; call/cc used for early exit from a loop.
(define (list-product items)
  (call/cc
    (lambda (break)
      (let loop ((xs items) (acc 1))
        (cond ((null? xs) acc)
              ((= (car xs) 0) (break 0))
              (else (loop (cdr xs) (* acc (car xs)))))))))

(display "product 1..5 = ")
(display (list-product '(1 2 3 4 5)))
(newline)
(display "product with a zero = ")
(display (list-product '(1 2 0 4 5)))
(newline)

; call/cc with re-entry: a captured continuation is invoked repeatedly
; to build a loop that sums 1..5 within a single expression.
(display "reentry sum 1..5 = ")
(display
  (let ((sum 0)
        (i 0)
        (k #f))
    (call/cc (lambda (c) (set! k c)))
    (set! i (+ i 1))
    (set! sum (+ sum i))
    (if (< i 5)
        (k #f)
        sum)))
(newline)