Bend/docs/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

type 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

type 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"]

Tree

type Tree:
  Node { ~left, ~right }
  Leaf { value }

Tree represents a tree with values stored in the leaves. Trees are a structure that naturally lends itself to parallel recursion, so writing your problem in terms of trees is a good first approach to parallelize your code.

• Node { ~left ~right }: Represents a tree node with left and right subtrees.
• Leaf { value }: Represents one of the ends of the tree, storing value.

Syntax

Bend provides the ![] operator to create tree branches and the ! operator to create a tree leaf.

# ![a, b] => Equivalent to Tree/Node { left: a, right: b }
# !x      => Equivalent to Tree/Leaf { value: x }
tree = ![![!1, !2],![!3, !4]]

Technically your trees don't need to end with leaves, but if you don't, your program will be very hard to reason about.

Map

type Map:
  Node { value ~left ~right }
  Leaf

Map represents a tree with values stored in the branches. It is meant to be used as an efficient map data structure with integer keys and O(log n) read and write operations.

• Node { value ~left ~right }: Represents a map node with a value and left and right subtrees. Empty nodes have * stored in the value field.
• Leaf: Represents an unwritten, empty portion of the map.

Syntax

Here's how you create a new Map with some initial values.:

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

The keys must be U24 numbers, and can be given as literals or any other expression that evaluates to a U24.

The values can be anything, but storing data of different types in a Map will make it harder for you to reason about it.

You can read and write a value of a map with the [] operator:

map = { 0: "zero", 1: "one", 2: "two", 3: "three" }
map[0] = "not zero"
map[1] = 2
map[2] = 3
map[3] = map[1] + map[map[1]]

Here, map must be the name of the Map variable, and the keys inside [] can be any expression that evaluates to a U24.

Map functions

Map/empty

Initializes an empty map.

Map/empty = Map/Leaf

Map/get

Retrieves a value from the map based on the key. Returns a tuple with the value and the map unchanged.

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 map

{ 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. Returns the map with the new value.

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"}

Map/map

Applies a function to a value in the map. Returns the map with the value mapped.

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

Syntax

With the same map that we set in the previous section, we can map it's values with @=:

x[0] @= lambda y: String/concat(y, " and mapped")
# x[0] now contains "swapped and mapped"

Nat

type 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

IO

IO Functions are in the next milestone!