data.monad

Description

javascript monad structure.

Type Signature

interface.

interface M<T> {
    // return
    function unit<T>(value: T): M<T> {
    }

    // >>=
    function bind<T, U>(instance: M<T>, transform: (value: T) => M<U>): M<U> {
    }
}

1. bind(unit(x), f) == f(x)
2. bind(m, unit) == m
3. bind(bind(m, f), g) == bind(m, x => bind(f(x), g))

Usage

Identity

new Identity(5).bind(x =>
    new Identity(6).bind(x2 =>
        new Identity(x + x2)
    )
);
// => Identity(11)

Maybe

new Just(5).bind(x =>
    new Just(6).bind(x2 =>
        new Just(x + x2)
    )
);
// => Just(11)

new Just(5).bind(x =>
    Nothing.bind(x2 =>
        new Just(x + x2)
    )
);
// => Nothing

do syntax

doM(function*() {
    let v1 = yield new Just(5);
    let v2 = yield new Just(6);
    return new Just(v1 + v2);
}());
// => Just(11)

Promise

let p1 = doM(function*() {
    let v1 = yield Promise.resolve(5);
    let v2 = yield Promise.resolve(6);
    return v1 + v2;
}());

p1.bind(v => console.log(v * v)); // 121

let p2 = doM(function*() {
    let v1 = yield Promise.resolve(5);
    let v2 = yield Promise.reject(new Error('Failure'));
    return v1 + v2;
}());

p2.bind(v => console.log(v * v)); // empty
p2.catch(e => console.log(e.message)); // 'Failure'

Installation

npm

Install

$ npm i -D data.monad

Use

var Monad = require('data.monad');

Author

to4iki

Licence

MIT