;;; queue.el --- queue data structure ;; Copyright (C) 1991-1995, 2008-2009 Free Software Foundation
;; Author: Inge Wallin <[email protected]> ;; rewritten by Toby Cubitt <[email protected]> ;; Version: 0.1 ;; Keywords: queue, extensions, lisp ;; This file is part of the GNU Emacs lisp library, Elib. ;; GNU Elib is free software; you can redistribute it and/or modify ;; it under the terms of the GNU General Public License as published by ;; the Free Software Foundation; either version 2, or (at your option) ;; any later version. ;; ;; GNU Elib is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public License ;; along with this program; if not, write to the Free Software ;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, ;; MA 02110-1301, USA. ;; ;;; Commentary: ;;; Code: (eval-when-compile (require 'cl)) (defstruct (queue ;; A tagged list is the pre-defstruct representation. ;; (:type list) :named (:constructor nil) (:constructor queue-create ()) (:copier nil)) head tail) (defun queue-enqueue (queue element) "Append an ELEMENT to the end of the QUEUE." (if (queue-head queue) (setcdr (queue-tail queue) (setf (queue-tail queue) (cons element nil))) (setf (queue-head queue) (setf (queue-tail queue) (cons element nil))))) (defalias 'queue-append 'queue-enqueue) (defun queue-prepend (queue element) "Prepend an ELEMENT to the front of the QUEUE." (if (queue-head queue) (push element (queue-head queue)) (setf (queue-head queue) (setf (queue-tail queue) (cons element nil))))) (defun queue-dequeue (queue) "Remove the first element of QUEUE and return it. Returns nil if the queue is empty." (unless (cdr (queue-head queue)) (setf (queue-tail queue) nil)) (pop (queue-head queue))) (defmacro queue-empty (queue) "Return t if QUEUE is empty, otherwise return nil." (null (queue-head queue))) (defmacro queue-first (queue) "Return the first element of QUEUE or nil if it is empty, without removing it from the QUEUE." (car (queue-head queue))) (defun queue-nth (queue n) "Return the nth element of a queue, without removing it. If the length of the queue is less than N, return nil. The first element in the queue has index 0." (nth n (queue-head queue))) (defun queue-last (queue) "Return the last element of QUEUE, without removing it. Returns nil if the QUEUE is empty." (car (queue-tail queue))) (defun queue-all (queue) "Return a list of all elements of QUEUE or nil if it is empty. The oldest element in the queue is the first in the list." (queue-head queue)) (defun queue-copy (queue) "Return a copy of QUEUE. The new queue contains the elements of QUEUE in the same order. The elements themselves are *not* copied." (let ((q (queue-create)) (list (queue-head queue))) (when (queue-head queue) (setf (queue-head q) (cons (car (queue-head queue)) nil) (queue-tail q) (queue-head q)) (while (setq list (cdr list)) (setf (queue-tail q) (setcdr (queue-tail q) (cons (car list) nil))))) q)) (defun queue-length (queue) "Return the number of elements in QUEUE." (length (queue-head queue))) (defun queue-clear (queue) "Remove all elements from QUEUE." (setf (queue-head queue) nil (queue-tail queue) nil)) (provide 'queue) ;;; queue.el ends here _______________________________________________ gnu-emacs-sources mailing list [email protected] http://lists.gnu.org/mailman/listinfo/gnu-emacs-sources
