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"]

Functions

List/length

def List/length(list: [a]) -> (length: u24, list: [a])

Returns a tuple containing the length and the list itself.

List/reverse

def List/reverse(list: [a]) -> [a]

Reverses the elements of a list.

List/flatten

def List/flatten(list: [[a]]) -> [a]

Returns a flattened list from a list of lists. Example:

List/flatten([[1], [2, 3], [4]])

# Result: [1, 2, 3, 4]

List/concat

def List/concat(xs: [a], ys: [a]) -> [a]

Appends two lists together. Example:

List/concat([1, 2], [4, 5])

# Result: [1, 2, 4, 5]

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

The basic builtin IO functions are under development and will be stable in the next milestone.

Here is the current list of functions, but be aware that they may change in the near future.

Printing

def IO/print(text)

Prints the string text to the standard output, encoded with utf-8.

Input

def IO/input() -> String

Reads characters from the standard input until a newline is found.

Returns the read input as a String decoded with utf-8.

File IO

File open

def IO/FS/open(path, mode)

Opens a file with with path being given as a string and mode being a string with the mode to open the file in. The mode should be one of the following:

• "r": Read mode
• "w": Write mode (write at the beginning of the file, overwriting any existing content)
• "a": Append mode (write at the end of the file)
• "r+": Read and write mode
• "w+": Read and write mode
• "a+": Read and append mode

Returns an U24 with the file descriptor. File descriptors are not necessarily the same as the ones assigned by the operating system, but rather unique identifiers internal to Bend's runtime.

File descriptors for standard files

The standard input/output files are always open and assigned the following file descriptors:

• IO/FS/STDIN = 0: Standard input
• IO/FS/STDOUT = 1: Standard output
• IO/FS/STDERR = 2: Standard error

File close

def IO/FS/close(file)

Closes the file with the given file descriptor.

File read

def IO/FS/read(file, num_bytes)

Reads num_bytes bytes from the file with the given file descriptor.

Returns a list of U24 with each element representing a byte read from the file.

def IO/FS/read_line(file)

Reads a line from the file with the given file descriptor.

Returns a list of U24 with each element representing a byte read from the file.

def IO/FS/read_until_end(file)

Reads until the end of the file with the given file descriptor.

Returns a list of U24 with each element representing a byte read from the file.

def IO/FS/read_file(path)

Reads an entire file with the given path and returns a list of U24 with each element representing a byte read from the file.

File write

def IO/FS/write(file, bytes)

Writes bytes, a list of U24 with each element representing a byte, to the file with the given file descriptor.

Returns nothing (*).

def IO/FS/write_file(path, bytes)

Writes bytes, a list of U24 with each element representing a byte, as the entire content of the file with the given path.

File seek

def IO/FS/seek(file, offset, mode)

Moves the current position of the file with the given file descriptor to the given offset, an I24 or U24 number, in bytes.

mode can be one of the following:

• IO/FS/SEEK_SET = 0: Seek from start of file
• IO/FS/SEEK_CUR = 1: Seek from current position
• IO/FS/SEEK_END = 2: Seek from end of file

Returns nothing (*).

Numeric operations

log

def log(x: f24, base: f24) -> f24

Computes the logarithm of x with the specified base.

atan2

def atan2(x: f24, y: f24) -> f24

Computes the arctangent of y / x.

Has the same behaviour as atan2f in the C math lib.

to_f24

def to_f24(x: any number) -> f24

Casts any native number to an f24.

to_u24

def to_u24(x: any number) -> u24

Casts any native number to a u24.

to_i24

def to_i24(x: any number) -> i24

Casts any native number to an i24.

String encoding / decoding

Bytes/decode_utf8

def Bytes/decode_utf8(bytes: [u24]) -> String

Decodes a sequence of bytes to a String using utf-8 encoding.

Bytes/decode_ascii

def Bytes/decode_ascii(bytes: [u24]) -> String

Decodes a sequence of bytes to a String using ascii encoding.

String/encode_utf8

def String/encode_utf8(s: String) -> [u24]

Encodes a String to a sequence of bytes using utf-8 encoding.

String/encode_ascii

def String/encode_ascii(s: String) -> [u24]

Encodes a String to a sequence of bytes using ascii encoding.

Utf8/decode_character

def Utf8/decode_character(bytes: [u24]) -> (rune: u24, rest: [u24])

Decodes a utf-8 character, returns a tuple containing the rune and the rest of the byte sequence.

Utf8/REPLACEMENT_CHARACTER

def Utf8/REPLACEMENT_CHARACTER: u24 = '\u{FFFD}'