;;;; This file implements a simple LIFO stack.
;; Copyright (C) 1991-1995 Free Software Foundation
;; Author: Inge Wallin <firstname.lastname@example.org>
;; Maintainer: email@example.com
;; 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
;;; 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.
;; Provide the function version and remove the macro version.
(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."
(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."
(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