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;;; :FILE-CREATED <Timestamp: #{2011-09-23T18:54:38-04:00Z}#{11385} - by MON>
;;; :FILE vivace-graph-v2-FORK/queue.lisp
;;; ==============================
(in-package #:vivace-graph-v2)
;; The following queueing code was borrowed and adapted from Russell & Norvig's
;; "Introduction to AI"
(defun print-queue (q stream depth)
(declare (ignore depth))
(format stream "<QUEUE: ~a>" (queue-elements q)))
(defstruct (queue ; make-queue
(:print-function print-queue))
(key #'identity) ; queue-key
(last nil) ; queue-last
(elements nil)) ; queue-elements
(defun make-empty-queue ()
(defun empty-queue? (q)
(= (length (queue-elements q)) 0))
(defun queue-front (q)
(elt (queue-elements q) 0))
(defun dequeue (q)
(when (listp (queue-elements q))
(pop (queue-elements q))))
(defun enqueue-front (q &rest items)
(cond ((null items) nil)
((or (null (queue-last q)) (null (queue-elements q)))
(setf (queue-elements q) (nconc items (queue-elements q))
(queue-last q) (last (queue-elements q))))
(t (setf (queue-elements q) (nconc items (queue-elements q))))))
(defun enqueue (q &rest items)
(cond ((null items) nil)
((or (null (queue-last q)) (null (queue-elements q)))
(setf (queue-last q) (last items)
(queue-elements q) (nconc (queue-elements q) items)))
(t (setf (cdr (queue-last q)) items
(queue-last q) (last items)))))
(defun queue-length (q)
(length (queue-elements q)))
;;; ==============================
;;; EOF