spontoreau/pattern-matching-ts

A simple & ambitionless pattern matching library for TypeScript!

pattern-matching-ts

A simple & ambitionless pattern matching library built with TypeScript!

Installation

$ npm install pattern-matching-ts

Getting started

The library use currying to achieve pattern matching. Nothing really hard to understand if you're familiar with functional programming. Otherwise, you can take a look on Eric Eliott's post: Curry and Function Composition.

To match someting, you have to use the match function. This one needs a value and a collection of patterns. Each pattern can be built with the when function. The when combine a condition and something to execute. If the condition succeed then the result will be returned by the function to execute.

Also, a wildcare is available as the last parameter to handle the default return if no pattern is matched (this parameter is optional).

Example with JavaScript:

import { match, when } from "pattern-matching-ts";

const isJohnOrEvelyn = (name) => {
  return match(name)(
    when(n => n === "John")((n /* original value is available as a parameter */) => true),
    when(n => n === "Evelyn")(() => true)
  )(() => false);
};

const isJohn = isJohnOrEvelyn("John"); // true
const isEvelyn = isJohnOrEvelyn("Eveyln"); // true
const isNotJohnOrEvelyn = isJohnOrEvelyn("Mike"); // false

This library is built with TypeScript so types are inferred correctly:

import { match, when } from "pattern-matching-ts";

const isJohn: boolean = match("John")(
  when(n => n === "John")(() => true)
)(_ => false);

With TypeScript, the when function only helps to infer the return type. If you want to match complex structure with it, you need to specify the type as generic argument.

import { match, when } from "pattern-matching-ts";

type Person = {
  readonly firstName: string; 
}

const john: Person = {
  firstName = "John"
}

const isJohn: boolean = match(john)(
  when<Person>(n => n.firstName === "John")(() => true)
)(_ => false);

Enjoy!

Licence

MIT