@miyauci/pattern-matching NPM

pattern-matching

Syntax-free pattern matching, feature parity with TC39 proposal-pattern-matching.

This project provides syntax-independent, type-safe pattern matching tools.

Install

deno.land:

import * as mod from "https://deno.land/x/pattern_matching/mod.ts";

npm:

npm i @miyauci/pattern-matching

Usage

To start pattern matching, use the match function and the arm function.

arm takes the role of Clause.

The names of the arm function and the proposal clause are as follows:

Name	Proposal name
when	when
whether	if
otherwise	default

import {
  match,
  otherwise,
  when,
} from "https://deno.land/x/pattern_matching/mod.ts";

declare const num: number;

const result = match(num)(
  when(1, () => "one"),
  when(2, () => "two"),
  otherwise(() => "many"),
);

Binding

Binding binds the value of matchable when matched. This allows subsequent handlers to reference the binding.

import {
  _,
  match,
  otherwise,
  when,
  whether,
} from "https://deno.land/x/pattern_matching/mod.ts";
import {
  assertType,
  type IsExact,
} from "https://deno.land/std/testing/types.ts";

interface Person {
  name: string;
  age: number;
  hobby?: string;
  greet?: string;
}
declare const person: Person;

const result = match(person)(
  whether(({ name, age }) => !name || !age, () => {
    throw new Error();
  }),
  when(
    { greet: _("introduction") },
    ({ introduction }) => `${introduction}`,
  ),
  when(
    { name: _("name"), hobby: _("hobby") },
    ({ name, hobby }) => `${name} hobby is ${hobby}`,
  ),
  otherwise(() => "profile does not exist"),
);

assertType<IsExact<typeof result, string>>(true);