From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via "Emacs development discussions." Newsgroups: gmane.emacs.devel Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Date: Sat, 02 Sep 2023 19:09:04 -0400 Message-ID: References: <877cpeko06.fsf@posteo.net> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="38247"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: emacs-devel@gnu.org Cancel-Lock: sha1:4UaliFOTAPtdXb/rfWZbcJSaHBc= Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Sun Sep 03 01:09:36 2023 Return-path: Envelope-to: ged-emacs-devel@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1qcZkG-0009oT-FO for ged-emacs-devel@m.gmane-mx.org; Sun, 03 Sep 2023 01:09:36 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qcZjx-0001RH-5T; Sat, 02 Sep 2023 19:09:17 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qcZjv-0001PZ-CH for emacs-devel@gnu.org; Sat, 02 Sep 2023 19:09:15 -0400 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qcZjs-00058u-Nw for emacs-devel@gnu.org; Sat, 02 Sep 2023 19:09:15 -0400 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1qcZjq-0009Sh-Tq for emacs-devel@gnu.org; Sun, 03 Sep 2023 01:09:10 +0200 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=ged-emacs-devel@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.devel:309919 Archived-At: > --8<---------------cut here---------------start------------->8--- > (defmacro cif (test then &rest else) > "Evaluate TEST during macro-expansion and return THEN or ELSE." > (if (eval test t) then else)) > --8<---------------cut here---------------end--------------->8--- FWIW I've used such macros in packages under the name `--if-when-compile`. Also, FWIW, I've used the following variant to let the compile-time check be reconsidered at runtime: (defmacro TeX--if-macro-fboundp (name then &rest else) "..." (declare (indent 2) (debug (symbolp form &rest form))) (if (fboundp name) ;If macro exists at compile-time, just use it. then `(if (fboundp ',name) ;Else, check if it exists at run-time. (eval ',then) ;If it does, then run the then code. ,@else))) -- Stefan