MONAD

README.md

モナド則

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))

JavaScript Primise Monado

• return (unit) = Promise.resolve
• bind = Promise.prototype.then

1. bind(unit(x), f) ≡ f(x)

// bind(unit(x), f)
Promise.resolve(1).then( (v) => console.log(v) );

// f(x)
((v) => console.log(v) )(1);

1. bind(m, unit) ≡ m

// bind(m, unit)
var m = Promise.resolve(1);
Promise.resolve(m).then((v) => console.log(v))

// m
var m = Promise.resolve(1);
m.then((v) => console.log(v) )

1. bind(bind(m, f), g) ≡ bind(m, x ⇒ bind(f(x), g))

var m = Promise.resolve(2);
var f = (v) => Promise.resolve(v * 3);
var g = (v) => Promise.resolve(v + 2);

// bind(bind(m, f), g)
m.then(f).then(g)
.then((v) => console.log(v) );

// bind(m, x ⇒ bind(f(x), g))
m.then((x) => f(x).then(g))
.then((x) => console.log(x)) 

参考

• monado in javascript