Zip List

A super simple TypeScript implementation of a basic zip list from the "Making Impossible States Impossible" talk at Elm Conf by Richard Feldman.

Used to model a list of data where one item is active. The underlying data structure is:

{ previous: [1], current: 2, next: [3] }

This module provides a nice wrapper around that data structure with a nice API.

Install

npm install @jackfranklin/zip-list
yarn add @jackfranklin/zip-list

Construct a zip list using the static fromArray method:

import ZipList from '@jackfranklin/zip-list';

const zip = ZipList.fromArray([1, 2, 3]);

This will set the first item (1) as active.

If you're using TypeScript, you can pass the type through as a generic to fromArray:

interface MyObj {
  name: string;
}

const zip = ZipList.fromArray<MyObj>([{ name: 'alice' }, { name: 'bob' }]);

Fetch and check if an item is active:

zip.active() === 1;
zip.isActive(2) === false;

Get the data as an array (useful for rendering):

zip.asArray() === [1, 2, 3];

And update the active value. This never mutates but returns a new zip:

const newZip = zip.setActive(2);