From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Jean Louis Newsgroups: gmane.emacs.help Subject: Re: Example use of macro to minimize and generalize the code Date: Tue, 1 Jun 2021 21:12:50 +0300 Message-ID: References: <87k0nes9s0.fsf@web.de> <878s3us8le.fsf@web.de> <87fsy1y97e.fsf@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="17820"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/2.0.7+183 (3d24855) (2021-05-28) Cc: Michael Heerdegen , help-gnu-emacs To: Yuri Khan Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Jun 01 20:31:01 2021 Return-path: Envelope-to: geh-help-gnu-emacs@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 1lo9AK-0004NR-T3 for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 01 Jun 2021 20:31:00 +0200 Original-Received: from localhost ([::1]:49218 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lo9AJ-0007FN-Ur for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 01 Jun 2021 14:30:59 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:45270) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lo8xT-0003QN-4s for help-gnu-emacs@gnu.org; Tue, 01 Jun 2021 14:17:43 -0400 Original-Received: from stw1.rcdrun.com ([217.170.207.13]:52811) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lo8xQ-0001Vk-U8 for help-gnu-emacs@gnu.org; Tue, 01 Jun 2021 14:17:42 -0400 Original-Received: from localhost ([::ffff:197.157.0.35]) (AUTH: PLAIN admin, TLS: TLS1.3,256bits,ECDHE_RSA_AES_256_GCM_SHA384) by stw1.rcdrun.com with ESMTPSA id 00000000000AE2D9.0000000060B679C2.00007C1F; Tue, 01 Jun 2021 11:17:37 -0700 Mail-Followup-To: Yuri Khan , Michael Heerdegen , help-gnu-emacs Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=217.170.207.13; envelope-from=bugs@gnu.support; helo=stw1.rcdrun.com X-Spam_score_int: -3 X-Spam_score: -0.4 X-Spam_bar: / X-Spam_report: (-0.4 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_SORBS_WEB=1.5, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.23 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-mx.org@gnu.org Original-Sender: "help-gnu-emacs" Xref: news.gmane.io gmane.emacs.help:130468 Archived-At: * Yuri Khan [2021-06-01 20:58]: > On Wed, 2 Jun 2021 at 00:27, Jean Louis wrote: > > > I have removed `id' argument and now I have: > > > > (macroexpand '(when-tabulated-id "people" (ignore))) > > ⇒ (if id (progn (ignore)) > > (if (or (eq "people" 'any) (string-equal "people" rcd-current-table)) > > (let ((id (tabulated-list-get-id))) > > (if id (progn (ignore)) (message "Did not get ID"))) > > (message "This function is for table `%s' only" "people"))) > > > > If I would use ,d it would expand into number or nil, it seem it would end up same. > > > > Now I don't have compiler warnings, and functions work fine. > > > > Let me know if I am making errors in this. > > Yes you are. Your macro expands to a form that refers to a symbol > named “id” from outer scope. Next, there are several possibilities: > > * The symbol is not defined, in which case the result of expansion > will signal (void-variable id): > > (when-tabulated-id "people" (ignore)) > ⇒ Debugger entered--Lisp error: (void-variable id) Macro is exclusively used in functions as this: (defun my-fun (&optional id) "" (interactive) (when-tabulated-id "hyobjects" )) > * The user of your macro has to define a variable named “id” globally > or buffer-locally. This is bad because the name “id” is not > namespaced. In your own package, any variable names you define should > start with a prefix unique to your package. Do you mean all, or just global variables to have prefix? > (setq id t) > (when-tabulated-id "people" (ignore)) > ⇒ nil I understand, just macro is used exclusively in functions as above. Is that alright? > * The user has to use your macro in a context where “id” is bound as a > local variable or a function argument. If that’s your intent, you > should document it in the docstring of the macro, but it’s fragile > because nobody expects forms to behave this way. > > (let ((id t)) > (when-tabulated-id "people" (ignore))) > ⇒ nil > > (defun foo (id) > (when-tabulated-id "people" (ignore))) > (foo t) > ⇒ nil (◍•ᴗ•◍) that can be, but that is exactly how I expected it to behave. As the ID is either obtained programmatically which makes the macro work or from (tabulated-list-get-id) > * Lastly, you might have intended this macro to be used only by you. Yes, and I see difficulties in future if somebody else wish to use it. > In that case, it should be namespaced to your package with a double > hyphen after the prefix. Anyway, three month later, you forget that > the macro depends on “id” and you stare at your (let ((id t)) …) or > (defun foo (id) …) which doesn’t obviously use “id” and remove the > binding. Suddenly everything breaks. Breaking I can also understand. Macro or not macro my goal is to minimize programming, as 400+ functions are asking for (tabulated-list-get-id) and the ID can be in different tables. Maybe it can be solved without any macro. -- Jean Take action in Free Software Foundation campaigns: https://www.fsf.org/campaigns Sign an open letter in support of Richard M. Stallman https://stallmansupport.org/