https://github.com/nathsou/itsamatch

Delightful Sum Types in TypeScript
https://github.com/nathsou/itsamatch

Last synced: about 2 months ago
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Delightful Sum Types in TypeScript

• Host: GitHub
• URL: https://github.com/nathsou/itsamatch
• Owner: nathsou
• Created: 2021-04-05T19:48:54.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2024-01-15T01:46:58.000Z (12 months ago)
• Last Synced: 2024-11-10T23:04:44.886Z (about 2 months ago)
• Language: TypeScript
• Size: 25.4 KB
• Stars: 1
• Watchers: 2
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.md

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README

        
[![NPM Package][npm]][npm-url]

[![Build Size][build-size]][build-size-url]

# It's a match!

Itsamatch is a tiny set of types and utilities to define and use variants / tagged unions / sum types in a more declarative way in TypeScript.

## Usage

itsamatch exposes three functions (match, matchMany, genConstructors) and a few types that make it easier to construct data types.

Below is a simple example showing how it can be used to create a [linked list data type](https://en.wikipedia.org/wiki/Cons#Lists) :

```typescript

import { DataType, constructors, match } from 'itsamatch';

// a list is a data type with two variants:

type List = DataType<{

    Nil: {},

    Cons: { head: T, tail: List }

}>;

// generate default variant constructors for lists of numbers

const { Nil, Cons } = constructors>().get('Nil', 'Cons');

// use the match function to compute the length of a list

const len = (list: List): number => match(list, {

    Nil: () => 0,

    Cons: ({ tail }) => 1 + len(tail)

});

const same = (a: List, b: List): boolean => matchMany([a, b], {

  'Nil Nil': () => true,

  'Cons Cons': (l, r) => l.head === r.head && same(l.tail, r.tail),

  _: () => false,

});

const size = len(Cons({ head: 1, tail: Cons({ head: 2, tail: Nil() }) })); // 2

const sameElems = same(Cons({ head: 1, tail: Nil() }), Nil()); // false

```

More examples are available in the /examples folder

[npm]: https://img.shields.io/npm/v/itsamatch

[npm-url]: https://www.npmjs.com/package/itsamatch

[build-size]: https://badgen.net/bundlephobia/minzip/itsamatch

[build-size-url]: https://bundlephobia.com/result?p=itsamatch