From: Richard M. Stallman <rms@gnu.org>
Date: Sun, 29 Aug 1999 20:23:54 +0000 (+0000)
Subject: (push, pop): New macros.
X-Git-Tag: emacs-pretest-21.0.90~7005
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=d270117a18a28a1bebdb687fd794b5cc89f1559d;p=emacs.git

(push, pop): New macros.
---

diff --git a/lisp/subr.el b/lisp/subr.el
index f4f695e8108..a80383467d3 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -51,6 +51,21 @@ BODY should be a list of lisp expressions."
   ;; depend on backquote.el.
   (list 'function (cons 'lambda cdr)))
 
+(defmacro push (value listname)
+  "Add VALUE to the list which is the value of LISTNAME.
+This is equivalent to (setq LISTNAME (cons VALUE LISTNAME)).
+LISTNAME must be a symbol."
+  (list 'setq list
+	(list 'cons value list)))
+
+(defmacro pop (listname)
+  "Return the first element of LISTNAME's value, and remove it from the list.
+LISTNAME must be a symbol whose value is a list.
+If the value is nil, `pop' returns nil but does not actually
+change the list."
+  (list 'prog1 (list 'car listname)
+	(list 'setq listname (list 'cdr listname))))
+
 (defmacro when (cond &rest body)
   "(when COND BODY...): if COND yields non-nil, do BODY, else return nil."
   (list 'if cond (cons 'progn body)))