ES6 Combinators

Combinators.js

// λh.(h h)
let U = f => f(f)

// (λ x. x x) (λ x. x x)
let Ω = _ => (x => x (x)) (x => x (x))

// λf.(λx.f (λv.((x x) v))) (λx.f (λv.((x x) v)))
let Z = f => (x => f(y => x(x)(y)))
             (x => f(y => x(x)(y)))

let fact = Z(f =>
    n => n == 0 ? 1 : n * f(n - 1)
)

let fact = U(f =>
    n => n == 0 ? 1 : n * (f(f)(n - 1))
)

var fix = f => (x => f(fix(f))(x));

var factabs = fact => (x => x == 0 ? 1 : x * fact(x - 1));

var a = fix(factabs)(5); /* 120 */

OOP.js

let fix = f => (x => f(fix(f))(x))

let New = fix

let Animal = body => body

let Base = Self => Animal({
    speak: repeats => "",
    move: repeats => "",
    act: repeats => Self.move(repeats) + Self.speak(repeats)
})

let Bird = Self => (Super => Animal({
    speak: repeats => Array(repeats).join("cheep "),
    move: repeats => Array(repeats).join("flap "),
    act: Super.act
}))(Base(Self))

let Dog = Self => (Super => Animal({
    speak: repeats => Array(repeats).join("bark "),
    move: repeats => Array(repeats).join("run "),
    act: Super.act
}))(Base(Self))

let b = New(Bird)
let d = New(Dog)

b.act(2) //b.act is not a function?

d.act(2) // d.act is not a function?