#lang eopl

(provide (all-defined-out))

;; queues

;; We maintain the queue by adding to the end and dequeuing from the
;; front. 

;; exercise: enqueue is expensive, since it uses append.  Do
;; something better than this.

(define empty-queue
  (lambda ()
    '()))

(define empty? null?)

(define enqueue
  (lambda (q val)
    (append q (list val))))

(define dequeue
  (lambda (q f)
    (f (car q) (cdr q))))