queue.knl

;;;
;;; Stateful Queue (after SICP 3.3.2)
;;;

($define! q? pair?)
($define! new-q
	($lambda ()
		(cons () ())))
($define! q-empty?
	($lambda (q)
		(null? (car q))))
($define! q-put!
	($lambda (q x)
		($let ((item (cons x ())))
			($if (null? (car q))
				(set-car! q item)
				(set-cdr! (cdr q) item))
			(set-cdr! q item))))
($define! q-take!
	($lambda (q)
		($let ((item (car q)))
			(set-car! q (cdr item))
			(car item))))