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Version: 0.60.0

List Module

List.empty : 'a list​

Returns an empty list.

let xs = List.empty

List.map : ('a -> 'b) -> 'a list -> 'b list​

Transforms each item.

let doubled = [1; 2; 3] |> List.map (fun n -> n * 2)

List.iter : ('a -> unit) -> 'a list -> unit​

Applies a side-effecting function to each item.

["a"; "b"] |> List.iter print

List.choose : ('a -> 'b option) -> 'a list -> 'b list​

Maps and keeps only Some results.

let parsed = ["1"; "x"; "2"] |> List.choose Int.tryParse

List.collect : ('a -> 'b list) -> 'a list -> 'b list​

Maps each item to a list, then concatenates.

let pairs = [1; 2] |> List.collect (fun n -> [n; n])

List.exists : ('a -> bool) -> 'a list -> bool​

Returns true if any item matches.

let hasEven = [1; 3; 4] |> List.exists (fun n -> n % 2 == 0)

List.contains : 'a -> 'a list -> bool​

Checks whether a value appears in a list.

let hasTwo = [1; 2; 3] |> List.contains 2

List.rev : 'a list -> 'a list​

Reverses a list.

let reversed = [1; 2; 3] |> List.rev

List.distinct : 'a list -> 'a list​

Removes duplicate values.

let unique = [1; 2; 2; 3] |> List.distinct

List.fold : ('state -> 'a -> 'state) -> 'state -> 'a list -> 'state​

Folds left over a list.

let sum = [1; 2; 3] |> List.fold (fun acc n -> acc + n) 0

List.filter : ('a -> bool) -> 'a list -> 'a list​

Keeps only matching items.

let odds = [1; 2; 3; 4] |> List.filter (fun n -> n % 2 == 1)

List.length : 'a list -> int​

Returns item count.

let n = ["a"; "b"] |> List.length

List.tryFind : ('a -> bool) -> 'a list -> 'a option​

Returns first matching element.

let maybeBig = [2; 4; 9] |> List.tryFind (fun n -> n > 5)

List.tryGet : ('a -> bool) -> 'a list -> int option​

Returns index of first matching element.

let maybeIndex = ["a"; "bb"; "ccc"] |> List.tryGet (fun s -> String.indexOf "c" s |> Option.isSome)

List.tryHead : 'a list -> 'a option​

Returns first item if present.

let maybeFirst = [10; 20] |> List.tryHead

List.tail : 'a list -> 'a list​

Returns all elements except the head.

let rest = [1; 2; 3] |> List.tail

List.append : 'a list -> 'a list -> 'a list​

Concatenates two lists.

let all = List.append [1; 2] [3; 4]