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;;; fifo.el --- FIFO queue.
;; Copyright (c) 2015 Chris Done.
;; This file 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 3, or (at your option)
;; any later version.
;; This file 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, see <http://www.gnu.org/licenses/>.
;;; Code:
(require 'cl-lib)
(defun fifo-make ()
"Make a fifo queue."
(cons 0 nil))
(defun fifo-push (q a)
"Push a new item onto the queue."
(cl-assert (consp q) nil "Must be a queue.")
(setcar q (1+ (car q)))
(let ((next q)
(continue t))
(while (not (null (cdr next)))
(setq next (cdr next)))
(setcdr next (cons a nil)))
q)
(defun fifo-pop (q)
"Pop the next item on the queue."
(cl-assert (consp q) nil "Must be a queue.")
(cl-assert (consp (cdr q)) nil "No items to pop from queue.")
(setcar q (1- (car q)))
(let ((a (car (cdr q))))
(setcdr q (cdr (cdr q)))
a))
(defun fifo-size (q)
"Get the size of the queue."
(cl-assert (consp q) nil "Must be a queue.")
(car q))
(defun fifo-null-p (q)
"Is the queue empty?"
(= (fifo-size q) 0))
(provide 'fifo)
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