List

t<'a>

RES
type t<'a> = list<'a>

length

let length: t<'a> => int

Returns the length of a list.

RES
Belt.List.length(list{1, 2, 3}) // 3

size

let size: t<'a> => int

See: list{length}(#length)

head

let head: t<'a> => option<'a>

Returns Some(value) where value is the first element in the list, or None if someList is an empty list.

RES
Belt.List.head(list{}) // None
Belt.List.head(list{1, 2, 3}) // Some(1)

headExn

let headExn: t<'a> => 'a

Same as head, but raises an exception if someList is empty. Use with care.

RES
Belt.List.headExn(list{1, 2, 3}) // 1

Belt.List.headExn(list{}) // Raises an Error

tail

let tail: t<'a> => option<t<'a>>

Returns None if someList is empty, otherwise it returns Some(tail) where tail is everything except the first element of someList.

RES
Belt.List.tail(list{1, 2, 3}) // Some(list{2, 3})

Belt.List.tail(list{}) // None

tailExn

let tailExn: t<'a> => t<'a>

Same as tail, but raises an exception if someList is empty. Use with care.

RES
Belt.List.tailExn(list{1, 2, 3}) // list{2, 3}

Belt.List.tailExn(list{}) // Raises an Error

add

let add: (t<'a>, 'a) => t<'a>

Adds value to the beginning of someList.

RES
Belt.List.add(list{2, 3}, 1) // list{1, 2, 3}

Belt.List.add(list{"World", "!"}, "Hello") // list{"Hello", "World", "!"}

get

let get: (t<'a>, int) => option<'a>

Return the nth element in someList, or None if index is larger than the length.

RES
let abc = list{"A", "B", "C"}

abc->Belt.List.get(1) // Some("B")

abc->Belt.List.get(4) // None

getExn

let getExn: (t<'a>, int) => 'a

Same as get, but raises an exception if index is larger than the length. Use with care.

RES
let abc = list{"A", "B", "C"}

abc->Belt.List.getExn(1) // "B"

abc->Belt.List.getExn(4) // Raises an Error

make

let make: (int, 'a) => t<'a>

Returns a list of length numItems with each element filled with value v. Returns an empty list if numItems is negative.

RES
Belt.List.make(3, 1) // list{1, 1, 1}

makeBy

let makeBy: (int, int => 'a) => t<'a>

Return a list of length numItems with element i initialized with f(i). Returns an empty list if numItems is negative.

RES
Belt.List.makeBy(5, i => i) // list{0, 1, 2, 3, 4}

Belt.List.makeBy(5, i => i * i) // list{0, 1, 4, 9, 16}

makeByU

let makeByU: (int, (. int) => 'a) => t<'a>

Uncurried version of makeBy

shuffle

let shuffle: t<'a> => t<'a>

Returns a new list in random order.

RES
Belt.List.shuffle(list{1, 2, 3}) // list{2, 1, 3}

drop

let drop: (t<'a>, int) => option<t<'a>>

Return a new list, dropping the first n elements. Returns None if someList has fewer than n elements.

RES
list{1, 2, 3}->Belt.List.drop(2) // Some(list{3})

list{1, 2, 3}->Belt.List.drop(3) // Some(list{})

list{1, 2, 3}->Belt.List.drop(4) // None

take

let take: (t<'a>, int) => option<t<'a>>

Returns a list with the first n elements from someList, or None if someList has fewer than n elements.

RES
list{1, 2, 3}->Belt.List.take(1) // Some(list{1})

list{1, 2, 3}->Belt.List.take(2) // Some(list{1, 2})

list{1, 2, 3}->Belt.List.take(4) // None

splitAt

let splitAt: (t<'a>, int) => option<(list<'a>, list<'a>)>

Split the list someList at index. Returns None when the length of someList is less than index.

RES
list{"Hello", "World"}->Belt.List.splitAt(1) // Some((list{"Hello"}, list{"World"}))

list{0, 1, 2, 3, 4}->Belt.List.splitAt(2) // Some((list{0, 1}, list{2, 3, 4}))

concat

let concat: (t<'a>, t<'a>) => t<'a>

Returns the list obtained by adding secondList after firstList.

RES
Belt.List.concat(list{1, 2, 3}, list{4, 5}) // list{1, 2, 3, 4, 5}

concatMany

let concatMany: array<t<'a>> => t<'a>

Returns the list obtained by concatenating all the lists in array a, in order.

RES
Belt.List.concatMany([list{1, 2, 3}, list{}, list{3}]) // list{1, 2, 3, 3}

reverseConcat

let reverseConcat: (t<'a>, t<'a>) => t<'a>

Equivalent to writing: concat(reverse(firstList, secondList)

RES
Belt.List.reverseConcat(list{1, 2}, list{3, 4}) // list{2, 1, 3, 4}

flatten

let flatten: t<t<'a>> => t<'a>

Return the list obtained by concatenating all the lists in list ls, in order.

RES
Belt.List.flatten(list{list{1, 2, 3}, list{}, list{3}}) // list{1, 2, 3, 3}

map

let map: (t<'a>, 'a => 'b) => t<'b>

Returns a new list with f applied to each element of someList.

RES
list{1, 2}->Belt.List.map(x => x + 1) // list{3, 4}

mapU

let mapU: (t<'a>, (. 'a) => 'b) => t<'b>

Uncurried version of map.

zip

let zip: (t<'a>, t<'b>) => t<('a, 'b)>

Returns a list of pairs from the two lists with the length of the shorter list.

RES
Belt.List.zip(list{1, 2}, list{3, 4, 5}) // list{(1, 3), (2, 4)}

zipBy

let zipBy: (t<'a>, t<'b>, ('a, 'b) => 'c) => t<'c>

See: zip

RES
Belt.List.zipBy(list{1, 2, 3}, list{4, 5}, (a, b) => 2 * a + b) // list{6, 9}

zipByU

let zipByU: (t<'a>, t<'b>, (. 'a, 'b) => 'c) => t<'c>

Uncurried version of zipBy.

mapWithIndex

let mapWithIndex: (t<'a>, (int, 'a) => 'b) => t<'b>

Applies f to each element of someList. Function f takes two arguments: the index starting from 0 and the element from someList, in that order.

RES
list{1, 2, 3}->Belt.List.mapWithIndex((index, x) => index + x) // list{1, 3, 5}

mapWithIndexU

let mapWithIndexU: (t<'a>, (. int, 'a) => 'b) => t<'b>

Uncurried version of mapWithIndex.

fromArray

let fromArray: array<'a> => t<'a>

Converts the given array to a list.

RES
Belt.List.fromArray([1, 2, 3]) // list{1, 2, 3}

toArray

let toArray: t<'a> => array<'a>

Converts the given list to an array.

RES
Belt.List.toArray(list{1, 2, 3}) // [1, 2, 3]

reverse

let reverse: t<'a> => t<'a>

Returns a new list whose elements are those of someList in reversed order.

RES
Belt.List.reverse(list{1, 2, 3}) /* list{3, 2, 1} */

mapReverse

let mapReverse: (t<'a>, 'a => 'b) => t<'b>

Equivalent to:

RES
map(someList, f)->reverse

RES
list{3, 4, 5}->Belt.List.mapReverse(x => x * x) /* list{25, 16, 9} */

mapReverseU

let mapReverseU: (t<'a>, (. 'a) => 'b) => t<'b>

Uncurried version of mapReverse.

forEach

let forEach: (t<'a>, 'a => 'b) => unit

Call f on each element of someList from the beginning to end. f returns unit, so no new array is created. Use forEach when you are primarily concerned with repetitively creating side effects.

RES
Belt.List.forEach(list{"a", "b", "c"}, x => Js.log("Item: " ++ x))
/*
  prints:
  Item: a
  Item: b
  Item: c
*/

forEachU

let forEachU: (t<'a>, (. 'a) => 'b) => unit

Uncurried version of forEach.

forEachWithIndex

let forEachWithIndex: (t<'a>, (int, 'a) => 'b) => unit

Call f on each element of someList from beginning to end. Function f takes two arguments: the index starting from 0 and the element from someList. f returns unit.

RES
Belt.List.forEachWithIndex(list{"a", "b", "c"}, (index, x) => {
  Js.log("Item " ++ Belt.Int.toString(index) ++ " is " ++ x)
})
/*
  prints:
  Item 0 is a
  Item 1 is b
  Item 2 is cc
*/

forEachWithIndexU

let forEachWithIndexU: (t<'a>, (. int, 'a) => 'b) => unit

Uncurried version of forEachWithIndex.

reduce

let reduce: (t<'a>, 'b, ('b, 'a) => 'b) => 'b

Applies f to each element of someList from beginning to end. Function f has two parameters: the item from the list and an “accumulator”, which starts with a value of initialValue. reduce returns the final value of the accumulator.

RES
list{1, 2, 3, 4}->Belt.List.reduce(0, (a, b) => a + b) /* 10 */

/* same as */

list{1, 2, 3, 4}->Belt.List.reduce(0, (acc, item) => acc + item) /* 10 */

reduceU

let reduceU: (t<'a>, 'b, (. 'b, 'a) => 'b) => 'b

Uncurried version of reduce.

reduceWithIndex

let reduceWithIndex: (t<'a>, 'b, ('b, 'a, int) => 'b) => 'b

Applies f to each element of someList from beginning to end. Function f has three parameters: the item from the list and an “accumulator”, which starts with a value of initialValue and the index of each element. reduceWithIndex returns the final value of the accumulator.

RES
list{1, 2, 3, 4}->Belt.List.reduceWithIndex(0, (acc, item, index) => acc + item + index) /* 16 */

reduceWithIndexU

let reduceWithIndexU: (t<'a>, 'b, (. 'b, 'a, int) => 'b) => 'b

Uncurried version of reduceWithIndex.

reduceReverse

let reduceReverse: (t<'a>, 'b, ('b, 'a) => 'b) => 'b

Works like reduce, except that function f is applied to each item of someList from the last back to the first.

RES
list{1, 2, 3, 4}->Belt.List.reduceReverse(0, (a, b) => a + b) /* 10 */

list{1, 2, 3, 4}->Belt.List.reduceReverse(10, (a, b) => a - b) /* 0 */

list{1, 2, 3, 4}->Belt.List.reduceReverse(list{}, Belt.List.add) // list{1, 2, 3, 4}

reduceReverseU

let reduceReverseU: (t<'a>, 'b, ('b, 'a) => 'b) => 'b

Uncurried version of reduceReverse.

mapReverse2

let mapReverse2: (t<'a>, t<'b>, ('a, 'b) => 'c) => t<'c>

Equivalent to: zipBy(xs, ys, f)->reverse

RES

Belt.List.mapReverse2(list{1, 2, 3}, list{1, 2}, (a, b) => a + b) // list{4, 2}

mapReverse2U

let mapReverse2U: (t<'a>, t<'b>, ('a, 'b) => 'c) => t<'c>

Uncurried version of mapReverse2.

forEach2

let forEach2: (t<'a>, t<'b>, ('a, 'b) => 'c) => unit

Stops at the length of the shorter list.

RES
Belt.List.forEach2(list{"Z", "Y"}, list{"A", "B", "C"}, (x, y) => Js.log2(x, y))

/*
  prints:
  "Z" "A"
  "Y" "B"
*/

forEach2U

let forEach2U: (t<'a>, t<'b>, (.'a, 'b) => 'c) => unit

Uncurried version of forEach2.

reduce2

let reduce2: (t<'b>, t<'c>, 'a, ('a, 'b, 'c) => 'a) => 'a

Applies f to each element of firstList and secondList from beginning to end. Stops with the shorter list. Function f has three parameters: an “accumulator” which starts with a value of initialValue, an item from firstList, and an item from secondList. reduce2 returns the final value of the accumulator.

RES
Belt.List.reduce2(list{1, 2, 3}, list{4, 5}, 0, (acc, x, y) => acc + x * x + y) /* 0 + (1 * 1 + 4) + (2 * 2 + 5) */

reduce2U

let reduce2U: (t<'b>, t<'c>, 'a, (.'a, 'b, 'c) => 'a) => 'a

Uncurried version of reduce2.

reduceReverse2

let reduceReverse2: (t<'a>, t<'b>, 'c, ('c, 'a, 'b) => 'c) => 'c

Applies f to each element of firstList and secondList from end to beginning. Stops with the shorter list. Function f has three parameters: an “accumulator” which starts with a value of init, an item from firstList, and an item from secondList. reduce2 returns the final value of the accumulator.

RES
Belt.List.reduceReverse2(list{1, 2, 3}, list{4, 5}, 0, (acc, x, y) => acc + x * x + y) /*  + (1 * 1 + 4) + (2 * 2 + 5) */

reduceReverse2U

let reduceReverse2U: (t<'a>, t<'b>, 'c, (.'c, 'a, 'b) => 'c) => 'c

Uncurried version of reduceReverse2.

every

let every: (t<'a>, 'a => bool) => bool

Returns true if all elements satisfy pred, where pred is a predicate: a function taking an element and returning a bool.

RES
let isBelow10 = value => value < 10

list{1, 9, 8, 2}->Belt.List.every(isBelow10) /* true */

list{1, 99, 8, 2}->Belt.List.every(isBelow10) /* false */

everyU

let everyU: (t<'a>, (.'a) => bool) => bool

Uncurried version of every.

some

let some: (t<'a>, 'a => bool) => bool

Returns true if at least one of the elements in someList satisfies pred, where pred is a predicate: a function taking an element and returning a bool.

RES
let isAbove100 = value => value > 100

list{101, 1, 2, 3}->Belt.List.some(isAbove100) /* true */

list{1, 2, 3, 4}->Belt.List.some(isAbove100) /* false */

someU

let someU: (t<'a>, (. 'a) => bool) => bool

Uncurried version of some.

every2

let every2: (t<'a>, t<'b>, ('a, 'b) => bool) => bool

Returns true if predicate pred(a, b) is true for all pairs of elements up to the shorter length (i.e. min(length(firstList), length(secondList)))

RES
Belt.List.every2(list{1, 2, 3}, list{0, 1}, (a, b) => a > b) /* true */

Belt.List.every2(list{}, list{1}, (a, b) => a > b) /* true */

Belt.List.every2(list{2, 3}, list{1}, (a, b) => a > b) /* true */

Belt.List.every2(list{0, 1}, list{5, 0}, (a, b) => a > b) /* false */

every2U

let every2U: (t<'a>, t<'b>, (. 'a, 'b) => bool) => bool

Uncurried version of every2.

some2

let some2: (t<'a>, t<'b>, ('a, 'b) => bool) => bool

Returns true if predicate pred(a, b) is true for any pair of elements up to the shorter length (i.e. min(length(firstList), length(secondList)))

RES
Belt.List.some2(list{1, 2, 3}, list{0, 1}, (a, b) => a > b) /* true */

Belt.List.some2(list{}, list{1}, (a, b) => a > b) /* false */

Belt.List.some2(list{2, 3}, list{1}, (a, b) => a > b) /* true */

Belt.List.some2(list{0, 1}, list{5, 0}, (a, b) => a > b) /* true */

some2U

let some2U: (t<'a>, t<'b>, (. 'a, 'b) => bool) => bool

Uncurried version of some2.

cmpByLength

let cmpByLength: (t<'a>, t<'a>) => int

RES
cmpByLength(firstList, secondList)

Compare two lists solely by length. Returns -1 if length(firstList) is less than length(secondList), 0 if length(firstList) equals length(secondList), and 1 if length(firstList) is greater than length(secondList).

RES
Belt.List.cmpByLength(list{1, 2}, list{3, 4, 5, 6}) /* -1 */

Belt.List.cmpByLength(list{1, 2, 3}, list{4, 5, 6}) /* = 0 */

Belt.List.cmpByLength(list{1, 2, 3, 4}, list{5, 6}) /* = 1 */

cmp

let cmp: (t<'a>, t<'a>, ('a, 'a) => int) => int

Compare elements one by one compareFn(a, b). compareFn returns a negative number if a is "less than" b, zero if a is "equal to" b, a positive number if a is "greater than" b.

The comparison returns the first non-zero result of compareFn, or zero if compareFn returns zero for all a and b.

If all items have compared equal, but firstList is exhausted first, return -1. (firstList is shorter). If all items have compared equal, but secondList is exhausted first, return 1 (firstList is longer).

RES
Belt.List.cmp(list{3}, list{3, 7}, (a, b) => compare(a, b)) /* (-1) */

Belt.List.cmp(list{5, 3}, list{5}, (a, b) => compare(a, b)) /* 1 */

Belt.List.cmp(list{1, 3, 5}, list{1, 4, 2}, (a, b) => compare(a, b)) /* (-1) */

Belt.List.cmp(list{1, 3, 5}, list{1, 2, 3}, (a, b) => compare(a, b)) /* 1 */

Belt.List.cmp(list{1, 3, 5}, list{1, 3, 5}, (a, b) => compare(a, b)) /* 0 */

Please note: The total ordering of List is different from Array, for Array, we compare the length first and, only if the lengths are equal, elements one by one. For lists, we just compare elements one by one.

cmpU

let cmpU: (t<'a>, t<'a>, (. 'a, 'a) => int) => int

Uncurried version of cmp.

eq

let eq: (t<'a>, t<'a>, ('a, 'a) => bool) => bool

Check equality of firstList and secondList using eqElem for equality on elements, where eqElem is a function that returns true if items x and y meet some criterion for equality, false otherwise. eq false if length of firstList and secondList are not the same.

RES
Belt.List.eq(list{1, 2, 3}, list{1, 2}, (a, b) => a == b) /* false */

Belt.List.eq(list{1, 2}, list{1, 2}, (a, b) => a == b) /* true */

Belt.List.eq(list{1, 2, 3}, list{(-1), (-2), (-3)}, (a, b) => abs(a) == abs(b)) /* true */

eqU

let eqU: (t<'a>, t<'a>, (. 'a, 'a) => bool) => bool

Uncurried version of eqU.

has

let has: (t<'a>, 'b, ('a, 'b) => bool) => bool

Returns true if the list contains at least one element for which eqFunction(x) returns true.

RES
list{1, 2, 3}->Belt.List.has(2, (a, b) => a == b) /* true */

list{1, 2, 3}->Belt.List.has(4, (a, b) => a == b) /* false */

list{(-1), (-2), (-3)}->Belt.List.has(2, (a, b) => abs(a) == abs(b)) /* true */

hasU

let hasU: (t<'a>, 'b, (. 'a, 'b) => bool) => bool

Uncurried version of has.

getBy

let getBy: (t<'a>, 'a => bool) => option<'a>

Returns Some(value) for the first value in someList that satisfies the predicate function pred. Returns None if no element satisfies the function.

RES
Belt.List.getBy(list{1, 4, 3, 2}, x => x > 3) /* Some(4) */

Belt.List.getBy(list{1, 4, 3, 2}, x => x > 4) /* None */

getByU

let getByU: (t<'a>, (. 'a) => bool) => option<'a>

Uncurried version of getBy.

keep

let keep: (t<'a>, 'a => bool) => t<'a>

Returns a list of all elements in someList which satisfy the predicate function pred.

RES
let isEven = x => mod(x, 2) == 0

Belt.List.keep(list{1, 2, 3, 4}, isEven) /* list{2, 4} */

Belt.List.keep(list{None, Some(2), Some(3), None}, Belt.Option.isSome) /* list{Some(2), Some(3)} */

keepU

let keepU: (t<'a>, (. 'a) => bool) => t<'a>

Uncurried version of keep.

filter

let filter: (t<'a>, 'a => bool) => t<'a>

Returns a list of all elements in someList which satisfy the predicate function pred.

RES
let isEven = x => mod(x, 2) == 0

Belt.List.filter(list{1, 2, 3, 4}, isEven) /* list{2, 4} */

Belt.List.filter(list{None, Some(2), Some(3), None}, Belt.Option.isSome) /* list{Some(2), Some(3)} */

keepWithIndex

let keepWithIndex: (t<'a>, ('a, int) => bool) => t<'a>

Returns a list of all elements in someList which satisfy the predicate function pred.

RES
let isEven = x => mod(x, 2) == 0

Belt.List.keepWithIndex(list{1, 2, 3, 4}, (_x, index) => isEven(index)) /* list{1, 3} */

keepWithIndexU

let keepWithIndexU: (t<'a>, (. 'a, int) => bool) => t<'a>

Uncurried version of keepWithIndex.

filterWithIndex

let filterWithIndex: (t<'a>, ('a, int) => bool) => t<'a>

Returns a list of all elements in someList which satisfy the predicate function pred.

RES
let isEven = x => mod(x, 2) == 0

Belt.List.filterWithIndex(list{1, 2, 3, 4}, (_x, index) => isEven(index)) /* list{1, 3} */

keepMap

let keepMap: (t<'a>, 'a => option<'b>) => t<'b>

Applies f to each element of someList. If f(x) returns Some(value), then value is kept in the resulting list. If f(x) returns None, the element is not retained in the result.

RES
let isEven = x => mod(x, 2) == 0

list{1, 2, 3, 4}
->Belt.List.keepMap(x =>
    if (isEven(x)) {
      Some(x)
    } else {
      None
    }
  ) /* list{2, 4} */

list{Some(1), Some(2), None}->Belt.List.keepMap(x => x) /* list{1, 2} */

keepMapU

let keepMapU: (t<'a>, (. 'a) => option<'b>) => t<'b>

Uncurried version of keepMap.

partition

let partition: (t<'a>, 'a => bool) => (t<'a>, t<'a>)

Creates a pair of lists; the first list consists of all elements of someList that satisfy the predicate function pred; the second list consists of all elements of someList that do not satisfy `pred.

In other words:

RES
(elementsThatSatisfies, elementsThatDoesNotSatisfy)

RES
Belt.List.partition(list{1, 2, 3, 4}, x => x > 2) /* (list{3, 4}, list{1, 2}) */

partitionU

let partitionU: (t<'a>, (. 'a) => bool) => (t<'a>, t<'a>)

Uncurried version of partition.

unzip

let unzip: t<('a, 'b)> => (t<'a>, t<'b>)

Takes a list of pairs and creates a pair of lists. The first list contains all the first items of the pairs; the second list contains all the second items.

RES
Belt.List.unzip(list{(1, 2), (3, 4)}) /* (list{1, 3}, list{2, 4}) */

Belt.List.unzip(list{("H", "W"), ("e", "o"), ("l", "r"), ("l", "l"), ("o", "d"), (" ", "!")})
/* (list{"H", "e", "l", "l", "o", " "}, list{"W", "o", "r", "l", "d", "!"}) */

getAssoc

let getAssoc: (t<('a, 'c)>, 'b, ('a, 'b) => bool) => option<'c>

Return the second element of a pair in someList where the first element equals k as per the predicate function eqFunction, or None if not found.

RES
list{(1, "a"), (2, "b"), (3, "c")}->Belt.List.getAssoc(3, (a, b) => a == b) /* Some("c") */

list{(9, "morning"), (15, "afternoon"), (22, "night")}
->Belt.List.getAssoc(15, (k, item) => k /* 15 */ == item /* 9, 5, 22 */)
/* Some("afternoon") */

getAssocU

let getAssocU: (t<('a, 'c)>, 'b, (. 'a, 'b) => bool) => option<'c>

Uncurried version of getAssoc.

hasAssoc

let hasAssoc: (t<('a, 'c)>, 'b, ('a, 'b) => bool) => bool

Returns true if there is a pair in someList where the first element equals k as per the predicate function eqFunction.

RES
list{(1, "a"), (2, "b"), (3, "c")}->Belt.List.hasAssoc(1, (a, b) => a == b) /* true */

list{(9, "morning"), (15, "afternoon"), (22, "night")}
->Belt.List.hasAssoc(25, (k, item) => k /* 25 */ == item /* 9, 5, 22 */) /* false */

hasAssocU

let hasAssocU: (t<('a, 'c)>, 'b, (. 'a, 'b) => bool) => bool

Uncurried version of hasAssoc.

removeAssoc

let removeAssoc: (t<('a, 'c)>, 'b, ('a, 'b) => bool) => t<('a, 'c)>

Return a list after removing the first pair whose first value is k per the equality predicate eqFunction; if not found, return a new list identical to someList.

RES
list{(1, "a"), (2, "b"), (3, "c")}->Belt.List.removeAssoc(1, (a, b) => a == b) /* list{(2, "b"), (3, "c")} */

list{(9, "morning"), (15, "afternoon"), (22, "night")}
->Belt.List.removeAssoc(9, (k, item) => k /* 9 */ == item /* 9, 5, 22 */)
/* list{(15, "afternoon"), (22, "night")} */

removeAssocU

let removeAssocU: (t<('a, 'c)>, 'b, (. 'a, 'b) => bool) => t<('a, 'c)>

Uncurried version of removeAssoc.

setAssoc

let setAssoc: (t<('a, 'c)>, 'a, 'c, ('a, 'a) => bool) => t<('a, 'c)>

If k exists in someList by satisfying the eqFunction predicate, return a new list with the key and value replaced by the new k and v; otherwise, return a new list with the pair k, v added to the head of someList.

RES
list{(1, "a"), (2, "b"), (3, "c")}->Belt.List.setAssoc(2, "x", (a, b) => a == b) /* list{(1, "a"), (2, "x"), (3, "c")} */

list{(1, "a"), (3, "c")}->Belt.List.setAssoc(2, "b", (a, b) => a == b) /* list{(2, "b"), (1, "a"), (3, "c")} */

list{(9, "morning"), (3, "morning?!"), (22, "night")}
->Belt.List.setAssoc(15, "afternoon", (a, b) => mod(a, 12) == mod(b, 12))
/* list{(9, "morning"), (15, "afternoon"), (22, "night")} */

Please note

In the last example, since: 15 mod 12 equals 3 mod 12

Both the key and the value are replaced in the list.

setAssocU

let setAssocU: (t<('a, 'c)>, 'a, 'c, (. 'a, 'a) => bool) => t<('a, 'c)>

Uncurried version of setAssoc.

sort

let sort: (t<'a>, ('a, 'a) => int) => t<'a>

Returns a sorted list.

RES
Belt.List.sort(list{5, 4, 9, 3, 7}, (a, b) => a - b) // list{3, 4, 5, 7, 9}

sortU

let sortU: (t<'a>, (. 'a, 'a) => int) => t<'a>

Uncurried version of sort.