From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: Predicate for true lists Date: Fri, 6 Jul 2018 10:30:08 -0700 Organization: UCLA Computer Science Department Message-ID: <4376bd7a-4bd0-4dad-6205-8f53bf120a7a@cs.ucla.edu> References: <87fu3vdjjk.fsf@tcd.ie> <87bmcqhhsf.fsf@tcd.ie> <87in6xgtpb.fsf@tcd.ie> <2af892df-26cb-60b2-4fd8-067fcb3d32e9@cs.ucla.edu> <87r2kh9uwx.fsf@tcd.ie> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: blaine.gmane.org 1530898130 17644 195.159.176.226 (6 Jul 2018 17:28:50 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 6 Jul 2018 17:28:50 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 Cc: emacs-devel@gnu.org To: "Basil L. 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:227012 Archived-At: > +@defun proper-list-length object > +This function returns the length of @var{object} if it is a proper > +list, @code{nil} otherwise. In addition to satisfying @code{listp}, a > +proper list is neither circular nor dotted. Please mention here that the function can be used as a predicate; otherwise, that fact would be documented only in NEWS. Also, as Eli suggested, mention the same thing in the doc string. > - (let ((a-proper-p (ert--proper-list-p a)) > - (b-proper-p (ert--proper-list-p b))) > - (if (not (eql (not a-proper-p) (not b-proper-p))) > + (let ((a-proper-p (proper-list-length a)) > + (b-proper-p (proper-list-length b))) > + (if (not (eq (not a-proper-p) (not b-proper-p))) > `(one-list-proper-one-improper ,a ,b) > (if a-proper-p > - (if (not (equal (length a) (length b))) > + (if (/= (length a) (length b)) This computes the lengths of A and B twice; just compute it once.