polyad v0.2.2

Polyad: Monads for JavaScript

Monads are a pattern in functional programming for encapsulating values in types with additional operations. This is a collection of such monads for JavaScript.

Using

import {Maybe, Either} from "polyad";

const m1 = new Maybe(1);
console.log(m1.isJust(), m1.isNothing(), m1.get());
// -> true false 1

const e1 = Either.right("success");
console.log(e1, e1.get(), e1.map(v => v.length).get());
// -> Either {} "success" 7

Monads

Maybe

Reason about empty values.

const maybeN = new Maybe();
console.log(maybeN.isJust(), maybeN.isNothing(), maybeN.get());
// -> false, true, undefined

Either

Select between two values.

const e2 = Either
  .right("Hello, world")
  .map(v => v.toUpperCase())
  .match({right: v => v.slice(0, 5)})
console.log(e2, e2.get());
// -> Either {} HELLO

Either.try is great for replacing try ... catch blocks.

Turn

const showError = error => console.log(error.message);
try {
  1 / f;
} catch (error) {
  showError(error);
}

into

Either.try(() => 1 / f).match({left: showError});
// -> f is not defined

Eager

Wrap your value in an eager promise, allowing you to chain operations on the value the promise resolves to.

const promise = Promise.resolve(" Test ");
const te = Eager.resolve(promise).trim().toLowerCase().slice(0, 2);
console.log(await te);
// -> "te"

Use then or catch to exit out of the Eager chain.

EagerEither

An Either wrapped inside an Eager, made for async computations; the same try ... catch replacement from before with async code:

Turn

const showError = error => console.log(error.message);
try {
  await 1 / f;
} catch (error) {
  showError(error);
}

into

await EagerEither.try(async () => await 1 / f).match({left: showError});
// -> f is not defined

License

BSD-3-Clause