Comparing Y Combinator: Scheme vs. ECMAScript 6

y-combinator.js

let Y =
  (fn => (f => f(f))
    (f => fn((...args) => f(f)(...args))));

let fac =
  Y(f => (n =>
    (n <= 2 ?
      n :
      n * f(n - 1))));

fac(5); // 120

y-combinator.rkt

(define (Y f)
  ((lambda (x) (x x))
   (lambda (g)
     (f (lambda args (apply (g g) args))))))

(define fac
  (Y
    (lambda (f)
      (lambda (x)
        (if (< x 2)
            1
            (* x (f (- x 1))))))))

(fac 5) ; 120

Why let instead of const?

I honest to god hate the fat-arrow.

Don't worry @leostera, the fat-arrow will never hear you, or be hurt or damaged by your hateful attitude.