q.scm

(define (make-queue)
  (let ((front-ptr '())
	(rear-ptr '()))
    (define (set-front-ptr! item)
      (set! front-ptr item))
    (define (set-rear-ptr! item)
      (set! rear-ptr item))
    (define (empty-queue?)
      (null? front-ptr))
    ;; (define (print-queue)

    ;; 	 (let ((a front-ptr)
    ;; 	       (b rear-ptr))
    ;; 	   (define (lo)
    ;; 	     (cond (null? a)
    ;; 		   '()
    ;; 		   (else (display (car a))
    ;; 			 (set! a (cdr a))
    ;; 			 (lo))))
    ;; 	   (lo)))
    (define (insert-queue! item)
      (let ((new-pair (cons item '())))
	(cond ((empty-queue?)
	       (set! front-ptr new-pair)
	       (set! rear-ptr new-pair))
	      (else 
	       (set-cdr! rear-ptr new-pair)
	       (set! rear-ptr new-pair)))))
    (define (delete-queue!)
      (cond ((empty-queue?) 
	     (error "DELETE! called with an empty queue" queue))
	    (else
	     (set! front-ptr (cdr front-ptr)))))
    (define (dispatch m)
      (cond ((eq? m 'emtpy-queue?) empty-queue?)
	    ((eq? m 'set-front-ptr!) set-front-ptr!)
	    ((eq? m 'set-rear-ptr!) set-rear-ptr!)
	    ((eq? m 'insert-queue!) insert-queue!)
	    ((eq? m 'delete-queue!) delete-queue!)
	    ((eq? m 'print-queue) print-queue)
	    (else
	     (error "Undefind operation -- -QUEUE" m))))
    dispatch))



(define (set-front-ptr! queue item)
  ((queue 'set-front-ptr!) item))
(define (set-rear-ptr! queue item)
  ((queue 'set-rear-ptr!) item))
(define (empty-queue? q)
  (q 'empty-queue?))

(define (insert-queue! queue item)
  ((queue 'insert-queue!) item))
(define (delete-queue! queue)
  ((queue 'delete-queue!)))
(define (print-queue queue)
  ((queue 'print-queue)))