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 enable two functions, namely getFirst and getSelected to return a value directly instead of a Maybe.

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 False).

In addition, non-empty-array offers 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.
• updateSelected: Updates the element at the currently selected index.

Finally, it offers update, removeAt and removeAtSafe, which are not in core Array but inspired by Array.Extra.

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

• 2.1.0 - 2018-11-19: Add functions for JSON decoding/encoding
• 2.0.0 - 2018-11-18: Update for Elm 0.19 (all credits go to Ignacio Gutierrez(@devnacho))
• 1.4.0 - 2017-12-24: Add mapSelected and indexedMapSelected (#2, #3, thanks to @cjduncana).
• 1.3.1 - 2017-10-19: Fix #1 (removeSafeAt removes last element)
• 1.3.0 - 2017-08-09: Add removeAt, removeSafeAt
• 1.2.0 - 2017-07-02: Add update, updateSelected and setSelectedIndexAndReport
• 1.1.1 - 2017-07-01: Fix typo in README
• 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.