(let ((time-stamp "Time-stamp: <2000-12-11 16:53:45 wand>"))
  (eopl:printf "2-4.scm ~a~%" (substring time-stamp 13 29)))

(define create-queue
  (lambda ()
    (let ((q-in '())
          (q-out '()))
      (letrec 
        ((reset-queue
           (lambda ()
             (set! q-in '())
             (set! q-out '())))
        (empty-queue?
          (lambda ()
            (and (null? q-in)
                 (null? q-out))))
        (enqueue
          (lambda (x)
            (set! q-in (cons x q-in))))
        (dequeue
          (lambda ()
            (if (empty-queue?)
              (eopl:error 'dequeue
                "Not on an empty queue")
              (begin
                (if (null? q-out)
                  (begin
                    (set! q-out (reverse q-in))
                    (set! q-in '())))
                  (let ((ans (car q-out)))
                    (set! q-out (cdr q-out))
                    ans))))))
        (vector reset-queue empty-queue? enqueue dequeue)))))

(define queue-get-reset-operation   
  (lambda (q) (vector-ref q 0)))
(define queue-get-empty?-operation  
  (lambda (q) (vector-ref q 1)))
(define queue-get-enqueue-operation 
  (lambda (q) (vector-ref q 2)))
(define queue-get-dequeue-operation 
  (lambda (q) (vector-ref q 3)))