     let preloaded_css =
-      if !only_replace_body
-      then Lwt.return_unit
-      else Eliommod_dom.preload_css new_page
+      if !only_replace_body then () else Eliommod_dom.preload_css new_page
     in
     (* Wait for CSS to be inlined before substituting global nodes: *)
-    let* () = preloaded_css in
+    let () = preloaded_css in
     (* Really change page contents *)
     replace_page ~do_insert_base:true new_page;
     Eliommod_dom.add_formdata_hack_onclick_handler ();
@@ -1600,35 +1622,33 @@ let set_content_local ?offset ?fragment new_page =
       flush_onload () @ [Eliom_client_core.broadcast_load_end]
     in
     locked := false;
-    Lwt_mutex.unlock Eliom_client_core.load_mutex;
+    Eio.Mutex.unlock Eliom_client_core.load_mutex;
     (* run callbacks upon page activation (or now), but just once *)
     Page_status.onactive ~once:true (fun () -> run_callbacks load_callbacks);
     scroll_to_fragment ?offset fragment;
     advance_page ();
     if !Eliom_config.debug_timings
-    then Console.console##(timeEnd (Js.string "set_content_local"));
-    Lwt.return_unit
+    then Console.console##(timeEnd (Js.string "set_content_local"))
   in
-  let cancel () = recover (); Lwt.return_unit in
-  Lwt.catch
-    (fun () ->
-       let* () = Lwt_mutex.lock Eliom_client_core.load_mutex in
-       Eliom_client_core.set_loading_phase ();
-       if !Eliom_config.debug_timings
-       then Console.console##(time (Js.string "set_content_local"));
-       run_onunload_wrapper really_set cancel)
-    (fun exn ->
-       recover ();
-       Logs.debug ~src:section (fun fmt ->
-         fmt ("set_content_local" ^^ "@\n%s") (Printexc.to_string exn));
-       Lwt.fail exn)
+  let cancel () = recover () in
+  try
+    let () = Eio.Mutex.lock Eliom_client_core.load_mutex in
+    Eliom_client_core.set_loading_phase ();
+    if !Eliom_config.debug_timings
+    then Console.console##(time (Js.string "set_content_local"));
+    run_onunload_wrapper really_set cancel
+  with exn ->
+    recover ();
+    Logs.debug ~src:section (fun fmt ->
+      fmt ("set_content_local" ^^ "@\n%s") (Printexc.to_string exn));
+    raise exn
 
 (* Function to be called for server side services: *)
 let set_content ~replace ~uri ?offset ?fragment content =
   Logs.debug ~src:section_page (fun fmt -> fmt "Set content");
   (* TODO: too early? *)
   let target_uri = uri in
-  let* () =
+  let () =
     run_lwt_callbacks
       { in_cache = is_in_cache !active_page.page_id
       ; origin_uri = get_current_uri ()
@@ -1638,8 +1658,8 @@ let set_content ~replace ~uri ?offset ?fragment content =
       (flush_onchangepage ())
   in
   match content with
-  | None -> Lwt.return_unit
-  | Some content ->
+  | None -> ()
+  | Some content -> (
       let locked = ref true in
       let really_set () =
         reload_function := None;
@@ -1654,9 +1674,7 @@ let set_content ~replace ~uri ?offset ?fragment content =
          Otherwise, the browser start to display the page before
          loading the CSS. *)
         let preloaded_css =
-          if !only_replace_body
-          then Lwt.return_unit
-          else Eliommod_dom.preload_css fake_page
+          if !only_replace_body then () else Eliommod_dom.preload_css fake_page
         in
         (* Unique nodes of scope request must be bound before the
          unmarshalling/unwrapping of page data. *)
@@ -1673,8 +1691,12 @@ let set_content ~replace ~uri ?offset ?fragment content =
           | _ -> None
         in
         Eliommod_cookies.update_cookie_table host cookies;
-        (* Wait for CSS to be inlined before substituting global nodes: *)
-        let* () = preloaded_css in
+        let
+            (* Wait for CSS to be inlined before substituting global nodes: *)
+              ()
+          =
+          preloaded_css
+        in
         (* Bind unique node (request and global) and register event
          handler.  Relinking closure nodes must take place after
          initializing the client values *)
@@ -1711,31 +1733,29 @@ let set_content ~replace ~uri ?offset ?fragment content =
           flush_onload ()
           @ [onload_closure_nodes; Eliom_client_core.broadcast_load_end]
         in
-        Lwt_mutex.unlock Eliom_client_core.load_mutex;
+        Eio.Mutex.unlock Eliom_client_core.load_mutex;
         run_callbacks load_callbacks;
         scroll_to_fragment ?offset fragment;
         advance_page ();
         if !Eliom_config.debug_timings
-        then Console.console##(timeEnd (Js.string "set_content"));
-        Lwt.return_unit
+        then Console.console##(timeEnd (Js.string "set_content"))
       and recover () =
-        if !locked then Lwt_mutex.unlock Eliom_client_core.load_mutex;
+        if !locked then Eio.Mutex.unlock Eliom_client_core.load_mutex;
         if !Eliom_config.debug_timings
         then Console.console##(timeEnd (Js.string "set_content"))
       in
-      Lwt.catch
-        (fun () ->
-           let* () = Lwt_mutex.lock Eliom_client_core.load_mutex in
-           Eliom_client_core.set_loading_phase ();
-           if !Eliom_config.debug_timings
-           then Console.console##(time (Js.string "set_content"));
-           let g () = recover (); Lwt.return_unit in
-           run_onunload_wrapper really_set g)
-        (fun exn ->
-           recover ();
-           Logs.debug ~src:section (fun fmt ->
-             fmt ("set_content" ^^ "@\n%s") (Printexc.to_string exn));
-           Lwt.fail exn)
+      try
+        let () = Eio.Mutex.lock Eliom_client_core.load_mutex in
+        Eliom_client_core.set_loading_phase ();
+        if !Eliom_config.debug_timings
+        then Console.console##(time (Js.string "set_content"));
+        let g () = recover () in
+        run_onunload_wrapper really_set g
+      with exn ->
+        recover ();
+        Logs.debug ~src:section (fun fmt ->
+          fmt ("set_content" ^^ "@\n%s") (Printexc.to_string exn));
+        raise exn)
 
 let ocamlify_params =
   List.map (function v, `String s -> v, Js.to_string s | _, _ -> assert false)
@@ -1768,13 +1788,13 @@ let route ({Eliom_route.i_subpath; i_get_params; i_post_params; _} as info) =
   Eliom_request_info.update_session_info ~path:i_subpath
     ~all_get_params:i_get_params ~all_post_params:(Some i_post_params)
   @@ fun () ->
-  let* result =
+  let result =
     Eliom_route.call_service
       { info with
         Eliom_route.i_get_params =
           Eliom_common.(remove_prefixed_param nl_param_prefix) i_get_params }
   in
-  Lwt.return (uri, result)
+  uri, result
 
 let switch_to_https () =
   let info = Eliom_process.get_info () in
@@ -1796,11 +1816,11 @@ let string_of_result result =
       "Reload_action with hidden and https as " ^ values
 
 let rec handle_result ~replace ~uri result =
-  let* result = result in
+  let result = result in
   Logs.debug ~src:section_page (fun fmt ->
     fmt "%s" ("handle_result: result is " ^ string_of_result result));
   match result with
-  | Eliom_service.No_contents -> Lwt.return_unit
+  | Eliom_service.No_contents -> ()
   | Dom d ->
       change_url_string ~replace uri;
       set_content_local d
@@ -1857,7 +1877,7 @@ and change_page :
   -> ?override_mime_type:string
   -> 'get
   -> 'post
-  -> unit Lwt.t
+  -> unit
   =
  fun (type m)
    ?(ignore_client_fun = false)
@@ -1890,10 +1910,9 @@ and change_page :
     let () =
       Logs.debug ~src:section_page (fun fmt -> fmt "change page: xhr is None")
     in
-    Lwt.return
-      (exit_to ?window_name ?window_features ?absolute ?absolute_path ?https
-         ~service ?hostname ?port ?fragment ?keep_nl_params ~nl_params
-         ?keep_get_na_params get_params post_params)
+    exit_to ?window_name ?window_features ?absolute ?absolute_path ?https
+      ~service ?hostname ?port ?fragment ?keep_nl_params ~nl_params
+      ?keep_get_na_params get_params post_params
   else
     with_progress_cursor
       (match xhr with
@@ -1905,7 +1924,7 @@ and change_page :
             Eliom_parameter.add_nl_parameter nl_params Eliom_request.nl_template
               tmpl
           in
-          let* uri, content =
+          let uri, content =
             raw_call_service ?absolute ?absolute_path ?https ~service ?hostname
               ?port ?fragment ?keep_nl_params ~nl_params ?keep_get_na_params
               ?progress ?upload_progress ?override_mime_type get_params
@@ -1939,7 +1958,7 @@ and change_page :
               ~path:(Url.path_of_url_string uri)
               ~all_get_params:l ~all_post_params:l'
             @@ fun () ->
-            let* () =
+            let () =
               run_lwt_callbacks
                 { in_cache = is_in_cache !active_page.page_id
                 ; origin_uri = get_current_uri ()
@@ -1953,10 +1972,9 @@ and change_page :
         | None when is_client_app () ->
             Logs.debug ~src:section_page (fun fmt ->
               fmt "change page: client_fun service is None and is_client_app");
-            Lwt.return
-            @@ exit_to ?absolute ?absolute_path ?https ~service ?hostname ?port
-                 ?fragment ?keep_nl_params ~nl_params ?keep_get_na_params
-                 get_params post_params
+            exit_to ?absolute ?absolute_path ?https ~service ?hostname ?port
+              ?fragment ?keep_nl_params ~nl_params ?keep_get_na_params
+              get_params post_params
         | _ ->
             Logs.debug ~src:section_page (fun fmt ->
               fmt "change page: client_fun service is anything else");
@@ -1969,7 +1987,7 @@ and change_page :
             with_new_page ~replace () @@ fun () ->
             reload_function := None;
             let cookies_info = Eliom_uri.make_cookies_info (https, service) in
-            let* uri, content =
+            let uri, content =
               match
                 create_request_ ?absolute ?absolute_path ?https ~service
                   ?hostname ?port ?fragment ?keep_nl_params ~nl_params
@@ -2009,28 +2027,26 @@ and change_page_unknown
     | _, _ -> `Post
   in
   with_new_page ~replace () @@ fun () ->
-  let* uri, result =
+  let uri, result =
     route
       {Eliom_route.i_sess_info; i_subpath; i_meth; i_get_params; i_post_params}
   in
-  handle_result ~replace ~uri (Lwt.return result)
+  handle_result ~replace ~uri result
 
 and reload ~replace ~uri ~fallback =
   Logs.debug ~src:section_page (fun fmt -> fmt "reload");
   let path, args = path_and_args_of_uri uri in
-  Lwt.catch
-    (fun () -> change_page_unknown ~replace path args [])
-    (fun _ ->
-       change_page ~replace ~ignore_client_fun:true ~service:fallback () ())
+  try change_page_unknown ~replace path args []
+  with _ ->
+    change_page ~replace ~ignore_client_fun:true ~service:fallback () ()
 
 and reload_without_na_params ~replace ~uri ~fallback =
   let path, args = path_and_args_of_uri uri in
   let args = Eliom_common.remove_na_prefix_params args in
   Logs.debug ~src:section_page (fun fmt -> fmt "reload_without_na_params");
-  Lwt.catch
-    (fun () -> change_page_unknown ~replace path args [])
-    (fun _ ->
-       change_page ~replace ~ignore_client_fun:true ~service:fallback () ())
+  try change_page_unknown ~replace path args []
+  with _ ->
+    change_page ~replace ~ignore_client_fun:true ~service:fallback () ()
 
 (* Function used in "onclick" event handler of <a>.  *)
 let change_page_uri_a ?cookies_info ?tmpl ?(get_params = []) full_uri =
@@ -2043,42 +2059,40 @@ let change_page_uri_a ?cookies_info ?tmpl ?(get_params = []) full_uri =
        then failwith "Change_page_uri_a called on client app";
        match tmpl with
        | Some t when tmpl = Eliom_request_info.get_request_template () ->
-           let* uri, content =
+           let uri, content =
              Eliom_request.http_get ?cookies_info uri
                ((Eliom_request.nl_template_string, t) :: get_params)
                Eliom_request.string_result
            in
            set_template_content ~replace:false ~uri ?fragment content
        | _ ->
-           let* uri, content =
+           let uri, content =
              Eliom_request.http_get ~expecting_process_page:true ?cookies_info
                uri get_params Eliom_request.xml_result
            in
            set_content ~replace:false ~uri ?fragment content)
      else (
        change_url_string ~replace:true full_uri;
-       scroll_to_fragment fragment;
-       Lwt.return_unit))
+       scroll_to_fragment fragment))
 
 let change_page_uri ?replace full_uri =
   Logs.debug ~src:section_page (fun fmt -> fmt "Change page uri");
-  Lwt.catch
-    (fun () ->
-       match Url.url_of_string full_uri with
-       | Some (Url.Http url | Url.Https url) ->
-           Logs.debug ~src:section_page (fun fmt ->
-             fmt "change page uri: url is http or https");
-           change_page_unknown ?replace url.Url.hu_path url.Url.hu_arguments []
-       | _ -> failwith "invalid url")
-    (fun _ ->
-       if is_client_app ()
-       then
-         failwith
-           (Printf.sprintf "Change page uri: can't find service for %s" full_uri)
-       else (
-         Logs.debug ~src:section (fun fmt ->
-           fmt "Change page uri: resort to server");
-         change_page_uri_a full_uri))
+  try
+    match Url.url_of_string full_uri with
+    | Some (Url.Http url | Url.Https url) ->
+        Logs.debug ~src:section_page (fun fmt ->
+          fmt "change page uri: url is http or https");
+        change_page_unknown ?replace url.Url.hu_path url.Url.hu_arguments []
+    | _ -> failwith "invalid url"
+  with _ ->
+    if is_client_app ()
+    then
+      failwith
+        (Printf.sprintf "Change page uri: can't find service for %s" full_uri)
+    else (
+      Logs.debug ~src:section (fun fmt ->
+        fmt "Change page uri: resort to server");
+      change_page_uri_a full_uri)
 
 (* Functions used in "onsubmit" event handler of <form>.  *)
 
@@ -2088,14 +2102,14 @@ let change_page_get_form ?cookies_info ?tmpl form full_uri =
      let uri, fragment = Url.split_fragment full_uri in
      match tmpl with
      | Some t when tmpl = Eliom_request_info.get_request_template () ->
-         let* uri, content =
+         let uri, content =
            Eliom_request.send_get_form
              ~get_args:[Eliom_request.nl_template_string, t]
              ?cookies_info form uri Eliom_request.string_result
          in
          set_template_content ~replace:false ~uri ?fragment content
      | _ ->
-         let* uri, content =
+         let uri, content =
            Eliom_request.send_get_form ~expecting_process_page:true
              ?cookies_info form uri Eliom_request.xml_result
          in
@@ -2107,14 +2121,14 @@ let change_page_post_form ?cookies_info ?tmpl form full_uri =
      let uri, fragment = Url.split_fragment full_uri in
      match tmpl with
      | Some t when tmpl = Eliom_request_info.get_request_template () ->
-         let* uri, content =
+         let uri, content =
            Eliom_request.send_post_form
              ~get_args:[Eliom_request.nl_template_string, t]
              ?cookies_info form uri Eliom_request.string_result
          in
          set_template_content ~replace:false ~uri ?fragment content
      | _ ->
-         let* uri, content =
+         let uri, content =
            Eliom_request.send_post_form ~expecting_process_page:true
              ?cookies_info form uri Eliom_request.xml_result
          in
@@ -2123,13 +2137,19 @@ let change_page_post_form ?cookies_info ?tmpl form full_uri =
 let _ =
   (Eliom_client_core.change_page_uri_ :=
      fun ?cookies_info ?tmpl href ->
-       Lwt.ignore_result (change_page_uri_a ?cookies_info ?tmpl href));
+       Fiber.fork
+         ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+         (fun () -> change_page_uri_a ?cookies_info ?tmpl href));
   (Eliom_client_core.change_page_get_form_ :=
      fun ?cookies_info ?tmpl form href ->
-       Lwt.ignore_result (change_page_get_form ?cookies_info ?tmpl form href));
+       Fiber.fork
+         ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+         (fun () -> change_page_get_form ?cookies_info ?tmpl form href));
   Eliom_client_core.change_page_post_form_ :=
     fun ?cookies_info ?tmpl form href ->
-      Lwt.ignore_result (change_page_post_form ?cookies_info ?tmpl form href)
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        (fun () -> change_page_post_form ?cookies_info ?tmpl form href)
 
 (* == Main (internal) function: change the content of the page without leaving
       the javascript application. *)
@@ -2178,110 +2198,121 @@ let () =
         ; target_id = Some target_id }
       in
       let tmpl = state.template in
-      Lwt.ignore_result @@ with_progress_cursor
-      @@
-      let uri, fragment = Url.split_fragment full_uri in
-      if uri = get_current_uri ()
-      then (
-        Logs.debug ~src:section_page (fun fmt ->
-          fmt "revisit: uri = get_current_uri");
-        !active_page.page_id <- state_id;
-        scroll_to_fragment ~offset:state.position fragment;
-        Lwt.return_unit)
-      else
-        try
-          (* serve cached page from the from history_doms *)
-          Logs.debug ~src:section_page (fun fmt ->
-            fmt "revisit: uri != get_current_uri");
-          if not (is_in_cache state_id) then raise Not_found;
-          let* () = run_lwt_callbacks ev (flush_onchangepage ()) in
-          restore_history_dom target_id;
-          set_current_uri uri;
-          let* () = Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame () in
-          scroll_to_fragment ~offset:state.position fragment;
-          (* Wait for the dom to be repainted before scrolling *)
-          let* () = Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame () in
-          scroll_to_fragment ~offset:state.position fragment;
-          (* When we use iPhone, we need to wait for one more
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        (fun () ->
+           with_progress_cursor
+           (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+           @@
+           let uri, fragment = Url.split_fragment full_uri in
+           if uri = get_current_uri ()
+           then (
+             Logs.debug ~src:section_page (fun fmt ->
+               fmt "revisit: uri = get_current_uri");
+             !active_page.page_id <- state_id;
+             scroll_to_fragment ~offset:state.position fragment)
+           else
+             try
+               (* serve cached page from the from history_doms *)
+               Logs.debug ~src:section_page (fun fmt ->
+                 fmt "revisit: uri != get_current_uri");
+               if not (is_in_cache state_id) then raise Not_found;
+               let () = run_lwt_callbacks ev (flush_onchangepage ()) in
+               restore_history_dom target_id;
+               set_current_uri uri;
+               let () =
+                 Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame ()
+               in
+               scroll_to_fragment ~offset:state.position fragment;
+               let
+                   (* Wait for the dom to be repainted before scrolling *)
+                     ()
+                 =
+                 Js_of_ocaml_lwt.Lwt_js_events.request_animation_frame ()
+               in
+               scroll_to_fragment ~offset:state.position fragment
+               (* When we use iPhone, we need to wait for one more
                    [request_animation_frame] before scrolling.The
                    function [scroll_to_fragment] is called twice. In
                    other words, we want to call [scroll_to_fragment]
                    as early as possible so that the scroll position
                    will not jump after the second [request_animation_frame]
                    if the dom has already be painted after the first one. *)
-          Lwt.return_unit
-        with Not_found -> (
-          let session_changed = state_id.session_id <> session_id in
-          if session_changed && is_client_app ()
-          then
-            failwith
-              (Printf.sprintf
-                 "revisit: session changed on client: %d => %d (%s)"
-                 state_id.session_id session_id full_uri);
-          try
-            (* same session *)
-            if session_changed then raise Not_found;
-            Logs.debug ~src:section_page (fun fmt ->
-              fmt "revisit: session has not changed");
-            let old_page = History.find_by_state_index state_id.state_index in
-            let rf =
-              Option.bind old_page @@ fun {reload_function = rf; _} -> rf
-            in
-            match rf with
-            | None -> raise Not_found
-            | Some f ->
-                reload_function := rf;
-                let* () = run_lwt_callbacks ev (flush_onchangepage ()) in
-                with_new_page ~state_id ?old_page ~replace:false () @@ fun () ->
-                set_current_uri uri;
-                History.replace (get_this_page ());
-                let* () =
-                  Lwt.bind (f () ()) (function
-                    | Eliom_service.Dom d -> set_content_local d
-                    | r ->
-                        handle_result ~uri:(get_current_uri ()) ~replace:true
-                          (Lwt.return r))
-                in
-                scroll_to_fragment ~offset:state.position fragment;
-                Lwt.return_unit
-          with Not_found -> (
-            (* different session ID *)
-            set_current_uri uri;
-            match tmpl with
-            | Some t when tmpl = Eliom_request_info.get_request_template () ->
-                Logs.debug ~src:section_page (fun fmt ->
-                  fmt
-                    "revisit: template is Some and equals to get_request_template");
-                let* uri, content =
-                  Eliom_request.http_get uri
-                    [Eliom_request.nl_template_string, t]
-                    Eliom_request.string_result
-                in
-                let* () = set_template_content content ~replace:true ~uri in
-                scroll_to_fragment ~offset:state.position fragment;
-                Lwt.return_unit
-            | _ ->
-                if is_client_app ()
-                then
-                  failwith
-                    (Printf.sprintf
-                       "revisit: could not generate page client-side (%s)"
-                       full_uri);
-                Logs.debug ~src:section_page (fun fmt ->
-                  fmt "revisit: template is anything else");
-                with_new_page
-                  ?state_id:(if session_changed then None else Some state_id)
-                  ~replace:false ()
-                @@ fun () ->
-                let* uri, content =
-                  Eliom_request.http_get ~expecting_process_page:true uri []
-                    Eliom_request.xml_result
-                in
-                let* () =
-                  set_content ~uri ~replace:true ~offset:state.position
-                    ?fragment content
-                in
-                Lwt.return_unit))
+             with Not_found -> (
+               let session_changed = state_id.session_id <> session_id in
+               if session_changed && is_client_app ()
+               then
+                 failwith
+                   (Printf.sprintf
+                      "revisit: session changed on client: %d => %d (%s)"
+                      state_id.session_id session_id full_uri);
+               try
+                 (* same session *)
+                 if session_changed then raise Not_found;
+                 Logs.debug ~src:section_page (fun fmt ->
+                   fmt "revisit: session has not changed");
+                 let old_page =
+                   History.find_by_state_index state_id.state_index
+                 in
+                 let rf =
+                   Option.bind old_page @@ fun {reload_function = rf; _} -> rf
+                 in
+                 match rf with
+                 | None -> raise Not_found
+                 | Some f ->
+                     reload_function := rf;
+                     let () = run_lwt_callbacks ev (flush_onchangepage ()) in
+                     with_new_page ~state_id ?old_page ~replace:false ()
+                     @@ fun () ->
+                     set_current_uri uri;
+                     History.replace (get_this_page ());
+                     let () =
+                       match f () () with
+                       | Eliom_service.Dom d -> set_content_local d
+                       | r ->
+                           handle_result ~uri:(get_current_uri ()) ~replace:true
+                             r
+                     in
+                     scroll_to_fragment ~offset:state.position fragment
+               with Not_found -> (
+                 (* different session ID *)
+                 set_current_uri uri;
+                 match tmpl with
+                 | Some t when tmpl = Eliom_request_info.get_request_template ()
+                   ->
+                     Logs.debug ~src:section_page (fun fmt ->
+                       fmt
+                         "revisit: template is Some and equals to get_request_template");
+                     let uri, content =
+                       Eliom_request.http_get uri
+                         [Eliom_request.nl_template_string, t]
+                         Eliom_request.string_result
+                     in
+                     let () = set_template_content content ~replace:true ~uri in
+                     scroll_to_fragment ~offset:state.position fragment
+                 | _ ->
+                     if is_client_app ()
+                     then
+                       failwith
+                         (Printf.sprintf
+                            "revisit: could not generate page client-side (%s)"
+                            full_uri);
+                     Logs.debug ~src:section_page (fun fmt ->
+                       fmt "revisit: template is anything else");
+                     with_new_page
+                       ?state_id:
+                         (if session_changed then None else Some state_id)
+                       ~replace:false ()
+                     @@ fun () ->
+                     let uri, content =
+                       Eliom_request.http_get ~expecting_process_page:true uri
+                         [] Eliom_request.xml_result
+                     in
+                     let () =
+                       set_content ~uri ~replace:true ~offset:state.position
+                         ?fragment content
+                     in
+                     ())))
     in
     let revisit_wrapper full_uri state_id =
       Logs.debug ~src:section_page (fun fmt -> fmt "revisit_wrapper");
@@ -2291,20 +2322,26 @@ let () =
       and cancel () = () in
       run_onunload_wrapper f cancel
     in
-    Lwt.ignore_result
-      (let* () = wait_load_end () in
-       Logs.debug ~src:section_page (fun fmt ->
-         fmt "revisit_wrapper: replaceState");
-       Dom_html.window##.history##(replaceState
-                                     (Js.Opt.return
-                                        (Js.string
-                                           (to_json ~typ:[%json: saved_state]
-                                              ( !active_page.page_id
-                                              , Js.to_string
-                                                  Dom_html.window##.location##.href
-                                              ))))
-                                     (Js.string "") Js.null);
-       Lwt.return_unit);
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         let
+             (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+               ()
+           =
+           wait_load_end ()
+         in
+         Logs.debug ~src:section_page (fun fmt ->
+           fmt "revisit_wrapper: replaceState");
+         Dom_html.window##.history##(replaceState
+                                       (Js.Opt.return
+                                          (Js.string
+                                             (to_json ~typ:[%json: saved_state]
+                                                ( !active_page.page_id
+                                                , Js.to_string
+                                                    Dom_html.window##.location##.
+                                                    href ))))
+                                       (Js.string "") Js.null));
     Dom_html.window##.onpopstate
     := Dom_html.handler (fun event ->
       Logs.debug ~src:section_page (fun fmt ->
@@ -2325,33 +2362,42 @@ let () =
     *)
     let read_fragment () = Js.to_string Dom_html.window##.location##.hash in
     let auto_change_page fragment =
-      Lwt.ignore_result
-        (let l = String.length fragment in
-         if l = 0 || (l > 1 && fragment.[1] = '!')
-         then
-           if fragment <> !current_pseudo_fragment
-           then (
-             current_pseudo_fragment := fragment;
-             let uri =
-               match l with
-               | 2 -> "./" (* fix for firefox *)
-               | 0 | 1 -> fst (Url.split_fragment Url.Current.as_string)
-               | _ -> String.sub fragment 2 (String.length fragment - 2)
-             in
-             Logs.debug ~src:section_page (fun fmt -> fmt "auto_change_page");
-             (* CCC TODO handle templates *)
-             change_page_uri uri)
-           else Lwt.return_unit
-         else Lwt.return_unit)
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        (fun () ->
+           (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+           let l = String.length fragment in
+           if l = 0 || (l > 1 && fragment.[1] = '!')
+           then
+             if fragment <> !current_pseudo_fragment
+             then (
+               current_pseudo_fragment := fragment;
+               let uri =
+                 match l with
+                 | 2 -> "./" (* fix for firefox *)
+                 | 0 | 1 -> fst (Url.split_fragment Url.Current.as_string)
+                 | _ -> String.sub fragment 2 (String.length fragment - 2)
+               in
+               Logs.debug ~src:section_page (fun fmt -> fmt "auto_change_page");
+               (* CCC TODO handle templates *)
+               change_page_uri uri)
+             else ()
+           else ())
     in
     Eliommod_dom.onhashchange (fun s -> auto_change_page (Js.to_string s));
     let first_fragment = read_fragment () in
     if first_fragment <> !current_pseudo_fragment
     then
-      Lwt.ignore_result
-        (let* () = wait_load_end () in
-         auto_change_page first_fragment;
-         Lwt.return_unit)
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        (fun () ->
+           let
+               (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+                 ()
+             =
+             wait_load_end ()
+           in
+           auto_change_page first_fragment)
 
 let () =
   Eliom_unwrap.register_unwrapper
diff --git a/src/lib/eliom_client.client.mli b/src/lib/eliom_client.client.mli
index 5ea2a171a1..2ee16b3a14 100644
--- a/src/lib/eliom_client.client.mli
+++ b/src/lib/eliom_client.client.mli
@@ -83,7 +83,7 @@ val change_page :
   -> ?override_mime_type:string
   -> 'a
   -> 'b
-  -> unit Lwt.t
+  -> unit
 (** Call a service and change the current page.  If the service
     belongs to the same application, the client side program is not
     stopped, and only the content (not the container) is reloaded.  If
@@ -123,7 +123,7 @@ val call_ocaml_service :
   -> ?override_mime_type:string
   -> 'a
   -> 'b
-  -> 'return Lwt.t
+  -> 'return
 (** Call a server side service that return an OCaml value.
 
     If the service raises an exception, the call to the
@@ -228,7 +228,7 @@ val call_service :
   -> ?override_mime_type:string
   -> 'a
   -> 'b
-  -> string Lwt.t
+  -> string
 (** (low level) Call a server side service and return the content
     of the resulting HTTP frame as a string. *)
 
@@ -272,7 +272,7 @@ val onload : (unit -> unit) -> unit
 
 *)
 
-val lwt_onload : unit -> unit Lwt.t
+val lwt_onload : unit -> unit
 (** Returns a Lwt thread that waits until the next page is loaded. *)
 
 type changepage_event =
@@ -290,7 +290,7 @@ type changepage_event =
     [target_id] is not [None] if and only if the onchangepage event
     takes place during a navigation in history. *)
 
-val onchangepage : (changepage_event -> unit Lwt.t) -> unit
+val onchangepage : (changepage_event -> unit) -> unit
 (** Run some code *before* the next page change, that is, before each
     call to a page-producing service handler.
     Just like onpreload, handlers registered with onchangepage only
@@ -348,11 +348,7 @@ module Page_status : sig
   val ondead : ?stop:unit React.E.t -> (unit -> unit) -> unit
   val oninactive : ?once:bool -> ?stop:unit React.E.t -> (unit -> unit) -> unit
 
-  val while_active :
-     ?now:bool
-    -> ?stop:unit React.E.t
-    -> (unit -> unit Lwt.t)
-    -> unit
+  val while_active : ?now:bool -> ?stop:unit React.E.t -> (unit -> unit) -> unit
   (** [while_active] initiates an action as [onactive] but cancels it whenever
       the page is not active anymore. *)
 end
@@ -377,7 +373,7 @@ val onunload : (unit -> unit) -> unit
     service calls, and sometimes by the browser [onunload] event.
     [onunload] can be used to register multiple callbacks. *)
 
-val wait_load_end : unit -> unit Lwt.t
+val wait_load_end : unit -> unit
 (** Wait for the initialization phase to terminate *)
 
 val get_application_name : unit -> string
@@ -392,7 +388,7 @@ val persist_document_head : unit -> unit
 
     See the {% <<a_manual chapter="clientserver-communication" fragment="rpc"|manual>> %}.*)
 
-type ('a, +'b) server_function = 'a -> 'b Lwt.t
+type ('a, +'b) server_function = 'a -> 'b
 (** A [('a, 'b) server_function] provides transparently access to a
     server side function which has been created by {% <<a_api
     subproject="server"| val Eliom_client.server_function>> %}.
@@ -404,7 +400,7 @@ type ('a, +'b) server_function = 'a -> 'b Lwt.t
     <<a_api subproject="client"|val Eliom_client.call_ocaml_service>>.
 *)
 
-val change_page_uri : ?replace:bool -> string -> unit Lwt.t
+val change_page_uri : ?replace:bool -> string -> unit
 (** [change_page_uri ?replace uri] identifies and calls the
     client-side service that implements [uri].
 
@@ -428,7 +424,7 @@ val change_page_unknown :
   -> string list
   -> (string * string) list
   -> (string * string) list
-  -> unit Lwt.t
+  -> unit
 (** [change_page_unknown path get_params post_params] calls the
     service corresponding to [(path, get_params, post_params)]. It may
     throw [Eliom_common.Eliom_404] or
@@ -438,7 +434,7 @@ val change_page_unknown :
 (* Documentation rather in eliom_client.ml *)
 
 val init : unit -> unit
-val set_reload_function : (unit -> unit -> Eliom_service.result Lwt.t) -> unit
+val set_reload_function : (unit -> unit -> Eliom_service.result) -> unit
 
 module History : sig
   val past : unit -> string list
@@ -495,7 +491,7 @@ val section : Logs.src
 val middleClick : Dom_html.mouseEvent Js.t -> bool
 (** Is it a middle-click event? *)
 
-type client_form_handler = Dom_html.event Js.t -> bool Lwt.t
+type client_form_handler = Dom_html.event Js.t -> bool
 
 (** headers to add to each of Eliom's HTTP requests. *)
 module Additional_headers : sig
diff --git a/src/lib/eliom_client.server.mli b/src/lib/eliom_client.server.mli
index c15d360796..b1f1f67dcf 100644
--- a/src/lib/eliom_client.server.mli
+++ b/src/lib/eliom_client.server.mli
@@ -34,9 +34,9 @@ val server_function :
   -> ?max_use:int
   -> ?timeout:float
   -> ?https:bool
-  -> ?error_handler:((string * exn) list -> 'b Lwt.t)
+  -> ?error_handler:((string * exn) list -> 'b)
   -> 'a Deriving_Json.t
-  -> ('a -> 'b Lwt.t)
+  -> ('a -> 'b)
   -> ('a, 'b) server_function
 (** [server_function argument_type f] creates a value of type {%
     <<a_api | type Eliom_client.server_function>> %}. This allows
diff --git a/src/lib/eliom_client_core.client.ml b/src/lib/eliom_client_core.client.ml
index 59e94d2cc9..b6a933dbbb 100644
--- a/src/lib/eliom_client_core.client.ml
+++ b/src/lib/eliom_client_core.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -263,20 +263,25 @@ let register_request_node, find_request_node, reset_request_nodes =
    *and* to the change_page phase
    *and* to the loading phase after caml services (added 2016-03 --V). *)
 
-let load_mutex = Lwt_mutex.create ()
-let _ = ignore (Lwt_mutex.lock load_mutex)
+let load_mutex = Eio.Mutex.create ()
+let _ = ignore (Eio.Mutex.lock load_mutex)
 
 let in_onload, broadcast_load_end, wait_load_end, set_loading_phase =
   let loading_phase = ref true in
-  let load_end = Lwt_condition.create () in
+  let load_end = Eio.Condition.create () in
   let set () = loading_phase := true in
   let in_onload () = !loading_phase in
   let broadcast_load_end () =
     loading_phase := false;
-    Lwt_condition.broadcast load_end ()
+    Eio.Condition.broadcast load_end
   in
   let wait_load_end () =
-    if !loading_phase then Lwt_condition.wait load_end else Lwt.return_unit
+    if !loading_phase
+    then
+      Eio.Condition.await
+        (* TODO: lwt-to-direct-style: A mutex must be passed *) load_end
+        __mutex__
+    else ()
   in
   in_onload, broadcast_load_end, wait_load_end, set
 
@@ -305,7 +310,7 @@ let change_page_get_form_ :
 let change_page_post_form_ =
   ref (fun ?cookies_info:_ ?tmpl:_ _form _href -> assert false)
 
-type client_form_handler = Dom_html.event Js.t -> bool Lwt.t
+type client_form_handler = Dom_html.event Js.t -> bool
 
 let raw_a_handler node cookies_info tmpl ev =
   let href = (Js.Unsafe.coerce node : Dom_html.anchorElement Js.t)##.href in
@@ -331,10 +336,11 @@ let raw_form_handler form kind cookies_info tmpl ev client_form_handler =
     | `Form_post -> !change_page_post_form_
   in
   let f () =
-    Lwt.async @@ fun () ->
-    let* b = client_form_handler ev in
-    if not b then change_page_form ?cookies_info ?tmpl form action;
-    Lwt.return_unit
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         let b = client_form_handler ev in
+         if not b then change_page_form ?cookies_info ?tmpl form action)
   in
   (not !Eliom_common.is_client_app)
   && ((https = Some true && not Eliom_request_info.ssl_)
@@ -567,7 +573,13 @@ let rec rebuild_rattrib node ra =
    and the function [Eliommod_dom.test_pageshow_pagehide]. *)
 
 let delay f =
-  Lwt.ignore_result (Lwt.pause () >>= fun () -> f (); Lwt.return_unit)
+  Fiber.fork
+    ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+    (fun () ->
+       Fiber.yield
+         (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+         ();
+       f ())
 
 module ReactState : sig
   type t
diff --git a/src/lib/eliom_client_main.eliom b/src/lib/eliom_client_main.eliom
index 3328cebfc9..39fcd29355 100644
--- a/src/lib/eliom_client_main.eliom
+++ b/src/lib/eliom_client_main.eliom
@@ -22,48 +22,44 @@ let%client _ = Eliom_client.init ()
 
 let _ =
   Eliommod.register_site_init (fun () ->
-    let sitedata = Eliom_request_info.get_sitedata () in
-    let ignored_get_params =
-      List.map fst sitedata.Eliom_common.ignored_get_params
-    in
-    let ignored_post_params =
-      List.map fst sitedata.Eliom_common.ignored_post_params
-    in
-    let _ =
-      [%client
-        (Eliom_process.set_ignored_params ~%ignored_get_params
-           ~%ignored_post_params;
-         Eliom_process.set_ignored_params ~%ignored_get_params
-           ~%ignored_post_params
-         : unit)]
-    in
-    ())
+      let sitedata = Eliom_request_info.get_sitedata () in
+      let ignored_get_params =
+        List.map fst sitedata.Eliom_common.ignored_get_params
+      in
+      let ignored_post_params =
+        List.map fst sitedata.Eliom_common.ignored_post_params
+      in
+      let _ =
+        [%client
+          (Eliom_process.set_ignored_params ~%ignored_get_params
+             ~%ignored_post_params;
+           Eliom_process.set_ignored_params ~%ignored_get_params
+             ~%ignored_post_params
+            : unit)]
+      in
+      ())
 
 [%%client.start]
 
 (* The following lines are for Eliom_bus, Eliom_comet and Eliom_react
    to be linked. *)
 let _force_link =
-  Eliom_react.force_link, Eliom_comet.force_link, Eliom_bus.force_link
+  (Eliom_react.force_link, Eliom_comet.force_link, Eliom_bus.force_link)
 
 (* Client side implementation of reload actions *)
 let%shared _ =
   Eliom_service.internal_set_client_fun ~service:Eliom_service.reload_action
     [%client
-      fun () () ->
-        Lwt.return (Eliom_service.Reload_action {hidden = false; https = false})];
+      fun () () -> Eliom_service.Reload_action { hidden = false; https = false }];
   Eliom_service.internal_set_client_fun
     ~service:Eliom_service.reload_action_https
     [%client
-      fun () () ->
-        Lwt.return (Eliom_service.Reload_action {hidden = false; https = true})];
+      fun () () -> Eliom_service.Reload_action { hidden = false; https = true }];
   Eliom_service.internal_set_client_fun
     ~service:Eliom_service.reload_action_hidden
     [%client
-      fun () () ->
-        Lwt.return (Eliom_service.Reload_action {hidden = true; https = false})];
+      fun () () -> Eliom_service.Reload_action { hidden = true; https = false }];
   Eliom_service.internal_set_client_fun
     ~service:Eliom_service.reload_action_https_hidden
     [%client
-      fun () () ->
-        Lwt.return (Eliom_service.Reload_action {hidden = true; https = true})]
+      fun () () -> Eliom_service.Reload_action { hidden = true; https = true }]
diff --git a/src/lib/eliom_comet.client.ml b/src/lib/eliom_comet.client.ml
index 119d65407e..565fe6f6af 100644
--- a/src/lib/eliom_comet.client.ml
+++ b/src/lib/eliom_comet.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -84,16 +84,24 @@ module Configuration = struct
         (first_conf configuration_table)
 
   let update_configuration_waiter, update_configuration_waker =
-    let t, u = Lwt.wait () in
+    let t, u =
+      Promise.create
+        (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+        ()
+    in
     ref t, ref u
 
   let update_configuration () =
     global_configuration := get_configuration ();
-    let t, u = Lwt.wait () in
+    let t, u =
+      Promise.create
+        (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+        ()
+    in
     update_configuration_waiter := t;
     let wakener = !update_configuration_waker in
     update_configuration_waker := u;
-    Lwt.wakeup wakener ()
+    Promise.resolve wakener ()
 
   let get () = !global_configuration
 
@@ -159,17 +167,17 @@ module Configuration = struct
       else (get ()).time_between_request
     in
     let rec aux t =
-      let* () =
-        Lwt.pick
-          [ Js_of_ocaml_lwt.Lwt_js.sleep t
-          ; !update_configuration_waiter
-          ; active_waiter () ]
+      let () =
+        Fiber.any
+          [ (fun () -> Js_of_ocaml_lwt.Lwt_js.sleep t)
+          ; (fun () -> Promise.await !update_configuration_waiter)
+          ; active_waiter ]
       in
       let remaining_time = sleep_duration () -. (Sys.time () -. time) in
-      if remaining_time > 0. then aux remaining_time else Lwt.return_unit
+      if remaining_time > 0. then aux remaining_time else ()
     in
     let sleep_duration = sleep_duration () in
-    if sleep_duration <= 0. then Lwt.return_unit else aux sleep_duration
+    if sleep_duration <= 0. then () else aux sleep_duration
 end
 
 exception Restart
@@ -186,16 +194,14 @@ let handle_exn, set_handle_exn_function =
       in
       match exn with
       | Some exn -> raise_error ~section ~exn "%s" s
-      | None ->
-          Logs.debug ~src:section (fun fmt -> fmt "%s" s);
-          Lwt.return_unit)
+      | None -> Logs.debug ~src:section (fun fmt -> fmt "%s" s))
   in
   ( (fun ?exn () ->
       if not !closed
       then (
         closed := true;
         !r ?exn ())
-      else Lwt.return_unit)
+      else ())
   , fun f -> r := f )
 
 type chan_id = string
@@ -211,9 +217,7 @@ module Service_handler : sig
   val stateful : stateful kind
   val make : Ecb.comet_service -> 'a kind -> 'a t
 
-  val wait_data :
-     'a t
-    -> (chan_id * int option * string Ecb.channel_data) list Lwt.t
+  val wait_data : 'a t -> (chan_id * int option * string Ecb.channel_data) list
   (** Returns the messages received in the last request. If the
       channel is stateless, it also returns the message number in the [int option] *)
 
@@ -239,11 +243,11 @@ end = struct
     ; mutable focused : float option
       (** [focused] is None when the page is visible and Some [t]
             when the page became hidden at time [t] (in ms) *)
-    ; mutable active_waiter : unit Lwt.t
+    ; mutable active_waiter : unit Promise.t
       (** [active_waiter] terminates when the page get visible *)
-    ; mutable active_wakener : unit Lwt.u
-    ; mutable restart_waiter : Ecb.answer Lwt.t
-    ; mutable restart_wakener : Ecb.answer Lwt.u
+    ; mutable active_wakener : unit Promise.u
+    ; mutable restart_waiter : Ecb.answer Promise.t
+    ; mutable restart_wakener : Ecb.answer Promise.u
     ; mutable active_channels : Eliom_lib.String.Set.t }
 
   type stateful_state = int ref (* id of the next request *)
@@ -284,11 +288,15 @@ end = struct
       | `Inactive -> hd.hd_activity.active <- `Inactive
       | _ ->
           hd.hd_activity.active <- v;
-          let t, u = Lwt.wait () in
+          let t, u =
+            Promise.create
+              (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+              ()
+          in
           hd.hd_activity.active_waiter <- t;
           let wakener = hd.hd_activity.active_wakener in
           hd.hd_activity.active_wakener <- u;
-          Lwt.wakeup wakener ()
+          Promise.resolve wakener ()
 
   let is_active hd = hd.hd_activity.active
 
@@ -354,11 +362,17 @@ end = struct
 
   let restart hd =
     let act = hd.hd_activity in
-    let t, u = Lwt.wait () in
+    let t, u =
+      Promise.create
+        (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+        ()
+    in
     act.restart_waiter <- t;
     let wakener = act.restart_wakener in
     act.restart_wakener <- u;
-    Lwt.wakeup_exn wakener Restart;
+    Promise.resolve_error
+      (* TODO: lwt-to-direct-style: This used to be a ['a Lwt.t] is now a [('a, exn) result Promise.t]. Use [resolve_ok] and [await_exn] instead of [resolve] and [await]. *)
+      wakener Restart;
     activate hd
 
   let max_retries = 10
@@ -375,16 +389,16 @@ end = struct
     match p with
     | _, Ecb.Stateful (Ecb.Commands commands) ->
         queue := List.rev_append (Array.to_list commands) !queue;
-        let* () = Eliom_client.wait_load_end () in
+        let () = Eliom_client.wait_load_end () in
         let q = !queue in
         if q <> []
         then (
           queue := [];
           Eliom_client.call_service ~service ()
             (false, Ecb.Stateful (Ecb.Commands (Array.of_list (List.rev q)))))
-        else Lwt.return ""
+        else ""
     | _ ->
-        let* () = Eliom_client.wait_load_end () in
+        let () = Eliom_client.wait_load_end () in
         Eliom_client.call_service ~service () p
 
   let make_request hd =
@@ -466,17 +480,17 @@ end = struct
   let call_service
         ({hd_activity; hd_service = Ecb.Comet_service (srv, queue); _} as hd)
     =
-    let* () =
+    let () =
       Configuration.sleep_before_next_request
         (fun () -> hd_activity.focused)
         (fun () -> hd_activity.active = `Idle)
         (fun () -> hd_activity.active_waiter)
     in
     let request = make_request hd in
-    let* s =
+    let s =
       call_service_after_load_end srv queue (hd_activity.active = `Idle, request)
     in
-    Lwt.return (Deriving_Json.from_string Ecb.answer_json s)
+    Deriving_Json.from_string Ecb.answer_json s
 
   let drop_message_index =
     let aux = function
@@ -501,64 +515,67 @@ end = struct
          || not (Configuration.get ()).Configuration.active_until_timeout)
     then set_activity hd (expected_activity hd)
 
-  let wait_data hd : (string * int option * string Ecb.channel_data) list Lwt.t =
+  let wait_data hd : (string * int option * string Ecb.channel_data) list =
     let rec aux retries =
       if hd.hd_activity.active = `Inactive
       then
-        let* () = hd.hd_activity.active_waiter in
+        let () = hd.hd_activity.active_waiter in
         aux 0
       else
-        Lwt.try_bind
-          (fun () -> Lwt.pick [call_service hd; hd.hd_activity.restart_waiter])
-          (fun s ->
-             match s with
-             | Ecb.Timeout ->
-                 update_activity ~timeout:true hd;
-                 aux 0
-             | Ecb.State_closed -> Lwt.return (close_all_channels hd)
-             | Ecb.Comet_error e -> Lwt.fail (Comet_error e)
-             | Ecb.Stateless_messages l ->
-                 let l = Array.to_list l in
-                 update_stateless_state hd l;
-                 Lwt.return (drop_message_index l)
-             | Ecb.Stateful_messages l ->
-                 let l = Array.to_list l in
-                 update_stateful_state hd l;
-                 Lwt.return (add_no_index l))
-          (fun e ->
-             match e with
-             | Eliom_request.Failed_request (0 | 502 | 504) ->
-                 if retries > max_retries
-                 then (
-                   Logs.app ~src:section (fun fmt -> fmt "connection failure");
-                   set_activity hd `Inactive;
-                   aux 0)
-                 else
-                   let* () = Js_of_ocaml_lwt.Lwt_js.sleep (delay retries) in
-                   aux (retries + 1)
-             | Restart ->
-                 Logs.info ~src:section (fun fmt -> fmt "restart");
-                 aux 0
-             | exn ->
-                 Logs.app ~src:section (fun fmt ->
-                   fmt
-                     ("connection failure" ^^ "@\n%s")
-                     (Printexc.to_string exn));
-                 let* () = handle_exn ~exn () in
-                 Lwt.fail exn)
+        match
+          Fiber.any
+            [ (fun () -> call_service hd)
+            ; (fun () ->
+                hd
+                (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+                  .hd_activity
+                  .restart_waiter) ]
+        with
+        | s -> (
+          match s with
+          | Ecb.Timeout ->
+              update_activity ~timeout:true hd;
+              aux 0
+          | Ecb.State_closed -> close_all_channels hd
+          | Ecb.Comet_error e -> raise (Comet_error e)
+          | Ecb.Stateless_messages l ->
+              let l = Array.to_list l in
+              update_stateless_state hd l;
+              drop_message_index l
+          | Ecb.Stateful_messages l ->
+              let l = Array.to_list l in
+              update_stateful_state hd l; add_no_index l)
+        | exception e -> (
+          match e with
+          | Eliom_request.Failed_request (0 | 502 | 504) ->
+              if retries > max_retries
+              then (
+                Logs.app ~src:section (fun fmt -> fmt "connection failure");
+                set_activity hd `Inactive;
+                aux 0)
+              else
+                let () = Js_of_ocaml_lwt.Lwt_js.sleep (delay retries) in
+                aux (retries + 1)
+          | Restart ->
+              Logs.info ~src:section (fun fmt -> fmt "restart");
+              aux 0
+          | exn ->
+              Logs.app ~src:section (fun fmt ->
+                fmt ("connection failure" ^^ "@\n%s") (Printexc.to_string exn));
+              let () = handle_exn ~exn () in
+              raise exn)
     in
     update_activity hd; aux 0
 
   let call_commands {hd_service = Ecb.Comet_service (srv, queue); _} command =
     ignore
-      (Lwt.catch
-         (fun () ->
-            call_service_after_load_end srv queue
-              (false, Ecb.Stateful (Ecb.Commands command)))
-         (fun exn ->
-            Logs.app ~src:section (fun fmt ->
-              fmt ("request failed" ^^ "@\n%s") (Printexc.to_string exn));
-            Lwt.return ""))
+      (try
+         call_service_after_load_end srv queue
+           (false, Ecb.Stateful (Ecb.Commands command))
+       with exn ->
+         Logs.app ~src:section (fun fmt ->
+           fmt ("request failed" ^^ "@\n%s") (Printexc.to_string exn));
+         "")
 
   let close hd chan_id =
     match hd.hd_state with
@@ -615,8 +632,16 @@ end = struct
         restart hd
 
   let init_activity () =
-    let active_waiter, active_wakener = Lwt.wait () in
-    let restart_waiter, restart_wakener = Lwt.wait () in
+    let active_waiter, active_wakener =
+      Promise.create
+        (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+        ()
+    in
+    let restart_waiter, restart_wakener =
+      Promise.create
+        (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+        ()
+    in
     { active = `Inactive
     ; focused = None
     ; active_waiter
@@ -637,16 +662,38 @@ end
 
 type 'a handler =
   { hd_service_handler : 'a Service_handler.t
-  ; hd_stream : (string * int option * string Ecb.channel_data) Lwt_stream.t }
+  ; mutable hd_callbacks :
+      (string * int option * string Ecb.channel_data -> unit) list
+  ; mutable hd_error_callbacks : (unit -> unit) list }
+
+let wait_data_daemon hd =
+  let on_error _ =
+    (* Notify callbacks of an error and release callbacks to avoid memory leaks. *)
+    hd.hd_callbacks <- [];
+    let () = List.iter (fun callback -> callback ()) hd.hd_error_callbacks in
+    hd.hd_error_callbacks <- []
+  in
+  let notify_callbacks data =
+    List.iter (fun callback -> callback data) hd.hd_callbacks
+  in
+  let rec wait_data_loop () =
+    match Service_handler.wait_data hd.hd_service_handler with
+    | data ->
+        let () = List.iter notify_callbacks data in
+        wait_data_loop ()
+    | exception v -> on_error v
+  in
+  Fiber.fork
+    ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+    wait_data_loop
+
+let register_callback hd callback =
+  hd.hd_callbacks <- callback :: hd.hd_callbacks
 
-let handler_stream hd =
-  Lwt_stream.map_list
-    (fun x -> x)
-    (Lwt_stream.from (fun () ->
-       Lwt.try_bind
-         (fun () -> Service_handler.wait_data hd)
-         (fun s -> Lwt.return_some s)
-         (fun _ -> Lwt.return_none)))
+(** Register a callback for when the channel closes and no more message will be
+    received for every channel ids. *)
+let register_error_callback hd callback =
+  hd.hd_error_callbacks <- callback :: hd.hd_error_callbacks
 
 let stateful_handler_table :
   (Ecb.comet_service, Service_handler.stateful handler) Hashtbl.t
@@ -660,8 +707,8 @@ let stateless_handler_table :
 
 let init (service : Ecb.comet_service) kind table =
   let hd_service_handler = Service_handler.make service kind in
-  let hd_stream = handler_stream hd_service_handler in
-  let hd = {hd_service_handler; hd_stream} in
+  let hd = {hd_service_handler; hd_callbacks = []; hd_error_callbacks = []} in
+  wait_data_daemon hd;
   Hashtbl.add table service hd;
   hd
 
@@ -739,54 +786,53 @@ let check_and_update_position position msg_pos data =
           true)
         else false)
 
-(* stateless channels are registered with a position: when a channel
-   is registered more than one time, it is possible to receive old
-   messages: the position is used to filter them out. *)
-let register' hd position (_ : Ecb.comet_service) (chan_id : 'a Ecb.chan_id) =
-  let chan_id = Ecb.string_of_chan_id chan_id in
-  let stream =
-    Lwt_stream.filter_map_s
-      (function
-        | id, pos, data
-          when id = chan_id && check_and_update_position position pos data -> (
-          match data with
-          | Ecb.Full -> Lwt.fail Channel_full
-          | Ecb.Closed -> Lwt.fail Channel_closed
-          | Ecb.Data x -> Lwt.return_some (unmarshal x : 'a))
-        | _ -> Lwt.return_none)
-      (Lwt_stream.clone hd.hd_stream)
-  in
-  let protect_and_close t =
-    let t' = Lwt.protected t in
-    Lwt.on_cancel t' (fun () ->
-      Service_handler.close hd.hd_service_handler chan_id);
-    t'
-  in
-  (* protect the stream from cancels *)
-  Lwt_stream.from (fun () -> protect_and_close (Lwt_stream.get stream))
+module Channel = struct
+  type 'a t =
+    | C : {hd : _ handler; chan_pos : position; chan_id : string} -> 'a t
 
-let register_stateful ?(wake = true) service chan_id =
+  let make hd chan_pos chan_id = C {hd; chan_pos; chan_id}
+  let wake (C {hd; _}) = Service_handler.activate hd.hd_service_handler
+
+  (* stateless channels are registered with a position: when a channel is
+   registered more than one time, it is possible to receive old messages: the
+   position is used to filter them out. *)
+  let register (C {hd; chan_pos; chan_id}) callback =
+    register_callback hd (fun (id, pos, data) ->
+      if id = chan_id && check_and_update_position chan_pos pos data
+      then
+        match data with
+        | Ecb.Full | Closed -> callback None
+        | Data x -> callback (Some (unmarshal x : 'a))
+      else ());
+    register_error_callback hd (fun () -> callback None)
+end
+
+let register_stateful service chan_id =
   let hd = get_stateful_hd service in
-  let stream = register' hd No_position service chan_id in
   let chan_id = Ecb.string_of_chan_id chan_id in
   Service_handler.add_channel_stateful hd.hd_service_handler chan_id;
-  if wake then Service_handler.activate hd.hd_service_handler;
-  stream
+  Channel.make hd No_position chan_id
 
-let register_stateless ?(wake = true) service chan_id kind =
+let register_stateless service chan_id kind =
   let hd = get_stateless_hd service in
-  let stream = register' hd (position_of_kind kind) service chan_id in
   let chan_id = Ecb.string_of_chan_id chan_id in
   Service_handler.add_channel_stateless hd.hd_service_handler chan_id kind;
-  if wake then Service_handler.activate hd.hd_service_handler;
-  stream
+  Channel.make hd (position_of_kind kind) chan_id
 
-let register ?(wake = true) (wrapped_chan : 'a Ecb.wrapped_channel) =
+let unwrap (wrapped_chan : 'a Ecb.wrapped_channel) : 'a Channel.t =
   match wrapped_chan with
-  | Ecb.Stateful_channel (s, c) -> register_stateful ~wake s c
-  | Ecb.Stateless_channel (s, c, kind) -> register_stateless ~wake s c kind
+  | Ecb.Stateful_channel (s, c) -> register_stateful s c
+  | Ecb.Stateless_channel (s, c, kind) -> register_stateless s c kind
+
+let register_wrapped ?(wake = true) wrapped_chan callback =
+  let chan = unwrap wrapped_chan in
+  Channel.register chan callback;
+  if wake then Channel.wake chan;
+  chan
 
-let internal_unwrap (wrapped_chan, _unwrapper) = register wrapped_chan
+let internal_unwrap (wrapped_chan, _unwrapper) =
+  let chan = unwrap wrapped_chan in
+  Channel.wake chan; chan
 
 let () =
   Eliom_unwrap.register_unwrapper Eliom_common.comet_channel_unwrap_id
@@ -808,8 +854,4 @@ let is_active () =
   max (Hashtbl.fold f stateless_handler_table `Active) (fun () ->
     Hashtbl.fold f stateful_handler_table `Active)
 
-module Channel = struct
-  type 'a t = 'a Lwt_stream.t
-end
-
 let force_link = ()
diff --git a/src/lib/eliom_comet.client.mli b/src/lib/eliom_comet.client.mli
index bd12ee9876..48e43d40e8 100644
--- a/src/lib/eliom_comet.client.mli
+++ b/src/lib/eliom_comet.client.mli
@@ -35,15 +35,10 @@
     will close the channel. *)
 
 exception Channel_full
-(** [Channel_full] is raised when trying to read on a channel marked
-    full by the server. It is not possible to read anything else from a
-    full channel. *)
+(** @deprecated Not raised anymore. *)
 
 exception Channel_closed
-(** [Channel_closed] is raised when reading on a channel and the
-    server side of the application closed channel ( the server was restarted,
-    a session was closed, or a stateless channel was garbage collected).
-     *)
+(** @deprecated Not raised anymore. *)
 
 val is_active : unit -> [`Active | `Idle | `Inactive]
 (** [is_active ()] returns the current activity state *)
@@ -52,7 +47,7 @@ val activate : unit -> unit
 (** if the client is inactive [activate ()] launch a new xhr
     connection to start receiving server messages *)
 
-val set_handle_exn_function : (?exn:exn -> unit -> unit Lwt.t) -> unit
+val set_handle_exn_function : (?exn:exn -> unit -> unit) -> unit
 (** Makes possible to customize the function called when comet fails
     for unknown reason.
     The usual practice is to warn the user and ask to reload the page.
@@ -115,17 +110,26 @@ module Configuration : sig
 end
 
 module Channel : sig
-  type 'a t = 'a Lwt_stream.t
+  type 'a t
+
+  val register : 'a t -> ('a option -> unit) -> unit
+  (** [register chan callback] registers a callback to be called for new messages
+    from the server. The callback receives [Some data] for each new messages
+    from the server and [None] when the server closes the channel or an error
+    occurs. Not thread-safe. *)
 end
 
 (**/**)
 
-val register :
+val register_wrapped :
    ?wake:bool
   -> 'a Eliom_comet_base.wrapped_channel
-  -> 'a Lwt_stream.t
-(** if wake is false, the registration of the channel won't
-    activate the handling loop ( no request will be sent ). Default is true *)
+  -> ('a option -> unit)
+  -> 'a Channel.t
+(** [register_wrapped ~wake chan callback] registers a callback to a wrapped
+    channel and return a [Channel.t]. If wake is false, the registration of the
+    channel won't activate the handling loop ( no request will be sent ),
+    default is true. *)
 
 val restart : unit -> unit
 (** [restart ()] Restarts the loop waiting for server messages. It is
@@ -142,7 +146,7 @@ val close : 'a Eliom_comet_base.wrapped_channel -> unit
 
 val force_link : unit
 
-val handle_exn : ?exn:exn -> unit -> unit Lwt.t
+val handle_exn : ?exn:exn -> unit -> unit
 (** This function calls manually the function
     that is usually called automatically when an exception
     is received during communication. *)
diff --git a/src/lib/eliom_comet.server.ml b/src/lib/eliom_comet.server.ml
index c9067d4c7b..7ca2bc718f 100644
--- a/src/lib/eliom_comet.server.ml
+++ b/src/lib/eliom_comet.server.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -52,7 +52,7 @@ exception New_connection
 module Comet_param = struct
   type page = string
 
-  let translate content = Lwt.return (content, json_content_type)
+  let translate content = content, json_content_type
 end
 
 module Comet =
@@ -64,16 +64,14 @@ let comet_global_path = ["__eliom_comet_global__"]
 let fallback_service =
   Eliom_common.lazy_site_value_from_fun @@ fun () ->
   Comet.create ~meth:(Eliom_service.Get Eliom_parameter.unit)
-    ~path:(Eliom_service.Path comet_path) (fun () () ->
-    Lwt.return state_closed_msg)
+    ~path:(Eliom_service.Path comet_path) (fun () () -> state_closed_msg)
 
 let fallback_global_service =
   Eliom_common.lazy_site_value_from_fun @@ fun () ->
   Comet.create ~meth:(Eliom_service.Get Eliom_parameter.unit)
     ~path:(Eliom_service.Path comet_global_path) (fun () () ->
-    Lwt.return
-      (error_msg
-         "request with no post parameters, or there isn't any registered site comet channel"))
+    error_msg
+      "request with no post parameters, or there isn't any registered site comet channel")
 
 let new_id = Eliom_lib.make_cryptographic_safe_string
 
@@ -105,7 +103,7 @@ end = struct
     ; mutable ch_index : int
     ; (* the number of messages already added to the channel *)
       ch_content : (string * int) Dlist.t
-    ; ch_wakeup : unit Lwt_condition.t
+    ; ch_wakeup : Eio.Condition.t
       (* condition broadcasted when there is a new message *) }
 
   module Channel_hash = struct
@@ -124,13 +122,13 @@ end = struct
       { ch_id = ""
       ; ch_index = 0
       ; ch_content = Dlist.create 1
-      ; ch_wakeup = Lwt_condition.create () }
+      ; ch_wakeup = Eio.Condition.create () }
     in
     fun ch_id ->
       let dummy = {dummy_channel with ch_id} in
       try Some (Weak_channel_table.find channels dummy) with Not_found -> None
 
-  let wakeup_waiters channel = Lwt_condition.broadcast channel.ch_wakeup ()
+  let wakeup_waiters channel = Eio.Condition.broadcast channel.ch_wakeup
 
   (* fill the channel with messages from the stream *)
   let run_channel channel stream =
@@ -141,19 +139,19 @@ end = struct
     let f msg =
       match Weak.get channel 0 with
       | None ->
-          Lwt.fail Not_found
+          raise Not_found
           (* terminates the loop: remove reference on the stream, etc ... *)
       | Some channel ->
           channel.ch_index <- succ channel.ch_index;
           ignore
             (Dlist.add (msg, channel.ch_index) channel.ch_content : 'a option);
-          wakeup_waiters channel;
-          Lwt.return_unit
+          wakeup_waiters channel
     in
     ignore
-      (Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-       Lwt_stream.iter_s f stream
-       : unit Lwt.t)
+      ((Stdlib.Option.fold ~none:Fiber.without_binding
+          ~some:(Fun.flip Fiber.with_binding)
+          None) Eliom_common.sp_key (fun () -> Lwt_stream.iter_s f stream)
+       : unit Promise.t)
 
   let make_name name = "stateless:" ^ name
 
@@ -166,7 +164,7 @@ end = struct
       { ch_id = name
       ; ch_index = 0
       ; ch_content = Dlist.create size
-      ; ch_wakeup = Lwt_condition.create () }
+      ; ch_wakeup = Eio.Condition.create () }
     in
     run_channel channel stream;
     match find_channel name with
@@ -240,17 +238,24 @@ end = struct
     let rec make_list = function
       | [] -> []
       | Eliom_lib.Left (channel, _) :: q ->
-          Lwt_condition.wait channel.ch_wakeup :: make_list q
+          Eio.Condition.await
+            (* TODO: lwt-to-direct-style: A mutex must be passed *)
+            channel.ch_wakeup __mutex__
+          :: make_list q
       | Eliom_lib.Right _ :: _ -> assert false
       (* closed channels are considered to have data *)
     in
-    Lwt.pick (make_list requests)
+    Fiber.any
+      ((* TODO: lwt-to-direct-style: This expression is a ['a Lwt.t list] but a [(unit -> 'a) list] is expected. *)
+       make_list requests)
 
   let wait_data requests =
     if List.exists has_data requests
-    then Lwt.return_unit
+    then ()
     else
-      Lwt_unix.with_timeout (timeout ()) (fun () -> really_wait_data requests)
+      Eio.Time.with_timeout_exn
+        (Stdlib.Option.get (Fiber.get Ocsigen_lib.env))#mono_clock (timeout ())
+        (fun () -> really_wait_data requests)
 
   let handle_request () (_, req) =
     match req with
@@ -259,15 +264,13 @@ end = struct
           "attempting to request data on stateless service with a stateful request"
     | Eliom_comet_base.Stateless requests ->
         let requests = List.map get_channel (Array.to_list requests) in
-        let* res =
-          Lwt.catch
-            (fun () ->
-               let* () = wait_data requests in
-               Lwt.return (List.flatten (List.map get_available_data requests)))
-            (function
-              | Lwt_unix.Timeout -> Lwt.return_nil | exc -> Lwt.reraise exc)
+        let res =
+          try
+            let () = wait_data requests in
+            List.flatten (List.map get_available_data requests)
+          with Eio.Time.Timeout -> []
         in
-        Lwt.return (encode_global_downgoing res)
+        encode_global_downgoing res
 
   let global_service =
     Eliom_common.lazy_site_value_from_fun @@ fun () ->
@@ -321,16 +324,12 @@ module Stateful : sig
   type comet_service = Eliom_comet_base.comet_service
 
   val get_service : t -> comet_service
-
-  val wait_timeout :
-     ?scope:Eliom_common.client_process_scope
-    -> float
-    -> unit Lwt.t
+  val wait_timeout : ?scope:Eliom_common.client_process_scope -> float -> unit
 end = struct
   type chan_id = string
   type comet_service = Eliom_comet_base.comet_service
   type internal_comet_service = Eliom_comet_base.internal_comet_service
-  type end_request_waiters = unit Lwt.u
+  type end_request_waiters = unit Promise.u
 
   type activity =
     | Active of end_request_waiters list
@@ -338,7 +337,7 @@ end = struct
     | Inactive of float
     (** The last request from the client completed at that time *)
 
-  type waiter = [`Data | `Update] Lwt.t
+  type waiter = [`Data | `Update] Promise.t
 
   type channel =
     | Events of
@@ -359,7 +358,7 @@ end = struct
       (** streams that are created on the server side, but client did not register *)
     ; mutable hd_registered_chan_id : chan_id list
       (** the fusion of all the streams from hd_active_channels *)
-    ; mutable hd_update_streams_w : [`Data | `Update] Lwt.u option
+    ; mutable hd_update_streams_w : [`Data | `Update] Promise.u option
       (** used to signal new data or new active streams. *)
     ; hd_service : internal_comet_service
     ; mutable hd_last : string * int
@@ -379,7 +378,7 @@ end = struct
     match handler.hd_activity with
     | Active l ->
         handler.hd_activity <- Inactive (Unix.gettimeofday ());
-        List.iter (fun waiter -> Lwt.wakeup waiter ()) l
+        List.iter (fun waiter -> Promise.resolve waiter ()) l
     | Inactive _ -> ()
 
   let update_inactive handler =
@@ -391,10 +390,15 @@ end = struct
     let rec run () =
       match handler.hd_activity with
       | Active l ->
-          let waiter, waker = Lwt.task () in
+          let waiter, waker =
+            Promise.create
+              (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+              (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+              ()
+          in
           let t =
-            let* () = waiter in
-            let* () = Lwt_unix.sleep t in
+            let () = waiter in
+            let () = Eio_unix.sleep t in
             run ()
           in
           handler.hd_activity <- Active (waker :: l);
@@ -402,9 +406,9 @@ end = struct
       | Inactive inactive_time ->
           let now = Unix.gettimeofday () in
           if now -. inactive_time > t
-          then Lwt.return_unit
+          then ()
           else
-            let* () = Lwt_unix.sleep (t -. (now -. inactive_time)) in
+            let () = Eio_unix.sleep (t -. (now -. inactive_time)) in
             run ()
     in
     run ()
@@ -420,7 +424,9 @@ end = struct
     | None -> ()
     | Some wakener ->
         handler.hd_update_streams_w <- None;
-        Lwt.wakeup_exn wakener New_connection
+        Promise.resolve_error
+          (* TODO: lwt-to-direct-style: This used to be a ['a Lwt.t] is now a [('a, exn) result Promise.t]. Use [resolve_ok] and [await_exn] instead of [resolve] and [await]. *)
+          wakener New_connection
 
   (** called when a new channel is made active. It restarts the thread
       wainting for inputs ( wait_data ) such that it can receive the messages from
@@ -430,13 +436,17 @@ end = struct
     | None -> ()
     | Some wakener ->
         handler.hd_update_streams_w <- None;
-        Lwt.wakeup wakener event
+        Promise.resolve wakener event
 
   let stream_waiter s =
-    Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-    Lwt.no_cancel
-      (let* _ = Lwt_stream.peek s in
-       Lwt.return `Data)
+    (Stdlib.Option.fold ~none:Fiber.without_binding
+       ~some:(Fun.flip Fiber.with_binding)
+       None) Eliom_common.sp_key (fun () ->
+      Lwt.no_cancel
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+        (let _ = Lwt_stream.peek s in
+         `Data))
 
   (** read up to [n] messages in the list of streams [streams] without blocking. *)
   let read_channels n handler =
@@ -452,8 +462,10 @@ end = struct
             else take (n - 1) ((id, Queue.take queue) :: acc) channels
         | (id, Stream ({stream; _} as s)) :: rem ->
             let l =
-              Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-              Lwt_stream.get_available_up_to n stream
+              (Stdlib.Option.fold ~none:Fiber.without_binding
+                 ~some:(Fun.flip Fiber.with_binding)
+                 None) Eliom_common.sp_key (fun () ->
+                Lwt_stream.get_available_up_to n stream)
             in
             if l <> [] then s.waiter <- stream_waiter stream;
             take (n - List.length l) (List.rev_map (fun v -> id, v) l @ acc) rem
@@ -472,16 +484,21 @@ end = struct
       handles new channels the server creates after that the client
       registered them *)
   let rec wait_data wait_closed_connection handler =
-    Lwt.bind
-      (let hd_update_streams, hd_update_streams_w = Lwt.task () in
-       handler.hd_update_streams_w <- Some hd_update_streams_w;
-       Lwt.choose
-         (wait_closed_connection :: hd_update_streams :: wait_channels handler))
-      (function
-        | `Data ->
-            handler.hd_update_streams_w <- None;
-            Lwt.return_unit
-        | `Update -> wait_data wait_closed_connection handler)
+    match
+      let hd_update_streams, hd_update_streams_w =
+        Promise.create
+          (* TODO: lwt-to-direct-style: Use [Switch] or [Cancel] for defining a cancellable context. *)
+          (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+          ()
+      in
+      handler.hd_update_streams_w <- Some hd_update_streams_w;
+      Lwt.choose
+        (* TODO: lwt-to-direct-style: [Lwt.choose] can't be automatically translated.Use Eio.Promise instead.  *)
+        (* TODO: lwt-to-direct-style: [Lwt.choose] can't be automatically translated.Use Eio.Promise instead.  *)
+        (wait_closed_connection :: hd_update_streams :: wait_channels handler)
+    with
+    | `Data -> handler.hd_update_streams_w <- None
+    | `Update -> wait_data wait_closed_connection handler
 
   let launch_channel handler chan_id channel =
     handler.hd_active_channels <-
@@ -513,10 +530,8 @@ end = struct
       List.filter (( <> ) chan_id) handler.hd_registered_chan_id
 
   let wait_closed_connection () =
-    let* () =
-      Ocsigen_request.connection_closed (Eliom_request_info.get_ri ())
-    in
-    Lwt.fail Connection_closed
+    let () = Ocsigen_request.connection_closed (Eliom_request_info.get_ri ()) in
+    raise Connection_closed
 
   (* register the service handler.hd_service *)
   let run_handler handler =
@@ -525,42 +540,41 @@ end = struct
       | Eliom_comet_base.Stateless _ ->
           failwith
             "attempting to request data on stateful service with a stateless request"
-      | Eliom_comet_base.Stateful (Eliom_comet_base.Request_data number) ->
+      | Eliom_comet_base.Stateful (Eliom_comet_base.Request_data number) -> (
           Logs.info ~src:section (fun fmt -> fmt "received request %i" number);
           (* if a new connection occurs for a service, we reply
            immediately to the previous with no data. *)
           new_connection handler;
           if snd handler.hd_last = number
-          then Lwt.return (fst handler.hd_last)
+          then fst handler.hd_last
           else
-            Lwt.catch
-              (fun () ->
-                 Lwt_unix.with_timeout (timeout ()) (fun () ->
-                   let* messages =
-                     let messages = read_channels 100 handler in
-                     if messages <> [] || idle
-                     then Lwt.return messages
-                     else
-                       let* () =
-                         wait_data (wait_closed_connection ()) handler
-                       in
-                       Lwt.return (read_channels 100 handler)
-                   in
-                   let message = encode_downgoing messages in
-                   handler.hd_last <- message, number;
-                   set_inactive handler;
-                   Lwt.return message))
-              (function
-                | New_connection -> Lwt.return (encode_downgoing [])
+            try
+              Eio.Time.with_timeout_exn
+                (Stdlib.Option.get (Fiber.get Ocsigen_lib.env))#mono_clock
+                (timeout ()) (fun () ->
+                let messages =
+                  let messages = read_channels 100 handler in
+                  if messages <> [] || idle
+                  then messages
+                  else
+                    let () = wait_data (wait_closed_connection ()) handler in
+                    read_channels 100 handler
+                in
+                let message = encode_downgoing messages in
+                handler.hd_last <- message, number;
+                set_inactive handler;
+                message)
+            with
+            | New_connection ->
+                encode_downgoing []
                 (* happens if an other connection has been opened on that service *)
                 (* CCC in this case, it would be beter to return code 204: no content *)
-                | Lwt_unix.Timeout ->
-                    set_inactive handler; Lwt.return timeout_msg
-                | Connection_closed ->
-                    set_inactive handler;
-                    (* it doesn't matter what we do here *)
-                    Lwt.return timeout_msg
-                | e -> set_inactive handler; Lwt.fail e)
+            | Eio.Time.Timeout -> set_inactive handler; timeout_msg
+            | Connection_closed ->
+                set_inactive handler;
+                (* it doesn't matter what we do here *)
+                timeout_msg
+            | e -> set_inactive handler; raise e)
       | Eliom_comet_base.Stateful (Eliom_comet_base.Commands commands) ->
           update_inactive handler;
           List.iter
@@ -571,7 +585,7 @@ end = struct
             (Array.to_list commands);
           (* command connections are replied immediately by an
                  empty answer *)
-          Lwt.return (encode_downgoing [])
+          encode_downgoing []
     in
     let {hd_service = Eliom_comet_base.Internal_comet_service (service, _); _} =
       handler
@@ -595,15 +609,15 @@ end = struct
      type: This is needed because bus and react create the channel at
      wrapping time, where it is impossible to block *)
   let get_ref eref =
-    match Lwt.state (Eliom_reference.get eref) with
-    | Lwt.Return v -> v
+    match Promise.peek (Eliom_reference.get eref) with
+    | Some v -> v
     | _ ->
         failwith
           "Eliom_comet: accessing channel references should not be blocking: this is an eliom bug"
 
   let set_ref eref v =
-    match Lwt.state (Eliom_reference.set eref v) with
-    | Lwt.Return () -> ()
+    match Promise.peek (Eliom_reference.set eref v) with
+    | Some () -> ()
     | _ ->
         failwith
           "Eliom_comet: accessing channel references should not be blocking: this is an eliom bug"
@@ -724,8 +738,10 @@ end = struct
     let handler = get_handler scope in
     Logs.info ~src:section (fun fmt -> fmt "create channel %s" name);
     let stream =
-      Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-      Lwt_stream.map (fun x -> Eliom_comet_base.Data (marshal x)) stream
+      (Stdlib.Option.fold ~none:Fiber.without_binding
+         ~some:(Fun.flip Fiber.with_binding)
+         None) Eliom_common.sp_key (fun () ->
+        Lwt_stream.map (fun x -> Eliom_comet_base.Data (marshal x)) stream)
     in
     let channel = Stream {stream; waiter = stream_waiter stream} in
     if List.mem name handler.hd_registered_chan_id
@@ -784,10 +800,7 @@ module Channel : sig
     -> unit
     -> 'a t
 
-  val wait_timeout :
-     ?scope:Eliom_common.client_process_scope
-    -> float
-    -> unit Lwt.t
+  val wait_timeout : ?scope:Eliom_common.client_process_scope -> float -> unit
 end = struct
   type 'a channel =
     | Stateless of Stateless.channel
@@ -828,14 +841,16 @@ end = struct
   let create_stateless_channel ?name ~size stream =
     Stateless
       (Stateless.create ?name ~size
-         ( Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-           Lwt_stream.map marshal stream ))
+         ((Stdlib.Option.fold ~none:Fiber.without_binding
+             ~some:(Fun.flip Fiber.with_binding)
+             None) Eliom_common.sp_key (fun () -> Lwt_stream.map marshal stream)))
 
   let create_stateless_newest_channel ?name stream =
     Stateless_newest
       (Stateless.create ?name ~size:1
-         ( Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-           Lwt_stream.map marshal stream ))
+         ((Stdlib.Option.fold ~none:Fiber.without_binding
+             ~some:(Fun.flip Fiber.with_binding)
+             None) Eliom_common.sp_key (fun () -> Lwt_stream.map marshal stream)))
 
   let create_stateful ?scope ?name ?(size = 1000) events =
     { channel = create_stateful_channel ?scope ?name ~size events
diff --git a/src/lib/eliom_comet.server.mli b/src/lib/eliom_comet.server.mli
index 77df666d9b..14ff244c0d 100644
--- a/src/lib/eliom_comet.server.mli
+++ b/src/lib/eliom_comet.server.mli
@@ -120,10 +120,7 @@ module Channel : sig
       number of messages retrieved at the first request. The default
       is [1]. *)
 
-  val wait_timeout :
-     ?scope:Eliom_common.client_process_scope
-    -> float
-    -> unit Lwt.t
+  val wait_timeout : ?scope:Eliom_common.client_process_scope -> float -> unit
   (** [wait_timeout ~scope time] waits for a period of inactivity of
       length [time] in the [scope]. Only activity on stateful
       channels is taken into accounts.
diff --git a/src/lib/eliom_common.server.ml b/src/lib/eliom_common.server.ml
index f4a33f5e8c..4b79f16a7c 100644
--- a/src/lib/eliom_common.server.ml
+++ b/src/lib/eliom_common.server.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -246,7 +246,6 @@ type 'a cookie_info1 =
       SCData_session_expired = the cookie has not been found in the table.
       For both of them, ask the browser to remove the cookie.
     *)
-    Lwt.t
     Lazy.t
     Full_state_name_table.t
     ref
@@ -300,7 +299,8 @@ let network_of_ip k mask4 mask6 =
 
 let network_of_request r ~mask4 ~mask6 =
   match Ocsigen_request.client_conn r with
-  | `Inet (ip, _) -> network_of_ip ip mask4 mask6
+  | `Inet (ip, _) ->
+      network_of_ip (Ipaddr.of_string_exn (ip :> string)) mask4 mask6
   | _ -> Ipaddr.(V6 V6.localhost)
 
 module Net_addr_Hashtbl : sig
@@ -383,7 +383,7 @@ and naservice_table_content =
   (* max_use *)
   * (float * float ref) option
   (* timeout and expiration date *)
-  * (server_params -> Ocsigen_response.t Lwt.t)
+  * (server_params -> Ocsigen_response.t)
   * (page_table ref * page_table_key, na_key_serv) leftright
       Ocsigen_cache.Dlist.node
       option
@@ -474,7 +474,7 @@ and sitedata =
   ; (* Limitation of the number of groups per site *)
     mutable remove_session_data : string -> unit
   ; mutable not_bound_in_data_tables : string -> bool
-  ; mutable exn_handler : exn -> Ocsigen_response.t Lwt.t
+  ; mutable exn_handler : exn -> Ocsigen_response.t
   ; mutable unregistered_services : Url.path list
   ; mutable unregistered_na_services : na_key_serv list
   ; mutable max_volatile_data_sessions_per_group : int * bool
@@ -597,11 +597,11 @@ let make_server_params
   ; sp_full_state_name = full_state_name
   ; sp_client_process_info = cpi }
 
-let sp_key = Lwt.new_key ()
-let get_sp_option () = Lwt.get sp_key
+let sp_key = Fiber.create_key ()
+let get_sp_option () = Fiber.get sp_key
 
 let get_sp () =
-  match Lwt.get sp_key with
+  match Fiber.get sp_key with
   | Some sp -> sp
   | None ->
       let msg =
@@ -831,7 +831,7 @@ let empty_tables max forsession =
                      Ocsigen_request.client_conn
                        sp.sp_request.Ocsigen_extensions.request_info
                    with
-                   | `Inet (ip, _) -> ip
+                   | `Inet (ip, _) -> Ipaddr.of_string_exn (ip :> string)
                    | _ -> default_ip_table_key
                  in
                  ( ip
@@ -860,7 +860,6 @@ let get_mask4 sitedata = get_mask4 sitedata.ipv4mask
 let get_mask6 sitedata = get_mask6 sitedata.ipv6mask
 
 (*****************************************************************************)
-open Lwt
 
 (* The cookie name is
 
@@ -940,7 +939,7 @@ let get_session_info ~sitedata ~req previous_extension_err =
       Ocsigen_request.post_params ri ci.Ocsigen_extensions.uploaddir
         ci.Ocsigen_extensions.maxuploadfilesize
     with
-    | None -> true, Lwt.return []
+    | None -> true, []
     | Some v -> false, v
   in
   let no_file_param, file_params =
@@ -948,10 +947,10 @@ let get_session_info ~sitedata ~req previous_extension_err =
       Ocsigen_request.files ri ci.Ocsigen_extensions.uploaddir
         ci.Ocsigen_extensions.maxuploadfilesize
     with
-    | None -> true, Lwt.return []
+    | None -> true, []
     | Some v -> false, v
   in
-  let* post_params = p in
+  let post_params = p in
   let previous_tab_cookies_info, tab_cookies, post_params =
     try
       let tci, utc, tc =
@@ -1027,7 +1026,7 @@ let get_session_info ~sitedata ~req previous_extension_err =
   *)
   let get_params0 = get_params in
   let post_params0 = post_params in
-  let* file_params0 = file_params in
+  let file_params0 = file_params in
   let ( get_params
       , post_params
       , file_params
@@ -1272,10 +1271,9 @@ let get_session_info ~sitedata ~req previous_extension_err =
       ; si_expect_process_data =
           epd (*204FORMS*     si_internal_form= internal_form; *) } )
   in
-  Lwt.return
-    ( {req_whole with Ocsigen_extensions.request_info = ri}
-    , sess
-    , previous_tab_cookies_info )
+  ( {req_whole with Ocsigen_extensions.request_info = ri}
+  , sess
+  , previous_tab_cookies_info )
 
 exception Eliom_retry_with of info
 
@@ -1299,7 +1297,7 @@ module Omit_persistent_storage = struct
     | _ -> false
 
   let not_if_omitting_storage f =
-    if check_if_omitting_storage () then Lwt.return_unit else f ()
+    if check_if_omitting_storage () then () else f ()
 end
 
 module Ocsipersist = struct
@@ -1371,34 +1369,38 @@ module Persistent_tables = struct
 
   (** removes the entry from all opened tables *)
   let remove_key_from_all_tables key =
-    (* doesn't remove entry from Persistent_cookies_expiry_dates; not a problem *)
-    Lwt_list.iter_s
+    List.iter
+      (* doesn't remove entry from Persistent_cookies_expiry_dates; not a problem *)
       (fun (module T : Ocsipersist.TABLE with type key = string) ->
          T.remove key)
-      !functorial_tables
-    >>= fun () ->
-    Lwt_list.iter_s (* could be replaced by iter_p *)
+      !functorial_tables;
+    List.iter
+      (* could be replaced by iter_p *)
       (fun t ->
-         Ocsipersist.Polymorphic.open_table t >>= fun table ->
-         Ocsipersist.Polymorphic.remove table key >>= Lwt.pause)
+         let table = Ocsipersist.Polymorphic.open_table t in
+         Fiber.yield (Ocsipersist.Polymorphic.remove table key))
       !polymorphic_tables
 
   let number_of_tables () =
     List.length !polymorphic_tables + List.length !functorial_tables
 
   let number_of_table_elements () =
-    Lwt_list.map_s
-      (fun t ->
-         Ocsipersist.Polymorphic.open_table t >>= fun table ->
-         Ocsipersist.Polymorphic.length table >>= fun e -> Lwt.return (t, e))
-      !polymorphic_tables
-    >>= fun polymorphic_counts ->
-    Lwt_list.map_s
-      (fun (module T : Ocsipersist.TABLE with type key = string) ->
-         T.length () >>= fun n -> Lwt.return (T.name, n))
-      !functorial_tables
-    >>= fun functorial_counts ->
-    Lwt.return @@ polymorphic_counts @ functorial_counts
+    let polymorphic_counts =
+      List.map
+        (fun t ->
+           let table = Ocsipersist.Polymorphic.open_table t in
+           let e = Ocsipersist.Polymorphic.length table in
+           t, e)
+        !polymorphic_tables
+    in
+    let functorial_counts =
+      List.map
+        (fun (module T : Ocsipersist.TABLE with type key = string) ->
+           let n = T.length () in
+           T.name, n)
+        !functorial_tables
+    in
+    polymorphic_counts @ functorial_counts
 end
 
 (**** Wrapper type shared by client/server side ***)
diff --git a/src/lib/eliom_common.server.mli b/src/lib/eliom_common.server.mli
index 8d8c3c8e69..c80dfc6337 100644
--- a/src/lib/eliom_common.server.mli
+++ b/src/lib/eliom_common.server.mli
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Module eliom_common.mli
@@ -358,7 +360,6 @@ type 'a cookie_info1 =
       ref
   * ((string * timeout * float option * perssessgrp option) option
     * one_persistent_cookie_info session_cookie ref)
-      Lwt.t
       Lazy.t
       Full_state_name_table.t
       ref
@@ -412,7 +413,7 @@ type ('params, 'result) service =
   { s_id : anon_params_type * anon_params_type
   ; mutable s_max_use : int option
   ; s_expire : (float * float ref) option
-  ; s_f : bool -> 'params -> 'result Lwt.t }
+  ; s_f : bool -> 'params -> 'result }
 
 type server_params =
   { sp_request : Ocsigen_extensions.request
@@ -455,7 +456,7 @@ and naservice_table_content =
   (* max_use *)
   * (float * float ref) option
   (* timeout and expiration date *)
-  * (server_params -> Ocsigen_response.t Lwt.t)
+  * (server_params -> Ocsigen_response.t)
   * (page_table ref * page_table_key, na_key_serv) leftright
       Ocsigen_cache.Dlist.node
       option
@@ -537,7 +538,7 @@ and sitedata =
   ; (* Limitation of the number of groups per site *)
     mutable remove_session_data : string -> unit
   ; mutable not_bound_in_data_tables : string -> bool
-  ; mutable exn_handler : exn -> Ocsigen_response.t Lwt.t
+  ; mutable exn_handler : exn -> Ocsigen_response.t
   ; mutable unregistered_services : Url.path list
   ; mutable unregistered_na_services : na_key_serv list
   ; mutable max_volatile_data_sessions_per_group : int * bool
@@ -604,10 +605,9 @@ val get_session_info :
    sitedata:sitedata
   -> req:Ocsigen_extensions.request
   -> int
-  -> (Ocsigen_extensions.request
+  -> Ocsigen_extensions.request
      * sess_info
-     * (tables cookie_info * Ocsigen_cookie_map.t) option)
-       Lwt.t
+     * (tables cookie_info * Ocsigen_cookie_map.t) option
 
 type ('a, 'b) foundornot = Found of 'a | Notfound of 'b
 
@@ -626,15 +626,15 @@ val make_full_state_name2 :
   -> full_state_name
 
 module Persistent_tables : sig
-  val create : string -> 'a Ocsipersist.table Lwt.t
+  val create : string -> 'a Ocsipersist.table
 
   val add_functorial_table :
      (module Ocsipersist.TABLE with type key = string)
     -> unit
 
-  val remove_key_from_all_tables : string -> unit Lwt.t
+  val remove_key_from_all_tables : string -> unit
   val number_of_tables : unit -> int
-  val number_of_table_elements : unit -> (string * int) list Lwt.t
+  val number_of_table_elements : unit -> (string * int) list
 end
 
 val absolute_change_sitedata : sitedata -> unit
@@ -695,7 +695,7 @@ val tab_cookie_action_info_key :
   * string Ocsigen_cookie_map.Map_inner.t)
     Polytables.key
 
-val sp_key : server_params Lwt.key
+val sp_key : server_params Fiber.key
 val get_sp_option : unit -> server_params option
 val get_sp : unit -> server_params
 val sp_of_option : server_params option -> server_params
diff --git a/src/lib/eliom_common_base.shared.ml b/src/lib/eliom_common_base.shared.ml
index 8b90bc1c34..ac3cc846a5 100644
--- a/src/lib/eliom_common_base.shared.ml
+++ b/src/lib/eliom_common_base.shared.ml
@@ -206,8 +206,8 @@ type sess_info =
       string Full_state_name_table.t
       * string Full_state_name_table.t
       * string Full_state_name_table.t
-    (* the same, but for secure cookies *)
-  ; (* now for tab cookies: *)
+  ; (* the same, but for secure cookies *)
+    (* now for tab cookies: *)
     si_service_session_cookies_tab : string Full_state_name_table.t
   ; si_data_session_cookies_tab : string Full_state_name_table.t
   ; si_persistent_session_cookies_tab : string Full_state_name_table.t
@@ -364,7 +364,7 @@ type ('params, 'result) service =
     s_id : anon_params_type * anon_params_type
   ; mutable s_max_use : int option
   ; s_expire : (float * float ref) option
-  ; s_f : bool -> 'params -> 'result Lwt.t }
+  ; s_f : bool -> 'params -> 'result }
 
 type 'a to_and_of = {of_string : string -> 'a; to_string : 'a -> string}
 
diff --git a/src/lib/eliom_content.client.mli b/src/lib/eliom_content.client.mli
index c9d9b399c2..b438ceaaf5 100644
--- a/src/lib/eliom_content.client.mli
+++ b/src/lib/eliom_content.client.mli
@@ -931,10 +931,10 @@ val force_link : unit
 val set_client_fun :
    ?app:string
   -> service:('a, 'b, _, _, _, _, _, _, _, _, _) Eliom_service.t
-  -> ('a -> 'b -> Eliom_service.result Lwt.t)
+  -> ('a -> 'b -> Eliom_service.result)
   -> unit
 
-val set_form_error_handler : (unit -> bool Lwt.t) -> unit
+val set_form_error_handler : (unit -> bool) -> unit
 (** With [set_form_error_handler f], [f] becomes the action to be
     called when we are unable to call a client-side service due to
     invalid form data.
diff --git a/src/lib/eliom_cscache.eliom b/src/lib/eliom_cscache.eliom
index 5a7287b3fc..48b432c557 100644
--- a/src/lib/eliom_cscache.eliom
+++ b/src/lib/eliom_cscache.eliom
@@ -1,10 +1,10 @@
-open Lwt.Syntax
+open%server Eio.Std
 
 (* Copyright Vincent Balat *)
 
 [%%shared.start]
 
-type ('a, 'b) t = (unit -> ('a, 'b Lwt.t) Hashtbl.t) Eliom_shared.Value.t
+type ('a, 'b) t = (unit -> ('a, 'b Promise.or_exn) Hashtbl.t) Eliom_shared.Value.t
 
 let%client create_ () =
   let c = Hashtbl.create 100 in
@@ -24,34 +24,40 @@ let do_cache_raw cache id data =
   let c = Eliom_shared.Value.local cache () in
   Hashtbl.replace c id data;
   (* Do not cache exceptions *)
-  ignore (Lwt.catch (fun _ -> data) (fun e -> Hashtbl.remove c id; Lwt.fail e))
+  ignore
+    (try data
+     with e ->
+       Hashtbl.remove c id;
+       raise e)
 
-let do_cache cache id data = do_cache_raw cache id (Lwt.return data)
+let do_cache cache id data = do_cache_raw cache id data
 
 let%server do_cache cache id v =
   do_cache cache id v;
   ignore [%client.unsafe (do_cache ~%cache ~%id ~%v : unit)]
 
 let%server find cache get_data id =
-  try Hashtbl.find ((Eliom_shared.Value.local cache) ()) id
+  try Promise.await_exn (Hashtbl.find ((Eliom_shared.Value.local cache) ()) id)
   with Not_found ->
     let th =
-      let* v = get_data id in
-
-      ignore [%client.unsafe (do_cache ~%cache ~%id ~%v : unit)];
-      Lwt.return v
+      Fiber.fork_promise
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        (fun () ->
+           let v = get_data id in
+           ignore [%client.unsafe (do_cache ~%cache ~%id ~%v : unit)];
+           v)
     in
-    (* On server side, we put immediately in table the thread that is
-       fetching the data.  in order to avoid fetching it several
-       times. *)
-    do_cache_raw cache id th; th
+    (* On server side, we put immediately in table the thread that is fetching
+       the data. in order to avoid fetching it several times. *)
+    do_cache_raw cache id th; Promise.await_exn th
 
 let%client load cache get_data id =
   let th = get_data id in
   (* On client side, we put immediately in table the thread that is
      fetching the data.  Thus, [get_data_from_cache] returns
      immediately (in order to display a spinner). *)
-  do_cache_raw cache id th; th
+  do_cache_raw cache id th;
+  Promise.await_exn th
 
 let%client find cache get_data id =
   try Hashtbl.find ((Eliom_shared.Value.local cache) ()) id
@@ -63,4 +69,7 @@ let local_find cache id = Hashtbl.find ((Eliom_shared.Value.local cache) ()) id
 
 let find_if_ready cache id =
   let v = local_find cache id in
-  match Lwt.state v with Lwt.Return v -> v | _ -> raise Not_ready
+  match Promise.peek v with
+  | Some (Ok v) -> v
+  | Some (Error e) -> raise e
+  | _ -> raise Not_ready
diff --git a/src/lib/eliom_cscache.eliomi b/src/lib/eliom_cscache.eliomi
index edfafed6ee..06a7be3008 100644
--- a/src/lib/eliom_cscache.eliomi
+++ b/src/lib/eliom_cscache.eliomi
@@ -32,7 +32,7 @@ type ('a, 'b) t
 
 [%%shared.start]
 
-val find : ('a, 'b) t -> ('a -> 'b Lwt.t) -> 'a -> 'b Lwt.t
+val find : ('a, 'b) t -> ('a -> 'b) -> 'a -> 'b
 (** [find cache get_from_db key] returns the value associated to [key]
     in cache.  If not present, it calls [get_from_db] to fetch the
     data from the database. [get_from_db] must be implemented both
@@ -40,14 +40,14 @@ val find : ('a, 'b) t -> ('a -> 'b Lwt.t) -> 'a -> 'b Lwt.t
     result in a single call to [get_from_db]. Exceptions are not
     cached.  *)
 
-val do_cache : ('a, 'b) t -> 'a -> 'b -> unit
+val do_cache : ('a, 'b) t -> 'a -> 'b Eio.Promise.or_exn -> unit
 (** [do_cache cache key value] adds the association from [key] to
     [value] in [cache], or replaces it if not already present.  Called
     from client side, it affects only client side cache.  Called from
     server side, it will have effect both on the server cache (scope:
     request) and the client side cache.  *)
 
-val local_find : ('a, 'b) t -> 'a -> 'b Lwt.t
+val local_find : ('a, 'b) t -> 'a -> 'b Eio.Promise.or_exn
 (** Find a piece of data in local cache, without trying to fetch it
     from server. Raises [Not_found] instead.  If the value is currently
     being retrieved, it waits for it to be ready before returning.  *)
@@ -61,7 +61,7 @@ val find_if_ready : ('a, 'b) t -> 'a -> 'b
 
 [%%client.start]
 
-val load : ('a, 'b) t -> ('a -> 'b Lwt.t) -> 'a -> 'b Lwt.t
+val load : ('a, 'b) t -> ('a -> 'b) -> 'a -> 'b
 (** Load (or reload) in cache the piece of data from server  *)
 
 [%%server.start]
diff --git a/src/lib/eliom_extension.server.ml b/src/lib/eliom_extension.server.ml
index 4ee5deab6b..88a285b238 100644
--- a/src/lib/eliom_extension.server.ml
+++ b/src/lib/eliom_extension.server.ml
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2008 Vincent Balat
@@ -23,7 +25,7 @@
 (*****************************************************************************)
 (*****************************************************************************)
 
-type eliom_extension_sig = unit -> Ocsigen_extensions.answer Lwt.t
+type eliom_extension_sig = unit -> Ocsigen_extensions.answer
 
 let module_action : eliom_extension_sig ref =
   ref (fun _ -> failwith "Eliommod_extension")
@@ -33,4 +35,7 @@ let get_eliom_extension () = !module_action
 
 let run_eliom_extension (fext : eliom_extension_sig) _now info sitedata =
   let sp = Eliom_common.make_server_params sitedata info None None in
-  Lwt.with_value Eliom_common.sp_key (Some sp) fext
+  (Stdlib.Option.fold ~none:Fiber.without_binding
+     ~some:(Fun.flip Fiber.with_binding)
+     (Some sp))
+    Eliom_common.sp_key fext
diff --git a/src/lib/eliom_extension.server.mli b/src/lib/eliom_extension.server.mli
index c873f45f66..9783f7ca9d 100644
--- a/src/lib/eliom_extension.server.mli
+++ b/src/lib/eliom_extension.server.mli
@@ -21,7 +21,7 @@
     manual for more information about {% <<a_manual chapter="workflow-configuration"
     fragment="extensions"| Eliom's extensions>>%} *)
 
-type eliom_extension_sig = unit -> Ocsigen_extensions.answer Lwt.t
+type eliom_extension_sig = unit -> Ocsigen_extensions.answer
 (** Type of the function that must be registered to declare an eliom extension. *)
 
 val register_eliom_extension : eliom_extension_sig -> unit
@@ -35,4 +35,4 @@ val run_eliom_extension :
   -> float
   -> Eliom_common.info
   -> Eliom_common.sitedata
-  -> Ocsigen_extensions.answer Lwt.t
+  -> Ocsigen_extensions.answer
diff --git a/src/lib/eliom_form.eliom b/src/lib/eliom_form.eliom
index 5d75aee819..927f5bb2c1 100644
--- a/src/lib/eliom_form.eliom
+++ b/src/lib/eliom_form.eliom
@@ -19,25 +19,25 @@
  *)
 
 open%shared Js_of_ocaml
+
 [%%client.start]
-open Lwt.Syntax
 
 let read_params form y =
   Eliom_parameter.reconstruct_params_form (Form.form_elements form) y
 
 let error_handler =
-  ref @@ fun _ -> Lwt.fail_with "Cannot parse params for client-side service"
+  ref @@ fun _ -> failwith "Cannot parse params for client-side service"
 
 let set_error_handler f = error_handler := f
 
 let iter_contents y ev f =
-  let fls () = Lwt.return_false in
+  let fls () = false in
   Js.Opt.case ev##.target fls @@ fun target ->
   Js.Opt.case (Dom_html.CoerceTo.form target) fls @@ fun target ->
   match read_params target y with
   | Some v ->
-      let* () = f v in
-      Lwt.return_true
+      let () = f v in
+      true
   | None -> !error_handler ()
 
 type client_form_handler = Eliom_client.client_form_handler
@@ -45,7 +45,7 @@ type client_form_handler = Eliom_client.client_form_handler
 let make_hdlr_get service : client_form_handler =
  fun ev ->
   match Eliom_service.client_fun service with
-  | None -> Lwt.return_false
+  | None -> false
   | Some _ ->
       iter_contents (Eliom_service.get_params_type service) ev @@ fun g ->
       Eliom_client.change_page ~service g ()
@@ -53,7 +53,7 @@ let make_hdlr_get service : client_form_handler =
 let make_hdlr_post service g : client_form_handler =
  fun ev ->
   match Eliom_service.client_fun service with
-  | None -> Lwt.return_false
+  | None -> false
   | Some _ ->
       iter_contents (Eliom_service.post_params_type service) ev @@ fun p ->
       Eliom_client.change_page ~service g p
@@ -64,31 +64,31 @@ let make_hdlr_post service g : client_form_handler =
 module type Html = sig
   include
     Html_sigs.T
-    with type 'a Xml.W.t = 'a
-     and type 'a Xml.W.tlist = 'a list
-     and type Xml.mouse_event_handler =
-      (Dom_html.mouseEvent Js.t -> unit) Eliom_client_value.t
+      with type 'a Xml.W.t = 'a
+       and type 'a Xml.W.tlist = 'a list
+       and type Xml.mouse_event_handler =
+        (Dom_html.mouseEvent Js.t -> unit) Eliom_client_value.t
 
   type ('a, 'b, 'c) lazy_star =
     ?a:'a attrib list -> 'b elt list Eliom_lazy.request -> 'c elt
 
   val lazy_form :
-    ( [< Html_types.form_attrib]
-      , [< Html_types.form_content_fun]
-      , [> Html_types.form] )
-      lazy_star
+    ( [< Html_types.form_attrib ],
+      [< Html_types.form_content_fun ],
+      [> Html_types.form ] )
+    lazy_star
 
   val uri_of_fun : (unit -> string) -> Xml.uri
 
   val attrib_of_service :
-     string
-    -> ([`A | `Form_get | `Form_post]
-       * (bool * string list) option
-       * string option
-       * Eliom_lib.poly)
-         option
-         Eliom_lazy.request
-    -> Html_types.form_attrib attrib
+    string ->
+    ([ `A | `Form_get | `Form_post ]
+    * (bool * string list) option
+    * string option
+    * Eliom_lib.poly)
+    option
+    Eliom_lazy.request ->
+    Html_types.form_attrib attrib
 
   val to_elt : 'a elt -> Eliom_content_core.Xml.elt
 end
@@ -101,8 +101,7 @@ module Make_links (Html : Html) = struct
   type +'a attrib = 'a Html.attrib
 
   let make_uri ?absolute ?absolute_path ?https ~service ?hostname ?port
-      ?fragment ?keep_nl_params ?nl_params gp
-    =
+      ?fragment ?keep_nl_params ?nl_params gp =
     Html.uri_of_fun @@ fun () ->
     Eliom_uri.make_string_uri ?absolute ?absolute_path ?https ?fragment ~service
       ?hostname ?port ?keep_nl_params ?nl_params gp
@@ -110,8 +109,7 @@ module Make_links (Html : Html) = struct
   let uri_of_string = Html.uri_of_fun
 
   let a ?absolute ?absolute_path ?https ?(a = []) ~service ?hostname ?port
-      ?fragment ?keep_nl_params ?nl_params ?xhr content getparams
-    =
+      ?fragment ?keep_nl_params ?nl_params ?xhr content getparams =
     let a =
       let a = (a :> Html_types.a_attrib attrib list) in
       let href =
@@ -120,21 +118,22 @@ module Make_links (Html : Html) = struct
           ?hostname ?port ?fragment ?keep_nl_params ?nl_params getparams
       in
       let href = Html.a_href href in
-      if get_xhr xhr
-      then
+      if get_xhr xhr then
         let f =
           [%client.unsafe
             fun ev ->
-              if not (Eliom_client.middleClick ev)
-              then (
+              let open Eio.Std in
+              if not (Eliom_client.middleClick ev) then (
                 Dom.preventDefault ev;
                 Dom_html.stopPropagation ev;
-                Lwt.async @@ fun () ->
-                Eliom_client.change_page ?absolute:~%absolute
-                  ?absolute_path:~%absolute_path ?https:~%https
-                  ~service:~%service ?hostname:~%hostname ?port:~%port
-                  ?fragment:~%fragment ?keep_nl_params:~%keep_nl_params
-                  ?nl_params:~%nl_params ~%getparams ())]
+                Fiber.fork
+                  ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+                  (fun () ->
+                    Eliom_client.change_page ?absolute:~%absolute
+                      ?absolute_path:~%absolute_path ?https:~%https
+                      ~service:~%service ?hostname:~%hostname ?port:~%port
+                      ?fragment:~%fragment ?keep_nl_params:~%keep_nl_params
+                      ?nl_params:~%nl_params ~%getparams ()))]
         in
         Html.a_onclick f :: href :: a
       else href :: a
@@ -145,7 +144,7 @@ module Make_links (Html : Html) = struct
     let a =
       Html.a_mime_type "text/css" :: (a :> Html_types.link_attrib attrib list)
     in
-    Html.link ~href:uri ~rel:[`Stylesheet] ~a ()
+    Html.link ~href:uri ~rel:[ `Stylesheet ] ~a ()
 
   let js_script ?(a = []) ~uri () =
     let a =
@@ -186,12 +185,12 @@ module Make (Html : Html) = struct
       :: (* Always Multipart!!! How to test if there is a file?? *)
          a_action action
       :: a_method `Post
-      :: (if inline then a_class ["inline"] :: a else a)
+      :: (if inline then a_class [ "inline" ] :: a else a)
     in
     lazy_form ~a elts
 
   let cons_hidden_fieldset fields content =
-    Html.fieldset ~a:[a_style "display: none;"] fields :: content
+    Html.fieldset ~a:[ a_style "display: none;" ] fields :: content
 
   let make_input ?(a = []) ?(checked = false) ~typ ?name ?src ?value () =
     let a = (a :> Html_types.input_attrib attrib list) in
@@ -232,8 +231,7 @@ module Make (Html : Html) = struct
 
   let get_form_ bind return ?absolute ?absolute_path ?https ?a ~service
       ?hostname ?port ?fragment
-      ?(nl_params = Eliom_parameter.empty_nl_params_set) ?keep_nl_params f
-    =
+      ?(nl_params = Eliom_parameter.empty_nl_params_set) ?keep_nl_params f =
     let issuffix, paramnames =
       Eliom_parameter.make_params_names (Eliom_service.get_params_type service)
     in
@@ -246,16 +244,15 @@ module Make (Html : Html) = struct
       Html.uri_of_fun @@ fun () ->
       let uri, _, fragment = Eliom_lazy.force components in
       let uri =
-        if issuffix
-        then
-          if uri.[String.length uri - 1] = '/'
-          then uri ^ Eliom_common.eliom_nosuffix_page
-          else String.concat "/" [uri; Eliom_common.eliom_nosuffix_page]
+        if issuffix then
+          if uri.[String.length uri - 1] = '/' then
+            uri ^ Eliom_common.eliom_nosuffix_page
+          else String.concat "/" [ uri; Eliom_common.eliom_nosuffix_page ]
         else uri
       in
       match fragment with
       | None -> uri
-      | Some f -> String.concat "#" [uri; Eliom_lib.Url.encode f]
+      | Some f -> String.concat "#" [ uri; Eliom_lib.Url.encode f ]
     in
     bind (f paramnames) @@ fun inside ->
     let inside =
@@ -270,14 +267,13 @@ module Make (Html : Html) = struct
       cons_hidden_fieldset (List.map f hiddenparams)
         (inside :> Html_types.form_content elt list)
     and a =
-      let a' = [a_method `Get; a_action uri] in
+      let a' = [ a_method `Get; a_action uri ] in
       match a with Some a -> a' @ a | _ -> a'
     in
     return (Html.lazy_form ~a inside)
 
   let get_form ?absolute ?absolute_path ?https ?a ~service ?hostname ?port
-      ?fragment ?keep_nl_params ?nl_params ?xhr:_ f
-    =
+      ?fragment ?keep_nl_params ?nl_params ?xhr:_ f =
     get_form_
       (fun x f -> f x)
       (fun x -> x)
@@ -287,9 +283,8 @@ module Make (Html : Html) = struct
   let post_form_ bind return ?absolute ?absolute_path ?https ?a ~service
       ?hostname ?port ?fragment
       ?(nl_params = Eliom_parameter.empty_nl_params_set)
-      ?(keep_nl_params : [`All | `Persistent | `None] option)
-      ?keep_get_na_params f get_params
-    =
+      ?(keep_nl_params : [ `All | `Persistent | `None ] option)
+      ?keep_get_na_params f get_params =
     let _, paramnames =
       Eliom_parameter.make_params_names (Eliom_service.post_params_type service)
     in
@@ -318,8 +313,7 @@ module Make (Html : Html) = struct
 
   let post_form ?absolute ?absolute_path ?https ?a ~service ?hostname ?port
       ?fragment ?keep_nl_params ?keep_get_na_params ?nl_params ?xhr:_ f
-      getparams
-    =
+      getparams =
     post_form_
       (fun x f -> f x)
       (fun x -> x)
@@ -368,7 +362,7 @@ module Make (Html : Html) = struct
     let a =
       let required = Html.a_required () in
       match a with
-      | None -> [required]
+      | None -> [ required ]
       | Some a -> required :: (a :> Html_types.input_attrib attrib list)
     in
     make_input ~a ?checked ~typ:`Radio
@@ -396,22 +390,23 @@ module Make (Html : Html) = struct
 
   type 'a select_opt =
     | Optgroup of
-        [Html_types.common | `Disabled] attrib list
+        [ Html_types.common | `Disabled ] attrib list
         * string (* label *)
         * 'a soption
         * 'a soption list
     | Option of 'a soption
 
   let gen_select ?a ?(multiple = false) ?required ~name (fl : 'a select_opt)
-      (ol : 'a select_opt list) string_of
-    =
+      (ol : 'a select_opt list) string_of =
     let a = (a :> Html_types.select_attrib attrib list option) in
     let a =
       match required with
       | None -> a
       | Some _ -> (
           let required = Html.a_required () in
-          match a with Some a -> Some (required :: a) | None -> Some [required])
+          match a with
+          | Some a -> Some (required :: a)
+          | None -> Some [ required ])
     in
     let normalize_selected l =
       (* We change the list of option to have exactly one selected
@@ -420,26 +415,26 @@ module Make (Html : Html) = struct
          the first selected if several are selected.  Thus all
          browsers will behave the same way.  *)
       let aux1 found ((a, b, c, selected) as line) =
-        if found then (a, b, c, false), true else line, selected
+        if found then ((a, b, c, false), true) else (line, selected)
       in
       let rec aux2 found = function
         | line :: l ->
             let line, found = aux1 found line in
             let l, found = aux2 found l in
-            line :: l, found
-        | [] -> [], found
+            (line :: l, found)
+        | [] -> ([], found)
       in
       let rec aux found = function
         | Option line :: l ->
             let line, found = aux1 found line in
             let l, found = aux found l in
-            Option line :: l, found
+            (Option line :: l, found)
         | Optgroup (a, b, fl, ol) :: l ->
             let fl, found = aux1 found fl in
             let ol, found = aux2 found ol in
             let l, found = aux found l in
-            Optgroup (a, b, fl, ol) :: l, found
-        | [] -> [], found
+            (Optgroup (a, b, fl, ol) :: l, found)
+        | [] -> ([], found)
       in
       let select_first = function
         | Option (a, b, c, _) -> Option (a, b, c, true)
@@ -447,22 +442,20 @@ module Make (Html : Html) = struct
             Optgroup (a, b, (c, d, e, true), ol)
       in
       let newl, found = aux false l in
-      if found
-      then List.hd newl, List.tl newl, true
+      if found then (List.hd newl, List.tl newl, true)
       else
         let first = List.hd newl in
         (* We select the first one by default *)
         let first =
           match required with None -> select_first first | _ -> first
         in
-        first, List.tl newl, false
+        (first, List.tl newl, false)
     in
     let fl, ol, has_selected =
-      if multiple
-      then
-        ( fl
-        , ol
-        , let _, _, hs = normalize_selected (fl :: ol) in
+      if multiple then
+        ( fl,
+          ol,
+          let _, _, hs = normalize_selected (fl :: ol) in
           hs )
       else normalize_selected (fl :: ol)
     in
@@ -476,12 +469,12 @@ module Make (Html : Html) = struct
       | Optgroup (a, label, og1, ogl) ->
           make_optgroup ~a ~label (make_opt og1) (List.map make_opt ogl)
     in
-    let fl2, ol2 = make_optg fl, List.map make_optg ol in
+    let fl2, ol2 = (make_optg fl, List.map make_optg ol) in
     let fl3, ol3 =
       match required with
-      | None -> fl2, ol2
+      | None -> (fl2, ol2)
       | Some label ->
-          make_option ~selected:(not has_selected) ~value:"" label, fl2 :: ol2
+          (make_option ~selected:(not has_selected) ~value:"" label, fl2 :: ol2)
     in
     make_select ?a ~multiple ~name fl3 ol3
 
@@ -503,22 +496,22 @@ module Make (Html : Html) = struct
       | None -> None
       | Some tmpl ->
           Some
-            ( (kind : [`Form_get | `Form_post] :> [`Form_get | `Form_post | `A])
-            , Eliom_uri.make_cookies_info (https, service)
-            , tmpl
-            , Eliom_lib.to_poly hdlr )
+            ( (kind
+                : [ `Form_get | `Form_post ]
+                :> [ `Form_get | `Form_post | `A ]),
+              Eliom_uri.make_cookies_info (https, service),
+              tmpl,
+              Eliom_lib.to_poly hdlr )
     in
     Eliom_lazy.from_fun f
 
   let a_onsubmit_service info = Html.attrib_of_service "onsubmit" info
 
   let get_form ?absolute ?absolute_path ?https ?(a = []) ~service ?hostname
-      ?port ?fragment ?keep_nl_params ?nl_params ?xhr contents
-    =
+      ?port ?fragment ?keep_nl_params ?nl_params ?xhr contents =
     let a =
       let a = (a :> Html_types.form_attrib attrib list) in
-      if get_xhr xhr
-      then
+      if get_xhr xhr then
         let hdlr =
           [%client.unsafe (make_hdlr_get ~%service : client_form_handler)]
         in
@@ -530,12 +523,10 @@ module Make (Html : Html) = struct
       ?fragment ?keep_nl_params ?nl_params contents
 
   let lwt_get_form ?absolute ?absolute_path ?https ?(a = []) ~service ?hostname
-      ?port ?fragment ?keep_nl_params ?nl_params ?xhr contents
-    =
+      ?port ?fragment ?keep_nl_params ?nl_params ?xhr contents =
     let a =
       let a = (a :> Html_types.form_attrib attrib list) in
-      if get_xhr xhr
-      then
+      if get_xhr xhr then
         let hdlr =
           [%client.unsafe (make_hdlr_get ~%service : client_form_handler)]
         in
@@ -543,17 +534,18 @@ module Make (Html : Html) = struct
         a_onsubmit_service info :: a
       else a
     in
-    get_form_ Lwt.bind Lwt.return ?absolute ?absolute_path ?https ~a ~service
-      ?hostname ?port ?fragment ?nl_params ?keep_nl_params contents
+    get_form_
+      (fun x1 x2 -> x2 x1)
+      (fun x1 -> x1)
+      ?absolute ?absolute_path ?https ~a ~service ?hostname ?port ?fragment
+      ?nl_params ?keep_nl_params contents
 
   let post_form ?absolute ?absolute_path ?https ?(a = []) ~service ?hostname
       ?port ?fragment ?keep_nl_params ?keep_get_na_params ?nl_params ?xhr
-      contents getparams
-    =
+      contents getparams =
     let a =
       let a = (a :> Html_types.form_attrib attrib list) in
-      if get_xhr xhr
-      then
+      if get_xhr xhr then
         let hdlr =
           [%client.unsafe
             (make_hdlr_post ~%service ~%getparams : client_form_handler)]
@@ -568,12 +560,10 @@ module Make (Html : Html) = struct
 
   let lwt_post_form ?absolute ?absolute_path ?https ?(a = []) ~service ?hostname
       ?port ?fragment ?keep_nl_params ?keep_get_na_params ?nl_params ?xhr
-      contents getparams
-    =
+      contents getparams =
     let a =
       let a = (a :> Html_types.form_attrib attrib list) in
-      if get_xhr xhr
-      then
+      if get_xhr xhr then
         let hdlr =
           [%client.unsafe
             (make_hdlr_post ~%service ~%getparams : client_form_handler)]
@@ -582,7 +572,9 @@ module Make (Html : Html) = struct
         a_onsubmit_service info :: a
       else a
     in
-    post_form_ Lwt.bind Lwt.return ?absolute ?absolute_path ?https ~a ~service
-      ?hostname ?port ?fragment ?keep_get_na_params ?keep_nl_params ?nl_params
-      contents getparams
+    post_form_
+      (fun x1 x2 -> x2 x1)
+      (fun x1 -> x1)
+      ?absolute ?absolute_path ?https ~a ~service ?hostname ?port ?fragment
+      ?keep_get_na_params ?keep_nl_params ?nl_params contents getparams
 end
diff --git a/src/lib/eliom_form.eliomi b/src/lib/eliom_form.eliomi
index 674b562012..de49ea8c44 100644
--- a/src/lib/eliom_form.eliomi
+++ b/src/lib/eliom_form.eliomi
@@ -20,7 +20,7 @@
 
 [%%client.start]
 
-val set_error_handler : (unit -> bool Lwt.t) -> unit
+val set_error_handler : (unit -> bool) -> unit
 
 [%%shared.start]
 
@@ -29,31 +29,31 @@ open Js_of_ocaml
 module type Html = sig
   include
     Html_sigs.T
-    with type 'a Xml.W.t = 'a
-     and type 'a Xml.W.tlist = 'a list
-     and type Xml.mouse_event_handler =
-      (Dom_html.mouseEvent Js.t -> unit) Eliom_client_value.t
+      with type 'a Xml.W.t = 'a
+       and type 'a Xml.W.tlist = 'a list
+       and type Xml.mouse_event_handler =
+        (Dom_html.mouseEvent Js.t -> unit) Eliom_client_value.t
 
   type ('a, 'b, 'c) lazy_star =
     ?a:'a attrib list -> 'b elt list Eliom_lazy.request -> 'c elt
 
   val lazy_form :
-    ( [< Html_types.form_attrib]
-      , [< Html_types.form_content_fun]
-      , [> Html_types.form] )
-      lazy_star
+    ( [< Html_types.form_attrib ],
+      [< Html_types.form_content_fun ],
+      [> Html_types.form ] )
+    lazy_star
 
   val uri_of_fun : (unit -> string) -> Xml.uri
 
   val attrib_of_service :
-     string
-    -> ([`A | `Form_get | `Form_post]
-       * (bool * string list) option
-       * string option
-       * Eliom_lib.poly)
-         option
-         Eliom_lazy.request
-    -> Html_types.form_attrib attrib
+    string ->
+    ([ `A | `Form_get | `Form_post ]
+    * (bool * string list) option
+    * string option
+    * Eliom_lib.poly)
+    option
+    Eliom_lazy.request ->
+    Html_types.form_attrib attrib
 
   val to_elt : 'a elt -> Eliom_content_core.Xml.elt
 end
@@ -62,13 +62,13 @@ type 'a param
 
 module Make_links (H : Html) :
   Eliom_form_sigs.LINKS
-  with type +'a elt := 'a H.elt
-   and type +'a attrib := 'a H.attrib
-   and type uri := H.uri
+    with type +'a elt := 'a H.elt
+     and type +'a attrib := 'a H.attrib
+     and type uri := H.uri
 
 module Make (H : Html) :
   Eliom_form_sigs.S
-  with type +'a elt := 'a H.elt
-   and type +'a attrib := 'a H.attrib
-   and type uri := H.uri
-   and type 'a param = 'a param
+    with type +'a elt := 'a H.elt
+     and type +'a attrib := 'a H.attrib
+     and type uri := H.uri
+     and type 'a param = 'a param
diff --git a/src/lib/eliom_form_sigs.shared.mli b/src/lib/eliom_form_sigs.shared.mli
index 440eb8b94b..d3937ad324 100644
--- a/src/lib/eliom_form_sigs.shared.mli
+++ b/src/lib/eliom_form_sigs.shared.mli
@@ -350,8 +350,8 @@ module type S = sig
     -> ?keep_nl_params:[`All | `Persistent | `None]
     -> ?nl_params:Eliom_parameter.nl_params_set
     -> ?xhr:bool
-    -> ('gn -> [< Html_types.form_content] elt list Lwt.t)
-    -> [> Html_types.form] elt Lwt.t
+    -> ('gn -> [< Html_types.form_content] elt list)
+    -> [> Html_types.form] elt
   (** Same as {!get_form} but taking a cooperative function for
       [<form>] content generation. *)
 
@@ -422,9 +422,9 @@ module type S = sig
     -> ?keep_get_na_params:bool
     -> ?nl_params:Eliom_parameter.nl_params_set
     -> ?xhr:bool
-    -> ('pn -> [< Html_types.form_content] elt list Lwt.t)
+    -> ('pn -> [< Html_types.form_content] elt list)
     -> 'get
-    -> [> Html_types.form] elt Lwt.t
+    -> [> Html_types.form] elt
   (** Same as {!post_form} but taking a cooperative function for
       [<form>] content generation. *)
 
diff --git a/src/lib/eliom_lib.client.ml b/src/lib/eliom_lib.client.ml
index 13c2abbc7f..ba775cf357 100644
--- a/src/lib/eliom_lib.client.ml
+++ b/src/lib/eliom_lib.client.ml
@@ -88,14 +88,7 @@ let raise_error ?exn ?section fmt =
 
 let log_inspect obj = Console.console##log (Obj.repr obj)
 let eliom_logs_src = Logs.Src.create "eliom"
-
-let _ =
-  Logs.set_reporter (Logs_browser.console_reporter ());
-  Lwt.async_exception_hook :=
-    fun exn ->
-      Console.console##error_3 (Js.string "Lwt.async:")
-        (Js.string (Printexc.to_string exn))
-        exn
+let _ = Logs.set_reporter (Logs_browser.console_reporter ())
 
 let trace fmts =
   if Eliom_config.get_tracing ()
diff --git a/src/lib/eliom_mkreg.server.ml b/src/lib/eliom_mkreg.server.ml
index 8da3d9d949..4b21b790e5 100644
--- a/src/lib/eliom_mkreg.server.ml
+++ b/src/lib/eliom_mkreg.server.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -21,7 +21,6 @@ open Lwt.Syntax
 *)
 
 module S = Eliom_service
-open Lwt.Infix
 
 let suffix_redir_uri_key = Polytables.make_key ()
 
@@ -33,7 +32,7 @@ type ('options, 'page, 'result) param =
       -> ?content_type:string
       -> ?headers:Ocsigen_header.t
       -> 'page
-      -> Ocsigen_response.t Lwt.t
+      -> Ocsigen_response.t
   ; send_appl_content : S.send_appl_content
     (** Whether the service is capable to send application content when
           required. This field is usually [Eliom_service.XNever]. This
@@ -102,7 +101,7 @@ let check_process_redir sp f param =
   if redir
   then
     let ri = Eliom_request_info.get_ri_sp sp in
-    Lwt.fail
+    raise
       (* we answer to the xhr
          by asking an HTTP redirection *)
       (Eliom_common.Eliom_do_half_xhr_redirection
@@ -116,7 +115,7 @@ let check_process_redir sp f param =
      It is ok with half or full xhr redirections. *)
   (* If an action occurred before,
      it may have removed some get params form ri *)
-  else Lwt.return_unit
+  else ()
 
 let send_with_cookies
       sp
@@ -128,11 +127,11 @@ let send_with_cookies
       ?headers
       content
   =
-  let* result =
+  let result =
     pages.send ?options ?charset ?code ?content_type ?headers content
   in
-  let* () = check_process_redir sp check_after result in
-  let* tab_cookies =
+  let () = check_process_redir sp check_after result in
+  let tab_cookies =
     Eliommod_cookies.compute_cookies_to_send sp.Eliom_common.sp_sitedata
       sp.Eliom_common.sp_tab_cookie_info sp.Eliom_common.sp_user_tab_cookies
   in
@@ -151,7 +150,7 @@ let send_with_cookies
       (Eliom_request_info.get_user_cookies ())
       (Ocsigen_response.cookies result)
   in
-  Lwt.return (Ocsigen_response.update result ~cookies ~response)
+  Ocsigen_response.update result ~cookies ~response
 
 let register_aux
       pages
@@ -197,92 +196,90 @@ let register_aux
           ; s_expire
           ; s_f =
               (fun nosuffixversion sp ->
-                Lwt.with_value Eliom_common.sp_key (Some sp) (fun () ->
+                (Stdlib.Option.fold ~none:Fiber.without_binding
+                   ~some:(Fun.flip Fiber.with_binding)
+                   (Some sp)) Eliom_common.sp_key (fun () ->
                   let ri = Eliom_request_info.get_ri_sp sp
                   and suff = Eliom_request_info.get_suffix_sp sp in
-                  Lwt.catch
-                    (fun () ->
-                       Eliom_parameter.reconstruct_params ~sp sgpt
-                         (Some (Lwt.return (Ocsigen_request.get_params_flat ri)))
-                         (Some (Lwt.return []))
-                         nosuffixversion suff
-                       >>= fun g ->
-                       let post_params =
-                         Eliom_request_info.get_post_params_sp sp
-                       in
-                       let files = Eliom_request_info.get_files_sp sp in
-                       Eliom_parameter.reconstruct_params ~sp sppt post_params
-                         files false None
-                       >>= fun p ->
-                       (* GRGR TODO: avoid
+                  let content =
+                    try
+                      let g =
+                        Eliom_parameter.reconstruct_params ~sp sgpt
+                          (Some (Ocsigen_request.get_params_flat ri))
+                          (Some []) nosuffixversion suff
+                      in
+                      let post_params =
+                        Eliom_request_info.get_post_params_sp sp
+                      in
+                      let files = Eliom_request_info.get_files_sp sp in
+                      let p =
+                        Eliom_parameter.reconstruct_params ~sp sppt post_params
+                          files false None
+                      in
+                      (* GRGR TODO: avoid
                            Eliom_uri.make_string_uri_. But we need to
                            "downcast" the type of service to the
                            correct "get service". *)
-                       (if
-                          Eliom_request_info.get_http_method () = `GET
-                          && nosuffixversion && suffix_with_redirect
-                        then (
-                          if
-                            (* it is a suffix service in version
+                      if
+                        Eliom_request_info.get_http_method () = `GET
+                        && nosuffixversion && suffix_with_redirect
+                      then
+                        if
+                          (* it is a suffix service in version
                                without suffix. We redirect. *)
-                            not (Eliom_request_info.expecting_process_page ())
-                          then
-                            let redir_uri =
-                              Eliom_uri.make_string_uri_ ~absolute:true
-                                ~service:
-                                  (service
-                                    : ( 'a
-                                        , 'b
-                                        , _
-                                        , _
-                                        , _
-                                        , S.non_ext
-                                        , S.reg
-                                        , _
-                                        , 'c
-                                        , 'd
-                                        , 'return )
-                                        S.t
-                                    :> ( 'a
-                                         , 'b
-                                         , _
-                                         , _
-                                         , _
-                                         , _
-                                         , _
-                                         , _
-                                         , 'c
-                                         , 'd
-                                         , 'return )
-                                         S.t)
-                                g
-                            in
-                            Lwt.fail
-                              (Eliom_common.Eliom_do_redirection redir_uri)
-                          else
-                            (* It is an internal application form.
+                          not (Eliom_request_info.expecting_process_page ())
+                        then
+                          let redir_uri =
+                            Eliom_uri.make_string_uri_ ~absolute:true
+                              ~service:
+                                (service
+                                  : ( 'a
+                                      , 'b
+                                      , _
+                                      , _
+                                      , _
+                                      , S.non_ext
+                                      , S.reg
+                                      , _
+                                      , 'c
+                                      , 'd
+                                      , 'return )
+                                      S.t
+                                  :> ( 'a
+                                       , 'b
+                                       , _
+                                       , _
+                                       , _
+                                       , _
+                                       , _
+                                       , _
+                                       , 'c
+                                       , 'd
+                                       , 'return )
+                                       S.t)
+                              g
+                          in
+                          raise (Eliom_common.Eliom_do_redirection redir_uri)
+                        else
+                          (* It is an internal application form.
                                We don't redirect but we set this
                                special information for url to be displayed
                                by the browser
                                (see Eliom_request_info.rebuild_uri_without_iternal_form_info_)
-                            *)
-                            let redir_uri =
-                              Eliom_uri.make_string_uri_ ~service g
-                            in
-                            let rc =
-                              Eliom_request_info.get_request_cache_sp sp
-                            in
-                            Polytables.set ~table:rc ~key:suffix_redir_uri_key
-                              ~value:redir_uri;
-                            Lwt.return_unit)
-                        else Lwt.return_unit)
-                       >>= fun () ->
-                       check_process_redir sp check_before service >>= fun () ->
-                       page_generator g p)
-                    (function
-                      | Eliom_common.Eliom_Typing_Error l -> error_handler l
-                      | e -> Lwt.fail e)
-                  >>= fun content ->
+                          *)
+                          let redir_uri =
+                            Eliom_uri.make_string_uri_ ~service g
+                          in
+                          let rc = Eliom_request_info.get_request_cache_sp sp in
+                          Polytables.set ~table:rc ~key:suffix_redir_uri_key
+                            ~value:redir_uri
+                      else ();
+                      check_process_redir sp check_before service;
+                      page_generator g p
+                    with
+                    | Eliom_common.Eliom_Typing_Error l -> error_handler l
+                    | e -> raise e
+                  in
                   send_with_cookies sp pages ?options ?charset ?code
                     ?content_type ?headers content)) }
       in
@@ -362,30 +359,33 @@ let register_aux
             | None -> None
             | Some t -> Some (t, ref (t +. Unix.time ())))
           , fun sp ->
-              Lwt.with_value Eliom_common.sp_key (Some sp) (fun () ->
+              (Stdlib.Option.fold ~none:Fiber.without_binding
+                 ~some:(Fun.flip Fiber.with_binding)
+                 (Some sp)) Eliom_common.sp_key (fun () ->
                 let ri = Eliom_request_info.get_ri_sp sp in
-                Lwt.catch
-                  (fun () ->
-                     Eliom_parameter.reconstruct_params ~sp
-                       (S.get_params_type service)
-                       (Some (Lwt.return (Ocsigen_request.get_params_flat ri)))
-                       (Some (Lwt.return []))
-                       false None
-                     >>= fun g ->
-                     let post_params =
-                       Eliom_request_info.get_post_params_sp sp
-                     in
-                     let files = Eliom_request_info.get_files_sp sp in
-                     Eliom_parameter.reconstruct_params ~sp
-                       (S.post_params_type service)
-                       post_params files false None
-                     >>= fun p ->
-                     check_process_redir sp check_before service >>= fun () ->
-                     page_generator g p)
-                  (function
-                    | Eliom_common.Eliom_Typing_Error l -> error_handler l
-                    | e -> Lwt.fail e)
-                >>= fun content ->
+                let content =
+                  try
+                    let g =
+                      Eliom_parameter.reconstruct_params ~sp
+                        (S.get_params_type service)
+                        (Some (Ocsigen_request.get_params_flat ri))
+                        (Some []) false None
+                    in
+                    let post_params =
+                      Eliom_request_info.get_post_params_sp sp
+                    in
+                    let files = Eliom_request_info.get_files_sp sp in
+                    let p =
+                      Eliom_parameter.reconstruct_params ~sp
+                        (S.post_params_type service)
+                        post_params files false None
+                    in
+                    check_process_redir sp check_before service;
+                    page_generator g p
+                  with
+                  | Eliom_common.Eliom_Typing_Error l -> error_handler l
+                  | e -> raise e
+                in
                 send_with_cookies sp pages ?options ?charset ?code ?content_type
                   ?headers content) )
       in
@@ -453,10 +453,10 @@ let register_aux
           f tablereg na_name)
 
 let send pages ?options ?charset ?code ?content_type ?headers content =
-  let* result =
+  let result =
     pages.send ?options ?charset ?code ?content_type ?headers content
   in
-  Lwt.return (pages.result_of_http_result result)
+  pages.result_of_http_result result
 
 let register
       pages
diff --git a/src/lib/eliom_notif.server.ml b/src/lib/eliom_notif.server.ml
index 41e6e1cf46..2a994e68b5 100644
--- a/src/lib/eliom_notif.server.ml
+++ b/src/lib/eliom_notif.server.ml
@@ -1,4 +1,4 @@
-open Lwt
+open Eio.Std
 
 (* We use a hashtable associating resourceid to a weak set of
    (userid option, notif_ev) corresponding to each tab that want to
@@ -12,7 +12,7 @@ module type S = sig
   type server_notif
   type client_notif
 
-  val init : unit -> unit Lwt.t
+  val init : unit -> unit
   val deinit : unit -> unit
   val listen : key -> unit
   val unlisten : key -> unit
@@ -36,10 +36,10 @@ module type ARG = sig
   type server_notif
   type client_notif
 
-  val prepare : identity -> server_notif -> client_notif option Lwt.t
+  val prepare : identity -> server_notif -> client_notif option
   val equal_key : key -> key -> bool
   val equal_identity : identity -> identity -> bool
-  val get_identity : unit -> identity Lwt.t
+  val get_identity : unit -> identity
   val max_resource : int
   val max_identity_per_resource : int
 end
@@ -102,16 +102,20 @@ module Make (A : ARG) :
       if not (Weak_tbl.mem wt v) then Weak_tbl.add wt v
 
     let iter =
-      let iter (f : Weak_tbl.data -> unit Lwt.t) wt : unit =
-        Weak_tbl.iter (fun data -> Lwt.async (fun () -> f data)) wt
+      let iter (f : Weak_tbl.data -> unit) wt : unit =
+        Weak_tbl.iter
+          (fun data ->
+             Fiber.fork
+               ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+               (fun () -> f data))
+          wt
       in
       fun f key ->
         try
           let wt = Notif_hashtbl.find tbl key in
           let g data =
             match data with
-            | None ->
-                Weak_tbl.remove wt data; remove_if_empty wt key; Lwt.return_unit
+            | None -> Weak_tbl.remove wt data; remove_if_empty wt key
             | Some v -> f v
           in
           iter g wt
@@ -149,9 +153,10 @@ module Make (A : ARG) :
     Eliom_reference.Volatile.set identity_r (Some (identity, notif_e))
 
   let set_current_identity () =
-    A.get_identity () >>= fun identity -> set_identity identity; Lwt.return_unit
+    let identity = A.get_identity () in
+    set_identity identity
 
-  let init : unit -> unit Lwt.t = fun () -> set_current_identity ()
+  let init : unit -> unit = fun () -> set_current_identity ()
   let deinit () = Eliom_reference.Volatile.set identity_r None
 
   let listen (key : A.key) =
@@ -180,14 +185,10 @@ module Make (A : ARG) :
         | None -> false
       in
       if blocked
-      then Lwt.return_unit
+      then ()
       else
-        A.prepare identity content >>= fun content ->
-        match content with
-        | Some content ->
-            send_e (key, content);
-            Lwt.return_unit
-        | None -> Lwt.return_unit
+        let content = A.prepare identity content in
+        match content with Some content -> send_e (key, content) | None -> ()
     in
     (* on all tabs listening on this resource *)
     I.iter f key
@@ -208,7 +209,7 @@ module type ARG_SIMPLE = sig
   type key
   type notification
 
-  val get_identity : unit -> identity Lwt.t
+  val get_identity : unit -> identity
 end
 
 module Make_Simple (A : ARG_SIMPLE) = Make (struct
@@ -217,7 +218,7 @@ module Make_Simple (A : ARG_SIMPLE) = Make (struct
     type server_notif = A.notification
     type client_notif = A.notification
 
-    let prepare _ n = Lwt.return_some n
+    let prepare _ n = Some n
     let equal_key = ( = )
     let equal_identity = ( = )
     let get_identity = A.get_identity
diff --git a/src/lib/eliom_notif.server.mli b/src/lib/eliom_notif.server.mli
index cb408d9aac..f3e07eaf13 100644
--- a/src/lib/eliom_notif.server.mli
+++ b/src/lib/eliom_notif.server.mli
@@ -48,7 +48,7 @@ module type S = sig
   type client_notif
   (** client notification type; Can be different from [server_notif]. *)
 
-  val init : unit -> unit Lwt.t
+  val init : unit -> unit
   (** Initialise the notification module for the current client. This function
       needs to be called before using most other functions of this module. It
       isn't called implicitly during module instantiation because it relies on
@@ -126,7 +126,7 @@ module type ARG = sig
   type client_notif
   (** see [S.client_notif] *)
 
-  val prepare : identity -> server_notif -> client_notif option Lwt.t
+  val prepare : identity -> server_notif -> client_notif option
   (** [prepare f] transforms server notifications into client
       notifications. It provides the [identity] as a parameter which identifies
       the client. You can suppress notifications for a specific client (for
@@ -140,7 +140,7 @@ module type ARG = sig
   (** [equal_identity] is the same as [equal_key] but for values of type
       [identity].*)
 
-  val get_identity : unit -> identity Lwt.t
+  val get_identity : unit -> identity
   (** [get_identity] is a function returning a value of type [identity]
       corresponding to a client. *)
 
@@ -187,7 +187,7 @@ module type ARG_SIMPLE = sig
 
   type notification
 
-  val get_identity : unit -> identity Lwt.t
+  val get_identity : unit -> identity
   (** see {!ARG.equal_key} *)
 end
 
diff --git a/src/lib/eliom_parameter.server.mli b/src/lib/eliom_parameter.server.mli
index bf7b609604..4e13733af0 100644
--- a/src/lib/eliom_parameter.server.mli
+++ b/src/lib/eliom_parameter.server.mli
@@ -20,7 +20,7 @@
 include
   Eliom_parameter_sigs.S
   with type raw_post_data =
-    ((string * string) * (string * string) list) option * Cohttp_lwt.Body.t
+    ((string * string) * (string * string) list) option * Cohttp_eio.Body.t
 
 val user_type :
    ?client_to_and_of:'a to_and_of Eliom_client_value.t
diff --git a/src/lib/eliom_parameter_base.shared.ml b/src/lib/eliom_parameter_base.shared.ml
index 7d655fc0a7..17f0340503 100644
--- a/src/lib/eliom_parameter_base.shared.ml
+++ b/src/lib/eliom_parameter_base.shared.ml
@@ -1,5 +1,3 @@
-open Lwt.Syntax
-
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2007 Vincent Balat
@@ -864,22 +862,16 @@ let reconstruct_params
       params
       files
       nosuffixversion
-      urlsuffix : a Lwt.t
+      urlsuffix : a
   =
   match typ, params, files with
   (* FIXME *)
   | TRaw_post_data, None, None -> Eliom_request_info.raw_post_data sp
   | typ, None, None -> (
-    try Lwt.return (reconstruct_params_ typ [] [] nosuffixversion urlsuffix)
-    with e -> Lwt.fail e)
+    try reconstruct_params_ typ [] [] nosuffixversion urlsuffix
+    with e -> raise e)
   | typ, _, _ -> (
-      let* params =
-        match params with Some params -> params | None -> Lwt.return_nil
-      in
-      let* files =
-        match files with Some files -> files | None -> Lwt.return_nil
-      in
-      try
-        Lwt.return
-          (reconstruct_params_ typ params files nosuffixversion urlsuffix)
-      with e -> Lwt.fail e)
+      let params = match params with Some params -> params | None -> [] in
+      let files = match files with Some files -> files | None -> [] in
+      try reconstruct_params_ typ params files nosuffixversion urlsuffix
+      with e -> raise e)
diff --git a/src/lib/eliom_parameter_sigs.shared.mli b/src/lib/eliom_parameter_sigs.shared.mli
index a87209ee7c..295cc30d91 100644
--- a/src/lib/eliom_parameter_sigs.shared.mli
+++ b/src/lib/eliom_parameter_sigs.shared.mli
@@ -377,11 +377,11 @@ module type S = sig
   val reconstruct_params :
      sp:Eliom_common.server_params
     -> ('a, [< `WithSuffix | `WithoutSuffix], 'c) params_type
-    -> (string * string) list Lwt.t option
-    -> (string * Eliom_lib.file_info) list Lwt.t option
+    -> (string * string) list option
+    -> (string * Eliom_lib.file_info) list option
     -> bool
     -> Eliom_lib.Url.path option
-    -> 'a Lwt.t
+    -> 'a
 
   val make_params_names : ('a, 'b, 'c) params_type -> bool * 'c
   (* bool = contains a suffix *)
diff --git a/src/lib/eliom_react.client.ml b/src/lib/eliom_react.client.ml
index 7e111aef95..837a8da9ad 100644
--- a/src/lib/eliom_react.client.ml
+++ b/src/lib/eliom_react.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -23,7 +23,6 @@ open Lwt.Syntax
 
 (* Module for event unwrapping *)
 open Lwt_react
-open Lwt.Infix
 
 let section = Logs.Src.create "eliom:comet"
 
@@ -41,8 +40,7 @@ module Down = struct
           "Exception during comet with react. Customize this with Eliom_react.set_handle_react_exn_function. "
         in
         Logs.msg ~src:section Logs.Debug (fun fmt ->
-          fmt "%s%a" s pp_exn_option exn);
-        Lwt.return_unit)
+          fmt "%s%a" s pp_exn_option exn))
     in
     (fun ~exn () -> !r ~exn ()), fun f -> r := f
 
@@ -51,14 +49,16 @@ module Down = struct
        in Eliom_comet. For example Channel_full. *)
     (* We transform the stream into a stream with exception: *)
     let stream = Lwt_stream.wrap_exn channel in
-    Lwt.async (fun () ->
-      Lwt_stream.iter_s
-        (function
-          | Error exn ->
-              let* () = handle_react_exn ~exn () in
-              Lwt.fail exn
-          | Ok () -> Lwt.return_unit)
-        stream);
+    Fiber.fork
+      ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+      (fun () ->
+         Lwt_stream.iter_s
+           (function
+             | Error exn ->
+                 let () = handle_react_exn ~exn () in
+                 raise exn
+             | Ok () -> ())
+           stream);
     E.of_stream channel
 
   let () =
@@ -67,10 +67,11 @@ module Down = struct
 end
 
 module Up = struct
-  type 'a t = 'a -> unit Lwt.t
+  type 'a t = 'a -> unit
 
   let internal_unwrap (service, _unwrapper) x =
-    Eliom_client.call_service ~service () x >|= fun _ -> ()
+    let _ = Eliom_client.call_service ~service () x in
+    ()
 
   let () =
     Eliom_unwrap.register_unwrapper Eliom_common.react_up_unwrap_id
diff --git a/src/lib/eliom_react.client.mli b/src/lib/eliom_react.client.mli
index 9fef00ad03..29dfc9d593 100644
--- a/src/lib/eliom_react.client.mli
+++ b/src/lib/eliom_react.client.mli
@@ -25,7 +25,7 @@
 module Down : sig
   type 'a t = 'a React.E.t
 
-  val set_handle_react_exn_function : (?exn:exn -> unit -> unit Lwt.t) -> unit
+  val set_handle_react_exn_function : (?exn:exn -> unit -> unit) -> unit
   (** Makes possible to customize the function called when comet fails
       in Eliom_react, for example because a channel is full or closed.
       It is called for each exception.
@@ -33,7 +33,7 @@ module Down : sig
 end
 
 module Up : sig
-  type 'a t = 'a -> unit Lwt.t
+  type 'a t = 'a -> unit
 end
 
 module S : sig
diff --git a/src/lib/eliom_react.server.ml b/src/lib/eliom_react.server.ml
index f80fe58624..a69e6e090b 100644
--- a/src/lib/eliom_react.server.ml
+++ b/src/lib/eliom_react.server.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -40,10 +40,12 @@ module Down = struct
 
   let wrap_stateful {throttling = t; scope; react = e; name; size} =
     let ee =
-      Lwt.with_value Eliom_common.sp_key None @@ fun () ->
-      match t with
-      | None -> e
-      | Some t -> E.limit (fun () -> Lwt_unix.sleep t) e
+      (Stdlib.Option.fold ~none:Fiber.without_binding
+         ~some:(Fun.flip Fiber.with_binding)
+         None) Eliom_common.sp_key (fun () ->
+        match t with
+        | None -> e
+        | Some t -> E.limit (fun () -> Eio_unix.sleep t) e)
     in
     let channel =
       Eliom_comet.Channel.create_from_events ?scope ?name ?size ee
@@ -66,7 +68,7 @@ module Down = struct
     let ee =
       match throttling with
       | None -> e
-      | Some t -> E.limit (fun () -> Lwt_unix.sleep t) e
+      | Some t -> E.limit (fun () -> Eio_unix.sleep t) e
     in
     Stateless
       (Eliom_comet.Channel.create_from_events ~scope:`Site ?name ?size ee)
@@ -125,7 +127,7 @@ module Up = struct
         ~path:Eliom_service.No_path ()
     in
     Eliom_registration.Action.register ~scope ~options:`NoReload
-      ~service:e_writer (fun () value -> push value; Lwt.return_unit);
+      ~service:e_writer (fun () value -> push value);
     {event = e; service = e_writer; wrapper = up_event_wrapper ()}
 end
 
@@ -155,21 +157,21 @@ module S = struct
       ; (* to avoid signal GC *)
         mutable value : 'a
       ; mutable read : bool
-      ; condition : unit Lwt_condition.t }
+      ; condition : Eio.Condition.t }
 
     let make_store signal =
       let rec store =
         { s = s'
         ; value = S.value signal
         ; read = false
-        ; condition = Lwt_condition.create () }
+        ; condition = Eio.Condition.create () }
       and s' =
         lazy
           (S.map
              (fun v ->
                 store.read <- false;
                 store.value <- v;
-                Lwt_condition.broadcast store.condition ();
+                Eio.Condition.broadcast store.condition;
                 ())
              signal)
       in
@@ -180,19 +182,27 @@ module S = struct
       let rec aux () =
         if store.read
         then
-          let* () = Lwt_condition.wait store.condition in
+          let () =
+            Eio.Condition.await
+              (* TODO: lwt-to-direct-style: A mutex must be passed *)
+              store.condition __mutex__
+          in
           aux ()
         else (
           store.read <- true;
-          Lwt.return_some store.value)
+          Some store.value)
       in
-      fun () -> Lwt.with_value Eliom_common.sp_key None @@ aux
+      fun () ->
+        (Stdlib.Option.fold ~none:Fiber.without_binding
+           ~some:(Fun.flip Fiber.with_binding)
+           None)
+          Eliom_common.sp_key aux
 
     let wrap_stateful {throttling = t; signal = s; name; _} =
       let s : 'a S.t =
         match t with
         | None -> s
-        | Some t -> S.limit (fun () -> Lwt_unix.sleep t) s
+        | Some t -> S.limit (fun () -> Eio_unix.sleep t) s
       in
       let store = make_store s in
       let stream = Lwt_stream.from (read_store store) in
@@ -221,7 +231,7 @@ module S = struct
       let s =
         match throttling with
         | None -> s
-        | Some t -> S.limit (fun () -> Lwt_unix.sleep t) s
+        | Some t -> S.limit (fun () -> Eio_unix.sleep t) s
       in
       let e = S.changes s in
       let stream = E.to_stream e in
diff --git a/src/lib/eliom_reference.server.ml b/src/lib/eliom_reference.server.ml
index ba7855b9d9..bab70b167e 100644
--- a/src/lib/eliom_reference.server.ml
+++ b/src/lib/eliom_reference.server.ml
@@ -21,23 +21,22 @@
 (** {2 Eliom references} *)
 
 open Eliom_state
-open Lwt.Infix
 
 module Ocsipersist = struct
   include Eliom_common.Ocsipersist.Store
   include Eliom_common.Ocsipersist.Polymorphic
 end
 
-let pers_ref_store = Ocsipersist.open_store "eliom__persistent_refs"
+let pers_ref_store = lazy (Ocsipersist.open_store "eliom__persistent_refs")
 
 type 'a eref_kind =
   | Req of 'a Polytables.key
   | Sit of 'a Polytables.key
   | Ref of 'a lazy_t ref (* Ocaml reference *)
   | Vol of 'a volatile_table Lazy.t (* Vol. table (group, session, process) *)
-  | Ocsiper of 'a option Ocsipersist.t Lwt.t (* Global persist. table *)
-  | Ocsiper_sit of 'a Ocsipersist.table Lwt.t (* Persist. table for site *)
-  | Per of 'a persistent_table Lwt.t
+  | Ocsiper of 'a option Ocsipersist.t Lazy.t (* Global persist. table *)
+  | Ocsiper_sit of 'a Ocsipersist.table Lazy.t (* Persist. table for site *)
+  | Per of 'a persistent_table Lazy.t
 (* Persist. table for group session or process *)
 
 type volatile = [`Volatile]
@@ -174,18 +173,20 @@ let eref_from_fun_ ~ext ~scope ?secure ?persistent f : 'a eref =
         ( f
         , ext
         , Ocsiper
-            ( pers_ref_store >>= fun store ->
-              Ocsipersist.make_persistent ~store ~name ~default:None ) ))
+            (lazy
+              (let (lazy store) = pers_ref_store in
+               Ocsipersist.make_persistent ~store ~name ~default:None)) ))
   | `Site -> (
     match persistent with
     | None -> (Volatile.eref_from_fun_ ~ext ~scope ?secure f :> _ eref)
     | Some name ->
         (*VVV!!! ??? CHECK! *)
-        f, ext, Ocsiper_sit (Ocsipersist.open_table name))
+        f, ext, Ocsiper_sit (lazy (Ocsipersist.open_table name)))
   | #Eliom_common.user_scope as scope -> (
     match persistent with
     | None -> (Volatile.eref_from_fun_ ~ext ~scope ?secure f :> _ eref)
-    | Some name -> f, ext, Per (create_persistent_table ~scope ?secure name))
+    | Some name ->
+        f, ext, Per (lazy (create_persistent_table ~scope ?secure name)))
 
 let eref_from_fun ~scope ?secure ?persistent f : 'a eref =
   eref_from_fun_ ~ext:false ~scope ?secure ?persistent f
@@ -201,86 +202,99 @@ let get_site_id () =
 let get ((f, _, table) as eref) =
   match table with
   | Per t -> (
-      t >>= fun t ->
-      get_persistent_data ~table:t () >>= function
-      | Data d -> Lwt.return d
+      let (lazy t) = t in
+      match get_persistent_data ~table:t () with
+      | Data d -> d
       | _ ->
           let value = f () in
-          set_persistent_data ~table:t value >>= fun () -> Lwt.return value)
+          set_persistent_data ~table:t value;
+          value)
   | Ocsiper r -> (
-      r >>= fun r ->
-      Ocsipersist.get r >>= function
-      | Some v -> Lwt.return v
+      let (lazy r) = r in
+      match Ocsipersist.get r with
+      | Some v -> v
       | None ->
           let value = f () in
-          Ocsipersist.set r (Some value) >>= fun () -> Lwt.return value)
-  | Ocsiper_sit t ->
-      t >>= fun t ->
+          Ocsipersist.set r (Some value);
+          value)
+  | Ocsiper_sit t -> (
+      let (lazy t) = t in
       let site_id = get_site_id () in
-      Lwt.catch
-        (fun () -> Ocsipersist.find t site_id)
-        (function
-          | Not_found ->
-              let value = f () in
-              Ocsipersist.add t site_id value >>= fun () -> Lwt.return value
-          | exc -> Lwt.reraise exc)
-  | _ -> Lwt.return (Volatile.get eref)
+      try Ocsipersist.find t site_id
+      with Not_found ->
+        let value = f () in
+        Ocsipersist.add t site_id value;
+        value)
+  | _ -> Volatile.get eref
 
 let set ((_, _, table) as eref) value =
   match table with
-  | Per t -> t >>= fun t -> set_persistent_data ~table:t value
-  | Ocsiper r -> r >>= fun r -> Ocsipersist.set r (Some value)
-  | Ocsiper_sit t -> t >>= fun t -> Ocsipersist.add t (get_site_id ()) value
-  | _ -> Lwt.return (Volatile.set eref value)
+  | Per t ->
+      let (lazy t) = t in
+      set_persistent_data ~table:t value
+  | Ocsiper r ->
+      let (lazy r) = r in
+      Ocsipersist.set r (Some value)
+  | Ocsiper_sit t ->
+      let (lazy t) = t in
+      Ocsipersist.add t (get_site_id ()) value
+  | _ -> Volatile.set eref value
 
-let modify eref f = get eref >>= fun x -> set eref (f x)
+let modify eref f =
+  let x = get eref in
+  set eref (f x)
 
 let unset ((_, _, table) as eref) =
   match table with
-  | Per t -> t >>= fun t -> remove_persistent_data ~table:t ()
-  | Ocsiper r -> r >>= fun r -> Ocsipersist.set r None
-  | Ocsiper_sit t -> t >>= fun t -> Ocsipersist.remove t (get_site_id ())
-  | _ -> Lwt.return (Volatile.unset eref)
+  | Per t ->
+      let (lazy t) = t in
+      remove_persistent_data ~table:t ()
+  | Ocsiper r ->
+      let (lazy r) = r in
+      Ocsipersist.set r None
+  | Ocsiper_sit t ->
+      let (lazy t) = t in
+      Ocsipersist.remove t (get_site_id ())
+  | _ -> Volatile.unset eref
 
 module Ext = struct
   let get state ((f, ext, table) as r) =
     let state = Eliom_state.Ext.untype_state state in
     match table with
-    | Vol _ -> Lwt.return (Volatile.Ext.get state r)
-    | Per t ->
-        t >>= fun t ->
-        Lwt.catch
-          (fun () ->
-             Eliom_state.Ext.Low_level.get_persistent_data ~state ~table:t)
-          (function
-            | Not_found ->
-                if ext (* We can run the function from another state *)
-                then
-                  let value = f () in
-                  Eliom_state.Ext.Low_level.set_persistent_data ~state ~table:t
-                    value
-                  >>= fun () -> Lwt.return value
-                else Lwt.fail Eref_not_initialized
-            | e -> Lwt.fail e)
+    | Vol _ -> Volatile.Ext.get state r
+    | Per t -> (
+        let (lazy t) = t in
+        try Eliom_state.Ext.Low_level.get_persistent_data ~state ~table:t with
+        | Not_found ->
+            if ext (* We can run the function from another state *)
+            then (
+              let value = f () in
+              Eliom_state.Ext.Low_level.set_persistent_data ~state ~table:t
+                value;
+              value)
+            else raise Eref_not_initialized
+        | e -> raise e)
     | _ -> failwith "wrong eref for this function"
 
   let set state ((_, _, table) as r) value =
     let state = Eliom_state.Ext.untype_state state in
     match table with
-    | Vol _ -> Lwt.return (Volatile.Ext.set state r value)
+    | Vol _ -> Volatile.Ext.set state r value
     | Per t ->
-        t >>= fun t ->
+        let (lazy t) = t in
         Eliom_state.Ext.Low_level.set_persistent_data ~state ~table:t value
-    | _ -> Lwt.fail (Failure "wrong eref for this function")
+    | _ -> raise (Failure "wrong eref for this function")
 
-  let modify state eref f = get state eref >>= fun v -> set state eref (f v)
+  let modify state eref f =
+    let v = get state eref in
+    set state eref (f v)
 
   let unset state ((_, _, table) as r) =
     let state = Eliom_state.Ext.untype_state state in
     match table with
-    | Vol _ -> Lwt.return (Volatile.Ext.unset state r)
+    | Vol _ -> Volatile.Ext.unset state r
     | Per t ->
-        t >>= fun t ->
+        let (lazy t) = t in
         Eliom_state.Ext.Low_level.remove_persistent_data ~state ~table:t
     | _ -> failwith "wrong eref for this function"
 end
diff --git a/src/lib/eliom_reference.server.mli b/src/lib/eliom_reference.server.mli
index cfa2db91dc..f3972e40d8 100644
--- a/src/lib/eliom_reference.server.mli
+++ b/src/lib/eliom_reference.server.mli
@@ -97,7 +97,7 @@ val eref_from_fun :
     if the value has not been set explicitly before (by {!Eliom_reference.set}).
   *)
 
-val get : 'a eref -> 'a Lwt.t
+val get : 'a eref -> 'a
 (** The function [get eref] returns the current value of the Eliom
     reference [eref].
 
@@ -111,7 +111,7 @@ val get : 'a eref -> 'a Lwt.t
 (* That function introduces a Lwt cooperation point only for persistent
    references. *)
 
-val set : 'a eref -> 'a -> unit Lwt.t
+val set : 'a eref -> 'a -> unit
 (** The function [set eref v] set [v] as current value of the Eliom
     reference [eref].
 
@@ -125,7 +125,7 @@ val set : 'a eref -> 'a -> unit Lwt.t
 (* That function introduces a Lwt cooperation point only for persistent
    references. *)
 
-val modify : 'a eref -> ('a -> 'a) -> unit Lwt.t
+val modify : 'a eref -> ('a -> 'a) -> unit
 (** The function [modify eref f] modifies the content of the Eliom
     reference [eref] by applying the function [f] on it.
 
@@ -139,7 +139,7 @@ val modify : 'a eref -> ('a -> 'a) -> unit Lwt.t
 (* That function introduces a Lwt cooperation point only for persistent
    references. *)
 
-val unset : 'a eref -> unit Lwt.t
+val unset : 'a eref -> unit
 (** The function [unset eref] reset the content of the Eliom reference
     [eref] to its initial value.
 
@@ -231,7 +231,7 @@ module Ext : sig
        , [< `Data | `Pers] )
        Eliom_state.Ext.state
     -> 'a eref
-    -> 'a Lwt.t
+    -> 'a
   (** get the value of a reference from outside the state.
       If the value has not been set yet for this state,
       it will raise exception [Eref_not_initialized].
@@ -243,7 +243,7 @@ module Ext : sig
        Eliom_state.Ext.state
     -> 'a eref
     -> 'a
-    -> unit Lwt.t
+    -> unit
 
   val modify :
      ( [< `Session_group | `Session | `Client_process]
@@ -251,7 +251,7 @@ module Ext : sig
        Eliom_state.Ext.state
     -> 'a eref
     -> ('a -> 'a)
-    -> unit Lwt.t
+    -> unit
   (** Warning: the function will be executed with the current context *)
 
   val unset :
@@ -259,5 +259,5 @@ module Ext : sig
        , [< `Data | `Pers] )
        Eliom_state.Ext.state
     -> 'a eref
-    -> unit Lwt.t
+    -> unit
 end
diff --git a/src/lib/eliom_registration.client.ml b/src/lib/eliom_registration.client.ml
index 8f08609602..6684856f41 100644
--- a/src/lib/eliom_registration.client.ml
+++ b/src/lib/eliom_registration.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -51,27 +51,36 @@ module type PARAM = sig
   type result
 
   val reset_reload_fun : bool
-  val send : ?options:options -> page -> [`Browser] kind Lwt.t
+  val send : ?options:options -> page -> [`Browser] kind
 end
 
 let typed_apply ~service f gp pp l l' suffix =
-  Lwt.catch
-    (fun () ->
-       let* g =
-         let l = Some (Lwt.return l) in
-         Eliom_parameter.reconstruct_params ~sp:() gp l None true suffix
-       and* p =
-         let l' = Some (Lwt.return l') in
-         Eliom_parameter.reconstruct_params ~sp:() pp l' None true suffix
-       in
-       (match Eliom_service.reload_fun service with
-       | Some _ -> Eliom_client.set_reload_function (fun () () -> f g p)
-       | None -> ());
-       f g p)
-    (function
-      | Eliom_common.Eliom_Wrong_parameter ->
-          Lwt.fail Eliom_common.Eliom_Wrong_parameter
-      | exc -> Lwt.reraise exc)
+  try
+    let p, g =
+      Fiber.pair
+        (fun () ->
+           let
+               (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+                 l'
+             =
+             Some l'
+           in
+           Eliom_parameter.reconstruct_params ~sp:() pp l' None true suffix)
+        (fun () ->
+           let
+               (* TODO: lwt-to-direct-style: This computation might not be suspended correctly. *)
+                 l
+             =
+             Some l
+           in
+           Eliom_parameter.reconstruct_params ~sp:() gp l None true suffix)
+    in
+    (match Eliom_service.reload_fun service with
+    | Some _ -> Eliom_client.set_reload_function (fun () () -> f g p)
+    | None -> ());
+    f g p
+  with Eliom_common.Eliom_Wrong_parameter ->
+    raise Eliom_common.Eliom_Wrong_parameter
 
 let wrap service att f _ suffix =
   let gp = Eliom_service.get_params_type service
@@ -90,8 +99,8 @@ let wrap service att f _ suffix =
       and l' = List.remove_assoc "__eliom__" l' in
       if eliom_name = s
       then typed_apply ~service f gp pp l l' suffix
-      else Lwt.fail Eliom_common.Eliom_Wrong_parameter
-    with Not_found -> Lwt.fail Eliom_common.Eliom_Wrong_parameter)
+      else raise Eliom_common.Eliom_Wrong_parameter
+    with Not_found -> raise Eliom_common.Eliom_Wrong_parameter)
   | _ -> typed_apply ~service f gp pp l l' suffix
 
 let wrap_na
@@ -172,7 +181,7 @@ module Make (P : PARAM) = struct
         (f : g -> p -> _)
     =
     let f g p =
-      let* page = f g p in
+      let page = f g p in
       P.send ?options page
     in
     register ~service f;
@@ -189,7 +198,7 @@ module Html = Make (struct
     let reset_reload_fun = false
 
     let send ?options:_ page =
-      Lwt.return (Eliom_service.Dom (Eliom_content.Html.To_dom.of_element page))
+      Eliom_service.Dom (Eliom_content.Html.To_dom.of_element page)
   end)
 
 module Action = Make (struct
@@ -203,9 +212,8 @@ module Action = Make (struct
     let send ?options _page =
       match options with
       | Some `Reload | None ->
-          Lwt.return
-            Eliom_service.(Reload_action {hidden = false; https = false})
-      | _ -> Lwt.return Eliom_service.No_contents
+          Eliom_service.(Reload_action {hidden = false; https = false})
+      | _ -> Eliom_service.No_contents
   end)
 
 module Unit = Make (struct
@@ -215,7 +223,7 @@ module Unit = Make (struct
     type result = browser_content kind
 
     let reset_reload_fun = true
-    let send ?options:_ _page = Lwt.return Eliom_service.No_contents
+    let send ?options:_ _page = Eliom_service.No_contents
   end)
 
 type appl_service_options = {do_not_launch : bool}
@@ -234,8 +242,7 @@ module App (P : Eliom_registration_sigs.APP_PARAM) = struct
       let reset_reload_fun = false
 
       let send ?options:_ page =
-        Lwt.return
-          (Eliom_service.Dom (Eliom_content.Html.To_dom.of_element page))
+        Eliom_service.Dom (Eliom_content.Html.To_dom.of_element page)
     end)
 end
 
@@ -279,7 +286,7 @@ module Redirection = struct
         ?headers:_
         (Redirection service)
     =
-    Lwt.return (Eliom_service.Redirect service)
+    Eliom_service.Redirect service
 
   let register
         ?app
@@ -296,7 +303,7 @@ module Redirection = struct
         (f : g -> p -> _)
     =
     let f g p =
-      let* page = f g p in
+      let page = f g p in
       send ?options page
     in
     register ~service f;
@@ -309,8 +316,7 @@ module Any = struct
   type 'a result = 'a kind
   type options = unit
 
-  let send ?options:_ ?charset:_ ?code:_ ?content_type:_ ?headers:_ page =
-    Lwt.return page
+  let send ?options:_ ?charset:_ ?code:_ ?content_type:_ ?headers:_ page = page
 
   let register
         ?app
@@ -326,7 +332,7 @@ module Any = struct
         f
     =
     let f g p =
-      let* page = f g p in
+      let page = f g p in
       send page
     in
     register ~service f;
diff --git a/src/lib/eliom_registration.client.mli b/src/lib/eliom_registration.client.mli
index 2648d4de93..61405520b6 100644
--- a/src/lib/eliom_registration.client.mli
+++ b/src/lib/eliom_registration.client.mli
@@ -106,9 +106,9 @@ module Any :
    and type 'a result = 'a kind
 
 val appl_self_redirect :
-   ('page -> [< 'a application_content | browser_content] kind Lwt.t)
+   ('page -> [< 'a application_content | browser_content] kind)
   -> 'page
-  -> 'appl application_content kind Lwt.t
+  -> 'appl application_content kind
 (** For compatibility with server-side [appl_self_redirect] *)
 
 (**/**)
diff --git a/src/lib/eliom_registration.server.ml b/src/lib/eliom_registration.server.ml
index b281c0c583..15e55cbd54 100644
--- a/src/lib/eliom_registration.server.ml
+++ b/src/lib/eliom_registration.server.ml
@@ -1,5 +1,3 @@
-open Lwt.Syntax
-
 (* Ocsigen
  * http://www.ocsigen.org
  * Module Eliom_registration
@@ -20,8 +18,6 @@ open Lwt.Syntax
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
-open Lwt.Infix
-
 let headers_with_content_type ?charset ?content_type headers =
   match content_type with
   | Some content_type ->
@@ -60,27 +56,19 @@ let result_of_content ?charset ?content_type ?headers ?status body =
       "cache-control" "no-cache"
   in
   let response = Cohttp.Response.make ?status ~headers () in
-  Lwt.return (Ocsigen_response.make ~body response)
+  Ocsigen_response.make ~body response
 
 module Result_types : sig
   type 'a kind
 
   val cast_result : Ocsigen_response.t -> 'a kind
   val cast_kind : 'a kind -> Ocsigen_response.t
-  val cast_kind_lwt : 'a kind Lwt.t -> Ocsigen_response.t Lwt.t
-  val cast_result_lwt : Ocsigen_response.t Lwt.t -> 'a kind Lwt.t
-
-  val cast_function_http :
-     ('c -> 'a kind Lwt.t)
-    -> 'c
-    -> Ocsigen_response.t Lwt.t
+  val cast_function_http : ('c -> 'a kind) -> 'c -> Ocsigen_response.t
 end = struct
   type 'a kind = Ocsigen_response.t
 
   let cast_result x = x
   let cast_kind x = x
-  let cast_kind_lwt x = x
-  let cast_result_lwt x = x
   let cast_function_http x = x
 end
 
@@ -149,7 +137,7 @@ module Flow5_base = struct
 
   let body l =
     Ocsigen_response.Body.make Cohttp.Transfer.Unknown (fun write ->
-      Lwt_list.iter_s (fun x -> write (Format.asprintf "%a" out x)) l)
+      List.iter (fun x -> write (Format.asprintf "%a" out x)) l)
 
   let send ?options:_ ?charset ?code ?content_type ?headers c =
     let status = Eliom_lib.Option.map Cohttp.Code.status_of_code code
@@ -283,16 +271,16 @@ module Action_base = struct
         | ( Eliom_common.RNa_no
           , (Eliom_common.RAtt_no, Eliom_common.RAtt_no)
           , `GET ) ->
-            Lwt.return (Ocsigen_response.make (Cohttp.Response.make ()))
+            Ocsigen_response.make (Cohttp.Response.make ())
         | _ ->
             let all_cookie_info = sp.Eliom_common.sp_cookie_info in
-            let* ric =
+            let ric =
               Eliommod_cookies.compute_new_ri_cookies (Unix.time ())
                 (Ocsigen_request.sub_path ri.request_info)
                 (Ocsigen_request.cookies ri.request_info)
                 all_cookie_info user_cookies
             in
-            let* all_new_cookies =
+            let all_new_cookies =
               Eliommod_cookies.compute_cookies_to_send sitedata all_cookie_info
                 user_cookies
             in
@@ -331,7 +319,7 @@ module Action_base = struct
             (*VVV Also put all_cookie_info in this, to avoid
           update_cookie_table and get_cookie_info (?) *)
             let ri = update_request ri.request_info si ric in
-            let* () =
+            let () =
               Eliommod_pagegen.update_cookie_table sitedata all_cookie_info
             in
             send_directly ri
@@ -387,7 +375,7 @@ module Any_base = struct
         (Cohttp.Response.headers cohttp_response)
     in
     let response = {cohttp_response with Cohttp.Response.headers} in
-    Lwt.return (Ocsigen_response.update ~response result)
+    Ocsigen_response.update ~response result
 end
 
 module Any = struct
@@ -396,7 +384,7 @@ module Any = struct
   type 'a result = 'a kind
 
   let send ?options ?charset ?code ?content_type ?headers content =
-    Result_types.cast_result_lwt
+    Result_types.cast_result
       (Any_base.send ?options ?charset ?code ?content_type ?headers content)
 end
 
@@ -413,10 +401,10 @@ let appl_self_redirect send page =
       in
       Cohttp.Response.make ~headers ()
     in
-    Ocsigen_response.make response |> Result_types.cast_result |> Lwt.return
+    Ocsigen_response.make response |> Result_types.cast_result
   else
-    let* r = (Result_types.cast_function_http send) page in
-    Lwt.return (Result_types.cast_result r)
+    let r = (Result_types.cast_function_http send) page in
+    Result_types.cast_result r
 
 (* File is a module allowing to register services that send files *)
 module File_base = struct
@@ -441,15 +429,12 @@ module File_base = struct
         raise Eliom_common.Eliom_404
     with
     | Ocsigen_local_files.RFile fname ->
-        let* res =
-          let headers =
-            Ocsigen_header.of_option headers
-            |> add_cache_header options
-            |> headers_with_content_type ?charset ?content_type
-          in
-          Cohttp_lwt_unix.Server.respond_file ~headers ~fname ()
+        let headers =
+          Ocsigen_header.of_option headers
+          |> add_cache_header options
+          |> headers_with_content_type ?charset ?content_type
         in
-        Lwt.return (Ocsigen_response.of_cohttp res)
+        Ocsigen_response.respond_file ~headers fname
     | Ocsigen_local_files.RDir _ ->
         (* FIXME COHTTP TRANSITION: implement directories *)
         raise Ocsigen_local_files.Failed_404
@@ -508,7 +493,7 @@ module Customize
     (T : sig
        type page
 
-       val translate : page -> R.page Lwt.t
+       val translate : page -> R.page
      end) =
 struct
   type page = T.page
@@ -518,12 +503,12 @@ struct
 
   let make_eh = function
     | None -> None
-    | Some eh -> Some (fun l -> eh l >>= T.translate)
+    | Some eh -> Some (fun l -> T.translate (eh l))
 
-  let make_service_handler f g p = f g p >>= T.translate
+  let make_service_handler f g p = T.translate (f g p)
 
   let send ?options ?charset ?code ?content_type ?headers content =
-    T.translate content >>= fun c ->
+    let c = T.translate content in
     R.send ?options ?charset ?code ?content_type ?headers c
 
   let register
@@ -537,7 +522,7 @@ struct
         ?secure_session
         ~service
         ?error_handler
-        (f : 'get -> 'post -> 'return Lwt.t)
+        (f : 'get -> 'post -> 'return)
     =
     R.register ?app ?scope ?options ?charset ?code ?content_type ?headers
       ?secure_session ~service ?error_handler:(make_eh error_handler)
@@ -631,7 +616,7 @@ module Ocaml_base = struct
   let send_appl_content = Eliom_service.XNever
 
   let send ?options:_ ?charset ?code ?content_type ?headers content =
-    Result_types.cast_kind_lwt
+    Result_types.cast_kind
       (String.send ?charset ?code ?content_type ?headers
          (content, Eliom_service.eliom_appl_answer_content_type))
 end
@@ -658,53 +643,52 @@ module Ocaml = struct
     in
     (*     debug_client_value_data (debug "%s") client_value_data; *)
     let r = {Eliom_runtime.ecs_request_data; ecs_data = data} in
-    Lwt.return (Eliom_types.encode_eliom_data r)
+    Eliom_types.encode_eliom_data r
 
   let make_eh = function
     | None -> None
-    | Some eh -> Some (fun l -> eh l >>= prepare_data)
+    | Some eh -> Some (fun l -> prepare_data (eh l))
 
   let string_regexp = Str.regexp "\"\\([^\\\"]\\|\\\\.\\)*\""
 
   let make_service_handler ~name f g p =
-    let* data =
-      Lwt.catch
-        (fun () ->
-           let* res = f g p in
-           Lwt.return (`Success res))
-        (fun exn ->
-           let code = Printf.sprintf "%06x" (Random.int 0x1000000) in
-           let argument =
-             let sp = Eliom_common.get_sp () in
-             let si = Eliom_request_info.get_si sp in
-             let post_params =
-               match si.Eliom_common.si_all_post_params with
-               | None -> []
-               | Some l -> l
-             in
-             try Printf.sprintf " (%s)" (List.assoc "argument" post_params)
-             with Not_found -> ""
-           in
-           (match name with
-           | Some name ->
-               Logs.err (fun fmt ->
-                 fmt
-                   ("Uncaught exception in service %s [%s]%s" ^^ "@\n%s")
-                   name code
-                   (Str.global_replace string_regexp "\"xxx\"" argument)
-                   (Printexc.to_string exn))
-           | None ->
-               Logs.err (fun fmt ->
-                 fmt
-                   ("Uncaught exception [%s]%s" ^^ "@\n%s")
-                   code argument (Printexc.to_string exn)));
-           Lwt.return (`Failure code))
+    let data =
+      try
+        let res = f g p in
+        `Success res
+      with exn ->
+        let code = Printf.sprintf "%06x" (Random.int 0x1000000) in
+        let argument =
+          let sp = Eliom_common.get_sp () in
+          let si = Eliom_request_info.get_si sp in
+          let post_params =
+            match si.Eliom_common.si_all_post_params with
+            | None -> []
+            | Some l -> l
+          in
+          try Printf.sprintf " (%s)" (List.assoc "argument" post_params)
+          with Not_found -> ""
+        in
+        (match name with
+        | Some name ->
+            Logs.err (fun fmt ->
+              fmt
+                ("Uncaught exception in service %s [%s]%s" ^^ "@\n%s")
+                name code
+                (Str.global_replace string_regexp "\"xxx\"" argument)
+                (Printexc.to_string exn))
+        | None ->
+            Logs.err (fun fmt ->
+              fmt
+                ("Uncaught exception [%s]%s" ^^ "@\n%s")
+                code argument (Printexc.to_string exn)));
+        `Failure code
     in
     prepare_data data
 
   let send ?options ?charset ?code ?content_type ?headers content =
-    let* content = prepare_data content in
-    Result_types.cast_result_lwt
+    let content = prepare_data content in
+    Result_types.cast_result
       (M.send ?options ?charset ?code ?content_type ?headers content)
 
   let register
@@ -729,8 +713,8 @@ module Ocaml = struct
              , _
              , 'return Eliom_service.ocaml )
              Eliom_service.t)
-        ?(error_handler : ((string * exn) list -> 'return Lwt.t) option)
-        (f : 'get -> 'post -> 'return Lwt.t)
+        ?(error_handler : ((string * exn) list -> 'return) option)
+        (f : 'get -> 'post -> 'return)
     =
     M.register ?app ?scope ?options ?charset ?code ?content_type ?headers
       ?secure_session
@@ -942,10 +926,9 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
         (Eliom_lib.jsmarshal (Eliommod_cli.client_sitedata sp))
         (Eliom_lib.jsmarshal sp.Eliom_common.sp_client_process_info)
     in
-    Lwt.return
-      Eliom_content.Html.(
-        Id.create_named_elt ~id:eliom_appl_data_script_id
-          (F.script (F.cdata_script script)))
+    Eliom_content.Html.(
+      Id.create_named_elt ~id:eliom_appl_data_script_id
+        (F.script (F.cdata_script script)))
 
   let make_eliom_data_script ?(keep_debug = false) ~sp page =
     let ejs_global_data =
@@ -980,11 +963,11 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
               (Eliom_content.Html.D.toelt page)
         ; ejs_sess_info = Eliommod_cli.client_si sp.Eliom_common.sp_si }
     in
-    let* tab_cookies =
+    let tab_cookies =
       Eliommod_cookies.compute_cookies_to_send sp.Eliom_common.sp_sitedata
         sp.Eliom_common.sp_tab_cookie_info sp.Eliom_common.sp_user_tab_cookies
     in
-    let* template = Eliom_reference.get request_template in
+    let template = Eliom_reference.get request_template in
     let script =
       Printf.sprintf
         "__eliom_request_data = \'%s\';\n__eliom_request_cookies = \'%s\';\n__eliom_request_template = \'%s\';"
@@ -992,7 +975,7 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
         (Eliom_lib.jsmarshal tab_cookies)
         (Eliom_lib.jsmarshal (template : string option))
     in
-    Lwt.return Eliom_content.Html.(F.script (F.cdata_script script))
+    Eliom_content.Html.(F.script (F.cdata_script script))
 
   let global_data_service =
     lazy
@@ -1012,7 +995,7 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
        String.create ~options:max_age
          ~path:(Eliom_service.Path (path @ [name]))
          ~meth:(Get Eliom_parameter.unit)
-         (fun _ _ -> Lwt.return (script, "application/x-javascript")))
+         (fun _ _ -> script, "application/x-javascript"))
 
   let add_eliom_global_data_script rem =
     if global_data_cache_options () <> None
@@ -1054,7 +1037,7 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
     | _ -> assert false
 
   let add_eliom_scripts ~sp page =
-    let* appl_data_script = make_eliom_appl_data_script ~sp in
+    let appl_data_script = make_eliom_appl_data_script ~sp in
     (* First we build a fake page to build the ref_tree... *)
     let html_attribs, (head_attribs, title, head_elts), body =
       split_page (Eliom_content.Html.D.toelt page)
@@ -1097,7 +1080,7 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
         (Eliom_content.Html.F.head ~a:head_attribs title head_elts)
         body
     in
-    let* data_script =
+    let data_script =
       make_eliom_data_script
         ~keep_debug:(Ocsigen_config.get_debugmode ())
         ~sp fake_page
@@ -1109,10 +1092,9 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
       List.hd head_elts :: data_script
       :: add_eliom_global_data_script (List.tl head_elts)
     in
-    Lwt.return
-      (Eliom_content.Html.F.html ~a:html_attribs
-         (Eliom_content.Html.F.head ~a:head_attribs title head_elts)
-         body)
+    Eliom_content.Html.F.html ~a:html_attribs
+      (Eliom_content.Html.F.head ~a:head_attribs title head_elts)
+      body
 
   let remove_eliom_scripts page =
     let html_attribs, (head_attribs, title, head_elts), body =
@@ -1121,10 +1103,9 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
     let head_elts =
       List.filter (fun x -> not (is_eliom_appl_script x)) head_elts
     in
-    Lwt.return
-      (Eliom_content.Html.F.html ~a:html_attribs
-         (Eliom_content.Html.F.head ~a:head_attribs title head_elts)
-         body)
+    Eliom_content.Html.F.html ~a:html_attribs
+      (Eliom_content.Html.F.head ~a:head_attribs title head_elts)
+      body
 
   let send_appl_content =
     Eliom_service.XSame_appl (App_param.application_name, None)
@@ -1149,11 +1130,12 @@ module App_base (App_param : Eliom_registration_sigs.APP_PARAM) = struct
       Eliom_state.set_cookie ~cookie_level:`Client_process
         ~name:Eliom_common.appl_name_cookie_name
         ~value:App_param.application_name ();
-    let* body =
-      (match sp.Eliom_common.sp_client_appl_name, options.do_not_launch with
+    let body =
+      let body =
+        match sp.Eliom_common.sp_client_appl_name, options.do_not_launch with
         | None, true -> remove_eliom_scripts content
-        | _ -> add_eliom_scripts ~sp content)
-      >|= fun body ->
+        | _ -> add_eliom_scripts ~sp content
+      in
       Ocsigen_response.Body.of_string (Format.asprintf "%a" out body)
     in
     let headers =
@@ -1188,7 +1170,7 @@ module App (App_param : Eliom_registration_sigs.APP_PARAM) = struct
   let typed_name = App_param.application_name
 
   let data_service_handler () () =
-    Lwt.return (get_global_data ~keep_debug:(Ocsigen_config.get_debugmode ()))
+    get_global_data ~keep_debug:(Ocsigen_config.get_debugmode ())
 
   let _ =
     match App_param.global_data_path with
@@ -1203,7 +1185,7 @@ module type TMPL_PARAMS = sig
   type t
 
   val name : string
-  val make_page : t -> Html_types.html Eliom_content.Html.elt Lwt.t
+  val make_page : t -> Html_types.html Eliom_content.Html.elt
   val update : t -> unit Eliom_client_value.t
 end
 
@@ -1233,13 +1215,13 @@ struct
     =
     match Eliom_parameter.get_non_localized_get_parameters nl_template with
     | None ->
-        let* () = Eliom_reference.set request_template (Some Tmpl_param.name) in
-        let* content = Tmpl_param.make_page content in
-        Result_types.cast_kind_lwt
+        let () = Eliom_reference.set request_template (Some Tmpl_param.name) in
+        let content = Tmpl_param.make_page content in
+        Result_types.cast_kind
           (Appl.send ~options ?charset ?code ?content_type ?headers content)
     | Some _ ->
         ignore (Tmpl_param.update content);
-        Result_types.cast_kind_lwt
+        Result_types.cast_kind
           (Ocaml.send ?charset ?code ?content_type ?headers ())
 end
 
@@ -1401,7 +1383,7 @@ module Redirection = struct
   include Eliom_mkreg.Make_poly (Redirection_base)
 
   let send ?options ?charset ?code ?content_type ?headers content =
-    Result_types.cast_result_lwt
+    Result_types.cast_result
       (Redirection_base.send ?options ?charset ?code ?content_type ?headers
          content)
 end
diff --git a/src/lib/eliom_registration.server.mli b/src/lib/eliom_registration.server.mli
index 59a68f5caf..3d70f32630 100644
--- a/src/lib/eliom_registration.server.mli
+++ b/src/lib/eliom_registration.server.mli
@@ -163,7 +163,7 @@ module type TMPL_PARAMS = sig
   type t
 
   val name : string
-  val make_page : t -> Html_types.html Eliom_content.Html.elt Lwt.t
+  val make_page : t -> Html_types.html Eliom_content.Html.elt
   val update : t -> unit Eliom_client_value.t
 end
 
@@ -301,7 +301,7 @@ module Redirection : sig
     -> ?content_type:string
     -> ?headers:Ocsigen_header.t
     -> _ page
-    -> _ kind Lwt.t
+    -> _ kind
   (** More polymorphic version of {!Eliom_registration_sigs.send} *)
 end
 
@@ -387,9 +387,9 @@ module Any :
    and type 'a result = 'a kind
 
 val appl_self_redirect :
-   ('page -> [< 'a application_content | browser_content] kind Lwt.t)
+   ('page -> [< 'a application_content | browser_content] kind)
   -> 'page
-  -> 'appl application_content kind Lwt.t
+  -> 'appl application_content kind
 (** The function [appl_self_redirect send page] is an helper function
     required for defining {!Any} service usable inside an Eliom
     application ({!App}). It allows casting an Eliom senders that do
@@ -446,7 +446,7 @@ module Customize
     (T : sig
        type page
 
-       val translate : page -> R.page Lwt.t
+       val translate : page -> R.page
      end) :
   Eliom_registration_sigs.S_with_create
   with type options = R.options
@@ -456,7 +456,7 @@ module Customize
 
 (** {2 Using your own error pages} *)
 
-val set_exn_handler : (exn -> browser_content kind Lwt.t) -> unit
+val set_exn_handler : (exn -> browser_content kind) -> unit
 (** The [set_exn_handler handler] allows redefinition of error pages:
     [404] or any exception during page generation.
 
diff --git a/src/lib/eliom_registration_sigs.shared.mli b/src/lib/eliom_registration_sigs.shared.mli
index d7b688a4b5..38fecc185c 100644
--- a/src/lib/eliom_registration_sigs.shared.mli
+++ b/src/lib/eliom_registration_sigs.shared.mli
@@ -32,7 +32,7 @@ module type PARAM = sig
     -> ?content_type:string
     -> ?headers:Cohttp.Header.t
     -> page
-    -> frame Lwt.t
+    -> frame
 
   val send_appl_content : Eliom_service.send_appl_content
   (** Whether the service is capable of sending application content
@@ -56,7 +56,7 @@ module type PARAM_POLY = sig
     -> ?content_type:string
     -> ?headers:Cohttp.Header.t
     -> _ page
-    -> frame Lwt.t
+    -> frame
 
   val send_appl_content : Eliom_service.send_appl_content
   (** See {!Eliom_reg_sigs.PARAM.send_appl_content}. *)
@@ -104,8 +104,8 @@ module type S = sig
            , _
            , return )
            Eliom_service.t
-    -> ?error_handler:((string * exn) list -> page Lwt.t)
-    -> ('get -> 'post -> page Lwt.t)
+    -> ?error_handler:((string * exn) list -> page)
+    -> ('get -> 'post -> page)
     -> unit
   (** The function [register ~service handler] associates the
       [service] to the function [handler]. The [handler] function takes
@@ -147,7 +147,7 @@ module type S = sig
     -> ?content_type:string
     -> ?headers:Cohttp.Header.t
     -> page
-    -> result Lwt.t
+    -> result
   (** The function [send page] builds the HTTP frame corresponding to
       [page]. This may be used for example in a service handler
       registered with {!Eliom_registration.Any.register}, or when
@@ -175,8 +175,8 @@ module type S_with_create = sig
     -> ?timeout:float
     -> meth:('m, 'gp, 'gn, 'pp, 'pn, 'tipo, 'gp_) Eliom_service.meth
     -> path:('att, 'co, 'gp_) Eliom_service.path_option
-    -> ?error_handler:((string * exn) list -> page Lwt.t)
-    -> ('gp -> 'pp -> page Lwt.t)
+    -> ?error_handler:((string * exn) list -> page)
+    -> ('gp -> 'pp -> page)
     -> ( 'gp
          , 'pp
          , 'm
@@ -224,8 +224,8 @@ module type S_with_create = sig
            , return )
            Eliom_service.t
     -> get_params:('gp, [`WithoutSuffix], 'gn) Eliom_parameter.params_type
-    -> ?error_handler:((string * exn) list -> page Lwt.t)
-    -> ('gp -> unit -> page Lwt.t)
+    -> ?error_handler:((string * exn) list -> page)
+    -> ('gp -> unit -> page)
     -> ( 'gp
          , unit
          , Eliom_service.get
@@ -273,8 +273,8 @@ module type S_with_create = sig
            , return )
            Eliom_service.t
     -> post_params:('pp, [`WithoutSuffix], 'pn) Eliom_parameter.params_type
-    -> ?error_handler:((string * exn) list -> page Lwt.t)
-    -> ('gp -> 'pp -> page Lwt.t)
+    -> ?error_handler:((string * exn) list -> page)
+    -> ('gp -> 'pp -> page)
     -> ( 'gp
          , 'pp
          , Eliom_service.post
@@ -320,8 +320,8 @@ module type S_poly = sig
            , _
            , 'a return )
            Eliom_service.t
-    -> ?error_handler:((string * exn) list -> 'a page Lwt.t)
-    -> ('get -> 'post -> 'a page Lwt.t)
+    -> ?error_handler:((string * exn) list -> 'a page)
+    -> ('get -> 'post -> 'a page)
     -> unit
   (** See {!S.register}. *)
 end
@@ -347,8 +347,8 @@ module type S_poly_with_create = sig
     -> ?timeout:float
     -> meth:('m, 'gp, 'gn, 'pp, 'pn, 'tipo, 'gp_) Eliom_service.meth
     -> path:('att, 'co, 'gp_) Eliom_service.path_option
-    -> ?error_handler:((string * exn) list -> 'a page Lwt.t)
-    -> ('gp -> 'pp -> 'a page Lwt.t)
+    -> ?error_handler:((string * exn) list -> 'a page)
+    -> ('gp -> 'pp -> 'a page)
     -> ( 'gp
          , 'pp
          , 'm
@@ -393,8 +393,8 @@ module type S_poly_with_create = sig
            , 'a return )
            Eliom_service.t
     -> get_params:('gp, [`WithoutSuffix], 'gn) Eliom_parameter.params_type
-    -> ?error_handler:((string * exn) list -> 'a page Lwt.t)
-    -> ('gp -> unit -> 'a page Lwt.t)
+    -> ?error_handler:((string * exn) list -> 'a page)
+    -> ('gp -> unit -> 'a page)
     -> ( 'gp
          , unit
          , Eliom_service.get
@@ -439,8 +439,8 @@ module type S_poly_with_create = sig
            , 'a return )
            Eliom_service.t
     -> post_params:('pp, [`WithoutSuffix], 'pn) Eliom_parameter.params_type
-    -> ?error_handler:((string * exn) list -> 'a page Lwt.t)
-    -> ('gp -> 'pp -> 'a page Lwt.t)
+    -> ?error_handler:((string * exn) list -> 'a page)
+    -> ('gp -> 'pp -> 'a page)
     -> ( 'gp
          , 'pp
          , Eliom_service.post
@@ -468,7 +468,7 @@ module type S_poly_with_send = sig
     -> ?content_type:string
     -> ?headers:Cohttp.Header.t
     -> 'a page
-    -> 'a result Lwt.t
+    -> 'a result
 end
 
 module type S_poly_with_create_with_send = sig
@@ -483,5 +483,5 @@ module type S_poly_with_create_with_send = sig
     -> ?content_type:string
     -> ?headers:Cohttp.Header.t
     -> 'a page
-    -> 'a result Lwt.t
+    -> 'a result
 end
diff --git a/src/lib/eliom_request.client.ml b/src/lib/eliom_request.client.ml
index fe42ebc5f3..e93cc052b6 100644
--- a/src/lib/eliom_request.client.ml
+++ b/src/lib/eliom_request.client.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -258,123 +258,117 @@ let send
           = Some (Eliom_process.get_application_name ())
       else true
     in
-    Lwt.catch
-      (fun () ->
-         let* r =
-           let contents =
-             match post_args with
-             | Some post_args -> Some (`POST_form post_args)
-             | None -> None
-           in
-           XmlHttpRequest.perform_raw_url ?with_credentials
-             ?headers:(Some headers) ?content_type:None ?contents ~get_args
-             ~check_headers ?progress ?upload_progress ?override_mime_type url
-         in
-         let wait_for_unlock, unlock = Lwt.wait () in
-         (if not @@ React.S.value locked
-          then Lwt.wakeup unlock ()
-          else
-            let unlock_event = React.E.once @@ React.S.changes locked in
-            Dom_reference.retain_generic wait_for_unlock
-              ~keep:(React.E.map (fun _ -> Lwt.wakeup unlock ()) unlock_event));
-         let* () = wait_for_unlock in
-         (if Js.Optdef.test Js.Unsafe.global##.___eliom_use_cookie_substitutes_
-          then
-            match
-              (* Cookie substitutes are for iOS WKWebView *)
-              r.XmlHttpRequest.headers
-                Eliom_common.set_cookie_substitutes_header_name
-            with
-            | None | Some "" -> ()
-            | Some cookie_substitutes ->
-                Eliommod_cookies.update_cookie_table ~in_local_storage:true host
-                  (Eliommod_cookies.cookieset_of_json cookie_substitutes));
-         (match
-            r.XmlHttpRequest.headers Eliom_common.set_tab_cookies_header_name
-          with
-         | None | Some "" -> () (* Empty tab_cookies for IE compat *)
-         | Some tab_cookies ->
-             let tab_cookies = Eliommod_cookies.cookieset_of_json tab_cookies in
-             Eliommod_cookies.update_cookie_table host tab_cookies);
-         if r.XmlHttpRequest.code = 204
-         then
-           match
-             r.XmlHttpRequest.headers Eliom_common.full_xhr_redir_header
-           with
-           | None | Some "" -> (
-             match
-               r.XmlHttpRequest.headers Eliom_common.half_xhr_redir_header
-             with
-             | None | Some "" -> Lwt.return (r.XmlHttpRequest.url, None)
-             | Some _uri ->
-                 redirect_post url
-                   (match post_args with
-                   | Some post_args -> post_args
-                   | None -> []);
-                 Lwt.fail Program_terminated)
-           | Some uri ->
-               if i < max_redirection_level
-               then aux (i + 1) (Url.resolve uri)
-               else Lwt.fail Looping_redirection
-         else if expecting_process_page
-         then
-           let url =
-             match
-               r.XmlHttpRequest.headers Eliom_common.response_url_header
-             with
-             | None | Some "" -> Url.add_get_args url (List.tl get_args)
-             | Some url -> Url.resolve url
-           in
-           Lwt.return (url, Some (result r))
-         else if
-           r.XmlHttpRequest.code = 200
-           || XmlHttpRequest.(r.code = 0 && r.content <> "")
-           (* HACK for file access within Cordova which yields code 0.
+    try
+      let r =
+        let contents =
+          match post_args with
+          | Some post_args -> Some (`POST_form post_args)
+          | None -> None
+        in
+        XmlHttpRequest.perform_raw_url ?with_credentials ?headers:(Some headers)
+          ?content_type:None ?contents ~get_args ~check_headers ?progress
+          ?upload_progress ?override_mime_type url
+      in
+      let wait_for_unlock, unlock =
+        Promise.create
+          (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+          ()
+      in
+      (if not @@ React.S.value locked
+       then Promise.resolve unlock ()
+       else
+         let unlock_event = React.E.once @@ React.S.changes locked in
+         Dom_reference.retain_generic wait_for_unlock
+           ~keep:(React.E.map (fun _ -> Promise.resolve unlock ()) unlock_event));
+      let () = Promise.await wait_for_unlock in
+      (if Js.Optdef.test Js.Unsafe.global##.___eliom_use_cookie_substitutes_
+       then
+         match
+           (* Cookie substitutes are for iOS WKWebView *)
+           r.XmlHttpRequest.headers
+             Eliom_common.set_cookie_substitutes_header_name
+         with
+         | None | Some "" -> ()
+         | Some cookie_substitutes ->
+             Eliommod_cookies.update_cookie_table ~in_local_storage:true host
+               (Eliommod_cookies.cookieset_of_json cookie_substitutes));
+      (match
+         r.XmlHttpRequest.headers Eliom_common.set_tab_cookies_header_name
+       with
+      | None | Some "" -> () (* Empty tab_cookies for IE compat *)
+      | Some tab_cookies ->
+          let tab_cookies = Eliommod_cookies.cookieset_of_json tab_cookies in
+          Eliommod_cookies.update_cookie_table host tab_cookies);
+      if r.XmlHttpRequest.code = 204
+      then
+        match r.XmlHttpRequest.headers Eliom_common.full_xhr_redir_header with
+        | None | Some "" -> (
+          match r.XmlHttpRequest.headers Eliom_common.half_xhr_redir_header with
+          | None | Some "" -> r.XmlHttpRequest.url, None
+          | Some _uri ->
+              redirect_post url
+                (match post_args with
+                | Some post_args -> post_args
+                | None -> []);
+              raise Program_terminated)
+        | Some uri ->
+            if i < max_redirection_level
+            then aux (i + 1) (Url.resolve uri)
+            else raise Looping_redirection
+      else if expecting_process_page
+      then
+        let url =
+          match r.XmlHttpRequest.headers Eliom_common.response_url_header with
+          | None | Some "" -> Url.add_get_args url (List.tl get_args)
+          | Some url -> Url.resolve url
+        in
+        url, Some (result r)
+      else if
+        r.XmlHttpRequest.code = 200
+        || XmlHttpRequest.(r.code = 0 && r.content <> "")
+        (* HACK for file access within Cordova which yields code 0.
                     Code 0 might mean a network error, but then we have no
                     content. *)
-         then Lwt.return (r.XmlHttpRequest.url, Some (result r))
-         else Lwt.fail (Failed_request r.XmlHttpRequest.code))
-      (function
-        | XmlHttpRequest.Wrong_headers (code, headers) -> (
-          (* We are requesting application content and the headers tels
+      then r.XmlHttpRequest.url, Some (result r)
+      else raise (Failed_request r.XmlHttpRequest.code)
+    with XmlHttpRequest.Wrong_headers (code, headers) -> (
+      (* We are requesting application content and the headers tels
            us that the answer is not application content *)
-          match headers Eliom_common.appl_name_header_name with
-          | None | Some "" ->
-              (* Empty appl_name for IE compat. *)
-              (match post_args with
-              | None -> redirect_get url
-              | _ ->
-                  raise_error ~section
-                    "can't silently redirect a Post request to non application content");
-              Lwt.fail Program_terminated
-          | Some appl_name ->
-              let current_appl_name = Eliom_process.get_application_name () in
-              if appl_name = current_appl_name
-              then
-                assert false
-                (* we can't go here:
+      match headers Eliom_common.appl_name_header_name with
+      | None | Some "" ->
+          (* Empty appl_name for IE compat. *)
+          (match post_args with
+          | None -> redirect_get url
+          | _ ->
+              raise_error ~section
+                "can't silently redirect a Post request to non application content");
+          raise Program_terminated
+      | Some appl_name ->
+          let current_appl_name = Eliom_process.get_application_name () in
+          if appl_name = current_appl_name
+          then
+            assert false
+            (* we can't go here:
                                      this case is already handled before *)
-              else (
-                Logs.warn ~src:section (fun fmt ->
-                  fmt
-                    "received content for application %S when running application %s"
-                    appl_name current_appl_name);
-                Lwt.fail (Failed_request code)))
-        | exc -> Lwt.reraise exc)
+          else (
+            Logs.warn ~src:section (fun fmt ->
+              fmt
+                "received content for application %S when running application %s"
+                appl_name current_appl_name);
+            raise (Failed_request code)))
   in
-  let* url, content = aux 0 ?cookies_info ?get_args ?post_args url in
+  let url, content = aux 0 ?cookies_info ?get_args ?post_args url in
   let filter_url url =
     { url with
       Url.hu_arguments =
         List.filter (fun (e, _) -> e <> nl_template_string) url.Url.hu_arguments
     }
   in
-  Lwt.return
-    ( (match Url.url_of_string url with
-      | Some (Url.Http url) -> Url.string_of_url (Url.Http (filter_url url))
-      | Some (Url.Https url) -> Url.string_of_url (Url.Https (filter_url url))
-      | _ -> url)
-    , content )
+  ( (match Url.url_of_string url with
+    | Some (Url.Http url) -> Url.string_of_url (Url.Http (filter_url url))
+    | Some (Url.Https url) -> Url.string_of_url (Url.Https (filter_url url))
+    | _ -> url)
+  , content )
 
 (* BEGIN FORMDATA HACK *)
 let add_button_arg inj args form =
diff --git a/src/lib/eliom_request.client.mli b/src/lib/eliom_request.client.mli
index a6b91d2990..ae221f9b36 100644
--- a/src/lib/eliom_request.client.mli
+++ b/src/lib/eliom_request.client.mli
@@ -72,7 +72,7 @@ val send :
   -> ?override_mime_type:string
   -> string
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val send_get_form :
    ?with_credentials:bool
@@ -86,7 +86,7 @@ val send_get_form :
   -> Dom_html.formElement Js.t
   -> string
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val send_post_form :
    ?with_credentials:bool
@@ -100,7 +100,7 @@ val send_post_form :
   -> Dom_html.formElement Js.t
   -> string
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val http_get :
    ?with_credentials:bool
@@ -112,7 +112,7 @@ val http_get :
   -> string
   -> (string * string) list
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val http_post :
    ?with_credentials:bool
@@ -124,7 +124,7 @@ val http_post :
   -> string
   -> (string * Eliommod_parameters.param) list
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val http_put :
    ?with_credentials:bool
@@ -136,7 +136,7 @@ val http_put :
   -> string
   -> (string * Eliommod_parameters.param) list
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val http_delete :
    ?with_credentials:bool
@@ -148,7 +148,7 @@ val http_delete :
   -> string
   -> (string * Eliommod_parameters.param) list
   -> 'a result
-  -> (string * 'a option) Lwt.t
+  -> string * 'a option
 
 val get_cookie_info_for_uri_js : Js.js_string Js.t -> bool * string list
 val max_redirection_level : int
diff --git a/src/lib/eliom_request_info.client.ml b/src/lib/eliom_request_info.client.ml
index 1283096eb4..efef235f13 100644
--- a/src/lib/eliom_request_info.client.ml
+++ b/src/lib/eliom_request_info.client.ml
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Module eliom_sessions.ml
@@ -35,10 +37,10 @@ let client_app_initialised = ref false
 type t = {path : string list; si : Eliom_common.sess_info}
 
 let default_ri = ref None
-let ri_key = Lwt.new_key ()
+let ri_key = Fiber.create_key ()
 
 let get_ri () =
-  match Lwt.get ri_key with
+  match Fiber.get ri_key with
   | Some p -> p
   | None -> (
     match !default_ri with
@@ -53,7 +55,10 @@ let set_session_info ~uri si f =
   let path = Url.path_of_url_string (if uri = "./" then "" else uri) in
   let ri = Some {path; si} in
   default_ri := ri;
-  Lwt.with_value ri_key ri f
+  (Stdlib.Option.fold ~none:Fiber.without_binding
+     ~some:(Fun.flip Fiber.with_binding)
+     ri)
+    ri_key f
 
 let matches_regexp name re =
   try
@@ -99,7 +104,10 @@ let update_session_info ~path ~all_get_params ~all_post_params cont =
   in
   let ri = Some {path; si} in
   default_ri := ri;
-  Lwt.with_value ri_key ri cont
+  (Stdlib.Option.fold ~none:Fiber.without_binding
+     ~some:(Fun.flip Fiber.with_binding)
+     ri)
+    ri_key cont
 
 let remove_first_slash path = match path with "" :: l -> l | l -> l
 
@@ -220,7 +228,7 @@ let get_request_data () =
 
 exception Eliom_no_raw_post_data_on_client
 
-let raw_post_data _ = Lwt.fail Eliom_no_raw_post_data_on_client
+let raw_post_data _ = raise Eliom_no_raw_post_data_on_client
 
 type raw_post_data = unit
 
diff --git a/src/lib/eliom_request_info.client.mli b/src/lib/eliom_request_info.client.mli
index e6f4ea7f95..0707a146d5 100644
--- a/src/lib/eliom_request_info.client.mli
+++ b/src/lib/eliom_request_info.client.mli
@@ -76,7 +76,7 @@ val ssl_ : bool
 
 type raw_post_data = unit
 
-val raw_post_data : unit -> _ Lwt.t
+val raw_post_data : unit -> _
 val client_app_initialised : bool ref
 val get_request_data : unit -> Eliom_common.eliom_js_page_data
 val get_request_cookies : unit -> Ocsigen_cookie_map.t
@@ -101,12 +101,12 @@ val get_sess_info : unit -> Eliom_common.sess_info
 val set_session_info :
    uri:string
   -> Eliom_common.sess_info
-  -> (unit -> 'a Lwt.t)
-  -> 'a Lwt.t
+  -> (unit -> 'a)
+  -> 'a
 
 val update_session_info :
    path:Url.path
   -> all_get_params:(string * string) list
   -> all_post_params:(string * string) list option
-  -> (unit -> 'a Lwt.t)
-  -> 'a Lwt.t
+  -> (unit -> 'a)
+  -> 'a
diff --git a/src/lib/eliom_request_info.server.ml b/src/lib/eliom_request_info.server.ml
index d67cabaeb5..6070998cb9 100644
--- a/src/lib/eliom_request_info.server.ml
+++ b/src/lib/eliom_request_info.server.ml
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2010 Vincent Balat
@@ -311,7 +313,7 @@ let get_site_dir_option () =
     None
 
 let get_site_dir_sp sp = Eliom_common.get_site_dir sp.Eliom_common.sp_sitedata
-let in_request_handler () = Lwt.get Eliom_common.sp_key <> None
+let in_request_handler () = Fiber.get Eliom_common.sp_key <> None
 
 let get_request () =
   let sp = Eliom_common.get_sp () in
@@ -338,8 +340,8 @@ let set_site_handler sitedata handler =
   sitedata.Eliom_common.exn_handler <- handler
 
 type raw_post_data =
-  ((string * string) * (string * string) list) option * Cohttp_lwt.Body.t
+  ((string * string) * (string * string) list) option * Cohttp_eio.Body.t
 
 let raw_post_data sp =
   let ri = get_ri_sp sp in
-  Lwt.return (Ocsigen_request.content_type ri, Ocsigen_request.body ri)
+  Ocsigen_request.content_type ri, Ocsigen_request.body ri
diff --git a/src/lib/eliom_request_info.server.mli b/src/lib/eliom_request_info.server.mli
index 4557d27eb7..c48ebb7a52 100644
--- a/src/lib/eliom_request_info.server.mli
+++ b/src/lib/eliom_request_info.server.mli
@@ -185,7 +185,7 @@ val get_persistent_nl_get_params :
 val get_nl_post_params : unit -> (string * string) list Eliom_lib.String.Table.t
 (** returns non localized POST parameters. *)
 
-val get_post_params : unit -> (string * string) list Lwt.t option
+val get_post_params : unit -> (string * string) list option
 (** returns the parameters in the body of the HTTP request (POST parameters)
     that concern the running service. None means that POST data where
     neither urlencoded form data or multipart data. *)
@@ -318,7 +318,7 @@ val get_sp_client_process_info : unit -> Eliom_common.client_process_info
 
 val set_site_handler :
    Eliom_common.sitedata
-  -> (exn -> Ocsigen_response.t Lwt.t)
+  -> (exn -> Ocsigen_response.t)
   -> unit
 
 val get_request_sp : Eliom_common.server_params -> Ocsigen_extensions.request
@@ -350,16 +350,16 @@ val get_ri_sp : Eliom_common.server_params -> Ocsigen_request.t
 
 val get_post_params_sp :
    Eliom_common.server_params
-  -> (string * string) list Lwt.t option
+  -> (string * string) list option
 
 val get_files_sp :
    Eliom_common.server_params
-  -> (string * Ocsigen_extensions.file_info) list Lwt.t option
+  -> (string * Ocsigen_extensions.file_info) list option
 
 val get_suffix_sp : Eliom_common.server_params -> Eliom_lib.Url.path option
 val get_request_cache_sp : Eliom_common.server_params -> Polytables.t
 
 type raw_post_data =
-  ((string * string) * (string * string) list) option * Cohttp_lwt.Body.t
+  ((string * string) * (string * string) list) option * Cohttp_eio.Body.t
 
-val raw_post_data : Eliom_common.server_params -> raw_post_data Lwt.t
+val raw_post_data : Eliom_common.server_params -> raw_post_data
diff --git a/src/lib/eliom_route.client.ml b/src/lib/eliom_route.client.ml
index a0d93e93fd..f4aa0d96e3 100644
--- a/src/lib/eliom_route.client.ml
+++ b/src/lib/eliom_route.client.ml
@@ -70,8 +70,7 @@ module A = struct
           (int * int * Table.t Eliom_common.dircontent ref) list
       ; mutable t_contains_timeout : bool
       ; mutable t_na_services :
-          (Eliom_common.na_key_serv, bool -> params -> result Lwt.t) Hashtbl.t
-      }
+          (Eliom_common.na_key_serv, bool -> params -> result) Hashtbl.t }
 
     let get {t_services; _} = t_services
     let set_contains_timeout a b = a.t_contains_timeout <- b
@@ -79,7 +78,7 @@ module A = struct
     let dlist_add ?sp:_ _tables _srv = ()
   end
 
-  let handle_directory _ = Lwt.return Eliom_service.No_contents
+  let handle_directory _ = Eliom_service.No_contents
 end
 
 include Eliom_route_base.Make (A)
@@ -95,7 +94,7 @@ let add_naservice k f {A.Container.t_na_services; _} =
 
 let call_naservice k {A.Container.t_na_services; _} =
   try (Hashtbl.find t_na_services k) true None
-  with Not_found -> Lwt.fail Eliom_common.Eliom_404
+  with Not_found -> raise Eliom_common.Eliom_404
 
 let rec na_key_of_params ~get = function
   | (k, v) :: _ when k = Eliom_common.naservice_name ->
diff --git a/src/lib/eliom_route.server.ml b/src/lib/eliom_route.server.ml
index 1b943081ae..016e18c24e 100644
--- a/src/lib/eliom_route.server.ml
+++ b/src/lib/eliom_route.server.ml
@@ -1,5 +1,4 @@
 open Eliom_lib
-open Lwt
 open Ocsigen_extensions
 include Eliom_route_base
 
@@ -61,30 +60,28 @@ include Eliom_route_base.Make (struct
     let make_params = Eliom_common.make_server_params
 
     let handle_directory {Eliom_common.request = r; _} =
-      Lwt.fail
-      @@ Ocsigen_extensions.Ocsigen_is_dir
-           (Ocsigen_extensions.new_url_of_directory_request r)
+      raise
+        (Ocsigen_extensions.Ocsigen_is_dir
+           (Ocsigen_extensions.new_url_of_directory_request r))
 
     let get_number_of_reloads () = Ocsigen_extensions.get_numberofreloads ()
   end)
 
-let find_aux now sitedata info _ sci : Ocsigen_response.t Lwt.t =
+let find_aux now sitedata info _ sci : Ocsigen_response.t =
   Eliom_common.Full_state_name_table.fold
     (fun fullsessname (_, r) beg ->
-       Lwt.catch
-         (fun () -> beg)
-         (function
-           | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter -> (
-             match !r with
-             | Eliom_common.SCData_session_expired
-             | Eliom_common.SCNo_data (* cookie removed *) ->
-                 beg
-             | Eliom_common.SC c ->
-                 find_service now !(c.Eliom_common.sc_table) (Some fullsessname)
-                   sitedata info)
-           | e -> fail e))
+       try beg with
+       | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter -> (
+         match !r with
+         | Eliom_common.SCData_session_expired
+         | Eliom_common.SCNo_data (* cookie removed *) ->
+             beg
+         | Eliom_common.SC c ->
+             find_service now !(c.Eliom_common.sc_table) (Some fullsessname)
+               sitedata info)
+       | e -> raise e)
     sci
-    (fail Eliom_common.Eliom_404)
+    (raise Eliom_common.Eliom_404)
 
 let session_tables {Eliom_common.all_cookie_info; tab_cookie_info; _} =
   let (service_cookies_info, _, _), (secure_service_cookies_info, _, _) =
@@ -104,89 +101,82 @@ let drop_most_params ri si =
 let get_page
       now
       ({Eliom_common.request = ri; session_info = si; _} as info)
-      sitedata : Ocsigen_response.t Lwt.t
+      sitedata : Ocsigen_response.t
   =
   let tables = session_tables info in
-  catch
-    (fun () ->
-       List.fold_left
-         (fun beg (table, table_name) ->
-            Lwt.catch
-              (fun () -> beg)
-              (function
-                | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter ->
-                    Logs.info ~src:section (fun fmt ->
-                      fmt "Looking for %s in the %s:"
-                        (Url.string_of_url_path ~encode:true
-                           (Ocsigen_request.sub_path ri.request_info))
-                        table_name);
-                    find_aux now sitedata info Eliom_common.Eliom_404 table
-                | e -> Lwt.fail e))
-         (Lwt.fail Eliom_common.Eliom_404)
-         tables)
-    (function
-      | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter ->
-          catch (* ensuite dans la table globale *)
-            (fun () ->
-               Logs.info ~src:section (fun fmt ->
-                 fmt "Searching in the global table:");
-               find_service now sitedata.Eliom_common.global_services None
-                 sitedata info)
-            (function
-              | (Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter) as
-                exn -> (
-                (* si pas trouvé avec, on essaie sans l'état *)
-                match si.Eliom_common.si_state_info with
-                | Eliom_common.RAtt_no, Eliom_common.RAtt_no -> fail exn
-                | g, Eliom_common.RAtt_anon _ | g, Eliom_common.RAtt_named _ ->
-                    (* There was a POST state.
+  try
+    List.fold_left
+      (fun beg (table, table_name) ->
+         try beg with
+         | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter ->
+             Logs.info ~src:section (fun fmt ->
+               fmt "Looking for %s in the %s:"
+                 (Url.string_of_url_path ~encode:true
+                    (Ocsigen_request.sub_path ri.request_info))
+                 table_name);
+             find_aux now sitedata info Eliom_common.Eliom_404 table
+         | e -> raise e)
+      (raise Eliom_common.Eliom_404)
+      tables
+  with
+  | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter -> (
+    try
+      (* ensuite dans la table globale *)
+      Logs.info ~src:section (fun fmt -> fmt "Searching in the global table:");
+      find_service now sitedata.Eliom_common.global_services None sitedata info
+    with
+    | (Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter) as exn -> (
+      (* si pas trouvé avec, on essaie sans l'état *)
+      match si.Eliom_common.si_state_info with
+      | Eliom_common.RAtt_no, Eliom_common.RAtt_no -> raise exn
+      | g, Eliom_common.RAtt_anon _ | g, Eliom_common.RAtt_named _ ->
+          (* There was a POST state.
                           We remove it, and remove POST parameters.
-                    *)
-                    Logs.info ~src:section (fun fmt ->
-                      fmt "Link too old. Try without POST parameters:");
-                    Polytables.set
-                      ~table:(Ocsigen_request.request_cache ri.request_info)
-                      ~key:Eliom_common.eliom_link_too_old ~value:true;
-                    let request =
-                      { ri with
-                        request_info =
-                          Ocsigen_request.update ri.request_info ~post_data:None
-                            ~meth:`GET }
-                    and session_info =
-                      { si with
-                        Eliom_common.si_nonatt_info = Eliom_common.RNa_no
-                      ; Eliom_common.si_state_info = g, Eliom_common.RAtt_no }
-                    in
-                    fail
-                    @@ Eliom_common.Eliom_retry_with
-                         {info with Eliom_common.request; session_info}
-                | Eliom_common.RAtt_named _, Eliom_common.RAtt_no
-                | Eliom_common.RAtt_anon _, Eliom_common.RAtt_no ->
-                    (* There was a GET state, but no POST state.
+          *)
+          Logs.info ~src:section (fun fmt ->
+            fmt "Link too old. Try without POST parameters:");
+          Polytables.set
+            ~table:(Ocsigen_request.request_cache ri.request_info)
+            ~key:Eliom_common.eliom_link_too_old ~value:true;
+          let request =
+            { ri with
+              request_info =
+                Ocsigen_request.update ri.request_info ~post_data:None
+                  ~meth:`GET }
+          and session_info =
+            { si with
+              Eliom_common.si_nonatt_info = Eliom_common.RNa_no
+            ; Eliom_common.si_state_info = g, Eliom_common.RAtt_no }
+          in
+          raise
+            (Eliom_common.Eliom_retry_with
+               {info with Eliom_common.request; session_info})
+      | Eliom_common.RAtt_named _, Eliom_common.RAtt_no
+      | Eliom_common.RAtt_anon _, Eliom_common.RAtt_no ->
+          (* There was a GET state, but no POST state.
                      We remove it with its parameters,
                      and remove POST parameters.
-                    *)
-                    Logs.info ~src:section (fun fmt ->
-                      fmt
-                        "Link to old. Trying without GET state parameters and POST parameters:");
-                    Polytables.set
-                      ~table:(Ocsigen_request.request_cache ri.request_info)
-                      ~key:Eliom_common.eliom_link_too_old ~value:true;
-                    let request =
-                      { ri with
-                        request_info = drop_most_params ri.request_info si }
-                    and session_info =
-                      let open Eliom_common in
-                      { si with
-                        si_nonatt_info = RNa_no
-                      ; si_state_info = RAtt_no, RAtt_no
-                      ; si_other_get_params = [] }
-                    in
-                    fail
-                    @@ Eliom_common.Eliom_retry_with
-                         {info with Eliom_common.request; session_info})
-              | e -> fail e)
-      | e -> fail e)
+          *)
+          Logs.info ~src:section (fun fmt ->
+            fmt
+              "Link to old. Trying without GET state parameters and POST parameters:");
+          Polytables.set
+            ~table:(Ocsigen_request.request_cache ri.request_info)
+            ~key:Eliom_common.eliom_link_too_old ~value:true;
+          let request =
+            {ri with request_info = drop_most_params ri.request_info si}
+          and session_info =
+            let open Eliom_common in
+            { si with
+              si_nonatt_info = RNa_no
+            ; si_state_info = RAtt_no, RAtt_no
+            ; si_other_get_params = [] }
+          in
+          raise
+            (Eliom_common.Eliom_retry_with
+               {info with Eliom_common.request; session_info}))
+    | e -> raise e)
+  | e -> raise e
 
 let add_naservice_table at (key, elt) =
   match at with
@@ -309,70 +299,72 @@ let make_naservice
     | Eliom_common.Notfound _ -> raise Not_found
   in
   let tables = session_tables info in
-  (try
-     try
-       let rec f = function
-         | [] -> raise Not_found
-         | (table, table_name) :: l -> (
-             Logs.info ~src:section (fun fmt ->
-               fmt "Looking for a non attached service in the %s:" table_name);
-             try return (find_aux table) with Not_found -> f l)
-       in
-       f tables
-     with Not_found ->
-       Logs.info ~src:section (fun fmt ->
-         fmt "Looking for a non attached service in the global table");
-       return
-         ( find_naservice now sitedata.Eliom_common.global_services
-             (Eliom_common.na_key_serv_of_req si.Eliom_common.si_nonatt_info)
-         , sitedata.Eliom_common.global_services
-         , None )
-   with Not_found -> (
-     (* The non-attached service has not been found.
-      We call the same URL without non-attached parameters.
-     *)
-     match si.Eliom_common.si_nonatt_info with
-     | Eliom_common.RNa_no -> assert false
-     | Eliom_common.RNa_post_ _ | Eliom_common.RNa_post' _ ->
-         (*VVV (Some, Some) or (_, Some)? *)
-         Logs.info ~src:section (fun fmt ->
-           fmt
-             "Link too old to a non-attached POST coservice. Try without POST parameters:");
-         Polytables.set
-           ~table:(Ocsigen_request.request_cache ri.request_info)
-           ~key:Eliom_common.eliom_link_too_old ~value:true;
-         Eliom_common.get_session_info ~sitedata
-           ~req:
-             { ri with
-               Ocsigen_extensions.request_info =
-                 drop_most_params ri.request_info si }
-           si.Eliom_common.si_previous_extension_error
-         >>= fun (ri', si', _previous_tab_cookies_info) ->
-         Lwt.fail
-         @@ Eliom_common.Eliom_retry_with
-              {info with request = ri'; session_info = si'}
-     | Eliom_common.RNa_get_ _ | Eliom_common.RNa_get' _ ->
-         Logs.info ~src:section (fun fmt ->
-           fmt "Link too old. Try without non-attached parameters:");
-         Polytables.set
-           ~table:(Ocsigen_request.request_cache ri.request_info)
-           ~key:Eliom_common.eliom_link_too_old ~value:true;
-         Eliom_common.get_session_info ~sitedata
-           ~req:
-             { ri with
-               Ocsigen_extensions.request_info =
-                 drop_most_params ri.request_info si }
-           si.Eliom_common.si_previous_extension_error
-         >>= fun (ri', si', _previous_tab_cookies_info) ->
-         Lwt.fail
-         @@ Eliom_common.Eliom_retry_with
-              {info with request = ri'; session_info = si'}))
-  >>=
-  fun ( (_, max_use, expdate, naservice, node)
+  let ( (_, max_use, expdate, naservice, node)
       , tablewhereithasbeenfound
-      , fullsessname ) ->
+      , fullsessname )
+    =
+    try
+      try
+        let rec f = function
+          | [] -> raise Not_found
+          | (table, table_name) :: l -> (
+              Logs.info ~src:section (fun fmt ->
+                fmt "Looking for a non attached service in the %s:" table_name);
+              try find_aux table with Not_found -> f l)
+        in
+        f tables
+      with Not_found ->
+        Logs.info ~src:section (fun fmt ->
+          fmt "Looking for a non attached service in the global table");
+        ( find_naservice now sitedata.Eliom_common.global_services
+            (Eliom_common.na_key_serv_of_req si.Eliom_common.si_nonatt_info)
+        , sitedata.Eliom_common.global_services
+        , None )
+    with Not_found -> (
+      (* The non-attached service has not been found.
+      We call the same URL without non-attached parameters.
+      *)
+      match si.Eliom_common.si_nonatt_info with
+      | Eliom_common.RNa_no -> assert false
+      | Eliom_common.RNa_post_ _ | Eliom_common.RNa_post' _ ->
+          (*VVV (Some, Some) or (_, Some)? *)
+          Logs.info ~src:section (fun fmt ->
+            fmt
+              "Link too old to a non-attached POST coservice. Try without POST parameters:");
+          Polytables.set
+            ~table:(Ocsigen_request.request_cache ri.request_info)
+            ~key:Eliom_common.eliom_link_too_old ~value:true;
+          let ri', si', _previous_tab_cookies_info =
+            Eliom_common.get_session_info ~sitedata
+              ~req:
+                { ri with
+                  Ocsigen_extensions.request_info =
+                    drop_most_params ri.request_info si }
+              si.Eliom_common.si_previous_extension_error
+          in
+          raise
+            (Eliom_common.Eliom_retry_with
+               {info with request = ri'; session_info = si'})
+      | Eliom_common.RNa_get_ _ | Eliom_common.RNa_get' _ ->
+          Logs.info ~src:section (fun fmt ->
+            fmt "Link too old. Try without non-attached parameters:");
+          Polytables.set
+            ~table:(Ocsigen_request.request_cache ri.request_info)
+            ~key:Eliom_common.eliom_link_too_old ~value:true;
+          let ri', si', _previous_tab_cookies_info =
+            Eliom_common.get_session_info ~sitedata
+              ~req:
+                { ri with
+                  Ocsigen_extensions.request_info =
+                    drop_most_params ri.request_info si }
+              si.Eliom_common.si_previous_extension_error
+          in
+          raise
+            (Eliom_common.Eliom_retry_with
+               {info with request = ri'; session_info = si'}))
+  in
   let sp = Eliom_common.make_server_params sitedata info None fullsessname in
-  naservice sp >>= fun r ->
+  let r = naservice sp in
   Logs.info ~src:section (fun fmt ->
     fmt "Non attached page found and generated successfully");
   (match expdate with Some (timeout, e) -> e := timeout +. now | None -> ());
@@ -385,4 +377,4 @@ let make_naservice
           (Eliom_common.na_key_serv_of_req si.Eliom_common.si_nonatt_info)
           node
       else r := !r - 1);
-  return r
+  r
diff --git a/src/lib/eliom_route.server.mli b/src/lib/eliom_route.server.mli
index aded0025e3..c9b4fb7799 100644
--- a/src/lib/eliom_route.server.mli
+++ b/src/lib/eliom_route.server.mli
@@ -24,7 +24,7 @@ val get_page :
    float
   -> Eliom_common.info
   -> Eliom_common.sitedata
-  -> Ocsigen_response.t Lwt.t
+  -> Ocsigen_response.t
 
 val add_service :
    int
@@ -46,7 +46,7 @@ val add_naservice :
   -> Eliom_common.NAserv_Table.key
   -> int ref option
      * (float * float ref) option
-     * (Eliom_common.server_params -> Ocsigen_response.t Lwt.t)
+     * (Eliom_common.server_params -> Ocsigen_response.t)
   -> unit
 
 val remove_naservice :
@@ -58,4 +58,4 @@ val make_naservice :
    float
   -> Eliom_common.info
   -> Eliom_common.sitedata
-  -> Ocsigen_response.t Lwt.t
+  -> Ocsigen_response.t
diff --git a/src/lib/eliom_route_base.shared.ml b/src/lib/eliom_route_base.shared.ml
index 10a5a2bfbb..96eb4b735f 100644
--- a/src/lib/eliom_route_base.shared.ml
+++ b/src/lib/eliom_route_base.shared.ml
@@ -19,7 +19,6 @@
 *)
 
 open Eliom_lib
-open Lwt
 
 let section = Logs.Src.create "eliom:service"
 
@@ -40,7 +39,7 @@ module type PARAM = sig
     -> Eliom_common.full_state_name option
     -> params
 
-  val handle_directory : info -> result Lwt.t
+  val handle_directory : info -> result
   val get_number_of_reloads : unit -> int
 
   module Node : sig
@@ -100,61 +99,60 @@ module Make (P : PARAM) = struct
         (site_data : P.site_data)
         (info : P.info)
         (urlsuffix : _ option)
-        k : P.result Lwt.t
+        k : P.result
     =
     let sp = P.make_params site_data info urlsuffix fullsessname in
-    Lwt.catch
-      (fun () -> Lwt.return (P.Table.find k !pagetableref))
-      (function Not_found -> fail Eliom_common.Eliom_404 | e -> fail e)
-    >>= fun (node, l) ->
+    let node, l =
+      try P.Table.find k !pagetableref with
+      | Not_found -> raise Eliom_common.Eliom_404
+      | e -> raise e
+    in
     let rec aux toremove = function
-      | [] ->
-          Lwt.return
-            (Eliom_common.Notfound Eliom_common.Eliom_Wrong_parameter, [])
+      | [] -> Eliom_common.Notfound Eliom_common.Eliom_Wrong_parameter, []
       | ({Eliom_common.s_max_use; s_expire; s_f; _} as a) :: l -> (
         match s_expire with
         | Some (_, e) when !e < now ->
             (* Service expired. Removing it. *)
             Logs.info ~src:section (fun fmt ->
               fmt "Service expired. Removing it");
-            aux toremove l >>= fun (r, toremove) -> Lwt.return (r, a :: toremove)
-        | _ ->
-            catch
-              (fun () ->
-                 Logs.info ~src:section (fun fmt -> fmt "Trying a service");
-                 s_f nosuffixversion sp >>= fun p ->
-                 (* warning: the list ll may change during funct
+            let r, toremove = aux toremove l in
+            r, a :: toremove
+        | _ -> (
+          try
+            Logs.info ~src:section (fun fmt -> fmt "Trying a service");
+            let p = s_f nosuffixversion sp in
+            (* warning: the list ll may change during funct
                   if funct register something on the same URL!! *)
-                 Logs.info ~src:section (fun fmt ->
-                   fmt "Page found and generated successfully");
-                 (* If this is an anonymous coservice,
+            Logs.info ~src:section (fun fmt ->
+              fmt "Page found and generated successfully");
+            (* If this is an anonymous coservice,
                   we place it at the top of the dlist
                   (limitation of number of coservices) *)
-                 (match node with
-                 | None -> ()
-                 | Some node -> P.Node.up node);
-                 (* We update the expiration date *)
-                 (match s_expire with
-                 | Some (timeout, e) -> e := timeout +. now
-                 | None -> ());
-                 let newtoremove =
-                   match s_max_use with
-                   | Some s_max_use ->
-                       if s_max_use = 1
-                       then a :: toremove
-                       else (
-                         a.s_max_use <- Some (s_max_use - 1);
-                         toremove)
-                   | _ -> toremove
-                 in
-                 Lwt.return (Eliom_common.Found p, newtoremove))
-              (function
-                | Eliom_common.Eliom_Wrong_parameter ->
-                    aux toremove l >>= fun (r, toremove) ->
-                    Lwt.return (r, toremove)
-                | e -> Lwt.return (Eliom_common.Notfound e, toremove)))
+            (match node with
+            | None -> ()
+            | Some node -> P.Node.up node);
+            (* We update the expiration date *)
+            (match s_expire with
+            | Some (timeout, e) -> e := timeout +. now
+            | None -> ());
+            let newtoremove =
+              match s_max_use with
+              | Some s_max_use ->
+                  if s_max_use = 1
+                  then a :: toremove
+                  else (
+                    a.s_max_use <- Some (s_max_use - 1);
+                    toremove)
+              | _ -> toremove
+            in
+            Eliom_common.Found p, newtoremove
+          with
+          | Eliom_common.Eliom_Wrong_parameter ->
+              let r, toremove = aux toremove l in
+              r, toremove
+          | e -> Eliom_common.Notfound e, toremove))
     in
-    aux [] l >>= fun (r, toremove) ->
+    let r, toremove = aux [] l in
     (match node, toremove with
     | _, [] -> ()
     | Some node, _ ->
@@ -184,8 +182,8 @@ module Make (P : PARAM) = struct
           | newlist -> P.Table.add k (None, newlist) newptr
       with Not_found -> ()));
     match r with
-    | Eliom_common.Found r -> Lwt.return (r : P.result)
-    | Eliom_common.Notfound e -> fail e
+    | Eliom_common.Found r -> (r : P.result)
+    | Eliom_common.Notfound e -> raise e
 
   let remove_id services id =
     List.filter (fun {Eliom_common.s_id; _} -> s_id <> id) services
@@ -355,8 +353,8 @@ module Make (P : PARAM) = struct
 
   exception Exn1
 
-  let find_service now tables fullsessname sitedata info : P.result Lwt.t =
-    let rec search_page_table dircontent : _ -> P.result Lwt.t =
+  let find_service now tables fullsessname sitedata info : P.result =
+    let rec search_page_table dircontent : _ -> P.result =
       let find nosuffixversion page_table_ref suffix =
         let si = P.sess_info_of_info info in
         find_page_table nosuffixversion now page_table_ref fullsessname sitedata
@@ -372,37 +370,35 @@ module Make (P : PARAM) = struct
         let aa =
           match a with None -> Eliom_common.defaultpagename | Some aa -> aa
         in
-        Lwt.catch
-          (fun () ->
-             let dc =
-               try !(find_dircontent dircontent aa)
-               with Not_found -> raise Exn1
-             in
-             match dc with
-             | Eliom_common.Dir dircontentref2 ->
-                 search_page_table !dircontentref2 l
-             | Eliom_common.File page_table_ref -> (
-               match l with
-               | [] -> find false page_table_ref None
-               | _ ->
-                   (* We have a file with suffix *)
-                   raise Eliom_common.Eliom_Wrong_parameter))
-          (function
-            | (Exn1 | Eliom_common.Eliom_Wrong_parameter) as e -> (
-              (* If no service matches, we try a suffix service *)
-              try
-                match
-                  !(try
-                      find_dircontent dircontent
-                        Eliom_common.eliom_suffix_internal_name
-                    with Not_found -> raise e)
-                with
-                | Eliom_common.Dir _ -> Lwt.fail Exn1
-                | Eliom_common.File page_table_ref ->
-                    find false page_table_ref
-                      (if a = None then Some [] else Some (aa :: l))
-              with e -> Lwt.fail e)
-            | e -> Lwt.fail e)
+        try
+          let dc =
+            try !(find_dircontent dircontent aa) with Not_found -> raise Exn1
+          in
+          match dc with
+          | Eliom_common.Dir dircontentref2 ->
+              search_page_table !dircontentref2 l
+          | Eliom_common.File page_table_ref -> (
+            match l with
+            | [] -> find false page_table_ref None
+            | _ ->
+                (* We have a file with suffix *)
+                raise Eliom_common.Eliom_Wrong_parameter)
+        with
+        | (Exn1 | Eliom_common.Eliom_Wrong_parameter) as e -> (
+          (* If no service matches, we try a suffix service *)
+          try
+            match
+              !(try
+                  find_dircontent dircontent
+                    Eliom_common.eliom_suffix_internal_name
+                with Not_found -> raise e)
+            with
+            | Eliom_common.Dir _ -> raise Exn1
+            | Eliom_common.File page_table_ref ->
+                find false page_table_ref
+                  (if a = None then Some [] else Some (aa :: l))
+          with e -> raise e)
+        | e -> raise e
       in
       function
       | [] ->
@@ -418,9 +414,9 @@ module Make (P : PARAM) = struct
                   Eliom_common.eliom_suffix_internal_name
               with Not_found -> raise Exn1)
           with
-          | Eliom_common.Dir _ -> Lwt.fail Exn1
+          | Eliom_common.Dir _ -> raise Exn1
           | Eliom_common.File page_table_ref -> find true page_table_ref None
-        with e -> Lwt.fail e)
+        with e -> raise e)
       (*      | ""::l -> search_page_table dircontent l *)
       (* We do not remove "//" any more
            because of optional suffixes *)
@@ -431,18 +427,17 @@ module Make (P : PARAM) = struct
          (generation, priority) *)
       List.fold_left
         (fun prev (_prio, _gen, table) ->
-           Lwt.catch
-             (fun () -> prev)
-             (function
-               | Exn1 | Eliom_common.Eliom_404
-               | Eliom_common.Eliom_Wrong_parameter ->
-                   search_page_table !table path
-               | e -> fail e))
-        (fail Exn1) tables
+           try prev with
+           | Exn1 | Eliom_common.Eliom_404 | Eliom_common.Eliom_Wrong_parameter
+             ->
+               search_page_table !table path
+           | e -> raise e)
+        (raise Exn1) tables
     in
-    Lwt.catch
-      (fun () ->
-         search_by_priority_generation (P.Container.get tables)
-           (Url.change_empty_list (P.subpath_of_info info)))
-      (function Exn1 -> Lwt.fail Eliom_common.Eliom_404 | e -> Lwt.fail e)
+    try
+      search_by_priority_generation (P.Container.get tables)
+        (Url.change_empty_list (P.subpath_of_info info))
+    with
+    | Exn1 -> raise Eliom_common.Eliom_404
+    | e -> raise e
 end
diff --git a/src/lib/eliom_service.client.ml b/src/lib/eliom_service.client.ml
index 0af2fb6908..d8a9ebefcc 100644
--- a/src/lib/eliom_service.client.ml
+++ b/src/lib/eliom_service.client.ml
@@ -44,7 +44,7 @@ let set_client_fun ?app ~service f =
   | None -> service.client_fun <- Some (ref (Some f))
 
 let reload_fun : type gp pp.
-  (gp, pp, _, _, _, _, _, _, _, _, _) t -> (gp -> unit -> result Lwt.t) option
+  (gp, pp, _, _, _, _, _, _, _, _, _) t -> (gp -> unit -> result) option
   =
  fun service ->
   match Eliom_parameter.is_unit (post_params_type service) with
diff --git a/src/lib/eliom_service.client.mli b/src/lib/eliom_service.client.mli
index 08df8b5669..21b837be3a 100644
--- a/src/lib/eliom_service.client.mli
+++ b/src/lib/eliom_service.client.mli
@@ -31,7 +31,7 @@ include Eliom_service_sigs.S
 val set_client_fun :
    ?app:string
   -> service:('a, 'b, _, _, _, _, _, _, _, _, _) t
-  -> ('a -> 'b -> result Lwt.t)
+  -> ('a -> 'b -> result)
   -> unit
 
 (**/**)
@@ -45,7 +45,7 @@ val pre_applied_parameters :
 
 val reload_fun :
    ('a, _, _, _, _, _, _, _, _, _, _) t
-  -> ('a -> unit -> result Lwt.t) Eliom_client_value.t option
+  -> ('a -> unit -> result) Eliom_client_value.t option
 
 module Cohttp : sig
   module Header : sig
diff --git a/src/lib/eliom_service_base.eliom b/src/lib/eliom_service_base.eliom
index bfe84a5b3e..da206d3d86 100644
--- a/src/lib/eliom_service_base.eliom
+++ b/src/lib/eliom_service_base.eliom
@@ -25,28 +25,25 @@ module rec Types : Eliom_service_sigs.TYPES = Types
 include Types
 module Url = Eliom_lib.Url
 
-type suff = [`WithSuffix | `WithoutSuffix]
-
-let params_of_meth :
-    type m gp gn pp pn x.
-    (m, gp, gn, pp, pn, 'tipo, x) meth
-    -> (gp, 'tipo, gn) params * (pp, [`WithoutSuffix], pn) params
-  = function
-  | Get gp -> gp, Eliom_parameter.unit
-  | Post (gp, pp) -> gp, pp
-  | Put gp -> gp, Eliom_parameter.raw_post_data
-  | Delete gp -> gp, Eliom_parameter.raw_post_data
-
-let which_meth_internal :
-    type m gp gn pp pn tipo x. (m, gp, gn, pp, pn, tipo, x) meth -> m which_meth
-  = function
+type suff = [ `WithSuffix | `WithoutSuffix ]
+
+let params_of_meth : type m gp gn pp pn x.
+    (m, gp, gn, pp, pn, 'tipo, x) meth ->
+    (gp, 'tipo, gn) params * (pp, [ `WithoutSuffix ], pn) params = function
+  | Get gp -> (gp, Eliom_parameter.unit)
+  | Post (gp, pp) -> (gp, pp)
+  | Put gp -> (gp, Eliom_parameter.raw_post_data)
+  | Delete gp -> (gp, Eliom_parameter.raw_post_data)
+
+let which_meth_internal : type m gp gn pp pn tipo x.
+    (m, gp, gn, pp, pn, tipo, x) meth -> m which_meth = function
   | Get _ -> Get'
   | Post _ -> Post'
   | Put _ -> Put'
   | Delete _ -> Delete'
 
-let is_post : type m gp gn pp pn x. (m, gp, gn, pp, pn, _, x) meth -> bool
-  = function
+let is_post : type m gp gn pp pn x. (m, gp, gn, pp, pn, _, x) meth -> bool =
+  function
   | Post (_, _) -> true
   | _ -> false
 
@@ -56,29 +53,30 @@ let is_post' : type m. m which_meth -> bool = function
 
 type reload_fun = Rf_keep | Rf_client_fun
 
-type att =
-  { prefix : string
-  ; (* name of the server and protocol for
+type att = {
+  prefix : string;
+  (* name of the server and protocol for
                                  external links, e.g.,
                                  http://ocsigen.org *)
-    subpath : Url.path
-  ; (* name of the service without parameters *)
-    fullpath : Url.path option ref
-  ; (* full path of the service = site_dir@subpath.
+  subpath : Url.path;
+  (* name of the service without parameters *)
+  fullpath : Url.path option ref;
+  (* full path of the service = site_dir@subpath.
        None means the service has been created before site_dir is known.
        In that case, the initialisation is deferred.  *)
-    get_name : Eliom_common.att_key_serv
-  ; post_name : Eliom_common.att_key_serv
-  ; redirect_suffix : bool
-  ; priority : int }
-
-type non_att =
-  { na_name : Eliom_common.na_key_serv
-  ; keep_get_na_params : bool
-  (* bool is used only for post and means "keep_get_na_params": do we
+  get_name : Eliom_common.att_key_serv;
+  post_name : Eliom_common.att_key_serv;
+  redirect_suffix : bool;
+  priority : int;
+}
+
+type non_att = {
+  na_name : Eliom_common.na_key_serv;
+  keep_get_na_params : bool;
+      (* bool is used only for post and means "keep_get_na_params": do we
      keep GET non-attached parameters in links (if any) (31/12/2007 -
      experimental - WAS: 'a, but may be removed (was not used)) *)
-  }
+}
 
 type 'a attached_info =
   | Attached : att -> att attached_info
@@ -88,7 +86,7 @@ type send_appl_content =
   | XNever
   | XAlways
   | XSame_appl of string * string option
-  (** Whether the service is capable to send application content or not.
+      (** Whether the service is capable to send application content or not.
     (application content has type Eliom_service.eliom_appl_answer:
     content of the application container, or xhr redirection ...).  A
     link towards a service with send_appl_content = XNever will always
@@ -104,88 +102,91 @@ type send_appl_content =
      belongs and the option is the name of template *)
 
 type service_kind =
-  [`Service | `AttachedCoservice | `NonattachedCoservice | `External]
+  [ `Service | `AttachedCoservice | `NonattachedCoservice | `External ]
 
 (* 'return is the value returned by the service *)
-type ('get
-     , 'post
-     , 'meth
-     , 'attached
-     , 'co
-     , 'ext
-     , 'reg
-     , +'tipo
-     , 'getnames
-     , 'postnames
-     , 'rt)
-     t =
-  { pre_applied_parameters :
-      (string * Eliommod_parameters.param) list Eliom_lib.String.Table.t
-      (* non localized parameters *)
-      * (string * Eliommod_parameters.param) list
-        (* regular parameters *)
-  ; get_params_type : ('get, 'tipo, 'getnames) Eliom_parameter.params_type
-  ; post_params_type :
-      ('post, [`WithoutSuffix], 'postnames) Eliom_parameter.params_type
-  ; max_use : int option
-  ; (* Max number of use of this service *)
-    timeout : float option
-  ; (* Timeout for this service (the service
+type ('get,
+       'post,
+       'meth,
+       'attached,
+       'co,
+       'ext,
+       'reg,
+       +'tipo,
+       'getnames,
+       'postnames,
+       'rt)
+     t = {
+  pre_applied_parameters :
+    (string * Eliommod_parameters.param) list Eliom_lib.String.Table.t
+    (* non localized parameters *)
+    * (string * Eliommod_parameters.param) list;
+      (* regular parameters *)
+  get_params_type : ('get, 'tipo, 'getnames) Eliom_parameter.params_type;
+  post_params_type :
+    ('post, [ `WithoutSuffix ], 'postnames) Eliom_parameter.params_type;
+  max_use : int option;
+  (* Max number of use of this service *)
+  timeout : float option;
+  (* Timeout for this service (the service
                              will disappear if it has not been used
                              during this amount of seconds) *)
-    meth : 'meth which_meth
-  ; kind : service_kind
-  ; info : 'attached attached_info
-  ; https : bool
-  ; (* force https *)
-    keep_nl_params : [`All | `Persistent | `None]
-  ; mutable send_appl_content : send_appl_content
-        (* XNever when we create the service, then changed at registration
+  meth : 'meth which_meth;
+  kind : service_kind;
+  info : 'attached attached_info;
+  https : bool;
+  (* force https *)
+  keep_nl_params : [ `All | `Persistent | `None ];
+  mutable send_appl_content : send_appl_content;
+  (* XNever when we create the service, then changed at registration
      :/ *)
-  ; (* If the service has a client-side implementation, we put the
+  (* If the service has a client-side implementation, we put the
      generating function here: *)
-    mutable client_fun :
-      ('get -> 'post -> result Lwt.t) option ref Eliom_client_value.t option
-        (* The function is in a client-side reference, so that it is shared
+  mutable client_fun :
+    ('get -> 'post -> result) option ref Eliom_client_value.t option;
+      (* The function is in a client-side reference, so that it is shared
      by all occurrences of the service sent from the server.
      For some service, we cannot create the client value immediately;
      this is done later on using [internal_set_client_fun].  *)
-  ; mutable reload_fun : reload_fun
-  ; service_mark :
-      (unit, unit, 'meth, 'attached, 'co, 'ext, 'reg, suff, unit, unit, unit) t
-        Eliom_common.wrapper }
-  constraint 'tipo = [< suff]
+  mutable reload_fun : reload_fun;
+  service_mark :
+    (unit, unit, 'meth, 'attached, 'co, 'ext, 'reg, suff, unit, unit, unit) t
+    Eliom_common.wrapper;
+}
+  constraint 'tipo = [< suff ]
 
 and result =
   | No_contents
   | Dom of Js_of_ocaml.Dom_html.element Js_of_ocaml.Js.t
   | Redirect :
-      (unit, unit, get, _, _, _, _, [`WithoutSuffix], unit, unit, non_ocaml) t
+      (unit, unit, get, _, _, _, _, [ `WithoutSuffix ], unit, unit, non_ocaml) t
       -> result
-  | Reload_action of {hidden : bool; https : bool}
+  | Reload_action of { hidden : bool; https : bool }
 
 let pre_wrap s =
-  { s with
-    get_params_type = Eliom_parameter.wrap_param_type s.get_params_type
-  ; post_params_type = Eliom_parameter.wrap_param_type s.post_params_type
-  ; service_mark = Eliom_common.empty_wrapper () }
+  {
+    s with
+    get_params_type = Eliom_parameter.wrap_param_type s.get_params_type;
+    post_params_type = Eliom_parameter.wrap_param_type s.post_params_type;
+    service_mark = Eliom_common.empty_wrapper ();
+  }
 
 type%shared unit_service =
-  ( unit
-    , unit
-    , get
-    , att
-    , non_co
-    , non_ext
-    , non_reg
-    , [`WithoutSuffix]
-    , unit
-    , unit
-    , non_ocaml )
-    t
+  ( unit,
+    unit,
+    get,
+    att,
+    non_co,
+    non_ext,
+    non_reg,
+    [ `WithoutSuffix ],
+    unit,
+    unit,
+    non_ocaml )
+  t
 
 let service_mark () = Eliom_common.make_wrapper pre_wrap
-let info {info; _} = info
+let info { info; _ } = info
 let pre_applied_parameters s = s.pre_applied_parameters
 let get_params_type s = s.get_params_type
 let post_params_type s = s.post_params_type
@@ -209,85 +210,94 @@ let https s = s.https
 let priority s = s.priority
 
 let internal_set_client_fun ~service
-    (f : ('get -> 'post -> result Lwt.t) Eliom_client_value.t)
-  =
+    (f : ('get -> 'post -> result) Eliom_client_value.t) =
   service.client_fun <- Some [%client.unsafe ref (Some ~%f)]
 
-let is_external = function {kind = `External; _} -> true | _ -> false
+let is_external = function { kind = `External; _ } -> true | _ -> false
 let default_priority = 0
-let meth {meth; _} = meth
+let meth { meth; _ } = meth
 
 let change_get_num service attser n =
-  { service with
-    service_mark = service_mark ()
-  ; info = Attached {attser with get_name = n} }
+  {
+    service with
+    service_mark = service_mark ();
+    info = Attached { attser with get_name = n };
+  }
 
 (** Static directories **)
 let static_dir_ ?(https = false) () =
-  { pre_applied_parameters = Eliom_lib.String.Table.empty, []
-  ; get_params_type =
+  {
+    pre_applied_parameters = (Eliom_lib.String.Table.empty, []);
+    get_params_type =
       Eliom_parameter.suffix
-        (Eliom_parameter.all_suffix Eliom_common.eliom_suffix_name)
-  ; post_params_type = Eliom_parameter.unit
-  ; max_use = None
-  ; timeout = None
-  ; kind = `Service
-  ; meth = Get'
-  ; info =
+        (Eliom_parameter.all_suffix Eliom_common.eliom_suffix_name);
+    post_params_type = Eliom_parameter.unit;
+    max_use = None;
+    timeout = None;
+    kind = `Service;
+    meth = Get';
+    info =
       Attached
-        { prefix = ""
-        ; subpath = [""]
-        ; fullpath =
+        {
+          prefix = "";
+          subpath = [ "" ];
+          fullpath =
             Eliom_common.defer Eliom_request_info.get_site_dir_option
               (fun site_dir ->
-                 site_dir @ [Eliom_common.eliom_suffix_internal_name])
-        ; get_name = Eliom_common.SAtt_no
-        ; post_name = Eliom_common.SAtt_no
-        ; redirect_suffix = true
-        ; priority = default_priority }
-  ; https
-  ; keep_nl_params = `None
-  ; service_mark = service_mark ()
-  ; send_appl_content = XNever
-  ; client_fun = None
-  ; (* It does not make sense to have a client function
+                site_dir @ [ Eliom_common.eliom_suffix_internal_name ]);
+          get_name = Eliom_common.SAtt_no;
+          post_name = Eliom_common.SAtt_no;
+          redirect_suffix = true;
+          priority = default_priority;
+        };
+    https;
+    keep_nl_params = `None;
+    service_mark = service_mark ();
+    send_appl_content = XNever;
+    client_fun = None;
+    (* It does not make sense to have a client function
                         for this service *)
-    reload_fun = Rf_client_fun }
+    reload_fun = Rf_client_fun;
+  }
 
 let static_dir () = static_dir_ ()
 let https_static_dir () = static_dir_ ~https:true ()
 
 let get_static_dir_ ?(https = false) ?(keep_nl_params = `None) ~get_params () =
-  { pre_applied_parameters = Eliom_lib.String.Table.empty, []
-  ; get_params_type =
+  {
+    pre_applied_parameters = (Eliom_lib.String.Table.empty, []);
+    get_params_type =
       Eliom_parameter.suffix_prod
         (Eliom_parameter.all_suffix Eliom_common.eliom_suffix_name)
-        get_params
-  ; post_params_type = Eliom_parameter.unit
-  ; max_use = None
-  ; timeout = None
-  ; kind = `Service
-  ; meth = Get'
-  ; info =
+        get_params;
+    post_params_type = Eliom_parameter.unit;
+    max_use = None;
+    timeout = None;
+    kind = `Service;
+    meth = Get';
+    info =
       Attached
-        { prefix = ""
-        ; subpath = [""]
-        ; fullpath =
+        {
+          prefix = "";
+          subpath = [ "" ];
+          fullpath =
             Eliom_common.defer Eliom_request_info.get_site_dir_option
               (fun site_dir ->
-                 site_dir @ [Eliom_common.eliom_suffix_internal_name])
-        ; get_name = Eliom_common.SAtt_no
-        ; post_name = Eliom_common.SAtt_no
-        ; redirect_suffix = true
-        ; priority = default_priority }
-  ; https
-  ; keep_nl_params
-  ; service_mark = service_mark ()
-  ; send_appl_content = XNever
-  ; client_fun = None
-  ; (* It does not make sense to have a client function
+                site_dir @ [ Eliom_common.eliom_suffix_internal_name ]);
+          get_name = Eliom_common.SAtt_no;
+          post_name = Eliom_common.SAtt_no;
+          redirect_suffix = true;
+          priority = default_priority;
+        };
+    https;
+    keep_nl_params;
+    service_mark = service_mark ();
+    send_appl_content = XNever;
+    client_fun = None;
+    (* It does not make sense to have a client function
                         for this service *)
-    reload_fun = Rf_client_fun }
+    reload_fun = Rf_client_fun;
+  }
 
 let static_dir_with_params ?keep_nl_params ~get_params () =
   get_static_dir_ ?keep_nl_params ~get_params ()
@@ -305,7 +315,7 @@ let set_send_appl_content s n = s.send_appl_content <- n
 let rec append_suffix l m =
   match l with
   | [] -> m
-  | [_eliom_suffix_internal_name] -> m
+  | [ _eliom_suffix_internal_name ] -> m
   | a :: ll -> a :: append_suffix ll m
 
 let preapply ~service getparams =
@@ -314,66 +324,74 @@ let preapply ~service getparams =
     Eliom_parameter.construct_params_list_raw nlp service.get_params_type
       getparams
   in
-  { service with
-    service_mark = service_mark ()
-  ; pre_applied_parameters = nlp, params @ preapp
-  ; get_params_type = Eliom_parameter.unit
-  ; info =
+  {
+    service with
+    service_mark = service_mark ();
+    pre_applied_parameters = (nlp, params @ preapp);
+    get_params_type = Eliom_parameter.unit;
+    info =
       (match service.info with
       | Attached k ->
           Attached
-            { k with
+            {
+              k with
               subpath =
                 (match suff with
                 | Some suff -> append_suffix k.subpath suff
-                | _ -> k.subpath)
-            ; fullpath =
+                | _ -> k.subpath);
+              fullpath =
                 Eliom_common.defer
                   (fun () -> !(k.fullpath))
                   (fun fp ->
-                     match suff with
-                     | Some suff -> append_suffix fp suff
-                     | _ -> fp) })
-  ; client_fun =
+                    match suff with
+                    | Some suff -> append_suffix fp suff
+                    | _ -> fp);
+            });
+    client_fun =
       Some
         [%client.unsafe
           ref
             (match ~%service.client_fun with
-            | Some {contents = Some f} -> Some (fun () pp -> f ~%getparams pp)
-            | _ -> None)] }
+            | Some { contents = Some f } -> Some (fun () pp -> f ~%getparams pp)
+            | _ -> None)];
+  }
 
 let reload_action_aux https =
-  { max_use = None
-  ; timeout = None
-  ; pre_applied_parameters = Eliom_lib.String.Table.empty, []
-  ; get_params_type = Eliom_parameter.unit
-  ; post_params_type = Eliom_parameter.unit
-  ; kind = `NonattachedCoservice
-  ; meth = Get'
-  ; info =
+  {
+    max_use = None;
+    timeout = None;
+    pre_applied_parameters = (Eliom_lib.String.Table.empty, []);
+    get_params_type = Eliom_parameter.unit;
+    post_params_type = Eliom_parameter.unit;
+    kind = `NonattachedCoservice;
+    meth = Get';
+    info =
       Nonattached
-        {na_name = Eliom_common.SNa_void_dontkeep; keep_get_na_params = true}
-  ; https
-  ; keep_nl_params = `All
-  ; service_mark = service_mark ()
-  ; send_appl_content = XAlways
-  ; client_fun = None
-  ; reload_fun = Rf_keep }
+        { na_name = Eliom_common.SNa_void_dontkeep; keep_get_na_params = true };
+    https;
+    keep_nl_params = `All;
+    service_mark = service_mark ();
+    send_appl_content = XAlways;
+    client_fun = None;
+    reload_fun = Rf_keep;
+  }
 
 let reload_action = reload_action_aux false
 let reload_action_https = reload_action_aux true
 
 let reload_action_hidden_aux https =
   let raa = reload_action_aux https in
-  { raa
+  {
+    raa
     (* We must create a reference for each one of the for reload
            actions *)
     with
-    kind = `NonattachedCoservice
-  ; meth = Get'
-  ; info =
+    kind = `NonattachedCoservice;
+    meth = Get';
+    info =
       Nonattached
-        {na_name = Eliom_common.SNa_void_keep; keep_get_na_params = true} }
+        { na_name = Eliom_common.SNa_void_keep; keep_get_na_params = true };
+  }
 
 let reload_action_hidden = reload_action_hidden_aux false
 let reload_action_https_hidden = reload_action_hidden_aux true
@@ -381,55 +399,59 @@ let reload_action_https_hidden = reload_action_hidden_aux true
 (*VVV Non localized parameters not implemented for client side
   services *)
 let add_non_localized_get_parameters ~params ~service =
-  { service with
-    get_params_type = Eliom_parameter.nl_prod service.get_params_type params
-  ; client_fun =
+  {
+    service with
+    get_params_type = Eliom_parameter.nl_prod service.get_params_type params;
+    client_fun =
       Some
         [%client.unsafe
           ref
             (match ~%service.client_fun with
-            | Some {contents = Some f} -> Some (fun (g, _) p -> f g p)
-            | _ -> None)] }
+            | Some { contents = Some f } -> Some (fun (g, _) p -> f g p)
+            | _ -> None)];
+  }
 
 let add_non_localized_post_parameters ~params ~service =
-  { service with
-    post_params_type = Eliom_parameter.nl_prod service.post_params_type params
-  ; client_fun =
+  {
+    service with
+    post_params_type = Eliom_parameter.nl_prod service.post_params_type params;
+    client_fun =
       Some
         [%client.unsafe
           ref
             (match ~%service.client_fun with
-            | Some {contents = Some f} -> Some (fun g (p, _) -> f g p)
-            | _ -> None)] }
+            | Some { contents = Some f } -> Some (fun g (p, _) -> f g p)
+            | _ -> None)];
+  }
 
 let keep_nl_params s = s.keep_nl_params
 
 let untype s =
   (s
-    : ( 'get
-        , 'post
-        , 'meth
-        , 'attached
-        , 'co
-        , 'ext
-        , 'tipo
-        , 'getnames
-        , 'postnames
-        , 'register
-        , _ )
-        t
-    :> ( 'get
-         , 'post
-         , 'meth
-         , 'attached
-         , 'co
-         , 'ext
-         , 'tipo
-         , 'getnames
-         , 'postnames
-         , 'register
-         , _ )
-         t)
+    : ( 'get,
+        'post,
+        'meth,
+        'attached,
+        'co,
+        'ext,
+        'tipo,
+        'getnames,
+        'postnames,
+        'register,
+        _ )
+      t
+    :> ( 'get,
+         'post,
+         'meth,
+         'attached,
+         'co,
+         'ext,
+         'tipo,
+         'getnames,
+         'postnames,
+         'register,
+         _ )
+       t)
 
 type (_, _, _) path_option =
   | Path : Eliom_lib.Url.path -> (att, non_co, _) path_option
@@ -459,14 +481,13 @@ let default_csrf_scope = function
 
 exception Unreachable_exn
 
-let attached_info = function {info = Attached k; _} -> k
-let non_attached_info = function {info = Nonattached k; _} -> k
+let attached_info = function { info = Attached k; _ } -> k
+let non_attached_info = function { info = Nonattached k; _ } -> k
 
 let%server no_client_fun () : _ ref Eliom_client_value.t option =
   (* It only makes sense to create a client value when in a global
      context. *)
-  if Eliom_syntax.global_context ()
-  then Some [%client.unsafe ref None]
+  if Eliom_syntax.global_context () then Some [%client.unsafe ref None]
   else None
 
 let%client no_client_fun () : _ ref Eliom_client_value.t option =
@@ -475,35 +496,38 @@ let%client no_client_fun () : _ ref Eliom_client_value.t option =
 (** Create a main service (not a coservice), internal or external *)
 let main_service ~https ~prefix ~(path : Url.path) ?force_site_dir ~kind ~meth
     ?(redirect_suffix = true) ?(keep_nl_params = `None)
-    ?(priority = default_priority) ~get_params ~post_params ~reload_fun ()
-  =
-  { pre_applied_parameters = Eliom_lib.String.Table.empty, []
-  ; get_params_type = get_params
-  ; post_params_type = post_params
-  ; max_use = None
-  ; timeout = None
-  ; meth
-  ; kind
-  ; info =
+    ?(priority = default_priority) ~get_params ~post_params ~reload_fun () =
+  {
+    pre_applied_parameters = (Eliom_lib.String.Table.empty, []);
+    get_params_type = get_params;
+    post_params_type = post_params;
+    max_use = None;
+    timeout = None;
+    meth;
+    kind;
+    info =
       Attached
-        { prefix
-        ; subpath = path
-        ; fullpath =
+        {
+          prefix;
+          subpath = path;
+          fullpath =
             (match force_site_dir with
             | Some site_dir -> ref (Some (site_dir @ path))
             | None ->
                 Eliom_common.defer Eliom_request_info.get_site_dir_option
-                  (fun site_dir -> site_dir @ path))
-        ; get_name = Eliom_common.SAtt_no
-        ; post_name = Eliom_common.SAtt_no
-        ; redirect_suffix
-        ; priority }
-  ; https
-  ; keep_nl_params
-  ; service_mark = service_mark ()
-  ; send_appl_content = XNever
-  ; client_fun = no_client_fun ()
-  ; reload_fun }
+                  (fun site_dir -> site_dir @ path));
+          get_name = Eliom_common.SAtt_no;
+          post_name = Eliom_common.SAtt_no;
+          redirect_suffix;
+          priority;
+        };
+    https;
+    keep_nl_params;
+    service_mark = service_mark ();
+    send_appl_content = XNever;
+    client_fun = no_client_fun ();
+    reload_fun;
+  }
 
 let extern ?keep_nl_params ~prefix ~path ~meth () =
   let get_params, post_params = params_of_meth meth in
@@ -515,11 +539,11 @@ let extern ?keep_nl_params ~prefix ~path ~meth () =
       (Url.remove_internal_slash
          (match suffix with
          | None -> path
-         | _ -> path @ [Eliom_common.eliom_suffix_internal_name]))
+         | _ -> path @ [ Eliom_common.eliom_suffix_internal_name ]))
     ~force_site_dir:[] ~kind:`External ~meth ?keep_nl_params
     ~redirect_suffix:false ~get_params ~post_params ~reload_fun:Rf_keep ()
 
-let which_meth {meth; _} = meth
+let which_meth { meth; _ } = meth
 
 let which_meth_untyped (type m) (s : (_, _, m, _, _, _, _, _, _, _, _) t) =
   match which_meth s with
diff --git a/src/lib/eliom_service_sigs.shared.mli b/src/lib/eliom_service_sigs.shared.mli
index 064029c7a6..5b48d733eb 100644
--- a/src/lib/eliom_service_sigs.shared.mli
+++ b/src/lib/eliom_service_sigs.shared.mli
@@ -424,7 +424,7 @@ module type S = sig
 
   val client_fun :
      ('a, 'b, _, _, _, _, _, _, _, _, _) t
-    -> ('a -> 'b -> result Lwt.t) Eliom_client_value.t option
+    -> ('a -> 'b -> result) Eliom_client_value.t option
 
   val has_client_fun : (_, _, _, _, _, _, _, _, _, _, _) t -> bool
 
@@ -481,6 +481,6 @@ module type S = sig
 
   val internal_set_client_fun :
      service:('a, 'b, _, _, _, _, _, _, _, _, _) t
-    -> ('a -> 'b -> result Lwt.t) Eliom_client_value.t
+    -> ('a -> 'b -> result) Eliom_client_value.t
     -> unit
 end
diff --git a/src/lib/eliom_shared.client.mli b/src/lib/eliom_shared.client.mli
index ff5edd3752..71dd50a3a7 100644
--- a/src/lib/eliom_shared.client.mli
+++ b/src/lib/eliom_shared.client.mli
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2014
@@ -30,7 +32,7 @@
 val to_signal :
    init:'a
   -> ?eq:('a -> 'a -> bool)
-  -> 'a React.S.t Lwt.t
+  -> 'a React.S.t Promise.t
   -> 'a React.S.t
 (** [to_signal ~init s] converts the Lwt-wrapped signal [s] into a
     regular signal with initial value [init]. *)
diff --git a/src/lib/eliom_shared.eliom b/src/lib/eliom_shared.eliom
index 14f33aef9c..6fdd5dc78e 100644
--- a/src/lib/eliom_shared.eliom
+++ b/src/lib/eliom_shared.eliom
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2014
@@ -19,16 +21,15 @@
  *)
 
 [%%shared
-open Lwt.Syntax
-
 (* put this in Lwt_react? Find a better name? *)
-let to_signal ~init ?eq (th : 'a React.S.t Lwt.t) : 'a React.S.t =
+let to_signal ~init ?eq (th : 'a React.S.t Promise.t) : 'a React.S.t =
   let s, set = React.S.create ?eq init in
-  Lwt.async (fun () ->
-    let* ss = th in
-    let effectful_signal = React.S.map (fun v -> set v) ss in
-    ignore (React.S.retain s (fun () -> ignore effectful_signal));
-    Lwt.return_unit);
+  Fiber.fork
+    ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+    (fun () ->
+      let ss = Promise.await th in
+      let effectful_signal = React.S.map (fun v -> set v) ss in
+      ignore (React.S.retain s (fun () -> ignore effectful_signal)));
   s]
 
 [%%client
@@ -42,22 +43,23 @@ end]
 
 [%%server
 module Value = struct
-  type +'a t =
-    { sh_server : 'a
-    ; sh_client : 'a Eliom_client_value.t
-    ; sh_mark : 'a t Eliom_wrap.wrapper }
+  type +'a t = {
+    sh_server : 'a;
+    sh_client : 'a Eliom_client_value.t;
+    sh_mark : 'a t Eliom_wrap.wrapper;
+  }
   [@@warning "-69"]
 
-  let internal_wrap {sh_client; _} = sh_client
+  let internal_wrap { sh_client; _ } = sh_client
 
   let shared_value_mark () : 'a t Eliom_wrap.wrapper =
     Eliom_wrap.create_wrapper internal_wrap
 
   let create sh_server sh_client =
-    {sh_server; sh_client; sh_mark = shared_value_mark ()}
+    { sh_server; sh_client; sh_mark = shared_value_mark () }
 
-  let client {sh_client; _} = sh_client
-  let local {sh_server; _} = sh_server
+  let client { sh_client; _ } = sh_client
+  let local { sh_server; _ } = sh_server
 end]
 
 [%%client
@@ -132,64 +134,74 @@ module ReactiveData = struct
     include ReactiveData.RList
 
     module Lwt = struct
-      let map_data_p_lwt = Lwt_list.map_p
+      let map_data_p_lwt = Fiber.List.map
 
       let map_patch_p_lwt f = function
         | I (i, x) ->
-            let* p = f x in
-            Lwt.return (I (i, p))
-        | R i -> Lwt.return (R i)
-        | X (i, j) -> Lwt.return (X (i, j))
+            let p = f x in
+            I (i, p)
+        | R i -> R i
+        | X (i, j) -> X (i, j)
         | U (i, x) ->
-            let* p = f x in
-            Lwt.return (U (i, p))
+            let p = f x in
+            U (i, p)
 
-      let map_patch_p_lwt f = Lwt_list.map_p (map_patch_p_lwt f)
+      let map_patch_p_lwt f = Fiber.List.map (map_patch_p_lwt f)
 
       let map_msg_p_lwt f = function
         | Set l ->
-            let* p = map_data_p_lwt f l in
-            Lwt.return (Set p)
+            let p = map_data_p_lwt f l in
+            Set p
         | Patch p ->
-            let* p = map_patch_p_lwt f p in
-            Lwt.return (Patch p)
+            let p = map_patch_p_lwt f p in
+            Patch p
 
       let map_p_aux r_th f l =
         (* We react to all events occurring on initial list *)
         let event = ReactiveData.RList.event l in
         (* the waiter is used a a lock to keep the order of events *)
-        let waiter = ref (Lwt.wait ()) in
-        Lwt.wakeup (snd !waiter) ();
+        let waiter =
+          ref
+            (Promise.create
+               (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+               ())
+        in
+        Promise.resolve (snd !waiter) ();
         React.E.map
           (fun msg ->
-             Lwt.async (fun () ->
-               let waiter1 = !waiter in
-               let new_waiter = Lwt.wait () in
-               waiter := new_waiter;
-               let* new_msg = map_msg_p_lwt f msg in
-               let* _, rhandle = r_th in
-               let* () = fst waiter1 in
-               (match new_msg with
-               | ReactiveData.RList.Set s -> ReactiveData.RList.set rhandle s
-               | ReactiveData.RList.Patch p ->
-                   ReactiveData.RList.patch rhandle p);
-               Lwt.wakeup (snd new_waiter) ();
-               Lwt.return_unit))
+            Fiber.fork
+              ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+              (fun () ->
+                let waiter1 = !waiter in
+                let new_waiter =
+                  Promise.create
+                    (* TODO: lwt-to-direct-style: Translation is incomplete, [Promise.await] must be called on the promise when it's part of control-flow. *)
+                    ()
+                in
+                waiter := new_waiter;
+                let new_msg = map_msg_p_lwt f msg in
+                let _, rhandle = r_th in
+                let () = fst waiter1 in
+                (match new_msg with
+                | ReactiveData.RList.Set s -> ReactiveData.RList.set rhandle s
+                | ReactiveData.RList.Patch p ->
+                    ReactiveData.RList.patch rhandle p);
+                Promise.resolve (snd new_waiter) ()))
           event
 
       (** Same as map_p but we do not compute the initial list.
           Instead, we give the initial list as parameter.  To be used
           when the initial list has been computed on server side.  *)
-      let map_p_init ~init (f : 'a -> 'b Lwt.t) (l : 'a t) : 'b t =
+      let map_p_init ~init (f : 'a -> 'b) (l : 'a t) : 'b t =
         let ((rr, _) as r) = ReactiveData.RList.create init in
-        let effectul_event = map_p_aux (Lwt.return r) f l in
+        let effectul_event = map_p_aux r f l in
         (* We keep a reference to the effectul_event in the resulting
            reactive list in order that the effectul_event is garbage
            collected only if the resulting list is garbage
            collected. *)
         ignore
           (React.E.retain (ReactiveData.RList.event rr) (fun () ->
-             ignore effectul_event));
+               ignore effectul_event));
         rr
 
       (** [map_p f l] is the equivalent of [ReactiveData.Rlist.map]
@@ -197,22 +209,22 @@ module ReactiveData = struct
           the previous one has not finished to be computed, we launch
           the computation of [f] in parallel, but we wait for the
           previous one to be applied before applying it.  *)
-      let map_p (f : 'a -> 'b Lwt.t) (l : 'a t) : 'b t Lwt.t =
+      let map_p (f : 'a -> 'b) (l : 'a t) : 'b t =
         (* First we build the initial value of the result list *)
         let r_th =
-          let* r = Lwt_list.map_p f (ReactiveData.RList.value l) in
-          Lwt.return (ReactiveData.RList.create r)
+          let r = Fiber.List.map f (ReactiveData.RList.value l) in
+          ReactiveData.RList.create r
         in
         let effectul_event = map_p_aux r_th f l in
-        let* rr, _ = r_th in
+        let rr, _ = r_th in
         (* We keep a reference to the effectul_event in the resulting
            reactive list in order that the effectul_event is garbage
            collected only if the resulting list is garbage
            collected. *)
         ignore
           (React.E.retain (ReactiveData.RList.event rr) (fun () ->
-             ignore effectul_event));
-        Lwt.return rr
+               ignore effectul_event));
+        rr
     end
 
     let create ?default ?(reset_default = false) v =
@@ -251,60 +263,55 @@ module FakeReact = struct
     val l3 : ('a -> 'b -> 'c -> 'd) -> 'a t -> 'b t -> 'c t -> 'd t
 
     val l4 :
-       ('a -> 'b -> 'c -> 'd -> 'e)
-      -> 'a t
-      -> 'b t
-      -> 'c t
-      -> 'd t
-      -> 'e t
+      ('a -> 'b -> 'c -> 'd -> 'e) -> 'a t -> 'b t -> 'c t -> 'd t -> 'e t
 
     val l5 :
-       ('a -> 'b -> 'c -> 'd -> 'e -> 'f)
-      -> 'a t
-      -> 'b t
-      -> 'c t
-      -> 'd t
-      -> 'e t
-      -> 'f t
+      ('a -> 'b -> 'c -> 'd -> 'e -> 'f) ->
+      'a t ->
+      'b t ->
+      'c t ->
+      'd t ->
+      'e t ->
+      'f t
 
     val l6 :
-       ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g)
-      -> 'a t
-      -> 'b t
-      -> 'c t
-      -> 'd t
-      -> 'e t
-      -> 'f t
-      -> 'g t
+      ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g) ->
+      'a t ->
+      'b t ->
+      'c t ->
+      'd t ->
+      'e t ->
+      'f t ->
+      'g t
   end = struct
     type 'a t = 'a * bool
 
     let create ?(synced = false) x =
-      ( (x, synced)
-      , fun ?step:_ _ ->
+      ( (x, synced),
+        fun ?step:_ _ ->
           failwith "Fact react values cannot be changed on server side" )
 
     let value (x, _) = x
-    let const ?(synced = false) x = x, synced
+    let const ?(synced = false) x = (x, synced)
     let synced (_, b) = b
-    let map (f : 'a -> 'b) ((x, b) : 'a t) : 'b t = f x, b
-    let fmap f i (s, b) = (match f s with Some v -> v | None -> i), b
+    let map (f : 'a -> 'b) ((x, b) : 'a t) : 'b t = (f x, b)
+    let fmap f i (s, b) = ((match f s with Some v -> v | None -> i), b)
 
     let merge f acc l =
-      let f (acc, acc_b) (x, b) = f acc x, acc_b && b in
+      let f (acc, acc_b) (x, b) = (f acc x, acc_b && b) in
       List.fold_left f (acc, true) l
 
-    let l2 f (x1, b1) (x2, b2) = f x1 x2, b1 && b2
-    let l3 f (x1, b1) (x2, b2) (x3, b3) = f x1 x2 x3, b1 && b2 && b3
+    let l2 f (x1, b1) (x2, b2) = (f x1 x2, b1 && b2)
+    let l3 f (x1, b1) (x2, b2) (x3, b3) = (f x1 x2 x3, b1 && b2 && b3)
 
     let l4 f (x1, b1) (x2, b2) (x3, b3) (x4, b4) =
-      f x1 x2 x3 x4, b1 && b2 && b3 && b4
+      (f x1 x2 x3 x4, b1 && b2 && b3 && b4)
 
     let l5 f (x1, b1) (x2, b2) (x3, b3) (x4, b4) (x5, b5) =
-      f x1 x2 x3 x4 x5, b1 && b2 && b3 && b4 && b5
+      (f x1 x2 x3 x4 x5, b1 && b2 && b3 && b4 && b5)
 
     let l6 f (x1, b1) (x2, b2) (x3, b3) (x4, b4) (x5, b5) (x6, b6) =
-      f x1 x2 x3 x4 x5 x6, b1 && b2 && b3 && b4 && b5 && b6
+      (f x1 x2 x3 x4 x5 x6, b1 && b2 && b3 && b4 && b5 && b6)
   end
 end
 
@@ -325,13 +332,13 @@ module FakeReactiveData = struct
     type 'a t = 'a list * bool
     type 'a handle = unit
 
-    let create ?(synced = false) l = (l, synced), ()
-    let concat (l1, b1) (l2, b2) = List.append l1 l2, b1 && b2
-    let singleton_s s = [FakeReact.S.value s], FakeReact.S.synced s
+    let create ?(synced = false) l = ((l, synced), ())
+    let concat (l1, b1) (l2, b2) = (List.append l1 l2, b1 && b2)
+    let singleton_s s = ([ FakeReact.S.value s ], FakeReact.S.synced s)
     let value (l, _) = l
     let synced (_, b) = b
     let signal ?eq:_ (l, synced) = fst (FakeReact.S.create ~synced l)
-    let map f (l, b) = List.map f l, b
+    let map f (l, b) = (List.map f l, b)
     let from_signal ?eq:_ s = FakeReact.S.(value s, synced s)
   end
 end]
@@ -352,23 +359,23 @@ module React = struct
     let create ?default ?(reset_default = false) ?(eq : _ Value.t option) x =
       let cv, synced =
         match default with
-        | None -> [%client.unsafe FakeReact.S.create ?eq:~%eq ~%x], true
+        | None -> ([%client.unsafe FakeReact.S.create ?eq:~%eq ~%x], true)
         | Some v ->
             ( [%client.unsafe
-                ((match (~%v : (_ * (?step:_ -> _ -> _)) option) with
+                (match (~%v : (_ * (?step:_ -> _ -> _)) option) with
                  | Some ((_, set) as s) ->
                      (* The reactive data is already on client side.  But
                   the value sent by server is more recent.  I update
                   the signal. *)
                      if ~%reset_default then set ?step:None ~%x;
                      s
-                 | None -> FakeReact.S.create ?eq:~%eq ~%x)
+                 | None -> FakeReact.S.create ?eq:~%eq ~%x
                  (*VVV Make possible to disable this?  Warning: removing
                  this or changing the default will break some existing
                  code relying on this!  Do not change the default
                  without wide announcement. *)
-                 : 'a FakeReact.S.t * (?step:React.step -> 'a -> unit))]
-            , reset_default )
+                  : 'a FakeReact.S.t * (?step:React.step -> 'a -> unit))],
+              reset_default )
       in
       let v, f = FakeReact.S.create ~synced x in
       let si = Value.create v [%client.unsafe (fst ~%cv : 'a FakeReact.S.t)]
@@ -376,7 +383,7 @@ module React = struct
         Value.create f
           [%client.unsafe (snd ~%cv : ?step:React.step -> 'a -> unit)]
       in
-      si, up
+      (si, up)
 
     let map ?eq (f : ('a -> 'b) Value.t) (s : 'a FakeReact.S.t Value.t) : 'b t =
       Value.create
@@ -385,16 +392,14 @@ module React = struct
 
     let fmap ?(eq : ('b -> 'b -> bool) Value.t option)
         (f : ('a -> 'b option) Value.t) (i : 'b Value.t)
-        (s : 'a FakeReact.S.t Value.t) : 'b t
-      =
+        (s : 'a FakeReact.S.t Value.t) : 'b t =
       Value.create
         (FakeReact.S.fmap (Value.local f) (Value.local i) (Value.local s))
         [%client.unsafe
           (FakeReact.S.fmap ?eq:~%eq ~%f ~%i ~%s : 'b FakeReact.S.t)]
 
     let merge ?eq (f : ('a -> 'b -> 'a) Value.t) (acc : 'a)
-        (l : 'b FakeReact.S.t Value.t list) : 'a t
-      =
+        (l : 'b FakeReact.S.t Value.t list) : 'a t =
       Value.create
         (FakeReact.S.merge (Value.local f) acc (List.map Value.local l))
         [%client.unsafe
@@ -406,16 +411,14 @@ module React = struct
         [%client.unsafe (React.S.const ~%v : 'a FakeReact.S.t)]
 
     let l2 ?eq (f : ('a -> 'b -> 'c) Value.t) (s1 : 'a FakeReact.S.t Value.t)
-        (s2 : 'b FakeReact.S.t Value.t) : 'c t
-      =
+        (s2 : 'b FakeReact.S.t Value.t) : 'c t =
       Value.create
         (FakeReact.S.l2 (Value.local f) (Value.local s1) (Value.local s2))
         [%client.unsafe (React.S.l2 ?eq:~%eq ~%f ~%s1 ~%s2 : 'd FakeReact.S.t)]
 
     let l3 ?eq (f : ('a -> 'b -> 'c -> 'd) Value.t)
         (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
-        (s3 : 'c FakeReact.S.t Value.t) : 'd t
-      =
+        (s3 : 'c FakeReact.S.t Value.t) : 'd t =
       Value.create
         (FakeReact.S.l3 (Value.local f) (Value.local s1) (Value.local s2)
            (Value.local s3))
@@ -424,8 +427,7 @@ module React = struct
 
     let l4 ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e) Value.t)
         (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
-        (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t) : 'e t
-      =
+        (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t) : 'e t =
       Value.create
         (FakeReact.S.l4 (Value.local f) (Value.local s1) (Value.local s2)
            (Value.local s3) (Value.local s4))
@@ -435,8 +437,7 @@ module React = struct
     let l5 ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f) Value.t)
         (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
         (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t)
-        (s5 : 'e FakeReact.S.t Value.t) : 'f t
-      =
+        (s5 : 'e FakeReact.S.t Value.t) : 'f t =
       Value.create
         (FakeReact.S.l5 (Value.local f) (Value.local s1) (Value.local s2)
            (Value.local s3) (Value.local s4) (Value.local s5))
@@ -446,14 +447,13 @@ module React = struct
     let l6 ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g) Value.t)
         (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
         (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t)
-        (s5 : 'e FakeReact.S.t Value.t) (s6 : 'f FakeReact.S.t Value.t) : 'g t
-      =
+        (s5 : 'e FakeReact.S.t Value.t) (s6 : 'f FakeReact.S.t Value.t) : 'g t =
       Value.create
         (FakeReact.S.l6 (Value.local f) (Value.local s1) (Value.local s2)
            (Value.local s3) (Value.local s4) (Value.local s5) (Value.local s6))
         [%client.unsafe
           (React.S.l6 ?eq:~%eq ~%f ~%s1 ~%s2 ~%s3 ~%s4 ~%s5 ~%s6
-           : 'g FakeReact.S.t)]
+            : 'g FakeReact.S.t)]
 
     let switch ?eq (s : 'a FakeReact.S.t Value.t FakeReact.S.t Value.t) : 'a t =
       (* TODO : setting synced to false is safe, but can we do
@@ -472,91 +472,81 @@ module React = struct
     end
 
     module Lwt = struct
-      let map_s ?eq (f : ('a -> 'b Lwt.t) Value.t)
-          (s : 'a FakeReact.S.t Value.t) : 'b t Lwt.t
-        =
+      let map_s ?eq (f : ('a -> 'b) Value.t) (s : 'a FakeReact.S.t Value.t) :
+          'b t =
         let s' = Value.local s in
-        let* server_result = (Value.local f) (FakeReact.S.value s') in
+        let server_result = (Value.local f) (FakeReact.S.value s') in
         let synced = FakeReact.S.synced s' in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.map_s_init ~init:~%server_result ?eq:~%eq ~%f ~%s
-                : 'b FakeReact.S.t)])
-
-      let l2_s ?eq (f : ('a -> 'b -> 'c Lwt.t) Value.t)
-          (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t) :
-          'c t Lwt.t
-        =
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.map_s_init ~init:~%server_result ?eq:~%eq ~%f ~%s
+              : 'b FakeReact.S.t)]
+
+      let l2_s ?eq (f : ('a -> 'b -> 'c) Value.t)
+          (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t) : 'c t
+          =
         let s1' = Value.local s1 and s2' = Value.local s2 in
-        let* server_result =
+        let server_result =
           (Value.local f) (FakeReact.S.value s1') (FakeReact.S.value s2')
         in
         let synced = FakeReact.S.(synced s1' && synced s2') in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.l2_s_init ~init:~%server_result ?eq:~%eq ~%f ~%s1
-                  ~%s2
-                : 'c FakeReact.S.t)])
-
-      let l3_s ?eq (f : ('a -> 'b -> 'c -> 'd Lwt.t) Value.t)
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.l2_s_init ~init:~%server_result ?eq:~%eq ~%f ~%s1 ~%s2
+              : 'c FakeReact.S.t)]
+
+      let l3_s ?eq (f : ('a -> 'b -> 'c -> 'd) Value.t)
           (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
-          (s3 : 'c FakeReact.S.t Value.t) : 'd t Lwt.t
-        =
+          (s3 : 'c FakeReact.S.t Value.t) : 'd t =
         let s1' = Value.local s1
         and s2' = Value.local s2
         and s3' = Value.local s3 in
-        let* server_result =
+        let server_result =
           (Value.local f) (FakeReact.S.value s1') (FakeReact.S.value s2')
             (FakeReact.S.value s3')
         in
         let synced = FakeReact.S.(synced s1' && synced s2' && synced s3') in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.l3_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1
-                  ~%s2 ~%s3
-                : 'd FakeReact.S.t)])
-
-      let l4_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e Lwt.t) Value.t)
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.l3_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1 ~%s2
+               ~%s3
+              : 'd FakeReact.S.t)]
+
+      let l4_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e) Value.t)
           (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
-          (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t) :
-          'e t Lwt.t
-        =
+          (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t) : 'e t
+          =
         let s1' = Value.local s1
         and s2' = Value.local s2
         and s3' = Value.local s3
         and s4' = Value.local s4 in
-        let* server_result =
+        let server_result =
           (Value.local f) (FakeReact.S.value s1') (FakeReact.S.value s2')
             (FakeReact.S.value s3') (FakeReact.S.value s4')
         in
         let synced =
           FakeReact.S.(synced s1' && synced s2' && synced s3' && synced s4')
         in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.l4_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1
-                  ~%s2 ~%s3 ~%s4
-                : 'e FakeReact.S.t)])
-
-      let l5_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f Lwt.t) Value.t)
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.l4_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1 ~%s2
+               ~%s3 ~%s4
+              : 'e FakeReact.S.t)]
+
+      let l5_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f) Value.t)
           (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
           (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t)
-          (s5 : 'e FakeReact.S.t Value.t) : 'f t Lwt.t
-        =
+          (s5 : 'e FakeReact.S.t Value.t) : 'f t =
         let s1' = Value.local s1
         and s2' = Value.local s2
         and s3' = Value.local s3
         and s4' = Value.local s4
         and s5' = Value.local s5 in
-        let* server_result =
+        let server_result =
           (Value.local f) (FakeReact.S.value s1') (FakeReact.S.value s2')
             (FakeReact.S.value s3') (FakeReact.S.value s4')
             (FakeReact.S.value s5')
@@ -565,27 +555,25 @@ module React = struct
           FakeReact.S.(
             synced s1' && synced s2' && synced s3' && synced s4' && synced s5')
         in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.l5_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1
-                  ~%s2 ~%s3 ~%s4 ~%s5
-                : 'f FakeReact.S.t)])
-
-      let l6_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g Lwt.t) Value.t)
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.l5_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1 ~%s2
+               ~%s3 ~%s4 ~%s5
+              : 'f FakeReact.S.t)]
+
+      let l6_s ?eq (f : ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g) Value.t)
           (s1 : 'a FakeReact.S.t Value.t) (s2 : 'b FakeReact.S.t Value.t)
           (s3 : 'c FakeReact.S.t Value.t) (s4 : 'd FakeReact.S.t Value.t)
-          (s5 : 'e FakeReact.S.t Value.t) (s6 : 'f FakeReact.S.t Value.t) :
-          'g t Lwt.t
-        =
+          (s5 : 'e FakeReact.S.t Value.t) (s6 : 'f FakeReact.S.t Value.t) : 'g t
+          =
         let s1' = Value.local s1
         and s2' = Value.local s2
         and s3' = Value.local s3
         and s4' = Value.local s4
         and s5' = Value.local s5
         and s6' = Value.local s6 in
-        let* server_result =
+        let server_result =
           (Value.local f) (FakeReact.S.value s1') (FakeReact.S.value s2')
             (FakeReact.S.value s3') (FakeReact.S.value s4')
             (FakeReact.S.value s5') (FakeReact.S.value s6')
@@ -595,33 +583,30 @@ module React = struct
             synced s1' && synced s2' && synced s3' && synced s4' && synced s5'
             && synced s6')
         in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.l6_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1
-                  ~%s2 ~%s3 ~%s4 ~%s5 ~%s6
-                : 'g FakeReact.S.t)])
-
-      let merge_s ?eq (f : ('a -> 'b -> 'a Lwt.t) Value.t) (acc : 'a)
-          (l : 'b FakeReact.S.t Value.t list) : 'a t Lwt.t
-        =
-        let* server_result, synced =
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.l6_s_init ?eq:~%eq ~init:~%server_result ~%f ~%s1 ~%s2
+               ~%s3 ~%s4 ~%s5 ~%s6
+              : 'g FakeReact.S.t)]
+
+      let merge_s ?eq (f : ('a -> 'b -> 'a) Value.t) (acc : 'a)
+          (l : 'b FakeReact.S.t Value.t list) : 'a t =
+        let server_result, synced =
           let f (acc, _acc_b) v =
             let v = Value.local v and f = Value.local f in
-            let* acc = f acc (FakeReact.S.value v) in
+            let acc = f acc (FakeReact.S.value v) in
             let acc_b = FakeReact.S.synced v in
-            Lwt.return (acc, acc_b)
+            (acc, acc_b)
           in
-          Lwt_list.fold_left_s f (acc, true) l
+          List.fold_left f (acc, true) l
         in
-        Lwt.return
-          (Value.create
-             (fst (FakeReact.S.create ~synced server_result))
-             [%client.unsafe
-               (React.S.Lwt.merge_s_init ~init:~%server_result ?eq:~%eq ~%f
-                  ~%acc ~%l
-                : 'a FakeReact.S.t)])
+        Value.create
+          (fst (FakeReact.S.create ~synced server_result))
+          [%client.unsafe
+            (React.S.Lwt.merge_s_init ~init:~%server_result ?eq:~%eq ~%f ~%acc
+               ~%l
+              : 'a FakeReact.S.t)]
     end
   end
 end
@@ -634,22 +619,22 @@ module ReactiveData = struct
     let create ?default ?(reset_default = false) x =
       let cv, synced =
         match default with
-        | None -> [%client.unsafe FakeReactiveData.RList.create ~%x], true
+        | None -> ([%client.unsafe FakeReactiveData.RList.create ~%x], true)
         | Some v ->
             ( [%client.unsafe
-                ((match ~%v with
+                (match ~%v with
                  | Some ((_, handle) as s) ->
                      if ~%reset_default then ReactiveData.RList.set handle ~%x;
                      s
-                 | None -> FakeReactiveData.RList.create ~%x)
-                 : 'a FakeReactiveData.RList.t
-                   * 'a FakeReactiveData.RList.handle)]
-            , reset_default )
+                 | None -> FakeReactiveData.RList.create ~%x
+                  : 'a FakeReactiveData.RList.t
+                    * 'a FakeReactiveData.RList.handle)],
+              reset_default )
       in
       let sv = FakeReactiveData.RList.create ~synced x in
       ( Value.create (fst sv)
-          [%client.unsafe (fst ~%cv : 'a FakeReactiveData.RList.t)]
-      , Value.create (snd sv)
+          [%client.unsafe (fst ~%cv : 'a FakeReactiveData.RList.t)],
+        Value.create (snd sv)
           [%client.unsafe (snd ~%cv : 'b FakeReactiveData.RList.handle)] )
 
     let concat a b =
@@ -665,7 +650,7 @@ module ReactiveData = struct
         (FakeReactiveData.RList.singleton_s (Value.local s))
         [%client.unsafe
           (FakeReactiveData.RList.singleton_s (Value.local ~%s)
-           : 'a FakeReactiveData.RList.t)]
+            : 'a FakeReactiveData.RList.t)]
 
     let value (s : 'a FakeReactiveData.RList.t Value.t) =
       Value.create
@@ -682,7 +667,7 @@ module ReactiveData = struct
       and cv =
         [%client.unsafe
           (FakeReactiveData.RList.signal ?eq:~%eq (Value.local ~%s)
-           : 'a list FakeReact.S.t)]
+            : 'a list FakeReact.S.t)]
       in
       Value.create sv cv
 
@@ -691,7 +676,7 @@ module ReactiveData = struct
         (FakeReactiveData.RList.map (Value.local f) (Value.local s))
         [%client.unsafe
           (FakeReactiveData.RList.map (Value.local ~%f) (Value.local ~%s)
-           : 'a FakeReactiveData.RList.t)]
+            : 'a FakeReactiveData.RList.t)]
 
     let from_signal ?eq (s : 'a list React.S.t) : 'a t =
       let sv =
@@ -711,26 +696,24 @@ module ReactiveData = struct
         [%client.unsafe
           (let f x = ReactiveData.RList.cons x (Value.local ~%h) in
            ignore (React.E.map f ~%e)
-           : unit)]
+            : unit)]
       in
       l
 
     let synced s = Value.local s |> FakeReactiveData.RList.synced
 
     module Lwt = struct
-      let map_p (f : ('a -> 'b Lwt.t) Value.t)
-          (l : 'a FakeReactiveData.RList.t Value.t) : 'b t Lwt.t
-        =
+      let map_p (f : ('a -> 'b) Value.t)
+          (l : 'a FakeReactiveData.RList.t Value.t) : 'b t =
         let l' = Value.local l in
-        let* server_result =
-          Lwt_list.map_p (Value.local f) (FakeReactiveData.RList.value l')
+        let server_result =
+          Fiber.List.map (Value.local f) (FakeReactiveData.RList.value l')
         in
         let synced = FakeReactiveData.RList.synced l' in
-        Lwt.return
-          (Value.create
-             (fst (FakeReactiveData.RList.create ~synced server_result))
-             [%client.unsafe
-               ReactiveData.RList.Lwt.map_p_init ~init:~%server_result ~%f ~%l])
+        Value.create
+          (fst (FakeReactiveData.RList.create ~synced server_result))
+          [%client.unsafe
+            ReactiveData.RList.Lwt.map_p_init ~init:~%server_result ~%f ~%l]
     end
   end
 end]
diff --git a/src/lib/eliom_shared.server.mli b/src/lib/eliom_shared.server.mli
index 12e3d450f0..7f28dfe65e 100644
--- a/src/lib/eliom_shared.server.mli
+++ b/src/lib/eliom_shared.server.mli
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2014
@@ -32,7 +34,7 @@
 val to_signal :
    init:'a
   -> ?eq:('a -> 'a -> bool)
-  -> 'a React.S.t Lwt.t
+  -> 'a React.S.t Promise.t
   -> 'a React.S.t
 (** [to_signal ~init s] converts the Lwt-wrapped signal [s] into a
     regular signal with initial value [init]. *)
diff --git a/src/lib/eliom_shared_sigs.shared.mli b/src/lib/eliom_shared_sigs.shared.mli
index c3fe877dd4..8f73f1718c 100644
--- a/src/lib/eliom_shared_sigs.shared.mli
+++ b/src/lib/eliom_shared_sigs.shared.mli
@@ -111,63 +111,59 @@ module type S = sig
 
   (** Cooperative versions of the React operators *)
   module Lwt : sig
-    val map_s :
-       ?eq:('b -> 'b -> bool) sv
-      -> ('a -> 'b Lwt.t) sv
-      -> 'a t
-      -> 'b t Lwt.t
+    val map_s : ?eq:('b -> 'b -> bool) sv -> ('a -> 'b) sv -> 'a t -> 'b t
 
     val l2_s :
        ?eq:('c -> 'c -> bool) sv
-      -> ('a -> 'b -> 'c Lwt.t) sv
+      -> ('a -> 'b -> 'c) sv
       -> 'a t
       -> 'b t
-      -> 'c t Lwt.t
+      -> 'c t
 
     val l3_s :
        ?eq:('d -> 'd -> bool) sv
-      -> ('a -> 'b -> 'c -> 'd Lwt.t) sv
+      -> ('a -> 'b -> 'c -> 'd) sv
       -> 'a t
       -> 'b t
       -> 'c t
-      -> 'd t Lwt.t
+      -> 'd t
 
     val l4_s :
        ?eq:('e -> 'e -> bool) sv
-      -> ('a -> 'b -> 'c -> 'd -> 'e Lwt.t) sv
+      -> ('a -> 'b -> 'c -> 'd -> 'e) sv
       -> 'a t
       -> 'b t
       -> 'c t
       -> 'd t
-      -> 'e t Lwt.t
+      -> 'e t
 
     val l5_s :
        ?eq:('f -> 'f -> bool) sv
-      -> ('a -> 'b -> 'c -> 'd -> 'e -> 'f Lwt.t) sv
+      -> ('a -> 'b -> 'c -> 'd -> 'e -> 'f) sv
       -> 'a t
       -> 'b t
       -> 'c t
       -> 'd t
       -> 'e t
-      -> 'f t Lwt.t
+      -> 'f t
 
     val l6_s :
        ?eq:('g -> 'g -> bool) sv
-      -> ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g Lwt.t) sv
+      -> ('a -> 'b -> 'c -> 'd -> 'e -> 'f -> 'g) sv
       -> 'a t
       -> 'b t
       -> 'c t
       -> 'd t
       -> 'e t
       -> 'f t
-      -> 'g t Lwt.t
+      -> 'g t
 
     val merge_s :
        ?eq:('a -> 'a -> bool) sv
-      -> ('a -> 'b -> 'a Lwt.t) sv
+      -> ('a -> 'b -> 'a) sv
       -> 'a
       -> 'b t list
-      -> 'a t Lwt.t
+      -> 'a t
   end
 end
 
@@ -217,6 +213,6 @@ module type RLIST = sig
 
   (** Cooperative versions of the ReactiveData operators *)
   module Lwt : sig
-    val map_p : ('a -> 'b Lwt.t) sv -> 'a t -> 'b t Lwt.t
+    val map_p : ('a -> 'b) sv -> 'a t -> 'b t
   end
 end
diff --git a/src/lib/eliom_state.server.ml b/src/lib/eliom_state.server.ml
index f4afdbaef4..8bab520107 100644
--- a/src/lib/eliom_state.server.ml
+++ b/src/lib/eliom_state.server.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -20,7 +20,6 @@ open Lwt.Syntax
 *)
 
 open Eliom_lib
-open Lwt
 
 (* Expired session? *)
 type state_status = Alive_state | Empty_state | Expired_state
@@ -48,15 +47,16 @@ let volatile_data_state_status ~scope ?secure () =
 
 let persistent_data_state_status ~scope ?secure () =
   let cookie_scope = Eliom_common.cookie_scope_of_user_scope scope in
-  catch
-    (fun () ->
-       Eliommod_persess.find_persistent_cookie_only ~cookie_scope
-         ~secure_o:secure ()
-       >>= fun _ -> return Alive_state)
-    (function
-      | Not_found -> Lwt.return Empty_state
-      | Eliom_common.Eliom_Session_expired -> Lwt.return Expired_state
-      | e -> fail e)
+  try
+    let _ =
+      Eliommod_persess.find_persistent_cookie_only ~cookie_scope
+        ~secure_o:secure ()
+    in
+    Alive_state
+  with
+  | Not_found -> Empty_state
+  | Eliom_common.Eliom_Session_expired -> Expired_state
+  | e -> raise e
 
 (************)
 (*
@@ -261,54 +261,44 @@ let get_volatile_data_state_timeout ~cookie_scope ?secure () =
     Eliommod_timeouts.get_global ~kind:`Data ~cookie_scope ~secure sitedata
 
 let set_persistent_data_state_timeout ~cookie_scope ?secure t =
-  let* c =
+  let c =
     Eliommod_persess.find_or_create_persistent_cookie ~cookie_scope
       ~secure_o:secure ()
   in
   let tor = c.Eliom_common.pc_timeout in
-  return
-    (match t with
-    | None -> tor := Eliom_common.TNone
-    | Some t -> tor := Eliom_common.TSome t)
+  match t with
+  | None -> tor := Eliom_common.TNone
+  | Some t -> tor := Eliom_common.TSome t
 
 let unset_persistent_data_state_timeout ~cookie_scope ?secure () =
-  Lwt.catch
-    (fun () ->
-       let* c =
-         Eliommod_persess.find_persistent_cookie_only ~cookie_scope
-           ~secure_o:secure ()
-       in
-       let tor = c.Eliom_common.pc_timeout in
-       tor := Eliom_common.TGlobal;
-       return_unit)
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired -> return_unit
-      | exc -> Lwt.reraise exc)
+  try
+    let c =
+      Eliommod_persess.find_persistent_cookie_only ~cookie_scope
+        ~secure_o:secure ()
+    in
+    let tor = c.Eliom_common.pc_timeout in
+    tor := Eliom_common.TGlobal
+  with Not_found | Eliom_common.Eliom_Session_expired -> ()
 
 let get_persistent_data_state_timeout ~cookie_scope ?secure () =
   let sp = Eliom_common.get_sp () in
   let sitedata = Eliom_request_info.get_sitedata_sp ~sp in
   let secure = Eliom_common.get_secure ~secure_o:secure ~sitedata () in
-  Lwt.catch
-    (fun () ->
-       let* c =
-         Eliommod_persess.find_persistent_cookie_only ~cookie_scope
-           ~secure_o:(Some secure) ~sp ()
-       in
-       let tor = c.Eliom_common.pc_timeout in
-       return
-         (match !tor with
-         | Eliom_common.TGlobal ->
-             Eliommod_timeouts.get_global ~kind:`Persistent ~cookie_scope
-               ~secure sitedata
-         | Eliom_common.TNone -> None
-         | Eliom_common.TSome t -> Some t))
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired ->
-          return
-            (Eliommod_timeouts.get_global ~kind:`Persistent ~cookie_scope
-               ~secure sitedata)
-      | exc -> Lwt.reraise exc)
+  try
+    let c =
+      Eliommod_persess.find_persistent_cookie_only ~cookie_scope
+        ~secure_o:(Some secure) ~sp ()
+    in
+    let tor = c.Eliom_common.pc_timeout in
+    match !tor with
+    | Eliom_common.TGlobal ->
+        Eliommod_timeouts.get_global ~kind:`Persistent ~cookie_scope ~secure
+          sitedata
+    | Eliom_common.TNone -> None
+    | Eliom_common.TSome t -> Some t
+  with Not_found | Eliom_common.Eliom_Session_expired ->
+    Eliommod_timeouts.get_global ~kind:`Persistent ~cookie_scope ~secure
+      sitedata
 
 (* Preventing memory leaks: we must close empty sessions *)
 
@@ -396,7 +386,7 @@ let rec close_volatile_state_if_empty ~scope ?secure () =
           ()
   with Not_found -> ()
 
-let close_persistent_state_if_empty ~scope:_ ?secure:_ () = Lwt.return_unit
+let close_persistent_state_if_empty ~scope:_ ?secure:_ () = ()
 (*VVV Can we implement this function? *)
 
 (* session groups *)
@@ -585,7 +575,7 @@ let set_persistent_data_session_group
   =
   let sp = Eliom_common.get_sp () in
   let sitedata = Eliom_request_info.get_sitedata_sp ~sp in
-  let* c =
+  let c =
     Eliommod_persess.find_or_create_persistent_cookie
       ~cookie_scope:(scope :> Eliom_common.cookie_scope)
       ~secure_o:secure ~sp ()
@@ -597,21 +587,20 @@ let set_persistent_data_session_group
       (Some n)
   in
   let grp = c.Eliom_common.pc_session_group in
-  let* l =
+  let l =
     Eliommod_sessiongroups.Pers.move sitedata ?set_max
       (fst sitedata.Eliom_common.max_persistent_data_sessions_per_group)
       Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
       !grp n
   in
-  let* () =
-    Lwt_list.iter_p
+  let () =
+    Fiber.List.iter
       (Eliommod_persess.close_persistent_state2
          ~scope:(scope :> Eliom_common.user_scope)
          sitedata None)
       l
   in
-  grp := n;
-  Lwt.return_unit
+  grp := n
 
 let unset_persistent_data_session_group
       ?(scope = Eliom_common.default_session_scope)
@@ -620,49 +609,42 @@ let unset_persistent_data_session_group
   =
   let sp = Eliom_common.get_sp () in
   let sitedata = Eliom_request_info.get_sitedata_sp ~sp in
-  Lwt.catch
-    (fun () ->
-       let* c =
-         Eliommod_persess.find_persistent_cookie_only
-           ~cookie_scope:(scope :> Eliom_common.cookie_scope)
-           ~secure_o:secure ~sp ()
-       in
-       let grp = c.Eliom_common.pc_session_group in
-       let* () =
-         Eliommod_sessiongroups.Pers.remove sitedata
-           Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
-           !grp
-       in
-       grp := None;
-       close_persistent_state_if_empty
-         ~scope:(scope :> Eliom_common.user_scope)
-         ?secure ())
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired -> Lwt.return_unit
-      | exc -> Lwt.reraise exc)
+  try
+    let c =
+      Eliommod_persess.find_persistent_cookie_only
+        ~cookie_scope:(scope :> Eliom_common.cookie_scope)
+        ~secure_o:secure ~sp ()
+    in
+    let grp = c.Eliom_common.pc_session_group in
+    let () =
+      Eliommod_sessiongroups.Pers.remove sitedata
+        Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
+        !grp
+    in
+    grp := None;
+    close_persistent_state_if_empty
+      ~scope:(scope :> Eliom_common.user_scope)
+      ?secure ()
+  with Not_found | Eliom_common.Eliom_Session_expired -> ()
 
 let get_persistent_data_session_group
       ?(scope = Eliom_common.default_session_scope)
       ?secure
       ()
   =
-  Lwt.catch
-    (fun () ->
-       let* c =
-         Eliommod_persess.find_persistent_cookie_only
-           ~cookie_scope:(scope :> Eliom_common.cookie_scope)
-           ~secure_o:secure ()
-       in
-       Lwt.return
-         (match !(c.Eliom_common.pc_session_group) with
-         | None -> None
-         | Some v -> (
-           match Eliommod_sessiongroups.getperssessgrp v with
-           | _, _, Left s -> Some s
-           | _ -> None)))
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired -> Lwt.return_none
-      | exc -> Lwt.reraise exc)
+  try
+    let c =
+      Eliommod_persess.find_persistent_cookie_only
+        ~cookie_scope:(scope :> Eliom_common.cookie_scope)
+        ~secure_o:secure ()
+    in
+    match !(c.Eliom_common.pc_session_group) with
+    | None -> None
+    | Some v -> (
+      match Eliommod_sessiongroups.getperssessgrp v with
+      | _, _, Left s -> Some s
+      | _ -> None)
+  with Not_found | Eliom_common.Eliom_Session_expired -> None
 
 (* max *)
 let set_default_max_service_sessions_per_group ?(override_configfile = false) n =
@@ -853,15 +835,14 @@ let set_volatile_data_cookie_exp_date ~cookie_scope ?secure t =
   | Some t -> exp := Eliom_common.CESome t
 
 let set_persistent_data_cookie_exp_date ~cookie_scope ?secure t =
-  let* c =
+  let c =
     Eliommod_persess.find_or_create_persistent_cookie ~cookie_scope
       ~secure_o:secure ()
   in
   let exp = c.Eliom_common.pc_cookie_exp in
-  return
-    (match t with
-    | None -> exp := Eliom_common.CEBrowser
-    | Some t -> exp := Eliom_common.CESome t)
+  match t with
+  | None -> exp := Eliom_common.CEBrowser
+  | Some t -> exp := Eliom_common.CESome t
 
 (* *)
 let get_global_table () =
@@ -913,11 +894,11 @@ module Ocsipersist = Eliom_common.Ocsipersist.Polymorphic
 type 'a persistent_table =
   Eliom_common.user_scope * bool * (int64 * 'a) Ocsipersist.table
 
-let create_persistent_table ~scope ?secure name : 'a persistent_table Lwt.t =
+let create_persistent_table ~scope ?secure name : 'a persistent_table =
   let sitedata = Eliom_request_info.find_sitedata "create_persistent_table" in
   let secure = Eliom_common.get_secure ~secure_o:secure ~sitedata () in
-  Eliom_common.Persistent_tables.create name >>= fun t ->
-  Lwt.return (scope, secure, t)
+  let t = Eliom_common.Persistent_tables.create name in
+  scope, secure, t
 
 let get_p_table_key_
       ~table:(scope, secure, table)
@@ -926,59 +907,57 @@ let get_p_table_key_
         -> secure_o:bool option
         -> ?sp:Eliom_common.server_params
         -> unit
-        -> Eliom_common.one_persistent_cookie_info Lwt.t)
+        -> Eliom_common.one_persistent_cookie_info)
   =
   let get_cookie () =
     let cookie_scope = Eliom_common.cookie_scope_of_user_scope scope in
-    let* c = find_cookie ~cookie_scope ~secure_o:(Some secure) () in
-    Lwt.return Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
+    let c = find_cookie ~cookie_scope ~secure_o:(Some secure) () in
+    Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
   in
-  let* key =
+  let key =
     match scope with
-    | `Session_group state_name ->
-        Lwt.bind
-          (get_persistent_data_session_group ~scope:(`Session state_name)
-             ~secure ())
-          (function
-            | Some a -> Lwt.return a
-            | None ->
-                (* No session group. We use the session cookie as key. *)
-                get_cookie ())
+    | `Session_group state_name -> (
+      match
+        get_persistent_data_session_group ~scope:(`Session state_name) ~secure
+          ()
+      with
+      | Some a -> a
+      | None ->
+          (* No session group. We use the session cookie as key. *)
+          get_cookie ())
     | _ -> get_cookie ()
   in
-  Lwt.return (table, key)
+  table, key
 
 let get_persistent_data ~table () =
-  catch
-    (fun () ->
-       get_p_table_key_ ~table Eliommod_persess.find_persistent_cookie_only
-       >>= fun (table, key) ->
-       Ocsipersist.find table key >>= fun (_, v) -> Lwt.return (Data v))
-    (function
-      | Eliom_common.Eliom_Session_expired -> return Data_session_expired
-      | Not_found -> return No_data
-      | e -> fail e)
+  try
+    let table, key =
+      get_p_table_key_ ~table Eliommod_persess.find_persistent_cookie_only
+    in
+    let _, v = Ocsipersist.find table key in
+    Data v
+  with
+  | Eliom_common.Eliom_Session_expired -> Data_session_expired
+  | Not_found -> No_data
+  | e -> raise e
 
 let set_persistent_data ~table value =
   let f__ ~cookie_scope ~secure_o ?sp () =
     Eliommod_persess.find_or_create_persistent_cookie ~cookie_scope ~secure_o
       ?sp ()
   in
-  get_p_table_key_ ~table f__ >>= fun (table, key) ->
+  let table, key = get_p_table_key_ ~table f__ in
   Ocsipersist.add table key (Int64.zero, value)
 
 let remove_persistent_data ~table () =
-  Lwt.catch
-    (fun () ->
-       let scope, secure, _ = table in
-       let* table, key =
-         get_p_table_key_ ~table Eliommod_persess.find_persistent_cookie_only
-       in
-       let* () = Ocsipersist.remove table key in
-       close_persistent_state_if_empty ~scope ~secure ())
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired -> return_unit
-      | exc -> Lwt.reraise exc)
+  try
+    let scope, secure, _ = table in
+    let table, key =
+      get_p_table_key_ ~table Eliommod_persess.find_persistent_cookie_only
+    in
+    let () = Ocsipersist.remove table key in
+    close_persistent_state_if_empty ~scope ~secure ()
+  with Not_found | Eliom_common.Eliom_Session_expired -> ()
 
 (*****************************************************************************)
 (** {2 session data in memory} *)
@@ -1069,8 +1048,7 @@ let remove_volatile_data ~table () =
 let discard_persistent_data ~scope ?secure () =
   match secure with
   | None ->
-      Eliommod_persess.close_persistent_state ~scope ~secure_o:(Some true) ()
-      >>= fun () ->
+      Eliommod_persess.close_persistent_state ~scope ~secure_o:(Some true) ();
       Eliommod_persess.close_persistent_state ~scope ~secure_o:(Some false) ()
   | _ -> Eliommod_persess.close_persistent_state ~scope ~secure_o:secure ()
 
@@ -1090,7 +1068,7 @@ let discard_volatile_data ~scope ?secure () =
 
 let discard_request_data () =
   let table = Eliom_request_info.get_request_cache () in
-  Polytables.clear ~table; Lwt.return_unit
+  Polytables.clear ~table
 
 let discard_data ?persistent ~scope ?secure () =
   match scope with
@@ -1101,7 +1079,7 @@ let discard_data ?persistent ~scope ?secure () =
       | _ -> ());
       match persistent with
       | None | Some true -> discard_persistent_data ~scope ?secure ()
-      | _ -> Lwt.return_unit)
+      | _ -> ())
 
 let discard ~scope ?secure () =
   match scope with
@@ -1113,12 +1091,12 @@ let discard ~scope ?secure () =
 
 let discard_all_scopes ?secure () =
   let discard_name scope_hierarchy =
-    let* () = discard ?secure ~scope:(`Session_group scope_hierarchy) () in
-    let* () = discard ?secure ~scope:(`Session scope_hierarchy) () in
+    let () = discard ?secure ~scope:(`Session_group scope_hierarchy) () in
+    let () = discard ?secure ~scope:(`Session scope_hierarchy) () in
     discard ?secure ~scope:(`Client_process scope_hierarchy) ()
   in
-  let* () = discard_request_data () in
-  Lwt_list.iter_p discard_name (Eliom_common.list_scope_hierarchies ())
+  let () = discard_request_data () in
+  Fiber.List.iter discard_name (Eliom_common.list_scope_hierarchies ())
 
 let discard_all_volatile_data ~scope ?secure () =
   let sitedata = Eliom_request_info.find_sitedata "discard_all_volatile_data" in
@@ -1135,14 +1113,14 @@ let discard_all_persistent_data ~scope ?secure () =
 (*VVV missing: scope group *)
 
 let discard_all_data ?persistent ~scope ?secure () =
-  let* () =
+  let () =
     match persistent with
     | None | Some false -> discard_all_volatile_data ~scope ?secure ()
-    | _ -> Lwt.return_unit
+    | _ -> ()
   in
   match persistent with
   | None | Some true -> discard_all_persistent_data ~scope ?secure ()
-  | _ -> Lwt.return_unit
+  | _ -> ()
 
 let discard_all_services ~scope ?secure () =
   let sitedata =
@@ -1153,17 +1131,17 @@ let discard_all_services ~scope ?secure () =
 (*VVV missing: scope group *)
 
 let discard_all ~scope ?secure () =
-  let* () = discard_all_services ~scope ?secure () in
+  let () = discard_all_services ~scope ?secure () in
   discard_all_data ~scope ?secure ()
 
 let discard_everything () =
   let discard_name scope_hierarchy =
-    let* () = discard_all ~scope:(`Session_group scope_hierarchy) () in
-    let* () = discard_all ~scope:(`Session scope_hierarchy) () in
+    let () = discard_all ~scope:(`Session_group scope_hierarchy) () in
+    let () = discard_all ~scope:(`Session scope_hierarchy) () in
     discard_all ~scope:(`Client_process scope_hierarchy) ()
   in
-  let* () = discard_request_data () in
-  Lwt_list.iter_p discard_name (Eliom_common.list_scope_hierarchies ())
+  let () = discard_request_data () in
+  Fiber.List.iter discard_name (Eliom_common.list_scope_hierarchies ())
 
 (*****************************************************************************)
 (* Administration *)
@@ -1248,22 +1226,18 @@ module Ext = struct
     =
     let scope = (scope :> Eliom_common.user_scope) in
     match scope with
-    | `Session_group h ->
-        Lwt.bind
-          (get_persistent_data_session_group ~scope:(`Session h) ?secure ())
-          (function
-            | Some g ->
-                persistent_data_group_state ~scope:(`Session_group h) g
-                |> Lwt.return
-            | None -> Lwt.fail Not_found)
+    | `Session_group h -> (
+      match
+        get_persistent_data_session_group ~scope:(`Session h) ?secure ()
+      with
+      | Some g -> persistent_data_group_state ~scope:(`Session_group h) g
+      | None -> raise Not_found)
     | #Eliom_common.cookie_scope as cookie_scope ->
-        Eliommod_persess.find_or_create_persistent_cookie ~secure_o:secure
-          ~cookie_scope ()
-        >>= fun cookie ->
-        Lwt.return
-          ( scope
-          , `Pers
-          , Eliom_common.(Hashed_cookies.to_string cookie.pc_hvalue) )
+        let cookie =
+          Eliommod_persess.find_or_create_persistent_cookie ~secure_o:secure
+            ~cookie_scope ()
+        in
+        scope, `Pers, Eliom_common.(Hashed_cookies.to_string cookie.pc_hvalue)
 
   let current_service_state
         ?secure
@@ -1308,8 +1282,8 @@ module Ext = struct
   let get_persistent_cookie_info
         ((_, _, cookie) : ([< Eliom_common.cookie_level], [`Pers]) state)
     =
-    Eliommod_cookies.Persistent_cookies.Cookies.find cookie >>= fun v ->
-    Lwt.return (cookie, v)
+    let v = Eliommod_cookies.Persistent_cookies.Cookies.find cookie in
+    cookie, v
 
   let discard_state
         ?(sitedata =
@@ -1321,22 +1295,20 @@ module Ext = struct
       Eliom_common.get_site_dir_string sitedata, `Session, Left n
     in
     match state with
-    | `Session_group _, `Data, group_name ->
-        (match
-           Eliommod_sessiongroups.Data.find_node_in_group_of_groups
-             (make_sessgrp group_name)
-         with
-        | Some node -> Eliommod_sessiongroups.Data.remove node
-        | None -> ());
-        Lwt.return_unit
-    | `Session_group _, `Service, group_name ->
-        (match
-           Eliommod_sessiongroups.Serv.find_node_in_group_of_groups
-             (make_sessgrp group_name)
-         with
-        | Some (_, node) -> Eliommod_sessiongroups.Serv.remove node
-        | None -> ());
-        Lwt.return_unit
+    | `Session_group _, `Data, group_name -> (
+      match
+        Eliommod_sessiongroups.Data.find_node_in_group_of_groups
+          (make_sessgrp group_name)
+      with
+      | Some node -> Eliommod_sessiongroups.Data.remove node
+      | None -> ())
+    | `Session_group _, `Service, group_name -> (
+      match
+        Eliommod_sessiongroups.Serv.find_node_in_group_of_groups
+          (make_sessgrp group_name)
+      with
+      | Some (_, node) -> Eliommod_sessiongroups.Serv.remove node
+      | None -> ())
     | `Session_group _, `Pers, group_name ->
         let sgr_o =
           Eliom_common.make_persistent_full_group_name ~cookie_level:`Session
@@ -1352,7 +1324,7 @@ module Ext = struct
           | _, {Eliom_common.Service_cookie.session_group_node; _} ->
               Eliommod_sessiongroups.Serv.remove session_group_node
         in
-        Lwt.return_unit
+        ()
     | _, `Data, _cookie ->
         let () =
           match get_volatile_data_cookie_info ~sitedata state with
@@ -1360,19 +1332,15 @@ module Ext = struct
           | _, {Eliom_common.Data_cookie.session_group_node; _} ->
               Eliommod_sessiongroups.Data.remove session_group_node
         in
-        Lwt.return_unit
-    | _, `Pers, _cookie ->
-        Lwt.try_bind
-          (fun () -> get_persistent_cookie_info state)
-          (function
-            | cookie, {Eliommod_cookies.full_state_name; session_group; _} ->
-                let scope = full_state_name.Eliom_common.user_scope in
-                let cookie_level =
-                  Eliom_common.cookie_level_of_user_scope scope
-                in
-                Eliommod_sessiongroups.Pers.close_persistent_session2
-                  ~cookie_level sitedata session_group cookie)
-          (function Not_found -> Lwt.return_unit | exc -> Lwt.reraise exc)
+        ()
+    | _, `Pers, _cookie -> (
+      match get_persistent_cookie_info state with
+      | cookie, {Eliommod_cookies.full_state_name; session_group; _} ->
+          let scope = full_state_name.Eliom_common.user_scope in
+          let cookie_level = Eliom_common.cookie_level_of_user_scope scope in
+          Eliommod_sessiongroups.Pers.close_persistent_session2 ~cookie_level
+            sitedata session_group cookie
+      | exception Not_found -> ())
   (*VVV!!! est-ce que session_group est fullsessgrp ? *)
 
   let fold_sub_states_aux_aux
@@ -1435,8 +1403,8 @@ module Ext = struct
 
   (** Fold over the snapshot of a Dlist. *)
   let dlist_lwt_fold f acc dlist =
-    Ocsigen_cache.Dlist.fold (fun acc x -> x :: acc) [] dlist
-    |> List.rev |> Lwt_list.fold_left_s f acc
+    List.fold_left f acc
+      (Ocsigen_cache.Dlist.fold (fun acc x -> x :: acc) [] dlist |> List.rev)
 
   let fold_sub_states ?sitedata ~state f e =
     let ((sitedata, sub_states_level, id, f) as a) =
@@ -1444,13 +1412,15 @@ module Ext = struct
     in
     match state with
     | _, `Pers, _ ->
-        Eliommod_sessiongroups.Pers.find
-          (Eliom_common.make_persistent_full_group_name
-             ~cookie_level:sub_states_level
-             (Eliom_common.get_site_dir_string sitedata)
-             (Some id))
-        >>= fun l -> Lwt_list.fold_left_s f e l
-    | _ -> fold_sub_states_aux dlist_lwt_fold Lwt.return a e state
+        let l =
+          Eliommod_sessiongroups.Pers.find
+            (Eliom_common.make_persistent_full_group_name
+               ~cookie_level:sub_states_level
+               (Eliom_common.get_site_dir_string sitedata)
+               (Some id))
+        in
+        List.fold_left f e l
+    | _ -> fold_sub_states_aux dlist_lwt_fold (fun x1 -> x1) a e state
 
   let iter_volatile_sub_states ?sitedata ~state f =
     fold_volatile_sub_states ?sitedata ~state (fun () -> f) ()
@@ -1470,8 +1440,7 @@ module Ext = struct
     let check_scopes table_scope state_scope =
       if table_scope <> state_scope then raise Wrong_scope
 
-    let lwt_check_scopes a b =
-      try check_scopes a b; Lwt.return_unit with e -> Lwt.fail e
+    let lwt_check_scopes a b = try check_scopes a b with e -> raise e
 
     (*VVV Does not work with volatile group data *)
     let get_volatile_data
@@ -1485,8 +1454,9 @@ module Ext = struct
           ~state:((state_scope, _, cookie) : ('s, [`Pers]) state)
           ~table:((table_scope, _, t) : 'a persistent_table)
       =
-      lwt_check_scopes table_scope state_scope >>= fun () ->
-      Ocsipersist.find t cookie >>= fun (_, a) -> Lwt.return a
+      lwt_check_scopes table_scope state_scope;
+      let _, a = Ocsipersist.find t cookie in
+      a
 
     let set_volatile_data
           ~state:((state_scope, _, cookie) : ('s, [`Data]) state)
@@ -1501,7 +1471,7 @@ module Ext = struct
           ~table:((table_scope, _, t) : 'a persistent_table)
           value
       =
-      lwt_check_scopes table_scope state_scope >>= fun () ->
+      lwt_check_scopes table_scope state_scope;
       Ocsipersist.add t cookie (Int64.zero, value)
 
     let remove_volatile_data
@@ -1515,7 +1485,7 @@ module Ext = struct
           ~state:((state_scope, _, cookie) : ('s, [`Pers]) state)
           ~table:((table_scope, _, t) : 'a persistent_table)
       =
-      lwt_check_scopes table_scope state_scope >>= fun () ->
+      lwt_check_scopes table_scope state_scope;
       Ocsipersist.remove t cookie
   end
 
@@ -1558,8 +1528,7 @@ module Ext = struct
 
   let unset_persistent_data_cookie_timeout ~cookie:(c, cookie) =
     Eliommod_cookies.Persistent_cookies.Cookies.add c
-      {cookie with Eliommod_cookies.timeout = TGlobal}
-    >>= fun () ->
+      {cookie with Eliommod_cookies.timeout = TGlobal};
     let {Eliommod_cookies.expiry; _} = cookie in
     Eliommod_cookies.Persistent_cookies.Expiry_dates.remove_cookie expiry c
 
@@ -1625,16 +1594,13 @@ let get_volatile_data_cookie ~cookie_scope ?secure () =
   with Not_found | Eliom_common.Eliom_Session_expired -> None
 
 let get_persistent_data_cookie ~cookie_scope ?secure () =
-  Lwt.catch
-    (fun () ->
-       let* c =
-         Eliommod_persess.find_persistent_cookie_only ~cookie_scope
-           ~secure_o:secure ()
-       in
-       return_some c.Eliom_common.pc_hvalue)
-    (function
-      | Not_found | Eliom_common.Eliom_Session_expired -> return_none
-      | exc -> Lwt.reraise exc)
+  try
+    let c =
+      Eliommod_persess.find_persistent_cookie_only ~cookie_scope
+        ~secure_o:secure ()
+    in
+    Some c.Eliom_common.pc_hvalue
+  with Not_found | Eliom_common.Eliom_Session_expired -> None
 
 (*****************************************************************************)
 (** {2 User cookies} *)
diff --git a/src/lib/eliom_state.server.mli b/src/lib/eliom_state.server.mli
index 1139b8ed4a..a3d1bc7803 100644
--- a/src/lib/eliom_state.server.mli
+++ b/src/lib/eliom_state.server.mli
@@ -36,7 +36,7 @@ val discard :
    scope:[< Eliom_common.user_scope | Eliom_common.request_scope]
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** Delete server-side (volatile and persistent) state data and services
     for a session,
     a group of sessions, a client process or a request.
@@ -55,14 +55,14 @@ val discard :
 
 (* Discard services and (volatile and persistent) data
    for all user and request scopes *)
-val discard_all_scopes : ?secure:bool -> unit -> unit Lwt.t
+val discard_all_scopes : ?secure:bool -> unit -> unit
 
 val discard_data :
    ?persistent:bool
   -> scope:[< Eliom_common.user_scope | Eliom_common.request_scope]
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** Remove current state data.
 
     If the optional parameter [?persistent] is not present, will
@@ -109,7 +109,7 @@ val persistent_data_state_status :
    scope:[< Eliom_common.user_scope]
   -> ?secure:bool
   -> unit
-  -> state_status Lwt.t
+  -> state_status
 
 (*****************************************************************************)
 (** {3 User cookies}
@@ -259,7 +259,7 @@ val set_persistent_data_session_group :
   -> ?scope:Eliom_common.session_scope
   -> ?secure:bool
   -> string
-  -> unit Lwt.t
+  -> unit
 (** sets the group to which belong the persistent session.
 
     If the optional [?set_max] parameter is present, also sets the
@@ -273,7 +273,7 @@ val unset_persistent_data_session_group :
    ?scope:Eliom_common.session_scope
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** Remove the session from its group.
     Will not close the session if it contains data. *)
 
@@ -281,7 +281,7 @@ val get_persistent_data_session_group :
    ?scope:Eliom_common.session_scope
   -> ?secure:bool
   -> unit
-  -> string option Lwt.t
+  -> string option
 (** returns the group to which belong the persistent session.
     If the session does not belong to any group, or if no session is opened,
     return [None].
@@ -481,7 +481,7 @@ val set_persistent_data_cookie_exp_date :
    cookie_scope:Eliom_common.cookie_scope
   -> ?secure:bool
   -> float option
-  -> unit Lwt.t
+  -> unit
 (** Sets the cookie expiration date for the persistent state (see
     above).
 *)
@@ -658,7 +658,7 @@ val set_persistent_data_state_timeout :
    cookie_scope:[< Eliom_common.cookie_scope]
   -> ?secure:bool
   -> float option
-  -> unit Lwt.t
+  -> unit
 (** sets the (server side) timeout for persistent state for current user,
    in seconds. [None] = no timeout *)
 
@@ -666,7 +666,7 @@ val unset_persistent_data_state_timeout :
    cookie_scope:[< Eliom_common.cookie_scope]
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** remove the persistent state timeout for current user
    (and turn back to the default). *)
 
@@ -674,7 +674,7 @@ val get_persistent_data_state_timeout :
    cookie_scope:[< Eliom_common.cookie_scope]
   -> ?secure:bool
   -> unit
-  -> float option Lwt.t
+  -> float option
 (** returns the persistent state timeout for current user.
     [None] = no timeout *)
 
@@ -698,16 +698,12 @@ type 'a volatile_table
 type 'a persistent_table
 (** The type of persistent state data tables. *)
 
-val discard_everything : unit -> unit Lwt.t
+val discard_everything : unit -> unit
 (** Discard all services and persistent and volatile data for every scopes. *)
 
 (*CCC missing ~secure? *)
 
-val discard_all :
-   scope:Eliom_common.user_scope
-  -> ?secure:bool
-  -> unit
-  -> unit Lwt.t
+val discard_all : scope:Eliom_common.user_scope -> ?secure:bool -> unit -> unit
 (** Discard all services and persistent and volatile data for one scope. *)
 
 (*VVV missing: scope group *)
@@ -717,7 +713,7 @@ val discard_all_data :
   -> scope:Eliom_common.user_scope
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** Discard server side data for all clients, for the given scope.
 
     If the optional parameter [?persistent] is not present,
@@ -731,7 +727,7 @@ val discard_all_services :
    scope:Eliom_common.user_scope
   -> ?secure:bool
   -> unit
-  -> unit Lwt.t
+  -> unit
 (** Remove all services registered for clients for the given scope. *)
 
 (*VVV missing: scope group *)
@@ -795,7 +791,7 @@ module Ext : sig
      ?secure:bool
     -> ?scope:Eliom_common.user_scope
     -> unit
-    -> ([< Eliom_common.user_level], [< `Pers]) state Lwt.t
+    -> ([< Eliom_common.user_level], [< `Pers]) state
   (** Same for persistent data *)
 
   val current_service_state :
@@ -809,7 +805,7 @@ module Ext : sig
      ?sitedata:Eliom_common.sitedata
     -> state:('a, 'b) state
     -> unit
-    -> unit Lwt.t
+    -> unit
   (** Discard external states.
       See {!fold_volatile_sub_states} for explanation about the [?sitedata]
       parameter.
@@ -845,9 +841,9 @@ module Ext : sig
          ( [< `Session_group | `Session]
            , ([< `Data | `Pers | `Service] as 'k) )
            state
-    -> ('a -> ([< `Session | `Client_process], 'k) state -> 'a Lwt.t)
+    -> ('a -> ([< `Session | `Client_process], 'k) state -> 'a)
+    -> 'a
     -> 'a
-    -> 'a Lwt.t
   (** Fold all sessions in a groups, or all client processes in a session
       (volatile and persistent).
       See {!fold_volatile_sub_states} for explanation about the [?sitedata]
@@ -857,8 +853,8 @@ module Ext : sig
   val iter_sub_states :
      ?sitedata:Eliom_common.sitedata
     -> state:([< `Session_group | `Session], 'k) state
-    -> (([< `Session | `Client_process], 'k) state -> unit Lwt.t)
-    -> unit Lwt.t
+    -> (([< `Session | `Client_process], 'k) state -> unit)
+    -> unit
   (** Iter on all sessions in a groups, or all client processes in a session
       (volatile and persistent).
       See {!fold_volatile_sub_states} for explanation about the [?sitedata]
@@ -878,7 +874,7 @@ module Ext : sig
     val get_persistent_data :
        state:([< `Session_group | `Session | `Client_process], [< `Pers]) state
       -> table:'a persistent_table
-      -> 'a Lwt.t
+      -> 'a
     (** Fails with lwt exception [Not_found]
         if no data in the table for the cookie. *)
 
@@ -892,7 +888,7 @@ module Ext : sig
        state:([< `Session_group | `Session | `Client_process], [< `Pers]) state
       -> table:'a persistent_table
       -> 'a
-      -> unit Lwt.t
+      -> unit
     (** Fails with lwt exception [Not_found]
         if no data in the table for the cookie. *)
 
@@ -904,7 +900,7 @@ module Ext : sig
     val remove_persistent_data :
        state:([< `Session_group | `Session | `Client_process], [< `Pers]) state
       -> table:'a persistent_table
-      -> unit Lwt.t
+      -> unit
   end
 
   val get_service_cookie_info :
@@ -926,7 +922,7 @@ module Ext : sig
 
   val get_persistent_cookie_info :
      ([< Eliom_common.cookie_level], [`Pers]) state
-    -> persistent_cookie_info Lwt.t
+    -> persistent_cookie_info
 
   val get_service_cookie_scope :
      cookie:service_cookie_info
@@ -953,7 +949,7 @@ module Ext : sig
   val set_persistent_data_cookie_timeout :
      cookie:persistent_cookie_info
     -> float option
-    -> unit Lwt.t
+    -> unit
 
   val get_service_cookie_timeout : cookie:service_cookie_info -> timeout
   val get_volatile_data_cookie_timeout : cookie:data_cookie_info -> timeout
@@ -967,50 +963,40 @@ module Ext : sig
 
   val unset_persistent_data_cookie_timeout :
      cookie:persistent_cookie_info
-    -> unit Lwt.t
+    -> unit
 
   val get_session_group_list : unit -> string list
   (** Returns a list containing the names of all session group
       that are available for this site. *)
 
-  val iter_service_cookies : (service_cookie_info -> unit Lwt.t) -> unit Lwt.t
+  val iter_service_cookies : (service_cookie_info -> unit) -> unit
   (** Iterator on all active service cookies.
       [Lwt.pause] is called automatically after each iteration.
    *)
 
-  val iter_volatile_data_cookies :
-     (data_cookie_info -> unit Lwt.t)
-    -> unit Lwt.t
+  val iter_volatile_data_cookies : (data_cookie_info -> unit) -> unit
   (** Iterator on data cookies. [Lwt.pause] is called automatically
       after each iteration.
    *)
 
-  val iter_persistent_data_cookies :
-     (persistent_cookie_info -> unit Lwt.t)
-    -> unit Lwt.t
+  val iter_persistent_data_cookies : (persistent_cookie_info -> unit) -> unit
   (** Iterator on persistent cookies. [Lwt.pause] is called automatically
       after each iteration. *)
 
-  val fold_service_cookies :
-     (service_cookie_info -> 'b -> 'b Lwt.t)
-    -> 'b
-    -> 'b Lwt.t
+  val fold_service_cookies : (service_cookie_info -> 'b -> 'b) -> 'b -> 'b
   (** Iterator on service cookies. [Lwt.pause] is called automatically
       after each iteration.
   *)
 
-  val fold_volatile_data_cookies :
-     (data_cookie_info -> 'b -> 'b Lwt.t)
-    -> 'b
-    -> 'b Lwt.t
+  val fold_volatile_data_cookies : (data_cookie_info -> 'b -> 'b) -> 'b -> 'b
   (** Iterator on data cookies. [Lwt.pause] is called automatically
      after each iteration.
    *)
 
   val fold_persistent_data_cookies :
-     (persistent_cookie_info -> 'b -> 'b Lwt.t)
+     (persistent_cookie_info -> 'b -> 'b)
+    -> 'b
     -> 'b
-    -> 'b Lwt.t
   (** Iterator on persistent cookies. [Lwt.pause] is called automatically
      after each iteration. *)
 
@@ -1073,22 +1059,19 @@ val create_persistent_table :
    scope:Eliom_common.user_scope
   -> ?secure:bool
   -> string
-  -> 'a persistent_table Lwt.t
+  -> 'a persistent_table
 (** creates a table on hard disk where you can store the session data
     for all users. It uses {!Ocsipersist}.  (low level) *)
 
-val get_persistent_data :
-   table:'a persistent_table
-  -> unit
-  -> 'a state_data Lwt.t
+val get_persistent_data : table:'a persistent_table -> unit -> 'a state_data
 (** gets persistent session data for the current persistent session (if any).
     (low level) *)
 
-val set_persistent_data : table:'a persistent_table -> 'a -> unit Lwt.t
+val set_persistent_data : table:'a persistent_table -> 'a -> unit
 (** sets persistent session data for the current persistent session.
     (low level) *)
 
-val remove_persistent_data : table:'a persistent_table -> unit -> unit Lwt.t
+val remove_persistent_data : table:'a persistent_table -> unit -> unit
 (** removes session data for the current persistent session
     (but does not close the session).
     If the session does not exist, does nothing.
@@ -1170,7 +1153,7 @@ val get_persistent_data_cookie :
    cookie_scope:Eliom_common.cookie_scope
   -> ?secure:bool
   -> unit
-  -> Eliom_common.Hashed_cookies.t option Lwt.t
+  -> Eliom_common.Hashed_cookies.t option
 (** returns the hashed value of the Eliom's cookies for one persistent session.
     Returns [None] is no session is active.
  *)
@@ -1202,9 +1185,9 @@ val number_of_service_cookies : unit -> int
 val number_of_volatile_data_cookies : unit -> int
 val number_of_tables : unit -> int
 val number_of_table_elements : unit -> int list
-val number_of_persistent_data_cookies : unit -> int Lwt.t
+val number_of_persistent_data_cookies : unit -> int
 val number_of_persistent_tables : unit -> int
-val number_of_persistent_table_elements : unit -> (string * int) list Lwt.t
+val number_of_persistent_table_elements : unit -> (string * int) list
 (* Because of Dbm implementation, the result may be less than the expected
    result in some case (with a version of ocsipersist based on Dbm) *)
 
diff --git a/src/lib/eliom_tools.eliom b/src/lib/eliom_tools.eliom
index 172a2c65c1..1ae402f7a0 100644
--- a/src/lib/eliom_tools.eliom
+++ b/src/lib/eliom_tools.eliom
@@ -35,18 +35,18 @@ let string_prefix s1 s2 =
 
 type srv =
   | Srv :
-      ( unit
-        , unit
-        , Eliom_service.get
-        , _
-        , _
-        , _
-        , _
-        , [`WithoutSuffix]
-        , unit
-        , unit
-        , Eliom_service.non_ocaml )
-        Eliom_service.t
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t
       -> srv
 
 type 'a hierarchical_site_item = Disabled | Site_tree of 'a hierarchical_site
@@ -57,37 +57,37 @@ module type HTML5_TOOLS = sig
   (** {2 Simple menu } *)
 
   val menu :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> (( unit
-          , unit
-          , Eliom_service.get
-          , _
-          , _
-          , _
-          , _
-          , [`WithoutSuffix]
-          , unit
-          , unit
-          , Eliom_service.non_ocaml )
-          Eliom_service.t
-       * [< Html_types.flow5_without_interactive] Html.elt list)
-         list
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    (( unit,
+       unit,
+       Eliom_service.get,
+       _,
+       _,
+       _,
+       _,
+       [ `WithoutSuffix ],
+       unit,
+       unit,
+       Eliom_service.non_ocaml )
+     Eliom_service.t
+    * [< Html_types.flow5_without_interactive ] Html.elt list)
+    list ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt
   (** The function [menu elts ()], where [elts] is a list of pair
       [(service, content)], creates a list of link towards the
       [service]s. See the Eliom manual for an {% <<a_manual
@@ -105,25 +105,25 @@ module type HTML5_TOOLS = sig
   (** {2 Hierchical sites } *)
 
   val hierarchical_menu_depth_first :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> ?whole_tree:bool
-    -> [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt list
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    ?whole_tree:bool ->
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt list
   (** The function [hierarchical_menu_depth_first site ()] constructs
       a hieranrchical menu by exploring the hierarchical [site]
       description using a depth-first algorithm: the first menu item
@@ -140,24 +140,24 @@ module type HTML5_TOOLS = sig
       and [classe]. *)
 
   val hierarchical_menu_breadth_first :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt list
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt list
   (** The function [hierarchical_menu_breadth_first site ()]
       constructs a hierarchical menu by exploring the hierarchical
       [site] description using a breadth_first algorithm: the whole
@@ -172,22 +172,22 @@ module type HTML5_TOOLS = sig
       and [classe].  *)
 
   val structure_links :
-     [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Link] Html.elt list
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Link ] Html.elt list
   (** The function [structure_links site ()] returns the tags [<link
       rel="subsection" ...>] and [<link rev="subsection" ...>] for the
       given hierarchical [site].
@@ -197,24 +197,24 @@ module type HTML5_TOOLS = sig
       current service. *)
 
   val head :
-     title:string
-    -> ?css:string list list
-    -> ?js:string list list
-    -> ?other:[< Html_types.head_content_fun] Html.elt list
-    -> unit
-    -> [`Head] Html.elt
+    title:string ->
+    ?css:string list list ->
+    ?js:string list list ->
+    ?other:[< Html_types.head_content_fun ] Html.elt list ->
+    unit ->
+    [ `Head ] Html.elt
   (** An auxiliary function for creating an HTML head
       elements. Resources (JS, CSS) are taken from the static
       directory. *)
 
   val html :
-     title:string
-    -> ?a:[< Html_types.html_attrib] Html.attrib list
-    -> ?css:string list list
-    -> ?js:string list list
-    -> ?other_head:[< Html_types.head_content_fun] Html.elt list
-    -> Html_types.body Html.elt
-    -> Html_types.html Html.elt
+    title:string ->
+    ?a:[< Html_types.html_attrib ] Html.attrib list ->
+    ?css:string list list ->
+    ?js:string list list ->
+    ?other_head:[< Html_types.head_content_fun ] Html.elt list ->
+    Html_types.body Html.elt ->
+    Html_types.html Html.elt
 end
 
 let%server css_files =
@@ -257,8 +257,8 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
   let make_string_uri = Eliom_uri.make_string_uri
 
   let a_ul classes id level =
-    let classes = [a_class classes] in
-    match id, level with Some id, 0 -> a_id id :: classes | _ -> classes
+    let classes = [ a_class classes ] in
+    match (id, level) with Some id, 0 -> a_id id :: classes | _ -> classes
 
   let same_service_opt s sopt =
     let same_url url =
@@ -273,34 +273,36 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
     let l = (l :> (_ * flow5_without_interactive elt list) list) in
     let rec aux = function
       | [] -> []
-      | [(url, text)] ->
-          let classe = [last_class] in
-          let _ = li [a ~service:url text ()] in
-          if same_service_opt url current
-          then [li ~a:[a_class (current_class :: classe)] text]
-          else [li ~a:[a_class classe] [a ~service:url text ()]]
+      | [ (url, text) ] ->
+          let classe = [ last_class ] in
+          let _ = li [ a ~service:url text () ] in
+          if same_service_opt url current then
+            [ li ~a:[ a_class (current_class :: classe) ] text ]
+          else [ li ~a:[ a_class classe ] [ a ~service:url text () ] ]
       | (url, text) :: l ->
-          (if same_service_opt url current
-           then li ~a:[a_class [current_class]] text
-           else li [a ~service:url text ()])
+          (if same_service_opt url current then
+             li ~a:[ a_class [ current_class ] ] text
+           else li [ a ~service:url text () ])
           :: aux l
     in
     match l with
     | [] -> DorF.ul ~a:(a_ul (menu_class :: classe) id 0) []
-    | [(url, text)] ->
+    | [ (url, text) ] ->
         DorF.ul
           ~a:(a_ul (menu_class :: classe) id 0)
-          [ (let liclasse = [first_class; last_class] in
-             if same_service_opt url current
-             then li ~a:[a_class (current_class :: liclasse)] text
-             else li ~a:[a_class liclasse] [a ~service:url text ()]) ]
+          [
+            (let liclasse = [ first_class; last_class ] in
+             if same_service_opt url current then
+               li ~a:[ a_class (current_class :: liclasse) ] text
+             else li ~a:[ a_class liclasse ] [ a ~service:url text () ]);
+          ]
     | (url, text) :: l ->
         DorF.ul
           ~a:(a_ul (menu_class :: classe) id 0)
-          (let liclasse = [first_class] in
-           (if same_service_opt url current
-            then li ~a:[a_class (current_class :: liclasse)] text
-            else li ~a:[a_class liclasse] [a ~service:url text ()])
+          (let liclasse = [ first_class ] in
+           (if same_service_opt url current then
+              li ~a:[ a_class (current_class :: liclasse) ] text
+            else li ~a:[ a_class liclasse ] [ a ~service:url text () ])
            :: aux l)
 
   let service_prefix s sopt =
@@ -324,7 +326,7 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
             String.length (make_string_uri ~absolute_path:true ~service:s ())
           in
           let max =
-            if len >= max_len then len, List.rev (i :: prefix) else max
+            if len >= max_len then (len, List.rev (i :: prefix)) else max
           in
           let max = aux (i :: prefix) max 0 hsl in
           aux prefix max (i + 1) pages
@@ -341,101 +343,97 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
       | [] -> raise Not_found
       | (_, Site_tree (Main_page (Srv s), hsl)) :: _
         when same_service_opt s service -> (
-        try i :: aux service 0 hsl with Not_found -> [i])
+          try i :: aux service 0 hsl with Not_found -> [ i ])
       | (_, Disabled) :: l -> aux service (i + 1) l
       | (_, Site_tree (_, hsl)) :: l -> (
-        try i :: aux service 0 hsl with Not_found -> aux service (i + 1) l)
+          try i :: aux service 0 hsl with Not_found -> aux service (i + 1) l)
     in
     try aux service 0 pages
     with Not_found -> find_longest_prefix_in_hierarchy service (main, pages)
 
   let hierarchical_menu_depth_first ?(classe = []) ?id ?(whole_tree = false)
-      ((_page, pages) as the_menu) ?service ()
-    =
-    let rec depth_first_fun pages level pos : [`Ul] elt list =
+      ((_page, pages) as the_menu) ?service () =
+    let rec depth_first_fun pages level pos : [ `Ul ] elt list =
       let rec one_item first last i s =
         let s = (s :> flow5_without_interactive elt list * _) in
         let classe, pos2, deplier =
           match pos with
-          | [] -> [], [], false
-          | [a] when a = i -> [current_class], [], true
-          | a :: l when a = i -> [current_path_class], l, true
-          | _ :: _ -> [], [], false
+          | [] -> ([], [], false)
+          | [ a ] when a = i -> ([ current_class ], [], true)
+          | a :: l when a = i -> ([ current_path_class ], l, true)
+          | _ :: _ -> ([], [], false)
         in
         let classe = if last then last_class :: classe else classe in
         let classe = if first then first_class :: classe else classe in
-        let attclass = if classe = [] then [] else [a_class classe] in
+        let attclass = if classe = [] then [] else [ a_class classe ] in
         match s with
         | text, Site_tree (Default_page (Srv page), []) ->
-            li ~a:attclass [a ~service:page text ()]
+            li ~a:attclass [ a ~service:page text () ]
         | text, Site_tree (Main_page (Srv page), []) ->
-            li ~a:attclass [a ~service:page text ()]
+            li ~a:attclass [ a ~service:page text () ]
         | text, Site_tree (Not_clickable, []) -> li ~a:attclass text
-        | text, Disabled -> li ~a:[a_class (disabled_class :: classe)] text
+        | text, Disabled -> li ~a:[ a_class (disabled_class :: classe) ] text
         | text, Site_tree (Default_page (Srv page), hsl) ->
             li ~a:attclass
               (a ~service:page text ()
               ::
-              (if deplier || whole_tree
-               then
+              (if deplier || whole_tree then
                  (depth_first_fun hsl (level + 1) pos2
-                   : [`Ul] elt list
-                   :> [< li_content > `Ul] elt list)
+                   : [ `Ul ] elt list
+                   :> [< li_content > `Ul ] elt list)
                else []))
         | text, Site_tree (Main_page (Srv page), hsl) ->
             li ~a:attclass
               (a ~service:page text ()
               ::
-              (if deplier || whole_tree
-               then
+              (if deplier || whole_tree then
                  (depth_first_fun hsl (level + 1) pos2 :> li_content elt list)
                else []))
         | text, Site_tree (Not_clickable, hsl) ->
             li ~a:attclass
               ((text :> li_content elt list)
               @
-              if deplier || whole_tree
-              then (depth_first_fun hsl (level + 1) pos2 :> li_content elt list)
+              if deplier || whole_tree then
+                (depth_first_fun hsl (level + 1) pos2 :> li_content elt list)
               else [])
       and one_menu first i = function
         | [] -> []
-        | [a] -> [one_item first true i a]
+        | [ a ] -> [ one_item first true i a ]
         | a :: l -> one_item first false i a :: one_menu false (i + 1) l
       in
       let classe = (level_class ^ string_of_int level) :: classe in
       let ul = if level = 0 then DorF.ul else ul in
-      [ul ~a:(a_ul (menu_class :: classe) id level) (one_menu true 0 pages)]
+      [ ul ~a:(a_ul (menu_class :: classe) id level) (one_menu true 0 pages) ]
     in
     (depth_first_fun pages 0 (find_in_hierarchy service the_menu)
-      : [`Ul] elt list
-      :> [> `Ul] elt list)
+      : [ `Ul ] elt list
+      :> [> `Ul ] elt list)
 
   let hierarchical_menu_breadth_first ?(classe = []) ?id
-      ((_page, pages) as the_menu) ?service ()
-    =
-    let rec breadth_first_fun pages level pos : [`Ul] elt list =
+      ((_page, pages) as the_menu) ?service () =
+    let rec breadth_first_fun pages level pos : [ `Ul ] elt list =
       let rec one_item first last i s =
         let s = (s :> flow5_without_interactive elt list * _) in
         let classe, _pos2, _deplier =
           match pos with
-          | [] -> [], [], false
-          | [a] when a = i -> [current_class], [], true
-          | a :: l when a = i -> [current_path_class], l, true
-          | _ :: l -> [], l, false
+          | [] -> ([], [], false)
+          | [ a ] when a = i -> ([ current_class ], [], true)
+          | a :: l when a = i -> ([ current_path_class ], l, true)
+          | _ :: l -> ([], l, false)
         in
         let classe = if last then last_class :: classe else classe in
         let classe = if first then first_class :: classe else classe in
-        let attclass = if classe = [] then [] else [a_class classe] in
+        let attclass = if classe = [] then [] else [ a_class classe ] in
         match s with
         | text, Site_tree (Default_page (Srv page), _) ->
-            li ~a:attclass [a ~service:page text ()]
+            li ~a:attclass [ a ~service:page text () ]
         | text, Site_tree (Main_page (Srv page), _) ->
-            li ~a:attclass [a ~service:page text ()]
+            li ~a:attclass [ a ~service:page text () ]
         | text, Site_tree (Not_clickable, _) -> li ~a:attclass text
-        | text, Disabled -> li ~a:[a_class (disabled_class :: classe)] text
+        | text, Disabled -> li ~a:[ a_class (disabled_class :: classe) ] text
       and one_menu first i = function
         | [] -> []
-        | [a] -> [one_item first true i a]
+        | [ a ] -> [ one_item first true i a ]
         | a :: l -> one_item first false i a :: one_menu false (i + 1) l
       and submenu i pos pages =
         match snd (List.nth pages i) with
@@ -448,8 +446,8 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
       ul ~a:(a_ul (menu_class :: classe) id level) (one_menu true 0 pages) :: l
     in
     (breadth_first_fun pages 0 (find_in_hierarchy service the_menu)
-      : [`Ul] elt list
-      :> [> `Ul] elt list)
+      : [ `Ul ] elt list
+      :> [> `Ul ] elt list)
 
   let structure_links (default, pages) ?service () =
     let make_rev s endlist =
@@ -457,12 +455,12 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
       match s with
       | None -> endlist
       | Some (Srv s) ->
-          link ~rel:[`Next] (* ?? *) ~href:(make_uri ~service:s ()) ()
+          link ~rel:[ `Next ] (* ?? *) ~href:(make_uri ~service:s ()) ()
           :: endlist
     in
     let make_rel s =
       (* s is a subsection of mine *)
-      link ~rel:[`Next] ~href:(make_uri ~service:s ()) ()
+      link ~rel:[ `Next ] ~href:(make_uri ~service:s ()) ()
     in
     let make_rels beg a =
       match snd a with
@@ -479,15 +477,14 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
         when same_service_opt page service ->
           make_rev parent (List.fold_left make_rels [] hsl)
       | (_, Site_tree (Main_page page, hsl)) :: l -> (
-        try create_rev (Some page) hsl with Not_found -> create_rev parent l)
+          try create_rev (Some page) hsl with Not_found -> create_rev parent l)
       | (_, Site_tree (_, hsl)) :: l -> (
-        try create_rev None hsl with Not_found -> create_rev parent l)
+          try create_rev None hsl with Not_found -> create_rev parent l)
     in
     try
       match default with
       | Main_page (Srv def as def') ->
-          if same_service_opt def service
-          then List.fold_left make_rels [] pages
+          if same_service_opt def service then List.fold_left make_rels [] pages
           else create_rev (Some def') pages
       | _ -> create_rev None pages
     with Not_found -> []
@@ -500,7 +497,7 @@ module Make (DorF : module type of Eliom_content.Html.F) : HTML5_TOOLS = struct
     in
     let mk_js_script path =
       let uri = make_uri ~service:(Eliom_service.static_dir ()) path in
-      js_script ~a:[a_defer ()] ~uri ()
+      js_script ~a:[ a_defer () ] ~uri ()
     in
     DorF.head
       (title (txt ttl))
@@ -521,6 +518,6 @@ module F = Make (Html.F)
 module D = Make (Html.D)
 
 let wrap_handler information none some get post =
-  Lwt.bind (information ()) (function
-    | None -> none get post
-    | Some value -> some value get post)
+  match information () with
+  | None -> none get post
+  | Some value -> some value get post
diff --git a/src/lib/eliom_tools.eliomi b/src/lib/eliom_tools.eliomi
index a2bb328c1f..a688db4500 100644
--- a/src/lib/eliom_tools.eliomi
+++ b/src/lib/eliom_tools.eliomi
@@ -27,18 +27,18 @@ open Eliom_content
 
 type srv =
   | Srv :
-      ( unit
-        , unit
-        , Eliom_service.get
-        , _
-        , _
-        , _
-        , _
-        , [`WithoutSuffix]
-        , unit
-        , unit
-        , Eliom_service.non_ocaml )
-        Eliom_service.t
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t
       -> srv
 
 type 'a hierarchical_site = main_page * ('a * 'a hierarchical_site_item) list
@@ -52,16 +52,16 @@ and 'a hierarchical_site_item = Disabled | Site_tree of 'a hierarchical_site
 (** Main page description for a section of a hierarchical site. *)
 and main_page =
   | Main_page of srv
-  (** Main page for your subsite: all the subpages are subsections of
+      (** Main page for your subsite: all the subpages are subsections of
       that page. *)
   | Default_page of srv
-  (** Like [Main_page] but is not taken into account for computing
+      (** Like [Main_page] but is not taken into account for computing
       which is the current page in the menu. Use it for example when
       there is no main page, but you want one of the subpages to be
       the default page for your subsite.  The service you use as
       default page must appear another time in the subtree! *)
   | Not_clickable
-  (** When you do not want the menu entry to be a link but you want
+      (** When you do not want the menu entry to be a link but you want
       subpages. *)
 
 (** {2 Tools for generating certain HTML elements} *)
@@ -73,37 +73,37 @@ module type HTML5_TOOLS = sig
   (** {2 Simple menu } *)
 
   val menu :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> (( unit
-          , unit
-          , Eliom_service.get
-          , _
-          , _
-          , _
-          , _
-          , [`WithoutSuffix]
-          , unit
-          , unit
-          , Eliom_service.non_ocaml )
-          Eliom_service.t
-       * [< Html_types.flow5_without_interactive] Html.elt list)
-         list
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    (( unit,
+       unit,
+       Eliom_service.get,
+       _,
+       _,
+       _,
+       _,
+       [ `WithoutSuffix ],
+       unit,
+       unit,
+       Eliom_service.non_ocaml )
+     Eliom_service.t
+    * [< Html_types.flow5_without_interactive ] Html.elt list)
+    list ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt
   (** The function [menu elts ()], where [elts] is a list of pair
       [(service, content)], creates a list of link towards the
       [service]s. See the Eliom manual for an {% <<a_manual
@@ -121,25 +121,25 @@ module type HTML5_TOOLS = sig
   (** {2 Hierchical sites } *)
 
   val hierarchical_menu_depth_first :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> ?whole_tree:bool
-    -> [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt list
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    ?whole_tree:bool ->
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt list
   (** The function [hierarchical_menu_depth_first site ()] constructs
       a hieranrchical menu by exploring the hierarchical [site]
       description using a depth-first algorithm: the first menu item
@@ -156,24 +156,24 @@ module type HTML5_TOOLS = sig
       and [classe]. *)
 
   val hierarchical_menu_breadth_first :
-     ?classe:Html_types.nmtoken list
-    -> ?id:string
-    -> [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Ul] Html.elt list
+    ?classe:Html_types.nmtoken list ->
+    ?id:string ->
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Ul ] Html.elt list
   (** The function [hierarchical_menu_breadth_first site ()]
       constructs a hierarchical menu by exploring the hierarchical
       [site] description using a breadth_first algorithm: the whole
@@ -188,22 +188,22 @@ module type HTML5_TOOLS = sig
       and [classe].  *)
 
   val structure_links :
-     [< Html_types.a_content] Html.elt list hierarchical_site
-    -> ?service:
-         ( unit
-           , unit
-           , Eliom_service.get
-           , _
-           , _
-           , _
-           , _
-           , [`WithoutSuffix]
-           , unit
-           , unit
-           , Eliom_service.non_ocaml )
-           Eliom_service.t
-    -> unit
-    -> [> `Link] Html.elt list
+    [< Html_types.a_content ] Html.elt list hierarchical_site ->
+    ?service:
+      ( unit,
+        unit,
+        Eliom_service.get,
+        _,
+        _,
+        _,
+        _,
+        [ `WithoutSuffix ],
+        unit,
+        unit,
+        Eliom_service.non_ocaml )
+      Eliom_service.t ->
+    unit ->
+    [> `Link ] Html.elt list
   (** The function [structure_links site ()] returns the tags [<link
       rel="subsection" ...>] and [<link rev="subsection" ...>] for the
       given hierarchical [site].
@@ -213,24 +213,24 @@ module type HTML5_TOOLS = sig
       current service. *)
 
   val head :
-     title:string
-    -> ?css:string list list
-    -> ?js:string list list
-    -> ?other:[< Html_types.head_content_fun] Html.elt list
-    -> unit
-    -> [`Head] Html.elt
+    title:string ->
+    ?css:string list list ->
+    ?js:string list list ->
+    ?other:[< Html_types.head_content_fun ] Html.elt list ->
+    unit ->
+    [ `Head ] Html.elt
   (** An auxiliary function for creating an HTML head
       elements. Resources (JS, CSS) are taken from the static
       directory. *)
 
   val html :
-     title:string
-    -> ?a:[< Html_types.html_attrib] Html.attrib list
-    -> ?css:string list list
-    -> ?js:string list list
-    -> ?other_head:[< Html_types.head_content_fun] Html.elt list
-    -> [`Body] Html.elt
-    -> [`Html] Html.elt
+    title:string ->
+    ?a:[< Html_types.html_attrib ] Html.attrib list ->
+    ?css:string list list ->
+    ?js:string list list ->
+    ?other_head:[< Html_types.head_content_fun ] Html.elt list ->
+    [ `Body ] Html.elt ->
+    [ `Html ] Html.elt
 end
 
 module F : HTML5_TOOLS
@@ -249,12 +249,12 @@ val with_css_file : string list -> unit
 (** {2 Other tools} *)
 
 val wrap_handler :
-   (unit -> 'a option Lwt.t)
-  -> ('get -> 'post -> 'res Lwt.t)
-  -> ('a -> 'get -> 'post -> 'res Lwt.t)
-  -> 'get
-  -> 'post
-  -> 'res Lwt.t
+  (unit -> 'a option) ->
+  ('get -> 'post -> 'res) ->
+  ('a -> 'get -> 'post -> 'res) ->
+  'get ->
+  'post ->
+  'res
 (** This function allows one to wrap a service handler easily depending
     on whether certain information is available or not.
 
diff --git a/src/lib/server/dune b/src/lib/server/dune
index 5d9de4f93b..59567d6639 100644
--- a/src/lib/server/dune
+++ b/src/lib/server/dune
@@ -17,7 +17,7 @@
    (:include type_includes)))
  (library_flags
   (:standard -linkall))
- (libraries lwt_react ocsigenserver logs ocsipersist tyxml))
+ (libraries lwt_react ocsigenserver logs ocsipersist tyxml eio eio.unix))
 
 (include dune.server)
 
diff --git a/src/lib/server/eliommod.ml b/src/lib/server/eliommod.ml
index 3a8fed3ada..234eabebea 100644
--- a/src/lib/server/eliommod.ml
+++ b/src/lib/server/eliommod.ml
@@ -759,7 +759,7 @@ let load_eliom_module _sitedata cmo_or_name parent_tag content =
 (* If page has already been generated becauise there are several <eliom>
    tags in the same site:
 *)
-let gen_nothing () _ = Lwt.return Ocsigen_extensions.Ext_do_nothing
+let gen_nothing () _ = Ocsigen_extensions.Ext_do_nothing
 
 (*****************************************************************************)
 let default_module_action _ = failwith "default_module_action"
diff --git a/src/lib/server/eliommod.mli b/src/lib/server/eliommod.mli
index 2074431bce..98820fed77 100644
--- a/src/lib/server/eliommod.mli
+++ b/src/lib/server/eliommod.mli
@@ -162,7 +162,7 @@ val load_eliom_module :
   -> Xml_light_types.xml list
   -> unit
 
-val gen_nothing : unit -> 'a -> Ocsigen_extensions.answer Lwt.t
+val gen_nothing : unit -> 'a -> Ocsigen_extensions.answer
 val default_module_action : 'a -> 'b
 
 val set_timeout :
@@ -189,4 +189,4 @@ val parse_config :
   -> 'c
   -> Xml_light_types.xml
   -> Ocsigen_extensions.request_state
-  -> Ocsigen_extensions.answer Lwt.t
+  -> Ocsigen_extensions.answer
diff --git a/src/lib/server/eliommod_cookies.ml b/src/lib/server/eliommod_cookies.ml
index d6d002f2b7..de9ed6c15a 100644
--- a/src/lib/server/eliommod_cookies.ml
+++ b/src/lib/server/eliommod_cookies.ml
@@ -21,7 +21,6 @@
 open Eliom_lib
 (** Cookie management                                                       *)
 
-open Lwt
 include Eliom_cookies_base
 
 (*****************************************************************************)
@@ -90,7 +89,7 @@ module Persistent_cookies = struct
 
     let remove_cookie exp_o cookie =
       match exp_o with
-      | None -> Lwt.return_unit
+      | None -> ()
       | Some exp -> (
           modify_opt exp @@ function
           | None -> None
@@ -101,16 +100,20 @@ module Persistent_cookies = struct
   end
 
   let add cookie ({expiry; _} as content) =
-    (match expiry with
+    let _ =
+      match expiry with
       | Some t -> Expiry_dates.add_cookie t cookie
-      | None -> Lwt.return_unit)
-    >>= fun _ -> Cookies.add cookie content
+      | None -> ()
+    in
+    Cookies.add cookie content
 
   let replace_if_exists cookie ({expiry; _} as content) =
-    (match expiry with
+    let _ =
+      match expiry with
       | Some t -> Expiry_dates.add_cookie t cookie
-      | None -> Lwt.return_unit)
-    >>= fun _ -> Cookies.replace_if_exists cookie content
+      | None -> ()
+    in
+    Cookies.replace_if_exists cookie content
 
   let garbage_collect ~section gc_cookie =
     let now = Unix.time () in
@@ -121,7 +124,8 @@ module Persistent_cookies = struct
     in
     Logs.info ~src:section (fun fmt ->
       fmt "potentially expired cookies %.0f: %s" date cookies_log);
-    Lwt_list.iter_s gc_cookie cookies >>= fun _ -> Expiry_dates.remove date
+    let _ = List.iter gc_cookie cookies in
+    Expiry_dates.remove date
 end
 
 (*****************************************************************************)
@@ -258,95 +262,88 @@ let get_cookie_info
     Eliom_common.Full_state_name_table.map
       (fun value ->
          lazy
-           (catch
-              (fun () ->
-                 let hvalue = Eliom_common.Hashed_cookies.hash value in
-                 let hvalue_string =
-                   Eliom_common.Hashed_cookies.to_string hvalue
-                 in
-                 Persistent_cookies.Cookies.find
-                   (Eliom_common.Hashed_cookies.to_string hvalue)
-                 >>=
-                 fun { expiry = persexp
-                     ; timeout = perstimeout
-                     ; session_group = sessgrp
-                     ; _ } ->
-                 Eliommod_sessiongroups.Pers.up hvalue_string sessgrp
-                 >>= fun () ->
-                 match persexp with
-                 | Some t when t < now ->
-                     (* session expired by timeout *)
-                     Eliom_common.Persistent_tables.remove_key_from_all_tables
-                       hvalue_string
-                     >>= fun () ->
-                     return
-                       ( Some
-                           ( value
-                             (* value at the beginning
+           (try
+              let hvalue = Eliom_common.Hashed_cookies.hash value in
+              let hvalue_string =
+                Eliom_common.Hashed_cookies.to_string hvalue
+              in
+              let { expiry = persexp
+                  ; timeout = perstimeout
+                  ; session_group = sessgrp
+                  ; _ }
+                =
+                Persistent_cookies.Cookies.find
+                  (Eliom_common.Hashed_cookies.to_string hvalue)
+              in
+              Eliommod_sessiongroups.Pers.up hvalue_string sessgrp;
+              match persexp with
+              | Some t when t < now ->
+                  (* session expired by timeout *)
+                  Eliom_common.Persistent_tables.remove_key_from_all_tables
+                    hvalue_string;
+                  ( Some
+                      ( value
+                        (* value at the beginning
                                                  of the request *)
-                           , perstimeout
-                             (* user persistent timeout
+                      , perstimeout
+                        (* user persistent timeout
                                                  at the beginning
                                                  of the request *)
-                           , persexp
-                             (* expiration date (server)
+                      , persexp
+                        (* expiration date (server)
                                                  at the beginning
                                                  of the request *)
-                           , sessgrp (* session group at beginning *) )
-                       , ref Eliom_common.SCData_session_expired
-                         (* ask the browser to
+                      , sessgrp (* session group at beginning *) )
+                  , ref Eliom_common.SCData_session_expired
+                    (* ask the browser to
                                                  remove the cookie *)
-                       )
-                 | _ ->
-                     return
-                       ( Some
-                           ( value
-                             (* value at the beginning
+                  )
+              | _ ->
+                  ( Some
+                      ( value
+                        (* value at the beginning
                                               of the request *)
-                           , perstimeout
-                             (* user persistent timeout
+                      , perstimeout
+                        (* user persistent timeout
                                               at the beginning
                                               of the request *)
-                           , persexp
-                             (* expiration date (server)
+                      , persexp
+                        (* expiration date (server)
                                               at the beginning
                                               of the request *)
-                           , sessgrp (* session group at beginning *) )
-                       , ref
-                           (Eliom_common.SC
-                              { Eliom_common.pc_hvalue = hvalue (* value *)
-                              ; Eliom_common.pc_set_value = None
-                              ; Eliom_common.pc_timeout =
-                                  ref perstimeout
-                                  (* user persistent timeout ref *)
-                              ; Eliom_common.pc_cookie_exp =
-                                  ref Eliom_common.CENothing
-                                  (* persistent cookie expiration
+                      , sessgrp (* session group at beginning *) )
+                  , ref
+                      (Eliom_common.SC
+                         { Eliom_common.pc_hvalue = hvalue (* value *)
+                         ; Eliom_common.pc_set_value = None
+                         ; Eliom_common.pc_timeout =
+                             ref perstimeout (* user persistent timeout ref *)
+                         ; Eliom_common.pc_cookie_exp =
+                             ref Eliom_common.CENothing
+                             (* persistent cookie expiration
                                     date ref to send to the browser:
                                     We don't change it *)
-                              ; Eliom_common.pc_session_group = ref sessgrp })
-                       ))
-              (function
-                | Not_found ->
-                    return
-                      ( Some
-                          ( value
-                            (* value at the beginning
+                         ; Eliom_common.pc_session_group = ref sessgrp }) )
+            with
+           | Not_found ->
+               ( Some
+                   ( value
+                     (* value at the beginning
                                              of the request *)
-                          , Eliom_common.TGlobal
-                            (* user persistent timeout
+                   , Eliom_common.TGlobal
+                     (* user persistent timeout
                                              at the beginning
                                              of the request *)
-                          , Some 0.
-                            (* expiration date (server)
+                   , Some 0.
+                     (* expiration date (server)
                                              at the beginning
                                              of the request *)
-                          , None (* session group at beginning *) )
-                      , ref Eliom_common.SCData_session_expired
-                        (* ask the browser
+                   , None (* session group at beginning *) )
+               , ref Eliom_common.SCData_session_expired
+                 (* ask the browser
                                              to remove the cookie *)
-                      )
-                | e -> fail e)))
+               )
+           | e -> raise e))
       persistent_cookies
     (* the persistent cookies sent by the request *)
   in
@@ -384,104 +381,96 @@ let compute_session_cookies_to_send
       (endlist : Ocsigen_cookie_map.t)
   =
   let getservvexp (old, newi) =
-    return
-      (let newinfo =
-         match !newi with
-         | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired -> None
-         | Eliom_common.SC c ->
-             Some
-               ( c.Eliom_common.sc_hvalue
-               , c.Eliom_common.sc_set_value
-               , !(c.Eliom_common.sc_cookie_exp) )
-       in
-       old, newinfo)
+    let newinfo =
+      match !newi with
+      | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired -> None
+      | Eliom_common.SC c ->
+          Some
+            ( c.Eliom_common.sc_hvalue
+            , c.Eliom_common.sc_set_value
+            , !(c.Eliom_common.sc_cookie_exp) )
+    in
+    old, newinfo
   in
   let getdatavexp v =
     if Lazy.is_val v
     then
-      return
-        (let old, newi = Lazy.force v in
-         let newinfo =
-           match !newi with
-           | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired ->
-               None
-           | Eliom_common.SC c ->
-               Some
-                 ( c.Eliom_common.dc_hvalue
-                 , c.Eliom_common.dc_set_value
-                 , !(c.Eliom_common.dc_cookie_exp) )
-         in
-         old, newinfo)
-    else fail Not_found
+      let old, newi = Lazy.force v in
+      let newinfo =
+        match !newi with
+        | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired -> None
+        | Eliom_common.SC c ->
+            Some
+              ( c.Eliom_common.dc_hvalue
+              , c.Eliom_common.dc_set_value
+              , !(c.Eliom_common.dc_cookie_exp) )
+      in
+      old, newinfo
+    else raise Not_found
   in
   let getpersvexp v =
     if Lazy.is_val v
     then
-      Lazy.force v >>= fun (old, newi) ->
-      return
-        (let oldinfo =
-           match old with None -> None | Some (v, _, _, _) -> Some v
-         in
-         let newinfo =
-           match !newi with
-           | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired ->
-               None
-           | Eliom_common.SC c ->
-               Some
-                 ( c.Eliom_common.pc_hvalue
-                 , c.Eliom_common.pc_set_value
-                 , !(c.Eliom_common.pc_cookie_exp) )
-         in
-         oldinfo, newinfo)
-    else fail Not_found
+      let old, newi = Lazy.force v in
+      let oldinfo =
+        match old with None -> None | Some (v, _, _, _) -> Some v
+      in
+      let newinfo =
+        match !newi with
+        | Eliom_common.SCNo_data | Eliom_common.SCData_session_expired -> None
+        | Eliom_common.SC c ->
+            Some
+              ( c.Eliom_common.pc_hvalue
+              , c.Eliom_common.pc_set_value
+              , !(c.Eliom_common.pc_cookie_exp) )
+      in
+      oldinfo, newinfo
+    else raise Not_found
   in
   let ch_exp = function
     | Eliom_common.CENothing | Eliom_common.CEBrowser -> None
     | Eliom_common.CESome a -> Some a
   in
   let aux f cookiekind secure tab2 cooktab =
-    cooktab >>= fun cooktab ->
+    let cooktab = cooktab in
     Eliom_common.Full_state_name_table.fold
       (fun full_st_name value beg ->
-         beg >>= fun beg ->
-         catch
-           (fun () ->
-              f value >>= fun (old, newc) ->
-              return
-                (match old, newc with
-                | None, None -> beg
-                | Some _, None ->
-                    Ocsigen_cookie_map.add
-                      ~path:(Eliom_common.get_site_dir sitedata)
-                      (Eliom_common.make_full_cookie_name cookiekind
-                         full_st_name)
-                      OUnset beg
-                (* the path is always site_dir because the cookie cannot
+         let beg = beg in
+         try
+           let old, newc = f value in
+           match old, newc with
+           | None, None -> beg
+           | Some _, None ->
+               Ocsigen_cookie_map.add
+                 ~path:(Eliom_common.get_site_dir sitedata)
+                 (Eliom_common.make_full_cookie_name cookiekind full_st_name)
+                 OUnset beg
+           (* the path is always site_dir because the cookie cannot
                  have been unset by a service outside
                  this site directory *)
-                | _, Some (_, Some v, exp) ->
-                    (* New value *)
-                    Ocsigen_cookie_map.add
-                      ~path:(Eliom_common.get_site_dir sitedata)
-                      (Eliom_common.make_full_cookie_name cookiekind
-                         full_st_name)
-                      (OSet (ch_exp exp, v, secure))
-                      beg
-                | Some oldv, Some (_, None, exp) ->
-                    if exp = Eliom_common.CENothing
-                    then beg
-                    else
-                      Ocsigen_cookie_map.add
-                        ~path:(Eliom_common.get_site_dir sitedata)
-                        (Eliom_common.make_full_cookie_name cookiekind
-                           full_st_name)
-                        (OSet (ch_exp exp, oldv, secure))
-                        beg
-                | None, Some (_, None, _) ->
-                    (* Should not happen *)
-                    beg))
-           (function Not_found -> return beg | e -> fail e))
-      tab2 (return cooktab)
+           | _, Some (_, Some v, exp) ->
+               (* New value *)
+               Ocsigen_cookie_map.add
+                 ~path:(Eliom_common.get_site_dir sitedata)
+                 (Eliom_common.make_full_cookie_name cookiekind full_st_name)
+                 (OSet (ch_exp exp, v, secure))
+                 beg
+           | Some oldv, Some (_, None, exp) ->
+               if exp = Eliom_common.CENothing
+               then beg
+               else
+                 Ocsigen_cookie_map.add
+                   ~path:(Eliom_common.get_site_dir sitedata)
+                   (Eliom_common.make_full_cookie_name cookiekind full_st_name)
+                   (OSet (ch_exp exp, oldv, secure))
+                   beg
+           | None, Some (_, None, _) ->
+               (* Should not happen *)
+               beg
+         with
+         | Not_found -> beg
+         | e -> raise e)
+      tab2 cooktab
   in
   aux getpersvexp Eliom_common.persistentcookiename false !pers_cookies_info
     (aux getdatavexp Eliom_common.datacookiename false !data_cookie_info
@@ -494,7 +483,7 @@ let compute_session_cookies_to_send
              !pers_cookies_info
              (aux getdatavexp Eliom_common.datacookiename true !data_cookie_info
                 (aux getservvexp Eliom_common.servicecookiename true
-                   !service_cookie_info (return endlist))))))
+                   !service_cookie_info endlist)))))
 
 let compute_cookies_to_send = compute_session_cookies_to_send
 
@@ -532,7 +521,7 @@ let compute_new_ri_cookies
       (ricookies : string Ocsigen_cookie_map.Map_inner.t)
       ((ci, secure_ci) : Eliom_common.tables Eliom_common.cookie_info)
       (cookies_set_by_page : Ocsigen_cookie_map.t) :
-  string Ocsigen_cookie_map.Map_inner.t Lwt.t
+  string Ocsigen_cookie_map.Map_inner.t
   =
   (* first we add cookies set by page: *)
   let ric = compute_new_ri_cookies' now ripath ricookies cookies_set_by_page in
@@ -591,22 +580,22 @@ let compute_new_ri_cookies
                Eliom_common.make_full_cookie_name
                  Eliom_common.persistentcookiename full_st_name
              in
-             beg >>= fun beg ->
+             let beg = beg in
              if Lazy.is_val v
              then
-               Lazy.force v >>= fun (_, v) ->
+               let _, v = Lazy.force v in
                match !v with
                | Eliom_common.SCData_session_expired | Eliom_common.SCNo_data ->
-                   Lwt.return (Ocsigen_cookie_map.Map_inner.remove n beg)
+                   Ocsigen_cookie_map.Map_inner.remove n beg
                | Eliom_common.SC {Eliom_common.pc_set_value = Some v; _} ->
-                   Lwt.return (Ocsigen_cookie_map.Map_inner.add n v beg)
-               | Eliom_common.SC {Eliom_common.pc_set_value = None; _} ->
-                   Lwt.return beg
-             else return beg)
-        !pers_cookie_info (Lwt.return ric)
+                   Ocsigen_cookie_map.Map_inner.add n v beg
+               | Eliom_common.SC {Eliom_common.pc_set_value = None; _} -> beg
+             else beg)
+        !pers_cookie_info ric
     in
     ric
   in
-  f false ci ric >>= fun ric -> f true secure_ci ric
+  let ric = f false ci ric in
+  f true secure_ci ric
 (*VVV We always keep secure cookies, even if the protocol is not secure,
   because this function is for actions only. Is that right? *)
diff --git a/src/lib/server/eliommod_cookies.mli b/src/lib/server/eliommod_cookies.mli
index dcc3824cef..a1d14ef762 100644
--- a/src/lib/server/eliommod_cookies.mli
+++ b/src/lib/server/eliommod_cookies.mli
@@ -43,13 +43,13 @@ val compute_session_cookies_to_send :
    Eliom_common.sitedata
   -> Eliom_common.tables Eliom_common.cookie_info
   -> Ocsigen_cookie_map.t
-  -> Ocsigen_cookie_map.t Lwt.t
+  -> Ocsigen_cookie_map.t
 
 val compute_cookies_to_send :
    Eliom_common.sitedata
   -> Eliom_common.tables Eliom_common.cookie_info
   -> Ocsigen_cookie_map.t
-  -> Ocsigen_cookie_map.t Lwt.t
+  -> Ocsigen_cookie_map.t
 
 val compute_new_ri_cookies :
    float
@@ -57,7 +57,7 @@ val compute_new_ri_cookies :
   -> string Ocsigen_cookie_map.Map_inner.t
   -> Eliom_common.tables Eliom_common.cookie_info
   -> Ocsigen_cookie_map.t
-  -> string Ocsigen_cookie_map.Map_inner.t Lwt.t
+  -> string Ocsigen_cookie_map.Map_inner.t
 
 type date = float
 
@@ -74,15 +74,11 @@ module Persistent_cookies : sig
   module Expiry_dates : sig
     include Ocsipersist.TABLE with type key = date and type value = string
 
-    val add_cookie : date -> string -> unit Lwt.t
-    val remove_cookie : date option -> string -> unit Lwt.t
+    val add_cookie : date -> string -> unit
+    val remove_cookie : date option -> string -> unit
   end
 
-  val add : string -> cookie -> unit Lwt.t
-  val replace_if_exists : string -> cookie -> unit Lwt.t
-
-  val garbage_collect :
-     section:Logs.src
-    -> (Cookies.key -> unit Lwt.t)
-    -> unit Lwt.t
+  val add : string -> cookie -> unit
+  val replace_if_exists : string -> cookie -> unit
+  val garbage_collect : section:Logs.src -> (Cookies.key -> unit) -> unit
 end
diff --git a/src/lib/server/eliommod_gc.ml b/src/lib/server/eliommod_gc.ml
index f686e2e59f..58f010ebc4 100644
--- a/src/lib/server/eliommod_gc.ml
+++ b/src/lib/server/eliommod_gc.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -25,7 +25,6 @@ open Lwt.Syntax
 let section = Logs.Src.create "eliom:gc"
 
 open Eliom_lib
-open Lwt
 
 (*****************************************************************************)
 let servicesessiongcfrequency = ref (Some 1200.) (* 20 min ? *)
@@ -41,12 +40,12 @@ let get_persistentsessiongcfrequency () = !persistentsessiongcfrequency
 (* garbage collection of timeouted sessions *)
 let gc_timeouted_services now tables =
   let rec aux t filename direltr thr =
-    thr >>= fun () ->
+    thr;
     (* we wait for the previous one to be completed *)
     match !direltr with
-    | Eliom_common.Dir r ->
-        empty_one r >>= fun () ->
-        (match !r with
+    | Eliom_common.Dir r -> (
+        empty_one r;
+        match !r with
         | Eliom_common.Vide -> (
           match !t with
           | Eliom_common.Vide -> ()
@@ -55,13 +54,12 @@ let gc_timeouted_services now tables =
               if String.Table.is_empty newr
               then t := Eliom_common.Vide
               else t := Eliom_common.Table newr)
-        | _ -> ());
-        Lwt.return_unit
-    | Eliom_common.File ptr ->
+        | _ -> ())
+    | Eliom_common.File ptr -> (
         Eliom_common.Serv_Table.fold
           (*VVV not tail recursive: may be a problem if lots of coservices *)
           (fun ptk (`Ptc (nodeopt, l)) thr ->
-             let* _ = thr in
+             let _ = thr in
              (* we wait for the previous one to be completed *)
              (match nodeopt, l with
              | Some node, {Eliom_common.s_expire = Some (_, e); _} :: _
@@ -98,58 +96,49 @@ let gc_timeouted_services now tables =
                            (`Ptc (nodeopt, newl))
                            ll
                with Not_found -> ()));
-             Lwt.pause ())
-          !ptr return_unit
-        >>= fun () ->
-        (if Eliom_common.Serv_Table.is_empty !ptr
-         then
-           match !t with
-           | Eliom_common.Vide -> ()
-           | Eliom_common.Table tr ->
-               let newr = String.Table.remove filename tr in
-               if String.Table.is_empty newr
-               then t := Eliom_common.Vide
-               else t := Eliom_common.Table newr);
-        Lwt.return_unit
+             Fiber.yield ())
+          !ptr ();
+        if Eliom_common.Serv_Table.is_empty !ptr
+        then
+          match !t with
+          | Eliom_common.Vide -> ()
+          | Eliom_common.Table tr ->
+              let newr = String.Table.remove filename tr in
+              if String.Table.is_empty newr
+              then t := Eliom_common.Vide
+              else t := Eliom_common.Table newr)
   and empty_one t =
     match !t with
-    | Eliom_common.Vide -> Lwt.return_unit
-    | Eliom_common.Table r -> (
+    | Eliom_common.Vide -> ()
+    | Eliom_common.Table r ->
         if String.Table.is_empty r
-        then (
-          t := Eliom_common.Vide;
-          Lwt.return_unit)
-        else
-          String.Table.fold (aux t) r Lwt.return_unit >>= fun () ->
+        then t := Eliom_common.Vide
+        else (
+          String.Table.fold (aux t) r ();
           match !t with
           (* !t has probably changed *)
-          | Eliom_common.Vide -> Lwt.return_unit
+          | Eliom_common.Vide -> ()
           | Eliom_common.Table r ->
-              if String.Table.is_empty r then t := Eliom_common.Vide;
-              Lwt.return_unit)
+              if String.Table.is_empty r then t := Eliom_common.Vide)
   in
-  Lwt_list.iter_s
+  List.iter
     (fun (_, _prio, t) -> empty_one t)
-    tables.Eliom_common.table_services
-  >>= fun () ->
+    tables.Eliom_common.table_services;
   tables.Eliom_common.table_services <-
     List.filter
       (fun r -> !(Tuple3.thd r) <> Eliom_common.Vide)
-      tables.Eliom_common.table_services;
-  Lwt.return_unit
+      tables.Eliom_common.table_services
 
 let gc_timeouted_naservices now tr =
   match !tr with
-  | Eliom_common.AVide -> return_unit
+  | Eliom_common.AVide -> ()
   | Eliom_common.ATable t ->
       if Eliom_common.NAserv_Table.is_empty t
-      then (
-        tr := Eliom_common.AVide;
-        Lwt.return_unit)
+      then tr := Eliom_common.AVide
       else
         Eliom_common.NAserv_Table.fold
           (fun k (_, _, expdate, _, nodeopt) thr ->
-             thr >>= fun () ->
+             thr;
              (match expdate with
              | Some (_, e) when !e < now -> (
                match nodeopt with
@@ -158,8 +147,8 @@ let gc_timeouted_naservices now tr =
                    (* will remove from the table automatically *)
                | _ -> tr := Eliom_common.remove_naservice_table !tr k)
              | _ -> ());
-             Lwt.pause ())
-          t return_unit
+             Fiber.yield ())
+          t ()
 
 (* This is a thread that will work for example every hour. *)
 let service_session_gc sitedata =
@@ -168,70 +157,68 @@ let service_session_gc sitedata =
   | None -> () (* No garbage collection *)
   | Some t ->
       let rec f () =
-        Lwt_unix.sleep t >>= fun () ->
+        Eio_unix.sleep t;
         let service_cookie_table = sitedata.Eliom_common.session_services in
         let now = Unix.time () in
         Logs.info ~src:section (fun fmt -> fmt "GC of service sessions");
         (* public continuation tables: *)
-        (if tables.Eliom_common.table_contains_services_with_timeout
-         then gc_timeouted_services now tables
-         else return_unit)
-        >>= fun () ->
-        (if tables.Eliom_common.table_contains_naservices_with_timeout
-         then gc_timeouted_naservices now tables.Eliom_common.table_naservices
-         else return_unit)
-        >>= fun () ->
-        (* private continuation tables: *)
-        Eliom_common.SessionCookies.fold
-          (fun k
-            { Eliom_common.Service_cookie.session_table = tables
-            ; expiry
-            ; session_group
-            ; session_group_node
-            ; _ }
-            thr ->
-             thr >>= fun () ->
-             (match !expiry with
-               | Some exp when exp < now ->
-                   Eliommod_sessiongroups.Serv.remove session_group_node;
-                   Lwt.return_unit
-               | _ ->
-                   (if tables.Eliom_common.table_contains_services_with_timeout
-                    then gc_timeouted_services now tables
-                    else return_unit)
-                   >>= fun () ->
-                   (if
-                      tables.Eliom_common.table_contains_naservices_with_timeout
-                    then
-                      gc_timeouted_naservices now
-                        tables.Eliom_common.table_naservices
-                    else return_unit)
-                   >>= fun () ->
-                   (match !session_group with
-                   | _, _scope, Right _
-                   (* no group *)
-                   (*VVV check this *)
-                     when Eliommod_sessiongroups.Serv.group_size
-                            ( Eliom_common.get_site_dir_string sitedata
-                            , `Client_process
-                            , Left k )
-                          = 0
-                          (* no tab sessions *)
-                          && Eliom_common.service_tables_are_empty tables ->
-                       (* The session is not used in any table
+        if tables.Eliom_common.table_contains_services_with_timeout
+        then gc_timeouted_services now tables
+        else ();
+        if tables.Eliom_common.table_contains_naservices_with_timeout
+        then gc_timeouted_naservices now tables.Eliom_common.table_naservices
+        else ();
+        f
+          (* private continuation tables: *)
+          (Eliom_common.SessionCookies.fold
+             (fun k
+               { Eliom_common.Service_cookie.session_table = tables
+               ; expiry
+               ; session_group
+               ; session_group_node
+               ; _ }
+               thr ->
+                thr;
+                Fiber.yield
+                  (match !expiry with
+                  | Some exp when exp < now ->
+                      Eliommod_sessiongroups.Serv.remove session_group_node
+                  | _ -> (
+                      if
+                        tables.Eliom_common.table_contains_services_with_timeout
+                      then gc_timeouted_services now tables
+                      else ();
+                      if
+                        tables
+                          .Eliom_common.table_contains_naservices_with_timeout
+                      then
+                        gc_timeouted_naservices now
+                          tables.Eliom_common.table_naservices
+                      else ();
+                      match !session_group with
+                      | _, _scope, Right _
+                      (* no group *)
+                      (*VVV check this *)
+                        when Eliommod_sessiongroups.Serv.group_size
+                               ( Eliom_common.get_site_dir_string sitedata
+                               , `Client_process
+                               , Left k )
+                             = 0
+                             (* no tab sessions *)
+                             && Eliom_common.service_tables_are_empty tables ->
+                          (* The session is not used in any table
                    and is not in a group
                    (scope must be `Session,
                    as all tab sessions are in a group),
                    and is not associated to any tab session.
                    We can remove it. *)
-                       Eliommod_sessiongroups.Serv.remove session_group_node
-                   | _ -> () (*VVV enough? *));
-                   return_unit)
-             >>= Lwt.pause)
-          service_cookie_table return_unit
-        >>= f
+                          Eliommod_sessiongroups.Serv.remove session_group_node
+                      | _ -> () (*VVV enough? *))))
+             service_cookie_table ())
       in
-      Lwt.async f
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        f
 
 (* This is a thread that will work for example every hour. *)
 let data_session_gc sitedata =
@@ -239,58 +226,58 @@ let data_session_gc sitedata =
   | None -> () (* No garbage collection *)
   | Some t ->
       let rec f () =
-        Lwt_unix.sleep t >>= fun () ->
+        Eio_unix.sleep t;
         let data_cookie_table = sitedata.Eliom_common.session_data in
         let not_bound_in_data_tables =
           sitedata.Eliom_common.not_bound_in_data_tables
         in
         let now = Unix.time () in
         Logs.info ~src:section (fun fmt -> fmt "GC of session data");
-        (* private continuation tables: *)
-        Eliom_common.SessionCookies.fold
-          (fun k
-            { Eliom_common.Data_cookie.expiry
-            ; session_group
-            ; session_group_node
-            ; _ }
-            thr ->
-             thr >>= fun () ->
-             (match !expiry with
-               | Some exp when exp < now ->
-                   Eliommod_sessiongroups.Data.remove session_group_node;
-                   return_unit
-               | _ -> (
-                 match !session_group with
-                 | _, scope, Right _
-                 (* no group *)
-                   when Eliommod_sessiongroups.Data.group_size
-                          ( Eliom_common.get_site_dir_string sitedata
-                          , `Client_process
-                          , Left k )
-                        = 0
-                        (* no tab sessions *)
-                        && not_bound_in_data_tables k ->
-                     (* The session is not used in any table
+        f
+          (* private continuation tables: *)
+          (Eliom_common.SessionCookies.fold
+             (fun k
+               { Eliom_common.Data_cookie.expiry
+               ; session_group
+               ; session_group_node
+               ; _ }
+               thr ->
+                thr;
+                Fiber.yield
+                  (match !expiry with
+                  | Some exp when exp < now ->
+                      Eliommod_sessiongroups.Data.remove session_group_node
+                  | _ -> (
+                    match !session_group with
+                    | _, scope, Right _
+                    (* no group *)
+                      when Eliommod_sessiongroups.Data.group_size
+                             ( Eliom_common.get_site_dir_string sitedata
+                             , `Client_process
+                             , Left k )
+                           = 0
+                           (* no tab sessions *)
+                           && not_bound_in_data_tables k ->
+                        (* The session is not used in any table
                           and is not in a group
                           (scope must be `Session,
                           as all tab sessions are in a group),
                           and is not associated to any tab session.
                           We can remove it. *)
-                     if scope <> `Session
-                     then
-                       Logs.err ~src:section (fun fmt ->
-                         fmt
-                           "Eliom: Group associated to IP has scope different from `Session. Please report the problem.");
-                     Eliommod_sessiongroups.Data.remove session_group_node;
-                     (* See also the finalisers in Eliommod_sessiongroups
+                        if scope <> `Session
+                        then
+                          Logs.err ~src:section (fun fmt ->
+                            fmt
+                              "Eliom: Group associated to IP has scope different from `Session. Please report the problem.");
+                        Eliommod_sessiongroups.Data.remove session_group_node
+                        (* See also the finalisers in Eliommod_sessiongroups
                           and Eliommod.ml *)
-                     Lwt.return_unit
-                 | _ -> Lwt.return_unit))
-             >>= Lwt.pause)
-          data_cookie_table return_unit
-        >>= f
+                    | _ -> ())))
+             data_cookie_table ())
       in
-      Lwt.async f
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        f
 
 (* garbage collection of timeouted persistent sessions *)
 (* This is a thread that will work every hour/day *)
@@ -312,19 +299,15 @@ let persistent_session_gc sitedata =
       (*WAS: remove_from_all_persistent_tables k *)
       | _ ->
           Logs.info ~src:section (fun fmt ->
-            fmt "cookie not expired: %s" (log_hash cookie));
-          return_unit
+            fmt "cookie not expired: %s" (log_hash cookie))
     in
     let gc_cookie c =
-      Lwt.try_bind
-        (fun () -> Eliommod_cookies.Persistent_cookies.Cookies.find c)
-        (do_gc_cookie c)
-        (function
-          | Not_found ->
-              Logs.info ~src:section (fun fmt ->
-                fmt "cookie does not exist: %s" (log_hash c));
-              Lwt.return_unit
-          | exn -> Lwt.fail exn)
+      match Eliommod_cookies.Persistent_cookies.Cookies.find c with
+      | v -> (do_gc_cookie c) v
+      | exception Not_found ->
+          Logs.info ~src:section (fun fmt ->
+            fmt "cookie does not exist: %s" (log_hash c))
+      | exception exn -> raise exn
     in
     Logs.info ~src:section (fun fmt -> fmt "GC of persistent sessions");
     Eliommod_cookies.Persistent_cookies.garbage_collect ~section gc_cookie
@@ -332,5 +315,7 @@ let persistent_session_gc sitedata =
   match get_persistentsessiongcfrequency () with
   | None -> () (* No garbage collection *)
   | Some t ->
-      let rec f () = Lwt_unix.sleep t >>= gc >>= f in
-      Lwt.async f
+      let rec f () = f (gc (Eio_unix.sleep t)) in
+      Fiber.fork
+        ~sw:(Stdlib.Option.get (Fiber.get Ocsigen_lib.current_switch))
+        f
diff --git a/src/lib/server/eliommod_pagegen.ml b/src/lib/server/eliommod_pagegen.ml
index 0de9ab2a46..b6876c105b 100644
--- a/src/lib/server/eliommod_pagegen.ml
+++ b/src/lib/server/eliommod_pagegen.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -20,8 +20,6 @@ open Lwt.Syntax
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
 
-open Lwt.Infix
-
 let headers_with_content_type headers =
   Cohttp.Header.add_opt headers
     Ocsigen_header.Name.(to_string content_type)
@@ -38,13 +36,13 @@ let make_response ?headers ~status body =
     let headers = headers_with_content_type headers in
     Cohttp.Response.make ~status ~headers ()
   in
-  Lwt.return (Ocsigen_response.make ~body response)
+  Ocsigen_response.make ~body response
 
 (* module Html_content = Ocsigen_senders.Make_XML_Content(Xml)(Html.F) *)
 
 (* Exception handler for the site *)
 
-let def_handler e = Lwt.fail e
+let def_handler e = raise e
 
 (* Update cookie tables *)
 let update_cookie_table ?now sitedata (ci, sci) =
@@ -124,11 +122,11 @@ let update_cookie_table ?now sitedata (ci, sci) =
       Eliom_common.Full_state_name_table.fold
         (fun name v thr ->
            let thr2 =
-             Lazy.force v >>= fun (oldvalue, newr) ->
+             let oldvalue, newr = Lazy.force v in
              match !newr with
              | Eliom_common.SCData_session_expired | Eliom_common.SCNo_data ->
                  (* The cookie has been removed *)
-                 Lwt.return ()
+                 ()
              | Eliom_common.SC newc -> (
                  let newexp =
                    match !(newc.Eliom_common.pc_timeout) with
@@ -148,30 +146,27 @@ let update_cookie_table ?now sitedata (ci, sci) =
                         && oldti = !(newc.Eliom_common.pc_timeout)
                         && oldgrp = !(newc.Eliom_common.pc_session_group)
                         && newc.Eliom_common.pc_set_value = None ->
-                     Lwt.return ()
+                     ()
                  (* nothing to do *)
                  | Some (_, _oldti, oldexp, _oldgrp)
-                   when newc.Eliom_common.pc_set_value = None ->
-                     Lwt.catch
-                       (fun () ->
-                          let cookieid =
-                            Eliom_common.(
-                              Hashed_cookies.to_string newc.pc_hvalue)
-                          in
-                          Eliommod_cookies.Persistent_cookies.replace_if_exists
-                            cookieid
-                            { Eliommod_cookies.full_state_name = name
-                            ; expiry = newexp
-                            ; timeout = !(newc.Eliom_common.pc_timeout)
-                            ; session_group =
-                                !(newc.Eliom_common.pc_session_group) }
-                          >>= fun () ->
-                          Eliommod_cookies.Persistent_cookies.Expiry_dates
-                          .remove_cookie oldexp cookieid)
-                       (function
-                         | Not_found -> Lwt.return ()
-                         (* someone else closed the session *)
-                         | e -> Lwt.fail e)
+                   when newc.Eliom_common.pc_set_value = None -> (
+                   try
+                     let cookieid =
+                       Eliom_common.(Hashed_cookies.to_string newc.pc_hvalue)
+                     in
+                     Eliommod_cookies.Persistent_cookies.replace_if_exists
+                       cookieid
+                       { Eliommod_cookies.full_state_name = name
+                       ; expiry = newexp
+                       ; timeout = !(newc.Eliom_common.pc_timeout)
+                       ; session_group = !(newc.Eliom_common.pc_session_group)
+                       };
+                     Eliommod_cookies.Persistent_cookies.Expiry_dates
+                     .remove_cookie oldexp cookieid
+                   with
+                   | Not_found -> ()
+                   (* someone else closed the session *)
+                   | e -> raise e)
                  | _ ->
                      Eliommod_cookies.Persistent_cookies.add
                        Eliom_common.(Hashed_cookies.to_string newc.pc_hvalue)
@@ -185,11 +180,11 @@ let update_cookie_table ?now sitedata (ci, sci) =
           otherwise the server will crash!!!
              *)
            in
-           thr >>= fun () -> thr2)
-        !pers_cookies_info Lwt.return_unit
-    else Lwt.return_unit
+           thr; thr2)
+        !pers_cookies_info ()
+    else ()
   in
-  update_exp ci >>= fun () ->
+  update_exp ci;
   (* the same, for secure cookies: *)
   update_exp sci
 
@@ -203,14 +198,13 @@ let execute
       ({Eliom_common.all_cookie_info; tab_cookie_info; _} as info)
       sitedata
   =
-  let* result =
-    Lwt.catch
-      (fun () -> generate_page now info sitedata)
-      (fun e -> sitedata.Eliom_common.exn_handler e)
+  let result =
+    try generate_page now info sitedata
+    with e -> sitedata.Eliom_common.exn_handler e
   in
-  let* () = update_cookie_table ~now sitedata all_cookie_info in
-  let* () = update_cookie_table ~now sitedata tab_cookie_info in
-  Lwt.return result
+  let () = update_cookie_table ~now sitedata all_cookie_info in
+  let () = update_cookie_table ~now sitedata tab_cookie_info in
+  result
 
 (** Set expired sessions in request data *)
 let set_expired_sessions ri closedservsessions =
@@ -236,13 +230,13 @@ let do_redirection header_id status uri =
         in
         Cohttp.Response.make ~status ~headers ()
       in
-      Lwt.return (Ocsigen_response.make response))
+      Ocsigen_response.make response)
 
 let gen_req_not_found ~is_eliom_extension ~sitedata ~previous_extension_err ~req
   =
   let req = Eliom_common.patch_request_info req in
   let now = Unix.gettimeofday () in
-  let* ri, si, previous_tab_cookies_info =
+  let ri, si, previous_tab_cookies_info =
     Eliom_common.get_session_info ~sitedata ~req 404
   in
   let all_cookie_info, closedsessions =
@@ -275,105 +269,98 @@ let gen_req_not_found ~is_eliom_extension ~sitedata ~previous_extension_err ~req
     let sp = Eliom_common.make_server_params sitedata info None None in
     (* The last two arguments are not yet available, so for now we use None.
        This value will later be overwritten once this information is available. *)
-    Lwt.with_value Eliom_common.sp_key (Some sp) @@ fun () ->
-    let genfun =
-      match si.Eliom_common.si_nonatt_info with
-      | Eliom_common.RNa_no ->
-          (* page generation *)
-          Eliom_route.get_page
-      | _ ->
-          (* anonymous service *)
-          Eliom_route.make_naservice
-    in
-    Lwt.catch
-      (fun () ->
-         let* res = execute now genfun info sitedata in
-         let response = Ocsigen_response.response res
-         and all_user_cookies = Ocsigen_response.cookies res in
-         let* cookies =
-           Eliommod_cookies.compute_cookies_to_send sitedata all_cookie_info
-             all_user_cookies
-         in
-         let res =
-           match
-             Ocsigen_request.header ri.Ocsigen_extensions.request_info
-               (Ocsigen_header.Name.of_string
-                  Eliom_common_base.cookie_substitutes_header_name)
-           with
-           | Some _ ->
-               let response =
-                 let headers =
-                   Cohttp.Header.add
-                     (Cohttp.Response.headers response)
-                     Eliom_common_base.set_cookie_substitutes_header_name
-                     (Eliommod_cookies.cookieset_to_json cookies)
-                 in
-                 {response with Cohttp.Response.headers}
-               in
-               Ocsigen_response.update ~response ~cookies res
-           | None -> Ocsigen_response.update ~cookies res
-         in
-         try
-           Polytables.get
-             ~table:
-               (Ocsigen_request.request_cache ri.Ocsigen_extensions.request_info)
-             ~key:Eliom_common.found_stop_key;
-           (* if we find this information in request cache,
+    (Stdlib.Option.fold ~none:Fiber.without_binding
+       ~some:(Fun.flip Fiber.with_binding)
+       (Some sp)) Eliom_common.sp_key (fun () ->
+      let genfun =
+        match si.Eliom_common.si_nonatt_info with
+        | Eliom_common.RNa_no ->
+            (* page generation *)
+            Eliom_route.get_page
+        | _ ->
+            (* anonymous service *)
+            Eliom_route.make_naservice
+      in
+      try
+        let res = execute now genfun info sitedata in
+        let response = Ocsigen_response.response res
+        and all_user_cookies = Ocsigen_response.cookies res in
+        let cookies =
+          Eliommod_cookies.compute_cookies_to_send sitedata all_cookie_info
+            all_user_cookies
+        in
+        let res =
+          match
+            Ocsigen_request.header ri.Ocsigen_extensions.request_info
+              (Ocsigen_header.Name.of_string
+                 Eliom_common_base.cookie_substitutes_header_name)
+          with
+          | Some _ ->
+              let response =
+                let headers =
+                  Cohttp.Header.add
+                    (Cohttp.Response.headers response)
+                    Eliom_common_base.set_cookie_substitutes_header_name
+                    (Eliommod_cookies.cookieset_to_json cookies)
+                in
+                {response with Cohttp.Response.headers}
+              in
+              Ocsigen_response.update ~response ~cookies res
+          | None -> Ocsigen_response.update ~cookies res
+        in
+        try
+          Polytables.get
+            ~table:
+              (Ocsigen_request.request_cache ri.Ocsigen_extensions.request_info)
+            ~key:Eliom_common.found_stop_key;
+          (* if we find this information in request cache,
               the request has already been completed.
               (used after an action).
               Do not try the following extensions.
-           *)
-           Lwt.return
-             (Ocsigen_extensions.Ext_found_stop (fun () -> Lwt.return res))
-         with Not_found ->
-           Lwt.return (Ocsigen_extensions.Ext_found (fun () -> Lwt.return res)))
-      (function
-        (* FIXME COHTTP transition ; restore all that *)
-        | Eliom_common.Eliom_Typing_Error l ->
-            Lwt.return
-              (Ocsigen_extensions.Ext_found
-                 (fun () ->
-                   make_response ~status:`Bad_request
-                     (Eliom_error_pages.page_error_param_type l)))
-        | Eliom_common.Eliom_Wrong_parameter ->
-            let* ripp =
-              match
-                Ocsigen_request.post_params req.request_info
-                  ri.request_config.Ocsigen_extensions.uploaddir
-                  ri.request_config.Ocsigen_extensions.maxuploadfilesize
-              with
-              | None -> Lwt.return []
-              | Some l -> l
-            in
-            let response =
-              Eliom_error_pages.page_bad_param
-                (try
-                   ignore
-                   @@ Polytables.get
-                        ~table:(Ocsigen_request.request_cache ri.request_info)
-                        ~key:Eliom_common.eliom_params_after_action;
-                   true
-                 with Not_found -> false)
-                (Ocsigen_request.get_params_flat ri.request_info)
-                (List.map fst ripp)
-            in
-            Lwt.return
-            @@ Ocsigen_extensions.Ext_found
-                 (fun () -> make_response ~status:`Bad_request response)
-        | Eliom_common.Eliom_404 ->
-            Lwt.return (Ocsigen_extensions.Ext_next previous_extension_err)
-        | Eliom_common.Eliom_retry_with a -> gen_aux a
-        | Eliom_common.Eliom_do_redirection uri ->
-            Lwt.return
-            @@ do_redirection Ocsigen_header.Name.location `Temporary_redirect
-                 uri
-        | Eliom_common.Eliom_do_half_xhr_redirection uri ->
-            Lwt.return
-            @@ do_redirection
-                 (Ocsigen_header.Name.of_string
-                    Eliom_common.half_xhr_redir_header)
-                 `No_content uri
-        | e -> Lwt.fail e)
+          *)
+          Ocsigen_extensions.Ext_found_stop (fun () -> res)
+        with Not_found -> Ocsigen_extensions.Ext_found (fun () -> res)
+      with
+      (* FIXME COHTTP transition ; restore all that *)
+      | Eliom_common.Eliom_Typing_Error l ->
+          Ocsigen_extensions.Ext_found
+            (fun () ->
+              make_response ~status:`Bad_request
+                (Eliom_error_pages.page_error_param_type l))
+      | Eliom_common.Eliom_Wrong_parameter ->
+          let ripp =
+            match
+              Ocsigen_request.post_params req.request_info
+                ri.request_config.Ocsigen_extensions.uploaddir
+                ri.request_config.Ocsigen_extensions.maxuploadfilesize
+            with
+            | None -> []
+            | Some l -> l
+          in
+          let response =
+            Eliom_error_pages.page_bad_param
+              (try
+                 ignore
+                 @@ Polytables.get
+                      ~table:(Ocsigen_request.request_cache ri.request_info)
+                      ~key:Eliom_common.eliom_params_after_action;
+                 true
+               with Not_found -> false)
+              (Ocsigen_request.get_params_flat ri.request_info)
+              (List.map fst ripp)
+          in
+          Ocsigen_extensions.Ext_found
+            (fun () -> make_response ~status:`Bad_request response)
+      | Eliom_common.Eliom_404 ->
+          Ocsigen_extensions.Ext_next previous_extension_err
+      | Eliom_common.Eliom_retry_with a -> gen_aux a
+      | Eliom_common.Eliom_do_redirection uri ->
+          do_redirection Ocsigen_header.Name.location `Temporary_redirect uri
+      | Eliom_common.Eliom_do_half_xhr_redirection uri ->
+          do_redirection
+            (Ocsigen_header.Name.of_string Eliom_common.half_xhr_redir_header)
+            `No_content uri
+      | e -> raise e)
   in
   let info =
     { Eliom_common.request = ri
@@ -389,9 +376,9 @@ let gen_req_not_found ~is_eliom_extension ~sitedata ~previous_extension_err ~req
 let gen is_eliom_extension sitedata =
   let open Ocsigen_extensions in
   function
-  | Req_found _ -> Lwt.return Ext_do_nothing
+  | Req_found _ -> Ext_do_nothing
   | Req_not_found ((`Not_found as previous_extension_err), req)
     when handled_method (Ocsigen_request.meth req.request_info) ->
       gen_req_not_found ~is_eliom_extension ~sitedata ~previous_extension_err
         ~req
-  | Req_not_found (_, _ri) -> Lwt.return Ext_do_nothing
+  | Req_not_found (_, _ri) -> Ext_do_nothing
diff --git a/src/lib/server/eliommod_pagegen.mli b/src/lib/server/eliommod_pagegen.mli
index b10b1997b6..a9371f1c2c 100644
--- a/src/lib/server/eliommod_pagegen.mli
+++ b/src/lib/server/eliommod_pagegen.mli
@@ -17,26 +17,23 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *)
-val def_handler : exn -> 'b Lwt.t
+val def_handler : exn -> 'b
 
 val execute :
    float
-  -> (float
-      -> Eliom_common.info
-      -> Eliom_common.sitedata
-      -> Ocsigen_response.t Lwt.t)
+  -> (float -> Eliom_common.info -> Eliom_common.sitedata -> Ocsigen_response.t)
   -> Eliom_common.info
   -> Eliom_common.sitedata
-  -> Ocsigen_response.t Lwt.t
+  -> Ocsigen_response.t
 
 val gen :
    Eliom_extension.eliom_extension_sig option
   -> Eliom_common.sitedata
   -> Ocsigen_extensions.request_state
-  -> Ocsigen_extensions.answer Lwt.t
+  -> Ocsigen_extensions.answer
 
 val update_cookie_table :
    ?now:float
   -> Eliom_common.sitedata
   -> Eliom_common.tables Eliom_common.cookie_info
-  -> unit Lwt.t
+  -> unit
diff --git a/src/lib/server/eliommod_persess.ml b/src/lib/server/eliommod_persess.ml
index 91dd54471f..491040490b 100644
--- a/src/lib/server/eliommod_persess.ml
+++ b/src/lib/server/eliommod_persess.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -31,8 +31,6 @@ open Lwt.Syntax
 (*****************************************************************************)
 (* Persistent sessions: *)
 
-open Lwt
-
 let compute_cookie_info sitedata secure_o secure_ci cookie_info =
   let secure = Eliom_common.get_secure ~secure_o ~sitedata () in
   if secure
@@ -56,34 +54,32 @@ let close_persistent_state2 ~(scope : [< Eliom_common.user_scope]) sitedata sg v
 (* close current persistent session *)
 let close_persistent_state ~scope ~secure_o ?sp () =
   let sp = Eliom_common.sp_of_option sp in
-  catch
-    (fun () ->
-       let cookie_level = Eliom_common.cookie_level_of_user_scope scope in
-       let (_, _, cookie_info), secure_ci =
-         Eliom_common.get_cookie_info sp cookie_level
-       in
-       let sitedata = Eliom_request_info.get_sitedata_sp ~sp in
-       let cookie_info, secure =
-         compute_cookie_info sitedata secure_o secure_ci cookie_info
-       in
-       let full_st_name =
-         Eliom_common.make_full_state_name ~sp ~secure ~scope
-       in
-       Lazy.force
-         (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
-       >>= fun (_, ior) ->
-       match !ior with
-       | Eliom_common.SC c ->
-           close_persistent_state2
-             ~scope:(scope :> Eliom_common.user_scope)
-             sp.Eliom_common.sp_sitedata
-             !(c.Eliom_common.pc_session_group)
-             Eliom_common.(Hashed_cookies.to_string c.pc_hvalue)
-           >>= fun () ->
-           ior := Eliom_common.SCNo_data;
-           return_unit
-       | _ -> return_unit)
-    (function Not_found -> return_unit | e -> fail e)
+  try
+    let cookie_level = Eliom_common.cookie_level_of_user_scope scope in
+    let (_, _, cookie_info), secure_ci =
+      Eliom_common.get_cookie_info sp cookie_level
+    in
+    let sitedata = Eliom_request_info.get_sitedata_sp ~sp in
+    let cookie_info, secure =
+      compute_cookie_info sitedata secure_o secure_ci cookie_info
+    in
+    let full_st_name = Eliom_common.make_full_state_name ~sp ~secure ~scope in
+    let _, ior =
+      Lazy.force
+        (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
+    in
+    match !ior with
+    | Eliom_common.SC c ->
+        close_persistent_state2
+          ~scope:(scope :> Eliom_common.user_scope)
+          sp.Eliom_common.sp_sitedata
+          !(c.Eliom_common.pc_session_group)
+          Eliom_common.(Hashed_cookies.to_string c.pc_hvalue);
+        ior := Eliom_common.SCNo_data
+    | _ -> ()
+  with
+  | Not_found -> ()
+  | e -> raise e
 
 let fullsessgrp ~cookie_level ~sp session_group =
   Eliommod_sessiongroups.make_persistent_full_group_name ~cookie_level
@@ -101,13 +97,15 @@ let rec find_or_create_persistent_cookie_
   (* if it exists, do not create it, but returns its value *)
   let cookie_level = Eliom_common.cookie_level_of_user_scope cookie_scope in
   let new_persistent_cookie sitedata full_state_name =
-    let* set_session_group =
+    let set_session_group =
       match cookie_scope with
       | `Client_process n ->
-          (* We create a group whose name is the
+          let
+              (* We create a group whose name is the
                    browser session cookie
                    and put the tab session into it. *)
-          let* r =
+                r
+            =
             find_or_create_persistent_cookie_
               ~set_max_in_group:
                 (fst
@@ -115,8 +113,8 @@ let rec find_or_create_persistent_cookie_
                      .Eliom_common.max_persistent_data_tab_sessions_per_group)
               ~cookie_scope:(`Session n) ~secure_o ~sp ()
           in
-          Lwt.return_some Eliom_common.(Hashed_cookies.to_string r.pc_hvalue)
-      | _ -> Lwt.return set_session_group
+          Some Eliom_common.(Hashed_cookies.to_string r.pc_hvalue)
+      | _ -> set_session_group
     in
     let fullsessgrp = fullsessgrp ~cookie_level ~sp set_session_group in
     let c = Eliommod_cookies.make_new_session_id () in
@@ -128,7 +126,7 @@ let rec find_or_create_persistent_cookie_
       ref Eliom_common.TGlobal
       (* See global table *)
     in
-    let* () =
+    let () =
       Eliommod_cookies.Persistent_cookies.add hc_string
         { Eliommod_cookies.full_state_name
         ; expiry = None
@@ -136,23 +134,22 @@ let rec find_or_create_persistent_cookie_
           timeout = Eliom_common.TGlobal
         ; session_group = fullsessgrp }
     in
-    Eliommod_sessiongroups.Pers.add ?set_max:set_max_in_group
-      (fst sitedata.Eliom_common.max_persistent_data_sessions_per_group)
-      hc_string fullsessgrp
-    >>= fun l ->
-    Lwt_list.iter_p
+    let l =
+      Eliommod_sessiongroups.Pers.add ?set_max:set_max_in_group
+        (fst sitedata.Eliom_common.max_persistent_data_sessions_per_group)
+        hc_string fullsessgrp
+    in
+    Fiber.List.iter
       (close_persistent_state2
          ~scope:(cookie_scope :> Eliom_common.user_scope)
          sitedata None)
-      l
-    >>= fun () ->
-    Lwt.return
-      { Eliom_common.pc_hvalue = hc
-      ; Eliom_common.pc_set_value = Some c
-      ; Eliom_common.pc_timeout = usertimeout
-      ; Eliom_common.pc_cookie_exp =
-          ref (Eliom_common.default_client_cookie_exp ()) (* exp on client *)
-      ; Eliom_common.pc_session_group = ref fullsessgrp }
+      l;
+    { Eliom_common.pc_hvalue = hc
+    ; Eliom_common.pc_set_value = Some c
+    ; Eliom_common.pc_timeout = usertimeout
+    ; Eliom_common.pc_cookie_exp =
+        ref (Eliom_common.default_client_cookie_exp ()) (* exp on client *)
+    ; Eliom_common.pc_session_group = ref fullsessgrp }
   in
   let (_, _, cookie_info), secure_ci =
     Eliom_common.get_cookie_info sp cookie_level
@@ -164,29 +161,29 @@ let rec find_or_create_persistent_cookie_
   let full_st_name =
     Eliom_common.make_full_state_name ~sp ~secure ~scope:cookie_scope
   in
-  catch
-    (fun () ->
-       Lazy.force
-         (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
-       >>= fun (_old, ior) ->
-       match !ior with
-       | Eliom_common.SCData_session_expired
-         (* We do not trust the value sent by the client,
+  try
+    let _old, ior =
+      Lazy.force
+        (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
+    in
+    match !ior with
+    | Eliom_common.SCData_session_expired
+      (* We do not trust the value sent by the client,
              for security reasons *)
-       | Eliom_common.SCNo_data ->
-           new_persistent_cookie sitedata full_st_name >>= fun v ->
-           ior := Eliom_common.SC v;
-           return v
-       | Eliom_common.SC v -> return v)
-    (function
-      | Not_found ->
-          new_persistent_cookie sitedata full_st_name >>= fun v ->
-          cookie_info :=
-            Eliom_common.Full_state_name_table.add full_st_name
-              (Lazy.from_val (return (None, ref (Eliom_common.SC v))))
-              !cookie_info;
-          return v
-      | e -> fail e)
+    | Eliom_common.SCNo_data ->
+        let v = new_persistent_cookie sitedata full_st_name in
+        ior := Eliom_common.SC v;
+        v
+    | Eliom_common.SC v -> v
+  with
+  | Not_found ->
+      let v = new_persistent_cookie sitedata full_st_name in
+      cookie_info :=
+        Eliom_common.Full_state_name_table.add full_st_name
+          (Lazy.from_val (None, ref (Eliom_common.SC v)))
+          !cookie_info;
+      v
+  | e -> raise e
 
 let find_or_create_persistent_cookie
       ?set_session_group
@@ -206,13 +203,13 @@ let find_or_create_persistent_cookie =
       -> secure_o:bool option
       -> ?sp:Eliom_common.server_params
       -> unit
-      -> Eliom_common.one_persistent_cookie_info Lwt.t
+      -> Eliom_common.one_persistent_cookie_info
     :> ?set_session_group:string
        -> cookie_scope:[< Eliom_common.cookie_scope]
        -> secure_o:bool option
        -> ?sp:Eliom_common.server_params
        -> unit
-       -> Eliom_common.one_persistent_cookie_info Lwt.t)
+       -> Eliom_common.one_persistent_cookie_info)
 
 let find_persistent_cookie_only ~cookie_scope ~secure_o ?sp () =
   (* If the cookie does not exist, do not create it, raise Not_found.
@@ -229,10 +226,12 @@ let find_persistent_cookie_only ~cookie_scope ~secure_o ?sp () =
   let full_st_name =
     Eliom_common.make_full_state_name ~sp ~secure ~scope:cookie_scope
   in
-  Lazy.force (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
-  >>= fun (_, ior) ->
+  let _, ior =
+    Lazy.force
+      (Eliom_common.Full_state_name_table.find full_st_name !cookie_info)
+  in
   match !ior with
   | Eliom_common.SCNo_data -> raise Not_found
   | Eliom_common.SCData_session_expired ->
       raise Eliom_common.Eliom_Session_expired
-  | Eliom_common.SC v -> return v
+  | Eliom_common.SC v -> v
diff --git a/src/lib/server/eliommod_persess.mli b/src/lib/server/eliommod_persess.mli
index e5cd1aed0e..2c10664ee3 100644
--- a/src/lib/server/eliommod_persess.mli
+++ b/src/lib/server/eliommod_persess.mli
@@ -23,14 +23,14 @@ val close_persistent_state2 :
   -> Eliom_common.sitedata
   -> Eliom_common.perssessgrp option
   -> string
-  -> unit Lwt.t
+  -> unit
 
 val close_persistent_state :
    scope:[< Eliom_common.user_scope]
   -> secure_o:bool option
   -> ?sp:Eliom_common.server_params
   -> unit
-  -> unit Lwt.t
+  -> unit
 
 val find_or_create_persistent_cookie :
    ?set_session_group:string
@@ -38,11 +38,11 @@ val find_or_create_persistent_cookie :
   -> secure_o:bool option
   -> ?sp:Eliom_common.server_params
   -> unit
-  -> Eliom_common.one_persistent_cookie_info Lwt.t
+  -> Eliom_common.one_persistent_cookie_info
 
 val find_persistent_cookie_only :
    cookie_scope:[< Eliom_common.cookie_scope]
   -> secure_o:bool option
   -> ?sp:Eliom_common.server_params
   -> unit
-  -> Eliom_common.one_persistent_cookie_info Lwt.t
+  -> Eliom_common.one_persistent_cookie_info
diff --git a/src/lib/server/eliommod_sessadmin.ml b/src/lib/server/eliommod_sessadmin.ml
index f1cf2176d0..f0a8c17273 100644
--- a/src/lib/server/eliommod_sessadmin.ml
+++ b/src/lib/server/eliommod_sessadmin.ml
@@ -1,4 +1,4 @@
-open Lwt.Syntax
+open Eio.Std
 
 (* Ocsigen
  * http://www.ocsigen.org
@@ -28,8 +28,6 @@ open Lwt.Syntax
 (*****************************************************************************)
 (*****************************************************************************)
 
-open Lwt
-
 let section = Logs.Src.create "eliom:admin"
 
 (*
@@ -48,11 +46,11 @@ let close_all_service_states2 full_st_name sitedata =
       ; session_group_node
       ; _ }
       thr ->
-       let* () = thr in
+       let () = thr in
        if full_st_name = full_state_name && !timeout = Eliom_common.TGlobal
        then Eliommod_sessiongroups.Serv.remove session_group_node;
-       Lwt.pause ())
-    sitedata.Eliom_common.session_services return_unit
+       Fiber.yield ())
+    sitedata.Eliom_common.session_services ()
 
 (** Close all service states for one session name.
     If the optional parameter [?state_name] (session name) is not present,
@@ -76,11 +74,11 @@ let close_all_data_states2 full_st_name sitedata =
     (fun _
       {Eliom_common.Data_cookie.full_state_name; timeout; session_group_node; _}
       thr ->
-       thr >>= fun () ->
+       thr;
        if full_st_name = full_state_name && !timeout = Eliom_common.TGlobal
        then Eliommod_sessiongroups.Data.remove session_group_node;
-       Lwt.pause ())
-    sitedata.Eliom_common.session_data return_unit
+       Fiber.yield ())
+    sitedata.Eliom_common.session_data ()
 
 (** Close all in memory data sessions for one session name.
     If the optional parameter [?state_name] (session name) is not present,
@@ -108,10 +106,10 @@ let close_all_persistent_states2 full_st_name sitedata =
        let scope = full_state_name.Eliom_common.user_scope in
        if full_st_name = full_state_name && old_t = Eliom_common.TGlobal
        then
-         Eliommod_persess.close_persistent_state2 ~scope sitedata session_group
-           k
-         >>= Lwt.pause
-       else return_unit)
+         Fiber.yield
+           (Eliommod_persess.close_persistent_state2 ~scope sitedata
+              session_group k)
+       else ())
 
 (** Close all persistent sessions for one session name.
     If the optional parameter [?state_name] (session name) is not present,
@@ -148,7 +146,7 @@ let update_serv_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
           ; session_group_node
           ; _ }
           thr ->
-           let* () = thr in
+           let () = thr in
            (if full_st_name = full_state_name && !timeout = Eliom_common.TGlobal
             then
               let newexp =
@@ -161,8 +159,8 @@ let update_serv_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
               | Some t when t <= now ->
                   Eliommod_sessiongroups.Serv.remove session_group_node
               | _ -> expiry := newexp);
-           Lwt.pause ())
-        sitedata.Eliom_common.session_services return_unit
+           Fiber.yield ())
+        sitedata.Eliom_common.session_services ()
 
 (* Update the expiration date for all in memory data sessions                *)
 let update_data_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
@@ -182,7 +180,7 @@ let update_data_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
           ; session_group_node
           ; _ }
           thr ->
-           thr >>= fun () ->
+           thr;
            (if full_st_name = full_state_name && !timeout = Eliom_common.TGlobal
             then
               let newexp =
@@ -195,8 +193,8 @@ let update_data_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
               | Some t when t <= now ->
                   Eliommod_sessiongroups.Data.remove session_group_node
               | _ -> expiry := newexp);
-           Lwt.pause ())
-        sitedata.Eliom_common.session_data return_unit
+           Fiber.yield ())
+        sitedata.Eliom_common.session_data ()
 
 (* Update the expiration date for all sessions                               *)
 let update_pers_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
@@ -230,14 +228,14 @@ let update_pers_exp full_st_name sitedata old_glob_timeout new_glob_timeout =
                  Eliommod_persess.close_persistent_state2 ~scope sitedata
                    session_group k
              | _ ->
-                 let* () =
+                 let () =
                    Eliommod_cookies.Persistent_cookies.add k
                      { Eliommod_cookies.full_state_name
                      ; expiry = newexp
                      ; timeout = Eliom_common.TGlobal
                      ; session_group }
                  in
-                 Eliommod_cookies.Persistent_cookies.Expiry_dates.remove_cookie
-                   old_exp k
-                 >>= Lwt.pause
-           else return_unit)
+                 Fiber.yield
+                   (Eliommod_cookies.Persistent_cookies.Expiry_dates
+                    .remove_cookie old_exp k)
+           else ())
diff --git a/src/lib/server/eliommod_sessadmin.mli b/src/lib/server/eliommod_sessadmin.mli
index 2a7683bc76..2213c43730 100644
--- a/src/lib/server/eliommod_sessadmin.mli
+++ b/src/lib/server/eliommod_sessadmin.mli
@@ -22,39 +22,39 @@ val close_all_service_states :
    scope:Eliom_common.user_scope
   -> secure:bool
   -> Eliom_common.sitedata
-  -> unit Lwt.t
+  -> unit
 
 val close_all_data_states :
    scope:Eliom_common.user_scope
   -> secure:bool
   -> Eliom_common.sitedata
-  -> unit Lwt.t
+  -> unit
 
 val close_all_persistent_states :
    scope:Eliom_common.user_scope
   -> secure:bool
   -> Eliom_common.sitedata
-  -> unit Lwt.t
+  -> unit
 
 val update_serv_exp :
    Eliom_common.full_state_name
   -> Eliom_common.sitedata
   -> float option
   -> float option
-  -> unit Lwt.t
+  -> unit
 
 val update_data_exp :
    Eliom_common.full_state_name
   -> Eliom_common.sitedata
   -> float option
   -> float option
-  -> unit Lwt.t
+  -> unit
 
 val update_pers_exp :
    Eliom_common.full_state_name
   -> Eliom_common.sitedata
   -> float option
   -> float option
-  -> unit Lwt.t
+  -> unit
 
 val section : Logs.src
diff --git a/src/lib/server/eliommod_sessexpl.ml b/src/lib/server/eliommod_sessexpl.ml
index 04cada3d14..ca07d2d02e 100644
--- a/src/lib/server/eliommod_sessexpl.ml
+++ b/src/lib/server/eliommod_sessexpl.ml
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Module eliommod_sessexpl.ml
@@ -26,8 +28,6 @@
 (*****************************************************************************)
 (*****************************************************************************)
 
-open Lwt
-
 (*****************************************************************************)
 (* Iterators on cookies *)
 
@@ -37,8 +37,10 @@ let iter_service_cookies f =
     Eliom_request_info.find_sitedata "Eliommod_sessexpl.iter_service_cookies"
   in
   Eliom_common.SessionCookies.fold
-    (fun k v thr -> thr >>= fun () -> f (k, v) >>= Lwt.pause)
-    sitedata.Eliom_common.session_services return_unit
+    (fun k v thr ->
+       thr;
+       Fiber.yield (f (k, v)))
+    sitedata.Eliom_common.session_services ()
 
 (** Iterator on data cookies *)
 let iter_data_cookies f =
@@ -46,13 +48,15 @@ let iter_data_cookies f =
     Eliom_request_info.find_sitedata "Eliommod_sessexpl.iter_data_cookies"
   in
   Eliom_common.SessionCookies.fold
-    (fun k v thr -> thr >>= fun () -> f (k, v) >>= Lwt.pause)
-    sitedata.Eliom_common.session_data return_unit
+    (fun k v thr ->
+       thr;
+       Fiber.yield (f (k, v)))
+    sitedata.Eliom_common.session_data ()
 
 (** Iterator on persistent cookies *)
 let iter_persistent_cookies f =
   Eliommod_cookies.Persistent_cookies.Cookies.iter (fun k v ->
-    f (k, v) >>= Lwt.pause)
+    Fiber.yield (f (k, v)))
 
 (** Iterator on service cookies *)
 let fold_service_cookies f beg =
@@ -61,10 +65,10 @@ let fold_service_cookies f beg =
   in
   Eliom_common.SessionCookies.fold
     (fun k v thr ->
-       thr >>= fun res1 ->
-       f (k, v) res1 >>= fun res ->
-       Lwt.pause () >>= fun () -> return res)
-    sitedata.Eliom_common.session_services (return beg)
+       let res1 = thr in
+       let res = f (k, v) res1 in
+       Fiber.yield (); res)
+    sitedata.Eliom_common.session_services beg
 
 (** Iterator on data cookies *)
 let fold_data_cookies f beg =
@@ -73,17 +77,17 @@ let fold_data_cookies f beg =
   in
   Eliom_common.SessionCookies.fold
     (fun k v thr ->
-       thr >>= fun res1 ->
-       f (k, v) res1 >>= fun res ->
-       Lwt.pause () >>= fun () -> return res)
-    sitedata.Eliom_common.session_data (return beg)
+       let res1 = thr in
+       let res = f (k, v) res1 in
+       Fiber.yield (); res)
+    sitedata.Eliom_common.session_data beg
 
 (** Iterator on persistent cookies *)
 let fold_persistent_cookies f beg =
   Eliommod_cookies.Persistent_cookies.Cookies.fold
     (fun k v beg ->
-       f (k, v) beg >>= fun res ->
-       Lwt.pause () >>= fun () -> return res)
+       let res = f (k, v) beg in
+       Fiber.yield (); res)
     beg
 
 (*****************************************************************************)
diff --git a/src/lib/server/eliommod_sessexpl.mli b/src/lib/server/eliommod_sessexpl.mli
index e4ee7fa672..58b9337b9f 100644
--- a/src/lib/server/eliommod_sessexpl.mli
+++ b/src/lib/server/eliommod_sessexpl.mli
@@ -21,39 +21,35 @@
 val iter_service_cookies :
    (Eliom_common.SessionCookies.key
     * Eliom_common.tables Eliom_common.Service_cookie.t
-    -> unit Lwt.t)
-  -> unit Lwt.t
+    -> unit)
+  -> unit
 
 val iter_data_cookies :
-   (Eliom_common.SessionCookies.key * Eliom_common.Data_cookie.t -> unit Lwt.t)
-  -> unit Lwt.t
+   (Eliom_common.SessionCookies.key * Eliom_common.Data_cookie.t -> unit)
+  -> unit
 
-val iter_persistent_cookies :
-   (string * Eliommod_cookies.cookie -> unit Lwt.t)
-  -> unit Lwt.t
+val iter_persistent_cookies : (string * Eliommod_cookies.cookie -> unit) -> unit
 
 val fold_service_cookies :
    (Eliom_common.SessionCookies.key
     * Eliom_common.tables Eliom_common.Service_cookie.t
     -> 'a
-    -> 'a Lwt.t)
+    -> 'a)
+  -> 'a
   -> 'a
-  -> 'a Lwt.t
 
 val fold_data_cookies :
-   (Eliom_common.SessionCookies.key * Eliom_common.Data_cookie.t
-    -> 'a
-    -> 'a Lwt.t)
+   (Eliom_common.SessionCookies.key * Eliom_common.Data_cookie.t -> 'a -> 'a)
+  -> 'a
   -> 'a
-  -> 'a Lwt.t
 
 val fold_persistent_cookies :
-   (string * Eliommod_cookies.cookie -> 'a -> 'a Lwt.t)
+   (string * Eliommod_cookies.cookie -> 'a -> 'a)
+  -> 'a
   -> 'a
-  -> 'a Lwt.t
 
 val number_of_service_cookies : unit -> int
 val number_of_data_cookies : unit -> int
 val number_of_tables : unit -> int
 val number_of_table_elements : unit -> int list
-val number_of_persistent_cookies : unit -> int Lwt.t
+val number_of_persistent_cookies : unit -> int
diff --git a/src/lib/server/eliommod_sessiongroups.ml b/src/lib/server/eliommod_sessiongroups.ml
index cd8bce041e..362c127da3 100644
--- a/src/lib/server/eliommod_sessiongroups.ml
+++ b/src/lib/server/eliommod_sessiongroups.ml
@@ -1,3 +1,5 @@
+open Eio.Std
+
 (* Ocsigen
  * http://www.ocsigen.org
  * Module eliomsessiongroups.ml
@@ -419,7 +421,7 @@ module Pers = struct
 
   module Ocsipersist = Eliom_common.Ocsipersist.Polymorphic
 
-  let grouptable : (nbmax * string list) Ocsipersist.table Lwt.t Lazy.t =
+  let grouptable : (nbmax * string list) Ocsipersist.table Lazy.t =
     lazy (Ocsipersist.open_table "__eliom_session_group_table")
   (* It is lazy because if the module is linked statically,
          the creation of the table must happen after initialisation
@@ -428,162 +430,167 @@ module Pers = struct
 
   let find g =
     match g with
-    | None -> Lwt.return_nil
-    | Some g ->
-        Lwt.catch
-          (fun () ->
-             !!grouptable >>= fun grouptable ->
-             Ocsipersist.find grouptable (Eliom_common.string_of_perssessgrp g)
-             >>= fun (_, a) -> Lwt.return a)
-          (function Not_found -> Lwt.return_nil | e -> Lwt.fail e)
+    | None -> []
+    | Some g -> (
+      try
+        let grouptable = !!grouptable in
+        let _, a =
+          Ocsipersist.find grouptable (Eliom_common.string_of_perssessgrp g)
+        in
+        a
+      with
+      | Not_found -> []
+      | e -> raise e)
 
   let add ?set_max defaultmax sess_id sess_grp =
     match sess_grp with
-    | Some sg ->
+    | Some sg -> (
         let sg = Eliom_common.string_of_perssessgrp sg in
-        Lwt.catch
-          (fun () ->
-             !!grouptable >>= fun grouptable ->
-             Ocsipersist.find grouptable sg >>= fun (max2, cl) ->
-             let max, newmax =
-               match set_max with
-               | None ->
-                   ( (match max2 with
-                     | Default -> defaultmax
-                     | Nolimit -> None
-                     | Val m -> Some m)
-                   , max2 )
-               | Some None -> None, Nolimit
-               | Some (Some v) -> Some v, Val v
-             in
-             let cl, toclose = cut max cl in
-             Ocsipersist.replace_if_exists grouptable sg (newmax, sess_id :: cl)
-             >>= fun () -> Lwt.return toclose)
-          (function
-            | Not_found ->
-                let max =
-                  match set_max with
-                  | None -> Default
-                  | Some None -> Nolimit
-                  | Some (Some v) -> Val v
-                in
-                !!grouptable >>= fun grouptable ->
-                Ocsipersist.add grouptable sg (max, [sess_id]) >>= fun () ->
-                Lwt.return_nil
-            | e -> Lwt.fail e)
-    | None -> Lwt.return_nil
+        try
+          let grouptable = !!grouptable in
+          let max2, cl = Ocsipersist.find grouptable sg in
+          let max, newmax =
+            match set_max with
+            | None ->
+                ( (match max2 with
+                  | Default -> defaultmax
+                  | Nolimit -> None
+                  | Val m -> Some m)
+                , max2 )
+            | Some None -> None, Nolimit
+            | Some (Some v) -> Some v, Val v
+          in
+          let cl, toclose = cut max cl in
+          Ocsipersist.replace_if_exists grouptable sg (newmax, sess_id :: cl);
+          toclose
+        with
+        | Not_found ->
+            let max =
+              match set_max with
+              | None -> Default
+              | Some None -> Nolimit
+              | Some (Some v) -> Val v
+            in
+            let grouptable = !!grouptable in
+            Ocsipersist.add grouptable sg (max, [sess_id]);
+            []
+        | e -> raise e)
+    | None -> []
 
   let rec remove_group ~cookie_level sitedata sess_grp =
-    (* cookie_level is the scope of group members *)
-    (*VVV NEW 201007 closing all sessions in the group and removing group data *)
-    (*VVV VERIFY concurrent access *)
-    (*VVV Check this carefully!!!! Verify the order of actions. *)
-    Lwt.catch
-      (fun () ->
-         (* First we close all sessions in the group *)
-         find sess_grp >>= fun cl ->
-         Lwt_list.iter_p
-           (close_persistent_session2
-              ~cookie_level:
-                (match cookie_level with
-                | `Client_process _ -> `Client_process
-                | `Session -> `Session)
-              sitedata None)
-           cl
-         (* None because we will close the group *)
-         >>= fun () ->
-         (* Then, we remove group data: *)
-         (match sess_grp with
-           | None -> Lwt.return_unit
-           | Some sg -> (
-             match Eliom_common.getperssessgrp sg with
-             | _, _, Right _ ->
-                 (* No group has been set. No group table.
+    try
+      let cl =
+        (* cookie_level is the scope of group members *)
+        (*VVV NEW 201007 closing all sessions in the group and removing group data *)
+        (*VVV VERIFY concurrent access *)
+        (*VVV Check this carefully!!!! Verify the order of actions. *)
+
+        (* First we close all sessions in the group *)
+        find sess_grp
+      in
+      Fiber.List.iter
+        (close_persistent_session2
+           ~cookie_level:
+             (match cookie_level with
+             | `Client_process _ -> `Client_process
+             | `Session -> `Session)
+           sitedata None)
+        cl (* None because we will close the group *);
+      (* Then, we remove group data: *)
+      (match sess_grp with
+      | None -> ()
+      | Some sg -> (
+        match Eliom_common.getperssessgrp sg with
+        | _, _, Right _ -> ()
+        (* No group has been set. No group table.
                  Data associated to default (automatic) groups
                  is removed when closing associated sessions. *)
-                 Lwt.return_unit
-             | _, _, Left group_name -> (
-                 Eliom_common.Persistent_tables.remove_key_from_all_tables
-                   group_name
-                 >>= fun () ->
-                 (* If it is associated to a session,
+        | _, _, Left group_name -> (
+            Eliom_common.Persistent_tables.remove_key_from_all_tables group_name;
+            (* If it is associated to a session,
                  we remove the session from its group,
                  and we remove cookie info: *)
-                 match cookie_level with
-                 | `Client_process grp ->
-                     (* We are closing a browser session,
+            match cookie_level with
+            | `Client_process grp ->
+                (* We are closing a browser session,
                                            belonging to the group grp *)
-                     (* group_name is the cookie value *)
-                     remove sitedata group_name grp
-                 | _ -> Lwt.return_unit)))
-         >>= fun () ->
-         (* Then, we remove group from group table: *)
-         match sess_grp with
-         | Some sg ->
-             let sg = Eliom_common.string_of_perssessgrp sg in
-             !!grouptable >>= fun grouptable -> Ocsipersist.remove grouptable sg
-         | None -> Lwt.return_unit)
-      (function Not_found -> Lwt.return_unit | e -> Lwt.fail e)
+                (* group_name is the cookie value *)
+                remove sitedata group_name grp
+            | _ -> ())));
+      (* Then, we remove group from group table: *)
+      match sess_grp with
+      | Some sg ->
+          let sg = Eliom_common.string_of_perssessgrp sg in
+          let grouptable = !!grouptable in
+          Ocsipersist.remove grouptable sg
+      | None -> ()
+    with
+    | Not_found -> ()
+    | e -> raise e
 
   (* close a persistent session (tab or browser)
      and the associated group (if browser session) by cookie value *)
   and close_persistent_session2 ~cookie_level sitedata fullsessgrp cookie =
-    (*VVV Check this carefully!!!! *)
-    (*VVV Optimize the number of marshal/unmarshal (getperssessgrp) *)
-    Lwt.catch
-      (fun () ->
-         match cookie_level with
-         | `Client_process ->
-             (* We remove the session from its group: *)
-             remove sitedata cookie fullsessgrp >>= fun () ->
-             (* Then, we remove session data: *)
-             Eliom_common.Persistent_tables.remove_key_from_all_tables cookie
-         | `Session ->
-             remove_group ~cookie_level:(`Client_process fullsessgrp) sitedata
-               (Eliom_common.make_persistent_full_group_name
-                  ~cookie_level:`Client_process
-                  (Eliom_common.get_site_dir_string sitedata)
-                  (Some cookie)))
-      (function Not_found -> Lwt.return_unit | e -> Lwt.fail e)
+    try
+      (*VVV Check this carefully!!!! *)
+      (*VVV Optimize the number of marshal/unmarshal (getperssessgrp) *)
+      match cookie_level with
+      | `Client_process ->
+          (* We remove the session from its group: *)
+          remove sitedata cookie fullsessgrp;
+          (* Then, we remove session data: *)
+          Eliom_common.Persistent_tables.remove_key_from_all_tables cookie
+      | `Session ->
+          remove_group ~cookie_level:(`Client_process fullsessgrp) sitedata
+            (Eliom_common.make_persistent_full_group_name
+               ~cookie_level:`Client_process
+               (Eliom_common.get_site_dir_string sitedata)
+               (Some cookie))
+    with
+    | Not_found -> ()
+    | e -> raise e
 
   and remove _sitedata sess_id sess_grp =
     match sess_grp with
-    | Some sg0 ->
+    | Some sg0 -> (
         let sg = Eliom_common.string_of_perssessgrp sg0 in
-        Lwt.catch
-          (fun () ->
-             !!grouptable >>= fun grouptable ->
-             Ocsipersist.find grouptable sg >>= fun (max, cl) ->
-             let newcl = List.remove_first_if_any sess_id cl in
-             (* Before 2018-10-18, we were closing the session group
+        try
+          let grouptable = !!grouptable in
+          let max, cl = Ocsipersist.find grouptable sg in
+          let newcl = List.remove_first_if_any sess_id cl in
+          (* Before 2018-10-18, we were closing the session group
              when newcl was empty (no more session in the group).
              But persistent session groups are usually used to store persistent
              information about users. It makes no sense cleaning this
              information when user closes all their sessions.
              I remove this. -- Vincent
-             *)
-             Ocsipersist.replace_if_exists grouptable sg (max, newcl))
-          (function Not_found -> Lwt.return_unit | e -> Lwt.fail e)
-    | None -> Lwt.return_unit
+          *)
+          Ocsipersist.replace_if_exists grouptable sg (max, newcl)
+        with
+        | Not_found -> ()
+        | e -> raise e)
+    | None -> ()
 
   let up sess_id grp =
     match grp with
-    | None -> Lwt.return_unit
-    | Some sg ->
+    | None -> ()
+    | Some sg -> (
         let sg = Eliom_common.string_of_perssessgrp sg in
-        Lwt.catch
-          (fun () ->
-             !!grouptable >>= fun grouptable ->
-             Ocsipersist.find grouptable sg >>= fun (max, cl) ->
-             let newcl = List.remove_first_if_any sess_id cl in
-             Ocsipersist.replace_if_exists grouptable sg (max, sess_id :: newcl))
-          (function Not_found -> Lwt.return_unit | e -> Lwt.fail e)
+        try
+          let grouptable = !!grouptable in
+          let max, cl = Ocsipersist.find grouptable sg in
+          let newcl = List.remove_first_if_any sess_id cl in
+          Ocsipersist.replace_if_exists grouptable sg (max, sess_id :: newcl)
+        with
+        | Not_found -> ()
+        | e -> raise e)
 
   let move sitedata ?set_max max sess_id grp1 grp2 =
     if set_max <> None || grp1 <> grp2
-    then
-      remove sitedata sess_id grp1 >>= fun () -> add ?set_max max sess_id grp2
-    else Lwt.return_nil
+    then (
+      remove sitedata sess_id grp1;
+      add ?set_max max sess_id grp2)
+    else []
 
-  let nb_of_groups () = !!grouptable >>= Ocsipersist.length
+  let nb_of_groups () = Ocsipersist.length !!grouptable
 end
diff --git a/src/lib/server/eliommod_sessiongroups.mli b/src/lib/server/eliommod_sessiongroups.mli
index fd3b59b612..baf72317f2 100644
--- a/src/lib/server/eliommod_sessiongroups.mli
+++ b/src/lib/server/eliommod_sessiongroups.mli
@@ -99,26 +99,26 @@ module Data :
     [`Session] Eliom_common.sessgrp Ocsigen_cache.Dlist.node
 
 module Pers : sig
-  val find : Eliom_common.perssessgrp option -> string list Lwt.t
+  val find : Eliom_common.perssessgrp option -> string list
 
   val add :
      ?set_max:int option
     -> int option
     -> string
     -> Eliom_common.perssessgrp option
-    -> string list Lwt.t
+    -> string list
 
   val remove :
      Eliom_common.sitedata
     -> string
     -> Eliom_common.perssessgrp option
-    -> unit Lwt.t
+    -> unit
 
   val remove_group :
      cookie_level:[`Session | `Client_process of Eliom_common.perssessgrp option]
     -> Eliom_common.sitedata
     -> Eliom_common.perssessgrp option
-    -> unit Lwt.t
+    -> unit
 
   val move :
      Eliom_common.sitedata
@@ -127,15 +127,15 @@ module Pers : sig
     -> string
     -> Eliom_common.perssessgrp option
     -> Eliom_common.perssessgrp option
-    -> string list Lwt.t
+    -> string list
 
-  val up : string -> Eliom_common.perssessgrp option -> unit Lwt.t
-  val nb_of_groups : unit -> int Lwt.t
+  val up : string -> Eliom_common.perssessgrp option -> unit
+  val nb_of_groups : unit -> int
 
   val close_persistent_session2 :
      cookie_level:Eliom_common.cookie_level
     -> Eliom_common.sitedata
     -> Eliom_common.perssessgrp option
     -> string
-    -> unit Lwt.t
+    -> unit
 end
diff --git a/src/lib/server/eliommod_timeouts.ml b/src/lib/server/eliommod_timeouts.ml
index 56381c5bfa..511ab5a484 100644
--- a/src/lib/server/eliommod_timeouts.ml
+++ b/src/lib/server/eliommod_timeouts.ml
@@ -26,7 +26,6 @@
 (*****************************************************************************)
 
 open Eliom_lib
-open Lwt
 
 type kind = [`Service | `Data | `Persistent]
 
@@ -131,15 +130,12 @@ let set_timeout_
             | _, _, ct -> get_default ct)
         in
         ignore
-          (catch
-             (fun () -> update full_st_name sitedata oldt t)
-             (function
-               | exn ->
-               Logs.warn ~src:eliom_logs_src (fun fmt ->
-                 fmt
-                   ("Error while updating timeouts" ^^ "@\n%s")
-                   (Printexc.to_string exn));
-               Lwt.return_unit))
+          (try update full_st_name sitedata oldt t
+           with exn ->
+             Logs.warn ~src:eliom_logs_src (fun fmt ->
+               fmt
+                 ("Error while updating timeouts" ^^ "@\n%s")
+                 (Printexc.to_string exn)))
 (*VVV Check possible exceptions raised *)
 
 (* global timeout = timeout for the whole site (may be changed dynamically) *)
diff --git a/src/lib/server/monitor/eliom_monitor.ml b/src/lib/server/monitor/eliom_monitor.ml
index 9e29633f17..5cbc189f72 100644
--- a/src/lib/server/monitor/eliom_monitor.ml
+++ b/src/lib/server/monitor/eliom_monitor.ml
@@ -1,5 +1,3 @@
-open Lwt.Syntax
-
 (* Ocsigen
  * http://www.ocsigen.org
  * Copyright (C) 2014 Hugo Heuzard
@@ -108,72 +106,68 @@ let http_stats () =
            hosts) ]
 
 let eliom_stats () =
-  let* persist_nb_of_groups = Eliommod_sessiongroups.Pers.nb_of_groups () in
-  let* number_of_persistent_data_cookies =
+  let persist_nb_of_groups = Eliommod_sessiongroups.Pers.nb_of_groups () in
+  let number_of_persistent_data_cookies =
     Eliom_state.number_of_persistent_data_cookies ()
   in
-  Lwt.return
-    (div
-       [ h3 [ppf "Sessions"]
-       ; ul
-           [ li
-               [ ppf "%d service cookies."
-                   (Eliom_state.number_of_service_cookies ()) ]
-           ; li
-               [ ppf "%d volatile data cookies."
-                   (Eliom_state.number_of_volatile_data_cookies ()) ]
-           ; li
-               [ ppf "%d volatile data tables (volatile Eliom references)."
-                   (Eliom_state.number_of_tables ()) ]
-           ; li
-               [ ppf "%d persistent data cookies."
-                   number_of_persistent_data_cookies ]
-           ; li
-               [ ppf "%d persistent data tables (persistent data reference)."
-                   (Eliom_state.number_of_persistent_tables ()) ] ]
-       ; h3 [ppf "Client processes"]
-       ; p [em [txt "Not implemented yet"]]
-       ; h3 [ppf "Session groups"]
-       ; ul
-           [ li
-               [ ppf "%d service session groups."
-                   (Eliommod_sessiongroups.Serv.nb_of_groups ()) ]
-           ; li
-               [ ppf "%d volatile data session groups."
-                   (Eliommod_sessiongroups.Data.nb_of_groups ()) ]
-           ; li [ppf "%d persistent data session groups." persist_nb_of_groups]
-           ; li
-               [ ppf "Session groups: %s"
-                   (String.concat ", "
-                      (Eliom_state.Ext.get_session_group_list ())) ] ] ])
+  div
+    [ h3 [ppf "Sessions"]
+    ; ul
+        [ li
+            [ ppf "%d service cookies."
+                (Eliom_state.number_of_service_cookies ()) ]
+        ; li
+            [ ppf "%d volatile data cookies."
+                (Eliom_state.number_of_volatile_data_cookies ()) ]
+        ; li
+            [ ppf "%d volatile data tables (volatile Eliom references)."
+                (Eliom_state.number_of_tables ()) ]
+        ; li
+            [ppf "%d persistent data cookies." number_of_persistent_data_cookies]
+        ; li
+            [ ppf "%d persistent data tables (persistent data reference)."
+                (Eliom_state.number_of_persistent_tables ()) ] ]
+    ; h3 [ppf "Client processes"]
+    ; p [em [txt "Not implemented yet"]]
+    ; h3 [ppf "Session groups"]
+    ; ul
+        [ li
+            [ ppf "%d service session groups."
+                (Eliommod_sessiongroups.Serv.nb_of_groups ()) ]
+        ; li
+            [ ppf "%d volatile data session groups."
+                (Eliommod_sessiongroups.Data.nb_of_groups ()) ]
+        ; li [ppf "%d persistent data session groups." persist_nb_of_groups]
+        ; li
+            [ ppf "Session groups: %s"
+                (String.concat ", " (Eliom_state.Ext.get_session_group_list ()))
+            ] ] ]
 
 let content_div () =
-  let* eliom_stats = eliom_stats () in
-  Lwt.return
-    (div
-       [ h1 [ppf "Ocsigen server monitoring"]
-       ; general_stats ()
-       ; h2 [ppf "HTTP connexions"]
-       ; http_stats ()
-       ; h2 [ppf "Eliom sessions"]
-       ; eliom_stats
-       ; h2 [ppf "GC"]
-       ; gc_stats () ])
+  let eliom_stats = eliom_stats () in
+  div
+    [ h1 [ppf "Ocsigen server monitoring"]
+    ; general_stats ()
+    ; h2 [ppf "HTTP connexions"]
+    ; http_stats ()
+    ; h2 [ppf "Eliom sessions"]
+    ; eliom_stats
+    ; h2 [ppf "GC"]
+    ; gc_stats () ]
 
 let content_html () =
-  let* content_div = content_div () in
-  Lwt.return
-    (html
-       (head
-          (title (txt "Server monitoring"))
-          [ link ~rel:[`Stylesheet]
-              ~href:
-                (uri_of_string (fun () ->
-                   "//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css"))
-              ()
-          ; link ~rel:[`Stylesheet]
-              ~href:
-                (uri_of_string (fun () ->
-                   "//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap-theme.min.css"))
-              () ])
-       (body [div ~a:[a_class ["container"]] [content_div]]))
+  let content_div = content_div () in
+  html
+    (head
+       (title (txt "Server monitoring"))
+       [ link ~rel:[`Stylesheet]
+           ~href:
+             (uri_of_string (fun () ->
+                "//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css"))
+           ()
+       ; link ~rel:[`Stylesheet]
+           ~href:
+             (uri_of_string (fun () ->
+                "//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap-theme.min.css"))
+           () ])
+    (body [div ~a:[a_class ["container"]] [content_div]])
diff --git a/src/lib/server/monitor/eliom_monitor.mli b/src/lib/server/monitor/eliom_monitor.mli
index 79a648bf81..051bd2af01 100644
--- a/src/lib/server/monitor/eliom_monitor.mli
+++ b/src/lib/server/monitor/eliom_monitor.mli
@@ -20,5 +20,5 @@
 val uptime : unit -> float
 val pid : unit -> int
 val fd : pid:int -> [`Ok of int | `Error of string]
-val content_div : unit -> [> Html_types.div] Eliom_content.Html.elt Lwt.t
-val content_html : unit -> [> Html_types.html] Eliom_content.Html.elt Lwt.t
+val content_div : unit -> [> Html_types.div] Eliom_content.Html.elt
+val content_html : unit -> [> Html_types.html] Eliom_content.Html.elt