(add-to-list): New function.

diff --git a/lisp/subr.el b/lisp/subr.el
index 3c4308bf8c29b8b4f96da6c9306f51ea41c69051..7c0ae0cb9144048f9b68ad65c164f0038dfcf211 100644 (file)
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -710,6 +710,11 @@ To make a hook variable buffer-local, always use
          (if (equal hook-value function)
              (setq hook-value nil)))
        (set-default hook hook-value)))))
+
+(defun add-to-list (list-var element)
+  "Add to the value of LIST-VAR the element ELEMENT if it isn't there yet."
+  (or (member element (symbol-value list-var))
+      (set list-var (cons element (symbol-value list-var)))))
 \f
 ;;;; Specifying things to do after certain files are loaded.