Array.NonEmpty for Elm

An array that always contains at least one element.

Additionaly, it can track a currently selected index, which is guaranteed to point to an existing element in the array.

These additional constraints enables two functions, namely getFirst and getSelected to return a value directly instead of a Maybe.

The implementation uses Skinney/elm-array-exploration internally (which will be the default Array implementation in Elm core from version 0.19 on). For Elm 0.18, Skinney/elm-array-exploration is the only dependency besides elm-lang/core. For Elm 0.19, elm-lang/core will be the only dependency.

Inspired by mgold/elm-nonempty-list.

import Array.NonEmpty as NEA exposing (NonEmptyArray)


oneElement : NonEmptyArray
oneElement = NEA.fromElement 13

twoElements : NonEmptyArray
twoElements = NEA.push 42 one

createdFromList : Maybe NonEmptyArray
createdFromList = NEA.fromList ["a", "b", "b"]

All functions from core Array are available, with the exception of isEmpty (which would be an alias for True).

In addition, non-empty-array offer additional functions made possible due to the additional constraints:

• getFirst: Returns the first element. Since it is known that this element exists, this function does not return a Maybe but the actual element type.
• getSelected: Returns the element at the currently selected index. Since it is known that this element exists, this function does not return a Maybe but the actual element type.

Tests

The easiest way to run the tests is to install the npm packages elm-test and elm-verify-examples globally:

npm i elm-test -g
npm i elm-verify-examples -g

Then, from the project root directory, run

elm-verify-examples && elm-test

This will require downloading some packages on the first run.

Version History

• 1.1.0 - 2017-06-30: Selected index feature
• 1.0.0 - 2017-06-30: Initial version

License

This library uses the BSD3 License. See LICENSE for more information.