Ycombinator1

Ycombinator1.rkt

#lang racket

(define (factorial n)
  (if (= n 0)
      1
      (* n (factorial (- n 1)))))


(define factorial_lambda
  (lambda (n)
    (if (= n 0)
        1
        (* n (factorial_lambda (- n 1))))))


(define almost-factorial
  (lambda (f)
    (lambda (n)
      (if (= n 0)
          1
          (* n ((f f) (- n 1)))))))  ;; the (f f) is so important to understand

(define sort-of-factorial
  (lambda (n)
    (if (= n 0)
        1
        (* n ((almost-factorial almost-factorial) (- n 1))))))