From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Ulrich Mueller Newsgroups: gmane.emacs.devel Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Date: Mon, 28 Aug 2023 21:47:57 +0200 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="5419"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: emacs-devel@gnu.org To: Alan Mackenzie Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Mon Aug 28 21:48:55 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 1qaiEI-0001FY-TB for ged-emacs-devel@m.gmane-mx.org; Mon, 28 Aug 2023 21:48:54 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qaiDZ-00011l-NX; Mon, 28 Aug 2023 15:48:09 -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 1qaiDY-00011b-7Q for emacs-devel@gnu.org; Mon, 28 Aug 2023 15:48:08 -0400 Original-Received: from smtp.gentoo.org ([2001:470:ea4a:1:5054:ff:fec7:86e4]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_CHACHA20_POLY1305:256) (Exim 4.90_1) (envelope-from ) id 1qaiDW-0003aF-2n for emacs-devel@gnu.org; Mon, 28 Aug 2023 15:48:07 -0400 In-Reply-To: (Alan Mackenzie's message of "Mon, 28 Aug 2023 19:37:57 +0000") Received-SPF: pass client-ip=2001:470:ea4a:1:5054:ff:fec7:86e4; envelope-from=ulm@gentoo.org; helo=smtp.gentoo.org X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham 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:309450 Archived-At: >>>>> On Mon, 28 Aug 2023, Alan Mackenzie wrote: > In C, we have the very useful conditional compilation directives > introduced by #if or #ifdef, etc., which end at #end. > In Emacs Lisp we have no such construct. This is a Bad Thing. > More and more, especially recently, irritating warning messages are > occurring for, for example, obsolete variables and functions inside > conditionals which ensure they aren't used. For example: > (when (< emacs-major-version 24) > (defadvice .....)) > produces the warning about defadvice being obsolete. (I haven't actually > tested this example). What we really want here is for the defadvice only > to be _compiled_ when (< emacs-major-version 24), rather than compiled > unconditionally and not run. I believe (eval-when-compile (< emacs-major-version 24)) would work? > I propose a new function, hash-if, which would do what we want. The > above example could then be written something like: > (hash-if (< emacs-major-version 24) > (defadvice .....) > (advice-add .....)) But the old Emacs version wouldn't have the function, so it couldn't be used like this. What am I missing?