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192 lines
5.6 KiB
192 lines
5.6 KiB
;;; queue.el --- Queue data structure -*- lexical-binding: t; -*-
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;; Copyright (C) 1991-1995, 2008-2009, 2012, 2017 Free Software Foundation, Inc
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;; Author: Inge Wallin <inge@lysator.liu.se>
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;; Toby Cubitt <toby-predictive@dr-qubit.org>
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;; Maintainer: Toby Cubitt <toby-predictive@dr-qubit.org>
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;; Version: 0.2
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;; Keywords: extensions, data structures, queue
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;; URL: http://www.dr-qubit.org/emacs.php
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;; Repository: http://www.dr-qubit.org/git/predictive.git
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;; This file is part of Emacs.
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;;
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;; GNU Emacs is free software: you can redistribute it and/or modify it under
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;; the terms of the GNU General Public License as published by the Free
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;; Software Foundation, either version 3 of the License, or (at your option)
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;; any later version.
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;;
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;; GNU Emacs is distributed in the hope that it will be useful, but WITHOUT
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;; ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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;; FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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;; more details.
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;;
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;; You should have received a copy of the GNU General Public License along
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;; with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
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;;; Commentary:
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;;
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;; These queues can be used both as a first-in last-out (FILO) and as a
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;; first-in first-out (FIFO) stack, i.e. elements can be added to the front or
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;; back of the queue, and can be removed from the front. (This type of data
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;; structure is sometimes called an "output-restricted deque".)
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;;
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;; You create a queue using `make-queue', add an element to the end of the
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;; queue using `queue-enqueue', and push an element onto the front of the
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;; queue using `queue-prepend'. To remove the first element from a queue, use
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;; `queue-dequeue'. A number of other queue convenience functions are also
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;; provided, all starting with the prefix `queue-'. Functions with prefix
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;; `queue--' are for internal use only, and should never be used outside this
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;; package.
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;;; Code:
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(eval-when-compile (require 'cl))
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(defmacro queue--when-generators (then)
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"Evaluate THEN if `generator' library is available."
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(declare (debug t))
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(if (require 'generator nil 'noerror) then))
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(defstruct (queue
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;; A tagged list is the pre-defstruct representation.
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;; (:type list)
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:named
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(:constructor nil)
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(:constructor queue-create ())
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(:copier nil))
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head tail)
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;;;###autoload
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(defalias 'make-queue 'queue-create
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"Create an empty queue data structure.")
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(defun queue-enqueue (queue element)
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"Append an ELEMENT to the end of the QUEUE."
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(if (queue-head queue)
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(setcdr (queue-tail queue)
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(setf (queue-tail queue) (cons element nil)))
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(setf (queue-head queue)
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(setf (queue-tail queue) (cons element nil)))))
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(defalias 'queue-append 'queue-enqueue)
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(defun queue-prepend (queue element)
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"Prepend an ELEMENT to the front of the QUEUE."
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(if (queue-head queue)
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(push element (queue-head queue))
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(setf (queue-head queue)
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(setf (queue-tail queue) (cons element nil)))))
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(defun queue-dequeue (queue)
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"Remove the first element of QUEUE and return it.
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Returns nil if the queue is empty."
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(unless (cdr (queue-head queue)) (setf (queue-tail queue) nil))
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(pop (queue-head queue)))
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(defun queue-empty (queue)
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"Return t if QUEUE is empty, otherwise return nil."
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(null (queue-head queue)))
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(defun queue-first (queue)
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"Return the first element of QUEUE or nil if it is empty,
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without removing it from the QUEUE."
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(car (queue-head queue)))
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(defun queue-nth (queue n)
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"Return the nth element of a queue, without removing it.
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If the length of the queue is less than N, return nil. The first
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element in the queue has index 0."
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(nth n (queue-head queue)))
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(defun queue-last (queue)
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"Return the last element of QUEUE, without removing it.
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Returns nil if the QUEUE is empty."
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(car (queue-tail queue)))
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(defun queue-all (queue)
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"Return a list of all elements of QUEUE or nil if it is empty.
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The oldest element in the queue is the first in the list."
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(queue-head queue))
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(defun queue-copy (queue)
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"Return a copy of QUEUE.
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The new queue contains the elements of QUEUE in the same
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order. The elements themselves are *not* copied."
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(let ((q (queue-create))
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(list (queue-head queue)))
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(when (queue-head queue)
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(setf (queue-head q) (cons (car (queue-head queue)) nil)
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(queue-tail q) (queue-head q))
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(while (setq list (cdr list))
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(setf (queue-tail q)
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(setcdr (queue-tail q) (cons (car list) nil)))))
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q))
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(defun queue-length (queue)
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"Return the number of elements in QUEUE."
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(length (queue-head queue)))
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(defun queue-clear (queue)
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"Remove all elements from QUEUE."
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(setf (queue-head queue) nil
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(queue-tail queue) nil))
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(queue--when-generators
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(iter-defun queue-iter (queue)
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"Return a queue iterator object.
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Calling `iter-next' on this object will retrieve the next element
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from the queue. The queue itself is not modified."
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(let ((list (queue-head queue)))
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(while list (iter-yield (pop list))))))
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;;;; ChangeLog:
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;; 2017-08-16 Toby S. Cubitt <tsc25@cantab.net>
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;;
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;; Upgrade data structure packages to latest versions.
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;;
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;; 2014-05-15 Toby S. Cubitt <tsc25@cantab.net>
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;;
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;; queue.el: fix buggy queue-first and queue-empty definitions.
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;;
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;; 2012-04-30 Toby S. Cubitt <tsc25@cantab.net>
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;;
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;; Minor fixes to commentaries, package headers, and whitespace
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;;
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;; * queue.el: fix description of data structure in Commentary; add
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;; Maintainer
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;; header.
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;;
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;; * queue.el, heap.el, tNFA.el, trie.el, dict-tree.el: trivial whitespace
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;; fixes.
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;;
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;; 2012-04-29 Toby S. Cubitt <tsc25@cantab.net>
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;;
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;; Add queue.el
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;;
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(provide 'queue)
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;;; queue.el ends here
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