BUILTINS.md

this is a WIP based on Builtins.bend.

Built-in Types and Functions

Bend built-in types and functions, this document serves as a reference guide. Read more at FEATURES.md.

String

data String = (Cons head ~tail) | (Nil)

• Nil: Represents an empty string.
• Cons head ~tail: Represents a string with a head character and a tail string.

Syntax

A String literal is surrounded with ". Accepts the same values as characters literals.

"Hello, World!"

List

data List = (Cons head ~tail) | (Nil)

• Nil: Represents an empty list.
• Cons head ~tail: Represents a list with a head element and a tail list.

Syntax

A List of values can be written using [ ], it can have multiple values inside, using , you can divide its value in a list of multiple elements.

["This", "List", "Has", "Multiple", "Values"]

Nat

data Nat = (Succ ~pred) | (Zero)

• Succ ~pred: Represents a natural number successor.
• Zero: Represents the natural number zero.

Syntax

A Natural Number can be written with literals with a # before the literal number.

#1337

Result

data Result = (Ok val) | (Err val)

• Ok val: Represents a successful result with value val.
• Err val: Represents an error with value val.

Map

data Map = (Node value ~left ~right) | (Leaf)

• Node value ~left ~right: Represents a map node with a value and left and right subtrees.
• Leaf: Represents an empty map.

Syntax

Bend has a built-in binary tree map data structure where the key is a u24, meaning you can use numbers, characters, and symbols as keys.

{ 0: 4, `hi`: "bye", 'c': 2 + 3 }

Map/empty

Initializes an empty map.

Map/empty = Map/Leaf

Map/get

Retrieves a value from the map based on the key.

Map/get map key =
  match map {
    Map/Leaf: (*, map)
    Map/Node:
      switch _ = (== 0 key) {
        0: switch _ = (% key 2) {
          0:
            let (got, rest) = (Map/get map.left (/ key 2))
            (got, (Map/Node map.value rest map.right))
          _:
            let (got, rest) = (Map/get map.right (/ key 2))
            (got, (Map/Node map.value map.left rest))
        }
        _: (map.value, map)
      }
  }

Syntax

Considering the following tree

{ 0: "hello", 1: "bye", 2: "maybe", 3: "yes"}

The get function can be written as

return x[0]  # Gets the value of the key 0

And the value resultant from the get function would be:

"hello"

Map/set

Sets a value in the map at the specified key.

Map/set map key value =
  match map {
    Map/Node:
      switch _ = (== 0 key) {
        0: switch _ = (% key 2) {
          0: (Map/Node map.value (Map/set map.left (/ key 2) value) map.right)
          _: (Map/Node map.value map.left (Map/set map.right (/ key 2) value))
        }
        _: (Map/Node value map.left map.right)
      }
    Map/Leaf:
      switch _ = (== 0 key) {
        0: switch _ = (% key 2) {
          0: (Map/Node * (Map/set Map/Leaf (/ key 2) value) Map/Leaf)
          _: (Map/Node * Map/Leaf (Map/set Map/Leaf (/ key 2) value))
        }
        _: (Map/Node value Map/Leaf Map/Leaf)
      }
  }

Syntax

Considering the following tree

{ 0: "hello", 1: "bye", 2: "maybe", 3: "yes"}

The set function can be written as

x[0] = "swapped"     # Assigns the key 0 to the value "swapped"

And the value resultant from the get function would be:

{ 0: "swapped", 1: "bye", 2: "maybe", 3: "yes"}

If there's no matching key in the tree, it would add a new branch to that tree with the value set

x[4] = "added"     # Assigns the key 4 to the value "added"

The new tree

{ 0: "swapped", 1: "bye", 2: "maybe", 3: "yes", 4: "added"}

IO

IO Functions are in the next milestone!