(define (make-queue)
  (let ((front-ptr nil)
	(rear-ptr  nil))
    (define (empty-queue?)
      (null? front-ptr))
    (define (insert-queue! item)
      (let ((new-pair (cons item nil)))
	  (cond ((empty-queue?)
		 (set! front-ptr new-pair)
		 (set! rear-ptr new-pair)
		 front-ptr)
		(else
		 (set-cdr! rear-ptr new-pair)
		 (set! rear-ptr (cdr rear-ptr))
		 front-ptr))))
      (define (delete-queue!)
	(cond ((empty-queue?)
	       (error "DELETE-QUEUE! called with an empty queue"))
	      (else
	       (set! front-ptr (cdr front-ptr))
	       front-ptr)))
      (define (dispatch msg)
	(cond ((eq? msg 'insert-queue) (lambda (item) (insert-queue! item)))
	      ((eq? msg 'delete-queue) (delete-queue!))
	      (else (display "error"))))
      dispatch))

(define myqueue (make-queue))


((myqueue 'insert-queue) 10)
((myqueue 'insert-queue) 11)
((myqueue 'insert-queue) 12)
(myqueue 'delete-queue)
((myqueue 'insert-queue) 1)
(myqueue 'delete-queue)
(myqueue 'delete-queue)
(myqueue 'delete-queue)
(myqueue 'delete-queue)