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;;;; $Id: stack-f.el,v 0.8 1995/12/11 00:11:31 ceder Exp $
;;;; This file implements a simple LIFO stack.

;; Copyright (C) 1991-1995 Free Software Foundation

;; Author: Inge Wallin <inge@lysator.liu.se>
;; Maintainer: elib-maintainers@lysator.liu.se
;; Created: before 9 May 1991
;; Keywords: 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 GNU Elib; see the file COPYING.  If not, write to
;;;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;;;; Boston, MA 02111-1307, USA
;;;;
;;;; Author: Inge Wallin
;;;; 

;;; Commentary:

;;; The stack is implemented as a linked list with a tag 'STACK
;;; as the first element.  All entries and removals are done using
;;; destructive functions.
;;;

;;; Code:

;; Provide the function version and remove the macro version.

(provide 'stack-f)
(setq features (delq 'stack-m features))


;;; ================================================================


(defun stack-create ()
  "Create an empty lifo stack."
  (cons 'STACK nil))


(defun stack-p (stack)
  "Return t if STACK is a stack, otherwise return nil."
  (eq (car-safe stack) 'STACK))


(defun stack-push (stack element)
  "Push an element onto the stack.
Args: STACK ELEMENT"
  (setcdr stack (cons element (cdr stack))))


(defun stack-pop (stack)
  "Remove the topmost element from STACK and return it. 
If the stack is empty, return nil."
  (prog1
      (car-safe (cdr stack))
    (setcdr stack (cdr-safe (cdr stack)))))


(defun stack-empty (stack)
  "Return t if STACK is empty, otherwise return nil."
  (null (cdr stack)))


(defun stack-top (stack)
  "Return the topmost element of STACK or nil if it is empty."
  (car-safe (cdr stack)))


(defun stack-nth (stack n)
  "Return nth element of a stack, but don't remove it.
Args: STACK N
If the length of the stack is less than N, return nil.

The top stack element has number 0."
  (nth n (cdr stack)))


(defun stack-all (stack)
  "Return a list of all entries in STACK.
The element last pushed is first in the list."
  (cdr stack))


(defun stack-copy (stack)
  "Return a copy of STACK.
All entries in STACK are also copied."
  (cons 'STACK (copy-sequence (cdr stack))))


(defun stack-length (stack)
  "Return the number of elements on STACK."
  (length (cdr stack)))


(defun stack-clear (stack)
  "Remove all elements from STACK."
  (setcdr stack nil))

;;; stack-f.el ends here