(require 'rep.test.framework)

(define (make-stack)
  (let ((s '()))
    (define (push x)
      (setq s (cons x s)))
    (define (pop)
      (if (null s)
          (error "Empty stack -- POP")
        (prog1
            (car s)
          (setq s (cdr s)))))
    (define (initialize)
      (setq s '())
      'done)
    (define (dispatch message)
      (cond ((eq message 'push) push)
            ((eq message 'pop) (pop))
            ((eq message 'initialize) (initialize))
            (t (error "Unknown request -- STACK: %s" message))))
    dispatch))

(define (pop stack)
  (stack 'pop))

(define (push stack value)
  ((stack 'push) value))

(defvar st (make-stack))
(push st 3)
(push st 4)
(assert (= 4 (pop st)))
(assert (= 3 (pop st)))