From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stephen Berman Newsgroups: gmane.emacs.help Subject: Re: function arguments optional default values Date: Wed, 03 Jul 2024 23:51:28 +0200 Message-ID: <87zfqycffj.fsf@gmx.net> References: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="30106"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Cc: Heime via Users list for the GNU Emacs text editor To: Heime Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Wed Jul 03 23:52:11 2024 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 1sP7tb-0007cI-9d for geh-help-gnu-emacs@m.gmane-mx.org; Wed, 03 Jul 2024 23:52:11 +0200 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1sP7t2-0006gV-TR; Wed, 03 Jul 2024 17:51:36 -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 1sP7t1-0006gJ-7l for help-gnu-emacs@gnu.org; Wed, 03 Jul 2024 17:51:35 -0400 Original-Received: from mout.gmx.net ([212.227.15.19]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1sP7sy-0000kQ-Hh for help-gnu-emacs@gnu.org; Wed, 03 Jul 2024 17:51:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmx.net; s=s31663417; t=1720043489; x=1720648289; i=stephen.berman@gmx.net; bh=j6DBiWxl8ps9BL5zPqWvAFpqZcT4kzFlKMcJCNhsi4w=; h=X-UI-Sender-Class:From:To:Cc:Subject:In-Reply-To:References:Date: Message-ID:MIME-Version:Content-Type:Content-Transfer-Encoding:cc: content-transfer-encoding:content-type:date:from:message-id: mime-version:reply-to:subject:to; b=cVKLHRf89JMWt2jViCd9jl2GnjgvfurK7G61P11BirfhNxflZZMrPygJcHP90RWf jeQY8Ih8O59UU4t4JZ6jeEn6djm+MX/esdiIS9jWLb2LN2YubaNhqaY2IOvRqCCEZ JK4uV+Se1WBqu7BDbcWfDyzprfWqctq/BIYIaD9dmXFze0I3baUbYohsoECSsK4vf OMvDZylSKa+Dnpd915WJZ/WwBrjHOODL1OX7TTVSC3EhfI1YbhpQcP48El19g3Caf Yjfcp1NMzAnqpYop+128vNNiM+dbMq5eyOES1/qx5tynjQv9hcD6Ftuadl46f5/nu nIf4pHZKZgfal7lC2A== X-UI-Sender-Class: 724b4f7f-cbec-4199-ad4e-598c01a50d3a Original-Received: from strobelfs ([88.130.49.113]) by mail.gmx.net (mrgmx004 [212.227.17.190]) with ESMTPSA (Nemesis) id 1MBlxW-1sZ42P1zwq-00BoSz; Wed, 03 Jul 2024 23:51:29 +0200 In-Reply-To: (Heime's message of "Wed, 03 Jul 2024 21:21:34 +0000") X-Provags-ID: V03:K1:33bGqG3FfVcIQe28O/N6hZjImk1PpMGMBElqmVfD2ctx68uAql4 MDeLmMqDuGhodyxYq6GJOy6caYHwLrwBm2/9KKw6tFNtnc3bIAn7FnRhuM55OOw5i6Pp+Wg jxkIzTgX5iIAEhpbrO2RK6oS0l/Z0ImBqahv3pgGE4SGvaOfJFAUOKsLoX5Z540B1ZVTx5o IXXcSyU13EFKIkRC9rYXQ== UI-OutboundReport: notjunk:1;M01:P0:ByU9cpPoPww=;o+ZVvI9rrw2T6DEW6xYrSL9WAgH 6iX5IK9VV75NgfByclGySQxwcVPgk4b6aFQLXSDJ2aXeA6y7HvA8wTc5fDaMtEgZ66LUrjIoY bjh2XmfmXeUjc7vBtv4FF1sB0xLbetKXPYP7k17iQzdiyrualgZLf76m1ZAkuj/a4bDzQRI6J pFDWH1lrkkJy4x0CYwxhx27c203947GiKxkHgQd2fuyjD7um/s9DtolUo/xclcWt+S+7VC0Pj rnZq+/hDSFgxJaYgLh9cVxveQ1KpdbUVomnkJn1llVSikEpTT4RY3hMVdVp+mnt43mJevttkf gieDOsT/3TYbar1zZm6/3ztxAlf+C7SLTQN9BgVLR+IUoNkFwTZ1gOAadFviAuM+lFMD1xYec KlfsT+0WqPiqnisjThUY/klcAzDnllL4hP64oik3MbKLQQfbrEsx0Yk4nRDl8YmC2OWDujmB+ iS8F6OFOHyPMpn8GVedDaH4/Ul4fXMJlkvt0QiOzo6q1DRrlODWCOVq/K84TAprCOCrSbqlga PsDSZQi/d0tkai/TRMHdWEtxlUdRDuvVYXIORp6S68Oze7lK5GpMseuYHquwKgC/JC4h5bVKb ulryfbfy4H8Qjj9hKE9cLhDxWrtTV44fO4seHhb80WSTa3iDigQ1ix2m8yQw/4USQC/YxV5OK mc8fV/u349mAd5E2cPavuiHz+4vptpPz1sFKJ7siUjmy5aJkTiAmytrUZoFDuOhzJX70XLje+ EBVmfxcapUuK5HheFC2YjpWqL0btU3I03jJ+pX1SK6EMmCZWDtNiJ001YCEkWrTSX2JC5jUO Received-SPF: pass client-ip=212.227.15.19; envelope-from=stephen.berman@gmx.net; helo=mout.gmx.net X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham 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 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-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:147064 Archived-At: On Wed, 03 Jul 2024 21:21:34 +0000 Heime wrote: > Does elisp support function arguments optional default values ? The answer is in the Elisp manual (info "(elisp) Argument List"): If actual arguments for the optional and rest variables are omitted, then they always default to =E2=80=98nil=E2=80=99. There is no way for t= he function to distinguish between an explicit argument of =E2=80=98nil=E2=80=99 and an = omitted argument. However, the body of the function is free to consider =E2=80= =98nil=E2=80=99 an abbreviation for some other meaningful value. This is what =E2=80=98substring=E2=80=99 does; =E2=80=98nil=E2=80=99 as the third argu= ment to =E2=80=98substring=E2=80=99 means to use the length of the string supplied. =20=20 Common Lisp note: Common Lisp allows the function to specify what default value to use when an optional argument is omitted; Emacs Lisp always uses =E2=80=98nil=E2=80=99. Emacs Lisp does not support= =E2=80=98supplied-p=E2=80=99 variables that tell you whether an argument was explicitly passed. Steve Berman