regex.md

when using longest

lexmatch s using longest {
  ("re1" ("re2" as re2), next)  => ...
  ...
}

This adopts the Posix standard, the left side has an implicit "$" at the beginning (No shortest like ocamllex)

default

lexmatch s {
    (_,"re1" ("re2" as r) ,_) => ...
    "re3" => ... // implicit $ at the beginning and ^ at end
    (_, "\.(.*)") => ... // implicit  ^ at end
    ...
}

Top down, matched one by one using re2 style submatch semantics

if s lexmatch? (_,"re1" ("re2" as r) ,_) {
    ...
}