#lang racket
(require racket/trace)
;; This procedure has been warranted to work for top-level lists of integers.
(define product
  (lambda (ls)
    (cond [(null? ls) 1]
	  [(zero? (car ls)) 0]
	  [else (* (car ls) (product (cdr ls)))])))
(trace product)

(define productT
  (lambda (ls accu)
    (cond [(null? ls) accu]
	  [(zero? (car ls)) 0]
	  [else (productT (cdr ls) (* (car ls) accu))])))
(trace productT)

(define product-cps
  (lambda (ls k)
    (cond [(null? ls) (k 1)]
          [(zero? (car ls)) 0]
          [else (product-cps (cdr ls) (lambda (x) (k (* x (car ls)))))])))
(trace product-cps)

(define product-cps2
  (lambda (ls k exit)
    (cond [(null? ls) (k 1)]
          [(zero? (car ls)) (exit 0)]
          [else (product-cps2 (cdr ls) (lambda (x) (k (* x (car ls)))) exit)])))
(trace product-cps2)