;;; $Id: product-tail-recursive.scm,v 1.2 2005/12/30 18:11:06 leavens Exp $

(module product-tail-recursive (lib "typedscm.ss" "typedscm")

(provide product product-of-list product-of-list-traced)

(deftype product (-> ((list-of number)) number))
(define product
  (lambda args
    (product-of-list args 1)))

(deftype product-of-list (-> ((list-of number) number) number))
(define product-of-list
  (lambda (lon acc)
    (cond
     ((null? lon) acc)
     ((zero? (car lon)) 0)
     (else (product-of-list (cdr lon) (* (car lon) acc))))))

(deftype product-of-list-traced (-> ((list-of number) number) number))
(define product-of-list-traced
  (lambda (lon acc)
    (displayln ";; = (product-of-list '" lon " " acc ")")
    (cond
     ((null? lon)
      (displayln ";; = " acc)
      acc)
     ((zero? (car lon))
      (displayln ";; = 0")
      0)
     (else
      (product-of-list-traced (cdr lon) (* (car lon) acc))))))

;; = (product-of-list '(3 4 2 1 1 5 9 8 7 3 2) 1)
;; = (product-of-list '(4 2 1 1 5 9 8 7 3 2) 3)
;; = (product-of-list '(2 1 1 5 9 8 7 3 2) 12)
;; = (product-of-list '(1 1 5 9 8 7 3 2) 24)
;; = (product-of-list '(1 5 9 8 7 3 2) 24)
;; = (product-of-list '(5 9 8 7 3 2) 24)
;; = (product-of-list '(9 8 7 3 2) 120)
;; = (product-of-list '(8 7 3 2) 1080)
;; = (product-of-list '(7 3 2) 8640)
;; = (product-of-list '(3 2) 60480)
;; = (product-of-list '(2) 181440)
;; = (product-of-list '() 362880)
;; = 362880

;; (product-of-list '(3 4 2 0 1 5 9 8 7 3 2) 1)
;; = (product-of-list '(4 2 0 1 5 9 8 7 3 2) 3)
;; = (product-of-list '(2 0 1 5 9 8 7 3 2) 12)
;; = (product-of-list '(0 1 5 9 8 7 3 2) 24)
;; = 0

) ;; end module