From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Lars Ingebrigtsen Newsgroups: gmane.emacs.devel Subject: Re: lists, plain conses and length Date: Fri, 04 Sep 2020 04:29:47 +0200 Message-ID: <875z8ugtpg.fsf@gnus.org> References: <20200904022334.791EBC2177B@raman-glaptop.localdomain> Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="4930"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) Cc: emacs-devel@gnu.org To: "T.V Raman" Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane-mx.org@gnu.org Fri Sep 04 04:31:03 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 1kE1VG-0001CI-VB for ged-emacs-devel@m.gmane-mx.org; Fri, 04 Sep 2020 04:31:02 +0200 Original-Received: from localhost ([::1]:39348 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kE1VF-0004T9-Sb for ged-emacs-devel@m.gmane-mx.org; Thu, 03 Sep 2020 22:31:01 -0400 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:41966) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kE1UJ-0003qR-Tp for emacs-devel@gnu.org; Thu, 03 Sep 2020 22:30:03 -0400 Original-Received: from quimby.gnus.org ([2a01:4f9:2b:f0f::2]:60392) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kE1UI-0005Kl-8y for emacs-devel@gnu.org; Thu, 03 Sep 2020 22:30:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=gnus.org; s=20200322; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date: References:Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=IP4dnPfJVWDKaMWPRfjdrAEAh+zn9Td72elFXjeZLFE=; b=sdYGsbehVT5uJl75rKSELoxmA7 J4aJ1v7STkjUkNC6FsruweeIbspZicpoQfv9jucgarOaNv+q9WFrJd/QpOlUbIQIRL5PVKMLTmKmq qwOlJP12h/NkoKsB0W2PlFswbXuGrYGzlgSIbzVrIOBCEd9Q7Skw/fernp4bcbpFqXbE=; Original-Received: from cm-84.212.202.86.getinternet.no ([84.212.202.86] helo=xo) by quimby with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kE1U4-0001KY-RZ; Fri, 04 Sep 2020 04:29:58 +0200 X-Now-Playing: Herbert's _Early Herbert_ In-Reply-To: <20200904022334.791EBC2177B@raman-glaptop.localdomain> (T. V. Raman's message of "Thu, 3 Sep 2020 19:23:34 -0700 (PDT)") Received-SPF: pass client-ip=2a01:4f9:2b:f0f::2; envelope-from=larsi@gnus.org; helo=quimby.gnus.org X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. 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:254513 Archived-At: "T.V Raman" writes: > (length a)=> 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 wrong? `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. (length '(1 2 . 3)) -> (wrong-type-argument listp 3) The predicate to use here is `proper-list-p'. -- (domestic pets only, the antidote for overdose, milk.) bloggy blog: http://lars.ingebrigtsen.no