From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Philip Kaludercic Newsgroups: gmane.emacs.devel Subject: Re: Why shouldn't we have a #if .... #else .... #endif construct in Emacs Lisp? Date: Tue, 29 Aug 2023 12:54:17 +0000 Message-ID: <877cpeko06.fsf@posteo.net> 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="25120"; mail-complaints-to="usenet@ciao.gmane.io" Cc: emacs-devel@gnu.org To: Alan Mackenzie Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Tue Aug 29 14:56:00 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 1qayGF-0006G0-1g for ged-emacs-devel@m.gmane-mx.org; Tue, 29 Aug 2023 14:55:59 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qayEo-0007m1-EP; Tue, 29 Aug 2023 08:54:30 -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 1qayEl-0007lj-Dd for emacs-devel@gnu.org; Tue, 29 Aug 2023 08:54:28 -0400 Original-Received: from mout02.posteo.de ([185.67.36.66]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qayEg-0007yx-88 for emacs-devel@gnu.org; Tue, 29 Aug 2023 08:54:27 -0400 Original-Received: from submission (posteo.de [185.67.36.169]) by mout02.posteo.de (Postfix) with ESMTPS id 78E89240103 for ; Tue, 29 Aug 2023 14:54:18 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=posteo.net; s=2017; t=1693313658; bh=9fTbJ6kQlHdjDdBwX4Tt+kd10DNCjQ2uWTi4kVFpSeA=; h=From:To:Cc:Subject:Autocrypt:Date:Message-ID:MIME-Version:From; b=kz0m1qm3WCxrUdmc0jbedoOckgDUkC2SnLF3ec+axGC/keUuhKDu5qGDiY+80z7N7 dDV0zWspJqStLq8zSX5bFM3TKqSZUDtoSoJCBoTWABhl7fh9jwqHejUILVCSY4pmwB ogy616U7SsWBOAxOxWo4rQuyIKoPXITpBbwiQ5pFWzkf3TIWkDXrJ6jysUmUjxVkIu R0xgJ4JP28SgMd5P8mZw++xzS5p78mb3up5Tn+ugKQzzr8qbq599tiQ43ILlOq+lE6 M323zrzdXDr90IQvB/K/zz2tGhdxO2rKfy+Dz1OyYtIXlVmvLeU4+XySOXQ9ePH/AQ Kn/76BHIhqU8A== Original-Received: from customer (localhost [127.0.0.1]) by submission (posteo.de) with ESMTPSA id 4RZnSB04n0z9rxK; Tue, 29 Aug 2023 14:54:17 +0200 (CEST) In-Reply-To: (Alan Mackenzie's message of "Mon, 28 Aug 2023 19:37:57 +0000") Autocrypt: addr=philipk@posteo.net; keydata= mDMEZBBQQhYJKwYBBAHaRw8BAQdAHJuofBrfqFh12uQu0Yi7mrl525F28eTmwUDflFNmdui0QlBo aWxpcCBLYWx1ZGVyY2ljIChnZW5lcmF0ZWQgYnkgYXV0b2NyeXB0LmVsKSA8cGhpbGlwa0Bwb3N0 ZW8ubmV0PoiWBBMWCAA+FiEEDg7HY17ghYlni8XN8xYDWXahwukFAmQQUEICGwMFCQHhM4AFCwkI BwIGFQoJCAsCBBYCAwECHgECF4AACgkQ8xYDWXahwulikAEA77hloUiSrXgFkUVJhlKBpLCHUjA0 mWZ9j9w5d08+jVwBAK6c4iGP7j+/PhbkxaEKa4V3MzIl7zJkcNNjHCXmvFcEuDgEZBBQQhIKKwYB BAGXVQEFAQEHQI5NLiLRjZy3OfSt1dhCmFyn+fN/QKELUYQetiaoe+MMAwEIB4h+BBgWCAAmFiEE Dg7HY17ghYlni8XN8xYDWXahwukFAmQQUEICGwwFCQHhM4AACgkQ8xYDWXahwukm+wEA8cml4JpK NeAu65rg+auKrPOP6TP/4YWRCTIvuYDm0joBALw98AMz7/qMHvSCeU/hw9PL6u6R2EScxtpKnWof z4oM Received-SPF: pass client-ip=185.67.36.66; envelope-from=philipk@posteo.net; helo=mout02.posteo.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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:309503 Archived-At: Alan Mackenzie writes: > Hello, Emacs. > > 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. In this specific case, would it be possible to use the nadvice compatibility package on GNU ELPA? > 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 .....)) > > .. This is not actually all that difficult to write. My first attempt > uses a compiler-macro, and looks like this: > > (defun hash-if (condition if-part &rest else-part) > "A compiler macro analogous to C's #if. > CONDITION is evaluated at compile time. If it is non-nil, > IF-PART gets compiled. Otherwise ELSE-PART (enclosed in a > `progn') gets compiled." > (declare (indent 2)) > (error "hash-if has been called directly")) > > (put 'hash-if 'compiler-macro > (lambda (form condition if-part &rest else-part) > (if (eval condition lexical-binding) > if-part > (cons 'progn else-part)))) Would something like work as well: --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--- > .. I propose adding it to subr.el, just before (defmacro when ....). > > What do people think about this?