1.8 KiB
title
| title |
|---|
| List |
List
In Elm, a list is a data structure holding zero or more elements. While lists can per se hold elements of any type, a given list can hold only elements of a single type.
> [1, 2, 3]
[1,2,3] : List number
Working with lists
The core Elm package provides several useful functions for working with lists:
filter
filter accepts a predicate and a list and returns a new list containing all elements from the original list that fulfill the predicate.
> List.filter (\x -> x > 3) [1, 2, 3, 4, 5, 6 ]
[4,5,6] : List number
map
map accepts a transformation function and a list and returns a new list by applying the function to each element of the original list. The type of the input and output list can be different, e.g. it is possible to convert a list of String to a list of Maybe Int:
> List.map (\x -> String.toInt x) ["1", "2", "3"]
[Just 1,Just 2,Just 3]
: List (Maybe Int)
take
take accepts a count and a list and returns a new list that contains the first count elements of the input list. If the input list has fewer than count elements, the whole input list is returned.
> List.take 3 [1, 2, 3, 4, 5, 6]
[1,2,3] : List number
head
head returns the first element of a list. If the list is empty, it returns Nothing, otherwise Just .
> List.head [1, 2, 3]
Just 1 : Maybe number
tail
tail returns all but the first elements from the input list. If the list is empty, it returns Nothing, otherwise Just .
> List.tail [1, 2, 3]
Just [2,3] : Maybe (List number)
More Information:
- elm-lang.org | lists
- [package.elm-lang.org | list-extra (convenience functions for working with lists] (https://package.elm-lang.org/packages/elm-community/list-extra/latest)