From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.help Subject: Re: How to shadow a function temporarily? (flet and cl-flet) Date: Sun, 26 Jan 2014 09:50:15 -0500 Message-ID: References: <87k3dm4yv4.fsf@gmail.com> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: ger.gmane.org 1390747849 26864 80.91.229.3 (26 Jan 2014 14:50:49 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 26 Jan 2014 14:50:49 +0000 (UTC) To: help-gnu-emacs@gnu.org Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Sun Jan 26 15:50:55 2014 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W7R30-0006ut-Ru for geh-help-gnu-emacs@m.gmane.org; Sun, 26 Jan 2014 15:50:54 +0100 Original-Received: from localhost ([::1]:54931 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W7R30-00073G-IP for geh-help-gnu-emacs@m.gmane.org; Sun, 26 Jan 2014 09:50:54 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:60962) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W7R2i-000738-EP for help-gnu-emacs@gnu.org; Sun, 26 Jan 2014 09:50:43 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W7R2b-0005ww-2g for help-gnu-emacs@gnu.org; Sun, 26 Jan 2014 09:50:36 -0500 Original-Received: from plane.gmane.org ([80.91.229.3]:47303) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W7R2a-0005wl-Nm for help-gnu-emacs@gnu.org; Sun, 26 Jan 2014 09:50:28 -0500 Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1W7R2Y-0006cc-9E for help-gnu-emacs@gnu.org; Sun, 26 Jan 2014 15:50:26 +0100 Original-Received: from 75-119-255-243.dsl.teksavvy.com ([75.119.255.243]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 26 Jan 2014 15:50:26 +0100 Original-Received: from monnier by 75-119-255-243.dsl.teksavvy.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 26 Jan 2014 15:50:26 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 28 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 75-119-255-243.dsl.teksavvy.com User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) Cancel-Lock: sha1:BUS/t4cL8mFkpM/wt1euIVGC7V4= X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 80.91.229.3 X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.help:95668 Archived-At: > 1. The main question is: how can I override a function with another > compatible function (with the same args) temporarily? Be careful with "temporarily": it can be interpreted as "lexically" or "dynamically". From your example, it seems you want "dynamically". Note, tho, that (defun 8+ (arg) (+ 8 arg)) (flet ((+ (&rest args) (apply '- args))) (8+ 3)) ; => 5 will give you 11 when byte-compiled. IOW, you had better look for another solution to your problem. One option could be something along the following lines: (defvar my-plus-is-subtraction nil) (defun 8+ (arg) (funcall (if my-plus-is-subtraction #'- #'+) 8 arg)) (let ((my-plus-is-subtraction t)) (8+ 3)) ; => 5 -- Stefan