Markus Triska <markus.triska at gmx.at>

(byte-compile-normal-call): Warn when `mapcar' is called for effect.

lisp/ChangeLog

+2007-09-21  Markus Triska  <markus.triska@gmx.at>
+
+	* emacs-lisp/bytecomp.el (byte-compile-normal-call): Warn when
+	`mapcar' is called for effect.
+
 2007-09-21  Glenn Morris  <rgm@gnu.org>
 
 	* obsolete/sun-fns.el (emacs-quit-menu): Remove emacstool-related code.

lisp/emacs-lisp/bytecomp.el

@@ -2831,6 +2831,10 @@ That command is designed for interactive use only" fn))
 (defun byte-compile-normal-call (form)
   (if byte-compile-generate-call-tree
       (byte-compile-annotate-call-tree form))
+  (when (and for-effect (eq (car form) 'mapcar))
+    (byte-compile-set-symbol-position 'mapcar)
+    (byte-compile-warn
+     "`mapcar' called for effect; use `mapc' or `dolist' instead"))
   (byte-compile-push-constant (car form))
   (mapc 'byte-compile-form (cdr form))	; wasteful, but faster.
   (byte-compile-out 'byte-call (length (cdr form))))