Arrays in

About Arrays

An Array in Elm is a fast immutable collection of zero or more values of the same type. As arrays are immutable, once an array has been constructed, its value can never change. There is no literal syntax for arrays (like there is for list), so instead the Array.fromList syntax is used. For example, an Array with "a", "b" and "c" in it is usually shown as Array.fromList ["a", "b", "c"]. You will see this on console output, in the debugger, and other places like that.

Unlike List which is a default-import, the Array module must be explicity imported, using import Array or similar.

Type annotations for lists can be defined as follows

Array String --> an array of String
Array Int --> an array of Int

Arrays can be defined as follows:

import Array exposing (Array)

empty : Array Char
empty = Array.empty

singleValue = Array.fromList [ 5 ] --> Array Int

repeatSingleValue = Array.repeat 2 5 --> Array.fromList [ 5, 5 ]

initialiseFromIndex = Array.initialise 3 (\index -> index * 2) --> Array.fromList [ 0, 2, 4 ]

initialisefromList = Array.fromList [ "a", "b", "c" ] --> Array.fromList [ "a", "b", "c" ]

Elements are added to an Array using Array.push:

twoToFour = Array.fromList [ 2, 3, 4 ]
oneToFour = Array.push 1 twoToFour --> Array.fromList [ 1, 2, 3, 4 ]

Arrays are appended using Array.append:

sixSeven = Array.fromList [ 6, 7 ]
eightNine = Array.fromList [ 8, 9 ]
Array.append sixSeven eightNine --> Array.fromList [ 6, 7, 8, 9 ]

An element in an Array is retrieved using Array.get:

sixSeven = Array.fromList [ 6, 7 ]
Array.get 0 sixSeven --> Just 6

An element in an Array is set using Array.set:

sixSeven = Array.fromList [ 6, 7 ]
Array.set 1 8 sixSeven --> Array.fromList [ 6, 8 ]

Arrays are manipulated by functions defined in the Array module.

oneTwo = Array.fromList [ 1, 2 ]
Array.length oneTwo --> 2

Any function/operator that appears to modify an Array`` (such as adding an element), will actually return a new Array. Performance is usually not an issue though, as the implementation of Array` prevents unnecessary allocations/copies.