141 lines
3.5 KiB
Markdown
141 lines
3.5 KiB
Markdown
---
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id: list-reference
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title: List — Ordered collection of a type
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---
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## List.size(lst: a' list) : nat
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Get the number of elements in a list.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo
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function size_ (const m : list(int)) : nat is size(m)
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```
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<!--CameLIGO-->
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```cameligo
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let size_ (s: int list) : nat = List.size s
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```
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<!--ReasonLIGO-->
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```reasonligo
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let size_ = (s: list(int)): nat => List.size(s);
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## List.length(lst: a' list) : nat
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Alias of `List.size`.
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## List.map(map_function: a' -> b', lst: a' list) : 'b list
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Apply an operation defined by `map_function` to each element of a list and return
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a list of the modified elements.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--Pascaligo-->
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```pascaligo group=b
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function increment(const i: int): int is i + 1;
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// Creates a new list with elements incremented by 1
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const incremented_list: list(int) = list_map(increment, list 1; 2; 3; end );
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```
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<!--CameLIGO-->
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```cameligo group=b
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let increment (i: int) : int = i + 1
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(* Creates a new list with elements incremented by 1 *)
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let incremented_list: int list = List.map increment [1; 2; 3]
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```
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<!--ReasonLIGO-->
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```reasonligo group=b
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let increment = (i: int): int => i + 1;
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(* Creates a new list with elements incremented by 1 *)
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let incremented_list: list(int) = List.map(increment, [1, 2, 3]);
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## List.iter(iter_function: a' -> unit, lst: a' list) : unit
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Apply a side effecting function `iter_function` to each element of a list with no
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return value. This is useful for asserting that each element of a list satisfies
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a particular property.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--PascaLIGO-->
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```pascaligo
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function iter_op (const s : list(int)) : int is
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begin
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var r : int := 0 ;
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function aggregate (const i : int) : unit is
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begin
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r := r + i ;
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end with unit ;
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list_iter(aggregate, s) ;
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end with r
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```
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<!--CameLIGO-->
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```cameligo
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let iter_op (s : int list) : unit =
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let do_nothing = fun (_: int) -> unit
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in List.iter do_nothing s
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```
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<!--ReasonLIGO-->
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```reasonligo
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let iter_op = (s: list(int)): unit => {
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let do_nothing = (z: int) => unit;
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List.iter(do_nothing, s);
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};
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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## List.fold(fold_function: (a' * a') -> a', lst: a' list, acc: a') : 'a
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Combine the elements of a list into one value using the operation defined by
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`fold_function'. For example, you could define summation by folding a list of
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integers. Starting with some initial accumulator value `acc`, the fold:
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1. Consumes an element of the list.
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2. Passes the accumulator value to `fold_function` along with the element to produce
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a new accumulated value.
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3. The new accumulated value replaces the previous one.
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4. IF there are still elements in the list go back to 1, ELSE return the accumulator
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Summation would be defined then by using a `fold_function` that takes two integers and
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adds them together. Each step of the fold would consume an element from the list
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and add it to the total until you've summed over the list.
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<!--DOCUSAURUS_CODE_TABS-->
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<!--Pascaligo-->
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```pascaligo group=b
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function sum(const result: int; const i: int): int is result + i;
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const sum_of_a_list: int = list_fold(sum, list 1; 2; 3; end, 0);
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```
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<!--CameLIGO-->
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```cameligo group=b
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let sum (result, i: int * int) : int = result + i
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let sum_of_a_list: int = List.fold sum [1; 2; 3] 0
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```
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<!--ReasonLIGO-->
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```reasonligo group=b
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let sum = ((result, i): (int, int)): int => result + i;
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let sum_of_a_list: int = List.fold(sum, [1, 2, 3], 0);
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```
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<!--END_DOCUSAURUS_CODE_TABS-->
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