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(push, pop): New macros.

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This commit is contained in:
Richard M. Stallman 1999-08-29 20:23:54 +00:00
parent e3c0f9ded6
commit d270117a18
1 changed files with 15 additions and 0 deletions
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15
lisp/subr.el
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@ -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)))