From mboxrd@z Thu Jan  1 00:00:00 1970
Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail
From: Michael Heerdegen <michael_heerdegen@web.de>
Newsgroups: gmane.emacs.help
Subject: Re: Is there a way of setting a variable only when it exists?
Date: Mon, 14 Mar 2022 23:09:23 +0100
Message-ID: <87lexcnq3w.fsf@web.de>
References: <87lexdul8e.fsf@mbork.pl>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214";
	logging-data="2021"; mail-complaints-to="usenet@ciao.gmane.io"
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux)
To: help-gnu-emacs@gnu.org
Cancel-Lock: sha1:KA3KsCpKQhHltolJ4sr/GpR5PX8=
Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Mon Mar 14 23:09:54 2022
Return-path: <help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org>
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 <help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org>)
	id 1nTst0-0000Ie-Lh
	for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 14 Mar 2022 23:09:54 +0100
Original-Received: from localhost ([::1]:40114 helo=lists1p.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.90_1)
	(envelope-from <help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org>)
	id 1nTssz-0003Eh-9L
	for geh-help-gnu-emacs@m.gmane-mx.org; Mon, 14 Mar 2022 18:09:53 -0400
Original-Received: from eggs.gnu.org ([209.51.188.92]:59540)
 by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)
 (Exim 4.90_1) (envelope-from <geh-help-gnu-emacs@m.gmane-mx.org>)
 id 1nTssf-0003DC-Ci
 for help-gnu-emacs@gnu.org; Mon, 14 Mar 2022 18:09:33 -0400
Original-Received: from ciao.gmane.io ([116.202.254.214]:44616)
 by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)
 (Exim 4.90_1) (envelope-from <geh-help-gnu-emacs@m.gmane-mx.org>)
 id 1nTsse-0004QH-2k
 for help-gnu-emacs@gnu.org; Mon, 14 Mar 2022 18:09:33 -0400
Original-Received: from list by ciao.gmane.io with local (Exim 4.92)
 (envelope-from <geh-help-gnu-emacs@m.gmane-mx.org>)
 id 1nTssc-000APP-A9
 for help-gnu-emacs@gnu.org; Mon, 14 Mar 2022 23:09:30 +0100
X-Injected-Via-Gmane: http://gmane.org/
Received-SPF: pass client-ip=116.202.254.214;
 envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io
X-Spam_score_int: -13
X-Spam_score: -1.4
X-Spam_bar: -
X-Spam_report: (-1.4 / 5.0 requ) BAYES_00=-1.9,
 FREEMAIL_FORGED_FROMDOMAIN=0.249, FREEMAIL_FROM=0.001,
 HEADER_FROM_DIFFERENT_DOMAINS=0.249, SPF_HELO_NONE=0.001, SPF_PASS=-0.001,
 T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no autolearn_force=no
X-Spam_action: no action
X-BeenThere: help-gnu-emacs@gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Users list for the GNU Emacs text editor <help-gnu-emacs.gnu.org>
List-Unsubscribe: <https://lists.gnu.org/mailman/options/help-gnu-emacs>,
 <mailto:help-gnu-emacs-request@gnu.org?subject=unsubscribe>
List-Archive: <https://lists.gnu.org/archive/html/help-gnu-emacs>
List-Post: <mailto:help-gnu-emacs@gnu.org>
List-Help: <mailto:help-gnu-emacs-request@gnu.org?subject=help>
List-Subscribe: <https://lists.gnu.org/mailman/listinfo/help-gnu-emacs>,
 <mailto:help-gnu-emacs-request@gnu.org?subject=subscribe>
Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org
Original-Sender: "help-gnu-emacs"
 <help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org>
Xref: news.gmane.io gmane.emacs.help:136550
Archived-At: <http://permalink.gmane.org/gmane.emacs.help/136550>

Marcin Borkowski <mbork@mbork.pl> writes:

> I'd like to be able to say something like
> 
> (setq-safe hello "world")
> 
> so that `hello' is set to `"world"' if it is an existing variable (e.g.,
> defined by `defvar') and an error is raised if `hello' does not exist.

Byte compiling can help with things like name changes.

> I assume it would be fairly easy to code such a macro (using `boundp'),

Maybe rather using `special-variable-p'?

Michael.