;; Quite ugly, but that's a simple use of call/cc.

(define (mul-with-shortcut l)
  (display
    (list "result is "
          (call/cc
            (lambda (escape)
              (let loop ((l l))
                (if (null? l)
                  1
                  (let ((head (car l))
                        (tail (cdr l)))
                    (if (zero? head)
                      (begin
                        (display "exit!")
                        (newline)
                        (escape 0)) ;; you multiplied by zero. No need to continue multiplying. Just return 0.
                      (begin
                        (for-each display `("multiplying by " ,head #\newline))
                        (* head (loop tail))))))))))))

(define (test)
  (mul-with-shortcut '(1 2 3 4 5))
  (newline)
  (mul-with-shortcut '(1 2 0 4 5))
  (newline))