; fact.ss
; SICP section 1.2.1
; Chris Parrish

; a recursive process

(define fact
  (lambda (n)
    (if (zero? n)
      1
      (* n (fact (sub1 n))))))

(trace fact)

(fact 120)

; an iterative process

(define fact
  (lambda (n)
    (fact-iter 1 n 1)))

(define fact-iter
  (lambda (k n ans)
    (if (> k n)
      ans
      (fact-iter (add1 k) n (* k ans)))))

(trace fact-iter)

(fact 120)