Determine if all elements of the list satisfy the given predicate.

Note: an empty list always satisfies the predicate.

list.all([], fn(n) { n > 0 }) == True
list.all([1, 2, 3], fn(n) { n > 0 }) == True
list.all([1, 2, 3], fn(n) { n == 2 }) == False

Determine if at least one element of the list satisfies the given predicate.

Note: an empty list never satisfies the predicate.

list.any([], fn(n) { n > 2 }) == False
list.any([1, 2, 3], fn(n) { n > 0 }) == True
list.any([1, 2, 3], fn(n) { n == 2 }) == True
list.any([1, 2, 3], fn(n) { n < 0 }) == False

Return Some(item) at the index or None if the index is out of range. The index is 0-based.

list.at([1, 2, 3], 1) == Some(2)
list.at([1, 2, 3], 42) == None

Merge two lists together.

list.concat([], []) == []
list.concat([], [1, 2, 3]) == [1, 2, 3]
list.concat([1, 2, 3], [4, 5, 6]) == [1, 2, 3, 4, 5, 6]

Count how many items in the list satisfy the given predicate.

list.count([], fn(a) { a > 2}) == 0
list.count([1, 2, 3], fn(a) { n > 0 }) == 3
list.count([1, 2, 3], fn(a) { n >= 2 }) == 2
list.count([1, 2, 3], fn(a) { n > 5 }) == 0

Remove the first occurrence of the given element from the list.

list.delete([1, 2, 3, 1], 1) == [2, 3, 1]
list.delete([1, 2, 3], 14) == [1, 2, 3]

Remove the first occurrence of each element of the second list from the first one.

list.difference(["h", "e", "l", "l", "o"], ["l", "e", "l"]) == ["h", "o"]
list.difference([1, 2, 3, 4, 5], [1, 1, 2]) == [3, 4, 5]
list.difference([1, 2, 3], []) == [1, 2, 3]

Drop the first n elements of a list.

list.drop([1, 2, 3], 2) == [3]
list.drop([], 42) == []
list.drop([1, 2, 3], 42) == []

Returns the suffix of the given list after removing all elements that satisfy the predicate.

list.drop_while([1, 2, 3], fn(x) { x < 2 }) == [2, 3]
list.drop_while([], fn(x) { x > 2 }) == []
list.drop_while([1, 2, 3], fn(x) { x == 3 }) == [1, 2, 3]

Produce a list of elements that satisfy a predicate.

list.filter([1, 2, 3], fn(x) { x >= 2 }) == [2, 3]
list.filter([], fn(x) { x > 2 }) == []
list.filter([1, 2, 3], fn(x) { x == 3 }) == [3]

Produce a list of transformed elements that satisfy a predicate.

let transform = fn(x) { if x % 2 == 0 { None } else { Some(3*x) } }
list.filter_map([1, 2, 3], transform) == [3, 9]

Find the first element satisfying the given predicate, if any.

list.find([1, 2, 3], fn(x) { x == 2 }) == Some(2)
list.find([4, 5, 6], fn(x) { x == 2 }) == None

Map elements of a list into a new list and flatten the result.

list.flat_map([1, 2, 3], fn(a) { [a, 2*a] }) == [1, 2, 2, 4, 3, 6]

Reduce a list from left to right.

list.foldl([1, 2, 3], 0, fn(n, total) { n + total }) == 6
list.foldl([1, 2, 3], [], fn(x, xs) { [x, ..xs] }) == [3, 2, 1]

Reduce a list from right to left.

list.foldr([1, 2, 3], 0, fn(n, total) { n + total }) == 6
list.foldr([1, 2, 3], [], fn(x, xs) { [x, ..xs] }) == [1, 2, 3]

Figures out whether a list contain the given element.

list.has([1, 2, 3], 2) == True
list.has([1, 2, 3], 14) == False
list.has([], 14) == False

Get the first element of a list

list.head([1, 2, 3]) == Some(1)
list.head([]) == None

Gets the index of an element of a list, if any. Otherwise, returns None.

list.index_of([1, 5, 2], 2) == Some(2)
list.index_of([1, 7, 3], 4) == None
list.index_of([1, 0, 9, 6], 6) == 3
list.index_of([], 6) == None

Like foldr, but also provides the position (0-based) of the elements when iterating.

let group = fn(i, x, xs) { [(i, x), ..xs] }
list.indexed_foldr(["a", "b", "c"], [], group) == [
  (0, "a"),
  (1, "b"),
  (2, "c")
]

List map but provides the position (0-based) of the elements while iterating.

list.indexed_map([1, 2, 3], fn(i, x) { i + x }) == [1, 3, 5]

Return all elements except the last one.

list.init([]) == None
list.init([1, 2, 3]) == Some([1, 2])

Checks whether a list is empty.

list.is_empty([]) == True
list.is_empty([1, 2, 3]) == False

Get the last in the given list, if any.

list.last([]) == None
list.last([1, 2, 3]) == Some(3)

Get the number of elements in the given list.

list.length([]) == 0
list.length([1, 2, 3]) == 3

Apply a function to each element of a list.

list.map([1, 2, 3, 4], fn(n) { n + 1 }) == [2, 3, 4, 5]

Apply a function of two arguments, combining elements from two lists.

Note: if one list is longer, the extra elements are dropped.

list.map2([1, 2, 3], [1, 2], fn(a, b) { a + b }) == [2, 4]

Apply a function of three arguments, combining elements from three lists.

Note: if one list is longer, the extra elements are dropped.

list.map3([1, 2, 3], [1, 2], [1, 2, 3], fn(a, b, c) { a + b + c }) == [3, 6]

Returns a tuple with all elements that satisfy the predicate at first element, and the rest as second element.

list.partition([1, 2, 3, 4], fn(x) { x % 2 == 0 }) == ([2, 4], [1, 3])

Add an element in front of the list. Sometimes useful when combined with other functions.

list.push([2, 3], 1) == [1, ..[2, 3]] == [1, 2, 3]

Construct a list of a integer from a given range.

list.range(0, 3) == [0, 1, 2, 3]
list.range(-1, 1) == [-1, 0, 1]

Reduce a list from left to right using the accumulator as left operand. Said differently, this is foldl with callback arguments swapped.

list.reduce([#[1], #[2], #[3]], #[0], bytearray.concat) == #[0, 1, 2, 3]
list.reduce([True, False, True], False, fn(b, a) { or { b, a } }) == True

Construct a list filled with n copies of a value.

list.repeat("na", 3) == ["na", "na", "na"]

Return the list with its elements in the reserve order.

list.reverse([1, 2, 3]) == [3, 2, 1]

Extract a sublist from the given list using 0-based indexes. Negative indexes wrap over, so -1 refers to the last element of the list.

list.slice([1, 2, 3, 4, 5, 6], from: 2, to: 4) == [3, 4, 5]
list.slice([1, 2, 3, 4, 5, 6], from: -2, to: -1) == [5, 6]
list.slice([1, 2, 3, 4, 5, 6], from: 1, to: -1) == [2, 3, 4, 5, 6]

Sort a list in ascending order using the given comparison function.

use aiken/int

sort([3, 1, 4, 0, 2], int.compare) == [0, 1, 2, 3, 4]
sort([1, 2, 3], int.compare) == [1, 2, 3]

Cut a list in two, such that the first list contains the given number of / elements and the second list contains the rest.

Fundamentally equivalent to (but more efficient):

// span(xs, n) == (take(xs, n), drop(xs, n))
span([1, 2, 3, 4, 5], 3) == ([1, 2, 3], [4, 5])

Get elements of a list after the first one, if any.

list.tail([]) == None
list.tail([1, 2, 3]) == Some([2, 3])

Get the first n elements of a list.

list.take([1, 2, 3], 2) == [1, 2]
list.take([1, 2, 3], 14) == [1, 2, 3]

Returns the longest prefix of the given list where all elements satisfy the predicate.

list.take_while([1, 2, 3], fn(x) { x > 2 }) == []
list.take_while([1, 2, 3], fn(x) { x < 2 }) == [1]

Removes duplicate elements from a list.

list.unique([1, 2, 3, 1]) == [1, 2, 3]

Decompose a list of tuples into a tuple of lists.

list.unzip([(1, "a"), (2, "b")]) == ([1, 2], ["a", "b"])

Combine two lists together.

Note: if one list is longer, the extra elements are dropped.

list.zip([1, 2], ["a", "b", "c"]) == [(1, "a"), (2, "b")]