# List

## Definitions

`def ap(f: List[a -> b \ ef], x: List[a]): List[b] \ ef`Source

Apply every function from `f` to every argument from `x` and return a list with all results. For `f = f1, f2, ...` and `x = x1, x2, ...` the results appear in the order `f1(x1), f1(x2), ..., f2(x1), f2(x2), ...`.

`def append(l1: List[a], l2: List[a]): List[a]`Source

Returns `l2` appended to `l1`.

The infix operator `:::` is an alias for `append` (`l1 ::: l2 = append(l1, l2)`).

`def count(f: a -> Bool \ ef, l: List[a]): Int32 \ ef`Source

Returns the number of elements in `l` that satisfy the predicate `f`.

`def distinct(l: List[a]): List[a]`Source

Returns the list `l` with duplicates removed. The first occurence of an element is kept and except for the removal of subsequent duplicates the order of `l` is preserved.

`distinct` uses the Flix's builtin equality test. Use `distinctWith` if you need a custom equality test.

`def distinctWith(f: a -> (a -> Bool), l: List[a]): List[a]`Source

Returns the list `l` with duplicates removed using the supplied function `f` for comparison. The first occurrence of an element is kept and except for the removal of subsequent duplicates the order of `l` is preserved.

`def drop(n: Int32, l: List[a]): List[a]`Source

Returns `l` without the first `n` elements.

Returns `Nil` if `n > length(l)`. Returns `l` if `n < 0`.

`def dropWhile(f: a -> Bool \ ef, l: List[a]): List[a] \ ef`Source

Returns `l` without the longest prefix that satisfies the predicate `f`.

`def enumerator(rc: Region[r], l: List[a]): Iterator[(Int32, a), r, r] \ r`Source

Returns an iterator over `l` zipped with the indices of the elements.

`def exists(f: a -> Bool \ ef, l: List[a]): Bool \ ef`Source

Returns `true` if and only if at least one element in `l` satisfies the predicate `f`.

Returns `false` if `l` is empty.

`def filter(f: a -> Bool \ ef, l: List[a]): List[a] \ ef`Source

Returns a list of every element in `l` that satisfies the predicate `f`.

`def filterMap(f: a -> Option[b] \ ef, l: List[a]): List[b] \ ef`Source

Collects the results of applying the partial function `f` to every element in `l`.

`def find(f: a -> Bool \ ef, l: List[a]): Option[a] \ ef`Source

Alias for `findLeft`.

`def findLeft(f: a -> Bool \ ef, l: List[a]): Option[a] \ ef`Source

Optionally returns the first element of `l` that satisfies the predicate `f` when searching from left to right.

`def findMap(f: a -> Option[b] \ ef, l: List[a]): Option[b] \ ef`Source

Returns the first non-None result of applying the partial function `f` to each element of `l`.

Returns `None` if every element of `l` is `None`.

`def findRight(f: a -> Bool \ ef, l: List[a]): Option[a] \ ef`Source

Optionally returns the first element of `l` that satisfies the predicate `f` when searching from right to left.

`def flatMap(f: a -> List[b] \ ef, l: List[a]): List[b] \ ef`Source

Returns the result of applying `f` to every element in `l` and concatenating the results.

`def flatten(l: List[List[a]]): List[a]`Source

Returns the concatenation of the elements in `l`.

`def fold(l: List[a]): a`Source

Returns the result of applying `combine` to all the elements in `l`, using `empty` as the initial value.

`def fold2(f: c -> (a -> (b -> c \ ef)), c: c, l1: List[a], l2: List[b]): c \ ef`Source

Alias for `foldLeft2`.

`def foldLeft(f: b -> (a -> b \ ef), s: b, l: List[a]): b \ ef`Source

Applies `f` to a start value `s` and all elements in `l` going from left to right.

That is, the result is of the form: `f(...f(f(s, x1), x2)..., xn)`.

`def foldLeft2(f: c -> (a -> (b -> c \ ef)), c: c, l1: List[a], l2: List[b]): c \ ef`Source

Accumulates the result of applying `f` pairwise to the elements of `l1` and `l2` starting with the initial value `c` and going from left to right.

`def foldMap(f: a -> b \ ef, l: List[a]): b \ ef`Source

Returns the result of mapping each element and combining the results.

`def foldRight(f: a -> (b -> b \ ef), s: b, l: List[a]): b \ ef`Source

Applies `f` to a start value `s` and all elements in `l` going from right to left.

That is, the result is of the form: `f(x1, ...f(xn-1, f(xn, s))...)`.

`def foldRight2(f: a -> (b -> (c -> c \ ef)), c: c, l1: List[a], l2: List[b]): c \ ef`Source

Accumulates the result of applying `f` pairwise to the elements of `l1` and `l2` starting with the initial value `c` and going from right to left.

`def foldRightWithCont(f: a -> ((Unit -> b \ ef) -> b \ ef), z: b, l: List[a]): b \ ef`Source

Applies `f` to a start value `z` and all elements in `l` going from right to left.

That is, the result is of the form: `f(x1, ...f(xn-1, f(xn, z))...)`. A `foldRightWithCont` allows early termination by not calling the continuation.

`def forAll(f: a -> Bool \ ef, l: List[a]): Bool \ ef`Source

Returns `true` if and only if all elements in `l` satisfy the predicate `f`.

Returns `true` if `l` is empty.

`def forEach(f: a -> Unit \ ef, l: List[a]): Unit \ ef`Source

Applies `f` to every element of `l`.

`def forEachWithIndex(f: Int32 -> (a -> Unit \ ef), l: List[a]): Unit \ ef`Source

Applies `f` to every element of `l` along with that element's index.

`def groupBy(f: a -> (a -> Bool), l: List[a]): List[List[a]]`Source

Partitions `l` into sublists such that for any two elements `x` and `y` in a sublist, `f(x, y)` is true.

A sublist is created by iterating through the remaining elements of `l` from left to right and adding an element to the sublist if and only if doing so creates no conflicts with the elements already in the sublist.

The function `f` must be pure.

`def head(l: List[a]): Option[a]`Source

Returns `Some(x)` if `x` is the first element of `l`.

Returns `None` if `l` is empty.

`def indexOf(a: a, l: List[a]): Option[Int32]`Source

Optionally returns the position of `x` in `l`.

`def init(l: List[a]): Option[List[a]]`Source

Returns the sublist of `l` without the last element. Returns `None` if the list `l` is `Nil`.

`def intercalate(l1: List[a], l2: List[List[a]]): List[a]`Source

Returns the concatenation of the elements in `l2` with the elements of `l1` inserted between every two adjacent elements.

That is, returns `y1 :: x1 ... xn :: y2 :: ... yn-1 :: x1 :: ... :: xn :: yn :: Nil`.

`def intersperse(a: a, l: List[a]): List[a]`Source

Returns `l` with `x` inserted between every two adjacent elements.

`def isEmpty(l: List[a]): Bool`Source

Returns true if and only if `l` is the empty list, i.e. `Nil`.

`def isInfixOf(l1: List[a], l2: List[a]): Bool`Source

Returns `true` if and only if `l1` is an infix of `l2`.

`def isPrefixOf(l1: List[a], l2: List[a]): Bool`Source

Returns `true` if and only if `l1` is a prefix of `l2`.

`def isSuffixOf(l1: List[a], l2: List[a]): Bool`Source

Returns `true` if and only if `l1` is a suffix of `l2`.

`def iterator(rc: Region[r], xs: List[a]): Iterator[a, r, r] \ r`Source

Returns an iterator over `l`.

`def join(sep: String, l: List[a]): String`Source

Returns the concatenation of the string representation of each element in `l` with `sep` inserted between each element.

`def joinWith(f: a -> String \ ef, sep: String, l: List[a]): String \ ef`Source

Returns the concatenation of the string representation of each element in `l` according to `f` with `sep` inserted between each element.

`def last(l: List[a]): Option[a]`Source

Returns `Some(x)` if `x` is the last element of `l`.

Returns `None` if `l` is empty.

`def length(l: List[a]): Int32`Source

Returns the length of `l`.

`def map(f: a -> b \ ef, l: List[a]): List[b] \ ef`Source

Returns the result of applying `f` to every element in `l`.

That is, the result is of the form: `f(x1) :: f(x2) :: ...`.

`def map2(f: t1 -> (t2 -> r \ ef), l1: List[t1], l2: List[t2]): List[r] \ ef`Source

Lift a binary function to work on lists of its original arguments, returning a list of applying all combinations of arguments. For argument lists `l1 = x1, x2, ...` and `l2 = y1, y2, ...` the results appear in the order `f(x1,y1), f(x1,y2), ..., f(x2,y1), f(x2,y2), ...`.

`def map3(f: t1 -> (t2 -> (t3 -> r \ ef)), l1: List[t1], l2: List[t2], l3: List[t3]): List[r] \ ef`Source

Lift a ternary function to work on lists of its original arguments, returning a list of applying all combinations of arguments. For argument lists `l1 = x1, x2, ...`, `l2 = y1, y2, ...` and `l3 = z1, z2, ...` the results appear in the following order:

```` f(x1,y1,z1), f(x1,y1,z2), ..., f(x1,y2,z1), f(x1,y2,z2), ..., f(x2,y1,z1), f(x2,y1,z2), ..., f(x2,y2,z1), f(x2,y2,z2), ...` ... ````

`def map4(f: t1 -> (t2 -> (t3 -> (t4 -> r \ ef))), l1: List[t1], l2: List[t2], l3: List[t3], l4: List[t4]): List[r] \ ef`Source

Lift a 4-ary function to work on lists of its original arguments, returning a list of applying all combinations of arguments. The results appear in the order extending the pattern from `map3`.

`def map5(f: t1 -> (t2 -> (t3 -> (t4 -> (t5 -> r \ ef)))), l1: List[t1], l2: List[t2], l3: List[t3], l4: List[t4], l5: List[t5]): List[r] \ ef`Source

Lift a 5-ary function to work on lists of its original arguments, returning a list of applying all combinations of arguments. The results appear in the order extending the pattern from `map3`.

`def mapWithIndex(f: Int32 -> (a -> b \ ef), l: List[a]): List[b] \ ef`Source

Returns the result of applying `f` to every element in `l` along with that element's index.

That is, the result is of the form: `f(x1, 0) :: f(x2, 1) :: ...`.

`def maximum(l: List[a]): Option[a]`Source

Optionally finds the largest element of `l` according to the `Order` on `a`.

Returns `None` if `l` is empty.

`def maximumBy(cmp: a -> (a -> Comparison), l: List[a]): Option[a]`Source

Optionally finds the largest element of `l` according to the given comparator `cmp`.

Returns `None` if `l` is empty.

`def memberOf(a: a, l: List[a]): Bool`Source

Returns `true` if and only if `l` contains the element `x`.

`def merge(l1: List[a], l2: List[a]): List[a]`Source

Merges the two lists `l1` and `l2`. Assuming they are both sorted. If two elements compare `EqualTo`, then the element of `l1` is first in the result.

`def minimum(l: List[a]): Option[a]`Source

Optionally finds the smallest element of `l` according to the `Order` on `a`.

Returns `None` if `l` is empty.

`def minimumBy(cmp: a -> (a -> Comparison), l: List[a]): Option[a]`Source

Optionally finds the smallest element of `l` according to the given comparator `cmp`.

Returns `None` if `l` is empty.

`def partition(f: a -> Bool \ ef, l: List[a]): (List[a], List[a]) \ ef`Source

Returns a pair of lists `(l1, l2)`.

`l1` contains all elements of `l` that satisfy the predicate `f`. `l2` contains all elements of `l` that do not satisfy the predicate `f`.

`def patch(i: Int32, n: Int32, l1: List[a], l2: List[a]): List[a]`Source

Returns `l2` with the `n` elements starting at index `i` replaced with the elements of `l1`.

If any of the indices `i, i+1, i+2, ... , i+n-1` are out of range in `l2` then no patching is done at these indices. If `l1` becomes depleted then no further patching is done. If patching occurs at index `i+j` in `l2`, then the element at index `j` in `l1` is used.

`def permutations(l: List[a]): List[List[a]]`Source

Returns all permutations of `l` in lexicographical order by element indices in `l`.

That is, `l` is the first permutation and `reverse(l)` is the last permutation.

`def point(a: a): List[a]`Source

Return the singleton list with element `x`.

`def range(b: Int32, e: Int32): List[Int32]`Source

Returns a list of all integers between `b` (inclusive) and `e` (exclusive).

Returns `Nil` if `b >= e`.

`def reduceLeft(f: a -> (a -> a \ ef), l: List[a]): Option[a] \ ef`Source

Applies `f` to all elements in `l` going from left to right until a single value `v` is obtained. Returns `Some(v)`.

That is, the result is of the form: `Some(f(...f(f(x1, x2), x3)..., xn))`

Returns `None` if `l` is empty.

`def reduceRight(f: a -> (a -> a \ ef), l: List[a]): Option[a] \ ef`Source

Applies `f` to all elements in `l` going from right to left until a single value `v` is obtained. Returns `Some(v)`.

That is, the result is of the form: `Some(f(x1, ...f(xn-2, f(xn-1, xn))...))`

Returns `None` if `l` is empty.

`def repeat(n: Int32, a: a): List[a]`Source

Returns a list with the element `x` repeated `n` times.

Returns `Nil` if `n < 0`.

`def replace(from: { from = a }, to: { to = a }, l: List[a]): List[a]`Source

Returns `l` with every occurrence of `from` replaced by `to`.

`def reverse(l: List[a]): List[a]`Source

Returns the reverse of `l`.

`def rotateLeft(n: Int32, l: List[a]): List[a]`Source

Returns `l` with its elements rotated `n` positions to the left.

That is, returns a new list where the first `n mod length(l)` elements in `l` are the last `n mod length(l)` elements of the new list.

`def rotateRight(n: Int32, l: List[a]): List[a]`Source

Returns `l` with its elements rotated `n` positions to the right.

That is, returns a new list where the last `n mod length(l)` elements in `l` are the first `n mod length(l)` elements of the new list.

`def scan(f: b -> (a -> b \ ef), s: b, l: List[a]): List[b] \ ef`Source

Alias for `scanLeft`.

`def scanLeft(f: b -> (a -> b \ ef), s: b, l: List[a]): List[b] \ ef`Source

Accumulates the result of applying `f` to `l` going left to right.

That is, the result is of the form: `s :: f(s, x1) :: f(f(s, x1), x2) ...`.

`def scanRight(f: a -> (b -> b \ ef), s: b, l: List[a]): List[b] \ ef`Source

Accumulates the result of applying `f` to `l` going right to left.

That is, the result is of the form: `... f(xn-1, f(xn, s)) :: f(xn, s) :: s`.

`def sequence(l: List[m[a]]): m[List[a]]`Source

Returns the result of running all the actions in the list `l` going from left to right.

`def shuffle(rnd: Random, l: List[a]): List[a] \ IO`Source

Shuffles `l` using the Fisher–Yates shuffle.

`def slice(start: { start = Int32 }, end: { end = Int32 }, l: List[a]): List[a]`Source

Returns the sublist of `l` from index `start` (inclusive) to index `end` (exclusive).

That is, an element at index `i` in `l` is part of the returned sublist if and only if `i >= start` and `i < end`. Note: Indices that are out of bounds in `l` are not considered (i.e. slice(start, end, l) = slice(max(0, start), min(length(l), end), l)).

`def sort(l: List[a]): List[a]`Source

Sort list `l` so that elements are ordered from low to high according to their `Order` instance.

The sort is not stable, i.e., equal elements may appear in a different order than in the input `l`.

The sort implementation is a Quicksort.

`def sortBy(f: a -> b, l: List[a]): List[a]`Source

Sort list `l` so that elements are ordered from low to high according to the `Order` instance for the values obtained by applying `f` to each element.

The sort is not stable, i.e., equal elements may appear in a different order than in the input `l`.

The sort implementation is a Quicksort.

`def sortWith(cmp: a -> (a -> Comparison), l: List[a]): List[a]`Source

Sort list `l` so that elements are ordered from low to high according to the comparison function `cmp`.

The sort is not stable, i.e., equal elements may appear in a different order than in the input `l`.

The sort implementation is a Quicksort.

`def span(f: a -> Bool, l: List[a]): (List[a], List[a])`Source

Returns a pair of lists `(l1, l2)`.

`l1` is the longest prefix of `l` that satisfies the predicate `f`. `l2` is the remainder of `l`.

The function `f` must be pure.

`def splitAt(n: Int32, xs: List[a]): (List[a], List[a])`Source

Split the list `xs` at the position `n` returning the left and right parts. Position `n` is included in the right part.

Example: `splitAt(2, 1::2::3::4::Nil)` returns `(1::2::Nil, 3::4::Nil)`

Returns `(xs, Nil)` if `n > length(xs)`. Returns `(Nil, xs)` if `n < 0`.

`def subsequences(l: List[a]): List[List[a]]`Source

Returns all subsequences of `l` in lexicographical order by element indices in `l`.

That is, `l` is the first subsequence and `Nil` is the last subsequence.

`def sum(l: List[Int32]): Int32`Source

Returns the sum of all elements in the list `l`.

`def sumWith(f: a -> Int32 \ ef, l: List[a]): Int32 \ ef`Source

Returns the sum of all elements in the list `l` according to the function `f`.

`def take(n: Int32, l: List[a]): List[a]`Source

Returns the first `n` elements of `l`.

Returns `l` if `n > length(l)`. Returns `Nil` if `n < 0`.

`def takeWhile(f: a -> Bool \ ef, l: List[a]): List[a] \ ef`Source

Returns the longest prefix of `l` that satisfies the predicate `f`.

`def toArray(rc: Region[r], l: List[a]): Array[a, r] \ r`Source

Returns the list `l` as an array.

`def toChain(l: List[a]): Chain[a]`Source

Returns the list `l` as a chain.

`def toDelayList(l: List[a]): DelayList[a]`Source

Returns the elements of `l` as a `DelayList`.

`def toDelayMap(l: List[(a, b)]): DelayMap[a, b]`Source

Returns the association list `l` as a `DelayMap`.

If `l` contains multiple mappings with the same key, `toDelayMap` does not make any guarantees about which mapping will be in the resulting map.

`def toMap(l: List[(a, b)]): Map[a, b]`Source

Returns the association list `l` as a map.

If `l` contains multiple mappings with the same key, `toMap` does not make any guarantees about which mapping will be in the resulting map.

`def toMapWith(f: a -> b, l: List[a]): Map[a, b]`Source

Returns a map with elements of `s` as keys and `f` applied as values.

If `s` contains multiple mappings with the same key, `toMapWith` does not make any guarantees about which mapping will be in the resulting map.

`def toMutDeque(rc: Region[r], l: List[a]): MutDeque[a, r] \ r`Source

Returns `l` as a MutDeque.

`def toMutList(rc: Region[r], l: List[a]): MutList[a, r] \ r`Source

Returns `l` as a mutable list.

`def toNec(l: List[a]): Option[Nec[a]]`Source

Returns the list `l` as `Option[Nec[a]]`.

If `l` is empty return `None`, otherwise return the Nec wrapped in `Some`.

`def toNel(l: List[a]): Option[Nel[a]]`Source

Returns the list `l` as `Option[Nel[a]]`.

If `l` is empty return `None`, otherwise return the Nel wrapped in `Some`.

`def toSet(l: List[a]): Set[a]`Source

Returns the list `l` as a set.

`def toString(l: List[a]): String`Source

Renders the list `l` to a String.

`def toVector(l: List[a]): Vector[a]`Source

Returns the list `l` as a vector.

`def transpose(l: List[List[a]]): List[List[a]]`Source

Returns the transpose of `l`.

Returns `l` if the dimensions of the elements of `l` are mismatched.

`def traverse(f: a -> m[b] \ ef, l: List[a]): m[List[b]] \ ef`Source

Returns the result of applying the applicative mapping function `f` to all the elements of the list `l` going from left to right.

`def unfold(f: s -> Option[(a, s)] \ ef, st: s): List[a] \ ef`Source

Build a list by applying `f` to the seed value `st`.

`f` should return `Some(a,st1)` to signal a new list element `a` and a new seed value `st1`.

`f` should return `None` to signal the end of building the list.

`def unfoldWithIter(next: Unit -> Option[a] \ ef): List[a] \ ef`Source

Build a list by applying the function `next` to `()`. `next` is expected to encapsulate a stateful resource such as a file handle that can be iterated.

`next` should return `Some(a)` to signal a new list element `a`.

`next` should return `None` to signal the end of building the list.

`def unfoldWithOkIter(next: Unit -> Result[e, Option[a]] \ ef): Result[e, List[a]] \ ef`Source

Build a list by applying the function `next` to `()`. `next` is expected to encapsulate a stateful resource such as a file handle that can be iterated.

`next` should return `Ok(Some(a)` to signal a new list element `Ok(a)`.

`next` should return `Ok(None)` to signal the end of building the list.

`next` should return `Err(e)` to signal that an error occurred. The function returns `Err(e)`.

`def unzip(l: List[(a, b)]): (List[a], List[b])`Source

Returns a pair of lists, the first containing all first components in `l` and the second containing all second components in `l`.

`def unzip3(l: List[(a, b, c)]): (List[a], List[b], List[c])`Source

Returns a triple of lists, the first containing all first components in `l` the second containing all second components in `l` and the third containing all third components in `l`.

`def update(i: Int32, a: a, l: List[a]): List[a]`Source

Returns `l` with the element at index `i` replaced by `x`.

Returns `l` if `i < 0` or `i > length(l)-1`.

`def zip(l1: List[a], l2: List[b]): List[(a, b)]`Source

Returns a list where the element at index `i` is `(a, b)` where `a` is the element at index `i` in `l1` and `b` is the element at index `i` in `l2`.

If either `l1` or `l2` becomes depleted, then no further elements are added to the resulting list.

`def zip3(l1: List[a], l2: List[b], l3: List[c]): List[(a, b, c)]`Source

Returns a list where the element at index `i` is `(a, b, c)` where `a` is the element at index `i` in `l1`, `b` is the element at index `i` in `l2` and `c` is the element at index `i` in `l3`.

If any one of `l1`, `l2` or `l3` become depleted, then no further elements are added to the resulting list.

`def zipWith(f: a -> (b -> c \ ef), l1: List[a], l2: List[b]): List[c] \ ef`Source

Returns a list where the element at index `i` is `f(a, b)` where `a` is the element at index `i` in `l1` and `b` is the element at index `i` in `l2`.

If either `l1` or `l2` becomes depleted, then no further elements are added to the resulting list.

`def zipWith3(f: a -> (b -> (c -> d \ ef)), l1: List[a], l2: List[b], l3: List[c]): List[d] \ ef`Source

Returns a list where the element at index `i` is `f(a, b, c)` where `a` is the element at index `i` in `l1`, `b` is the element at index `i` in `l2` and `c` is the element at index `i` in `l3`.

If any one of `l1`, `l2` or `l3` become depleted, then no further elements are added to the resulting list.

`def zipWithA(f: a -> (b -> f[c] \ ef), xs: List[a], ys: List[b]): f[List[c]] \ ef`Source

Generalize `zipWith` to an applicative functor `f`.

`def zipWithIndex(l: List[a]): List[(Int32, a)]`Source

Returns a list where each element `e` is mapped to `(i, e)` where `i` is the index of `e`.