From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Newsgroups: gmane.emacs.devel Subject: Re: lists, plain conses and length Date: Fri, 4 Sep 2020 10:53:30 +0200 Message-ID: <20200904085330.GB25869@tuxteam.de> References: <20200904022334.791EBC2177B@raman-glaptop.localdomain> <875z8ugtpg.fsf@gnus.org> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="l76fUT7nc3MelDdI" Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="13047"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Mutt/1.5.21 (2010-09-15) To: emacs-devel@gnu.org Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Sep 04 10:54:31 2020 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 1kE7UN-0003Il-0S for ged-emacs-devel@m.gmane-mx.org; Fri, 04 Sep 2020 10:54:31 +0200 Original-Received: from localhost ([::1]:51904 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kE7UL-0004IQ-S0 for ged-emacs-devel@m.gmane-mx.org; Fri, 04 Sep 2020 04:54:29 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:53850) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kE7TW-0003kZ-9o for emacs-devel@gnu.org; Fri, 04 Sep 2020 04:53:38 -0400 Original-Received: from mail.tuxteam.de ([5.199.139.25]:39959) by eggs.gnu.org with esmtps (TLS1.2:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.90_1) (envelope-from ) id 1kE7TT-0007Ep-UW for emacs-devel@gnu.org; Fri, 04 Sep 2020 04:53:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tuxteam.de; s=mail; h=From:In-Reply-To:Content-Type:MIME-Version:References:Message-ID:Subject:To:Date; bh=icyLizqZXmOfKMtMm168fhYBacTFn2+DLLdI6L+N0gk=; b=F+/AAXbp/3TWjCwUvZ7ZK8XrF8KxqaXFAASOb2jkZ8qTwMp00IBpaL8z8/8HoK4Rqq5wAOTOapZgpnO/Apj76QUlDJzcx69KPyC7B+Db9wL2hwVzQlihi5w7NBQiQQKC23yb5Xxim8fv/sek3O25SFHWej76f4UjEMqSWJV8YBB8J1Ayt8M8bGzQ8SGcrufe+BUDqiefH9Jp5FkQ/J+0Kjce+qMrAUtPqc+ZKIWj8+07Myy9glwYCzzKxpsJwArTvMuTH+FW6tW8weyPWLKgZsRuIuNIwcV89qNwsIiVwJKSvFwJBm0skmENX8F+n6U4h80Me8A/LHwEfCF7ojZaUg==; Original-Received: from tomas by mail.tuxteam.de with local (Exim 4.80) (envelope-from ) id 1kE7TO-000759-Hd for emacs-devel@gnu.org; Fri, 04 Sep 2020 10:53:30 +0200 Content-Disposition: inline In-Reply-To: <875z8ugtpg.fsf@gnus.org> Received-SPF: pass client-ip=5.199.139.25; envelope-from=tomas@tuxteam.de; helo=mail.tuxteam.de X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/04 04:43:26 X-ACL-Warn: Detected OS = Linux 3.1-3.10 [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, 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: 2.1.23 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" Xref: news.gmane.io gmane.emacs.devel:254517 Archived-At: --l76fUT7nc3MelDdI Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Sep 04, 2020 at 04:29:47AM +0200, Lars Ingebrigtsen wrote: > "T.V Raman" writes: >=20 > > (length a)=3D> Debugger entered--Lisp error: (wrong-type-argument listp= 2) > > > > Q: how does one distinguish a cons from a list. > > The error message for length may need fixing since it says the > > argument passed to it is not a list (it's correct) but then listp is wr= ong? >=20 > `length' (and many other functions) require what's called a "proper > list", which simply means that the cdr of the last cons cell is nil. >=20 > (length '(1 2 . 3)) > -> (wrong-type-argument listp 3) >=20 > The predicate to use here is `proper-list-p'. Note that `proper-list-p' has to run down the whole list to make sure. For short lists, that's fine. Cheers - t --l76fUT7nc3MelDdI Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iEYEARECAAYFAl9SAIoACgkQBcgs9XrR2kbnggCfXSw2UpSdDt+06FIZfIHjx3ri WPYAn17SX2s7+4TrXG94Fx0cw5xsEOD3 =nknV -----END PGP SIGNATURE----- --l76fUT7nc3MelDdI--