;; (use srfi-1)

;; (sys-srandom (sys-time))
;; (define (random i)
;;   (modulo (sys-random) i))

;; (define queue
;;  (list-tabulate 1000 (lambda (i) (exact->inexact (random (+ i 1))))))

;; (define (enq x)
;;  (append! queue (list x)))

;; (define (deq)
;;  (unless (null? queue) (begin0 (car queue) (set! queue (cdr queue)))))

;; ;; run program run
;; (let L ([i 100000000])
;;   (unless (= i 0)
;;     (enq (exact->inexact i))
;;     (deq)
;;     (L (- i 1))))

;; r5rs
(define queue
  (let L ([i 1000]) (if (= i 0) '() (cons (exact->inexact i) (L (- i 1))))))

(define (enq x)
  (let L ([q queue])
    (if (null? (cdr q)) (set-cdr! q (list x)) (L (cdr q)))))

(define (deq)
  (if (null? queue)
      (void)
      (let ([old queue])
        (set! queue (cdr queue))
        (set-cdr! old #f)
        (car old))))

;; run program run
(let L ([i 100000000])
  (if (= i 0)
      (void)
      (begin
        (enq (exact->inexact i))
        (deq)
        (L (- i 1)))))