+(defun riece-make-queue ()
+ "Make a queue object."
+ (vector nil nil))
+
+(defun riece-queue-enqueue (queue object)
+ "Add OBJECT to the end of QUEUE."
+ (if (aref queue 1)
+ (let ((last (list object)))
+ (nconc (aref queue 1) last)
+ (aset queue 1 last))
+ (aset queue 0 (list object))
+ (aset queue 1 (aref queue 0))))
+
+(defun riece-queue-dequeue (queue)
+ "Remove an object from the beginning of QUEUE."
+ (unless (aref queue 0)
+ (error "Empty queue"))
+ (prog1 (car (aref queue 0))
+ (unless (aset queue 0 (cdr (aref queue 0)))
+ (aset queue 1 nil))))
+
+(defun riece-queue-empty (queue)
+ "Return t if QUEUE is empty."
+ (null (aref queue 0)))
+