ligo/gitlab-pages/docs/reference/list.md

id	title
list-reference	List

List.size(lst: a' list) : nat

Get the number of elements in a list.

function size_ (const m : list(int)) : nat is size(m)

let size_ (s: int list) : nat = List.size s

let size_ = (s: list(int)): nat => List.size(s);

List.length(lst: a' list) : nat

Alias of List.size.

List.map(map_function: a' -> b', lst: a' list) : 'b list

Apply an operation defined by map_function to each element of a list and return a list of the modified elements.

function increment(const i: int): int is i + 1;
// Creates a new list with elements incremented by 1
const incremented_list: list(int) = list_map(increment, list 1; 2; 3; end );

let increment (i: int) : int = i + 1
(* Creates a new list with elements incremented by 1 *)
let incremented_list: int list = List.map increment [1; 2; 3]

let increment = (i: int): int => i + 1;
(* Creates a new list with elements incremented by 1 *)
let incremented_list: list(int) = List.map(increment, [1, 2, 3]);

List.iter(iter_function: a' -> unit, lst: a' list) : unit

Apply a side effecting function iter_function to each element of a list with no return value. This is useful for asserting that each element of a list satisfies a particular property.

function iter_op (const s : list(int)) : int is
  begin
    var r : int := 0 ;
    function aggregate (const i : int) : unit is
      begin
        r := r + i ;
      end with unit ;
    list_iter(aggregate, s) ;
  end with r

let iter_op (s : int list) : unit =
  let do_nothing = fun (_: int) -> unit
  in List.iter do_nothing s

let iter_op = (s: list(int)): unit => {
  let do_nothing = (z: int) => unit;
  List.iter(do_nothing, s);
};

List.fold(fold_function: (a' * a') -> a', lst: a' list, acc: a') : 'a

Combine the elements of a list into one value using the operation defined by fold_function'. For example, you could define summation by folding a list of integers. Starting with some initial accumulator value acc`, the fold:

1. Consumes an element of the list.
2. Passes the accumulator value to fold_function along with the element to produce a new accumulated value.
3. The new accumulated value replaces the previous one.
4. IF there are still elements in the list go back to 1, ELSE return the accumulator

Summation would be defined then by using a fold_function that takes two integers and adds them together. Each step of the fold would consume an element from the list and add it to the total until you've summed over the list.

function sum(const result: int; const i: int): int is result + i;
const sum_of_a_list: int = list_fold(sum, list 1; 2; 3; end, 0);

let sum (result, i: int * int) : int = result + i
let sum_of_a_list: int = List.fold sum [1; 2; 3] 0

let sum = ((result, i): (int, int)): int => result + i;
let sum_of_a_list: int = List.fold(sum, [1, 2, 3], 0);