TypeScript Pattern Match

What is This?

A type-safe way to pattern match on more than just a single value. Think pattern matching on tuples.

Installation

In your terminal:

$ npm install --save typescript-pattern-match

In your TypeScript files:

import { patternMatch } from 'typescript-pattern-match'

API

Think of it like a more powerful switch statement.

patternMatch<A, B> :: (scrutinee: A, cases: ReadonlyArray<CaseBlock<A, B>>, defaultBlock: () => B): B

The scrutinee is the value you’re trying to match against. The cases are similar to the list of case statements in a standard switch block and are passed in as an array to patternMatch. Each case block must have a .case value and a .do function. patternMatch will invoke and return the return value of the .do function associated with the first .case value to match the scrutinee. There is no fallthrough.

The third and final argument passed to patternMatch is a function whose return value is the default value returned if none of the cases match the scrutinee.

Example Usage

We can now match on type-safe tuples!

patternMatch([ true, 'noob noob' ], [
  {
    case: [ true, 'MPB' ],
    do: () => 'oooo weee!',
  },
  {
    case: [ false, 'noob noob' ],
    do: () => 'this guy gets it',
  },
  {
    case: [ true, 'noob noob' ],
    do: () => {
      console.log('you can perform calculations or do whatever here')
      return 'this is the matched case'
    },
  },
], () => {
  return 'the default'
})