calculate factorial of 5 in 4 ways

factorial.scm

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

(fact 5)

(define (fact n)
  (define (iter n result)
    (if (= 0 n)
	result
	(iter (- n 1) (* n result))))
  (iter n 1))

(fact 5)

(define (fact n)
  (define (fact/cps n cont)
    (if (= 0 n)
	(cont 1)
	(fact/cps (- n 1)
		  (lambda (x)
		    (cont (* n x))))))
  (fact/cps n (lambda (x) x)))

(fact 5)

(((lambda (f)
    ((lambda (proc)
       (f (lambda (arg) ((proc proc) arg))))
     (lambda (proc)
       (f (lambda (arg) ((proc proc) arg))))))
  (lambda (f)
    (lambda (n)
      (if (= 0 n)
	  1
	  (* n (f (- n 1))))))) 5)