From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Stefan Monnier Newsgroups: gmane.emacs.devel Subject: Re: Common Lisp like feature expressions Date: Mon, 27 Dec 2010 20:01:02 -0500 Message-ID: References: NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: dough.gmane.org 1293498080 17901 80.91.229.12 (28 Dec 2010 01:01:20 GMT) X-Complaints-To: usenet@dough.gmane.org NNTP-Posting-Date: Tue, 28 Dec 2010 01:01:20 +0000 (UTC) Cc: emacs-devel@gnu.org To: Leo Original-X-From: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Tue Dec 28 02:01:14 2010 Return-path: Envelope-to: ged-emacs-devel@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by lo.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1PXNw9-0006Uw-Kc for ged-emacs-devel@m.gmane.org; Tue, 28 Dec 2010 02:01:13 +0100 Original-Received: from localhost ([127.0.0.1]:33857 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PXNw8-0001Hb-LO for ged-emacs-devel@m.gmane.org; Mon, 27 Dec 2010 20:01:12 -0500 Original-Received: from [140.186.70.92] (port=45378 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PXNw1-0001HH-1b for emacs-devel@gnu.org; Mon, 27 Dec 2010 20:01:06 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PXNvz-00007q-MK for emacs-devel@gnu.org; Mon, 27 Dec 2010 20:01:04 -0500 Original-Received: from ironport2-out.teksavvy.com ([206.248.154.181]:51617 helo=ironport2-out.pppoe.ca) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PXNvz-00007h-G7 for emacs-devel@gnu.org; Mon, 27 Dec 2010 20:01:03 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AvsEACLFGE3O+LP+/2dsb2JhbACkLXS/PIVKBIRljhs X-IronPort-AV: E=Sophos;i="4.60,237,1291611600"; d="scan'208";a="86581534" Original-Received: from 206-248-179-254.dsl.teksavvy.com (HELO pastel.home) ([206.248.179.254]) by ironport2-out.pppoe.ca with ESMTP/TLS/ADH-AES256-SHA; 27 Dec 2010 20:01:02 -0500 Original-Received: by pastel.home (Postfix, from userid 20848) id 12B1458B89; Mon, 27 Dec 2010 20:01:02 -0500 (EST) In-Reply-To: (Leo's message of "Mon, 27 Dec 2010 19:57:55 +0000") User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-BeenThere: emacs-devel@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Emacs development discussions." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Xref: news.gmane.org gmane.emacs.devel:133993 Archived-At: > (defun eval-feature-expression (form) > (cond > ((atom form) (featurep form nil)) > ((eq (car form) 'not) > (not (eval-feature-expression (cadr form)))) > ((eq (car form) 'and) > (if (not (cdr form)) > t > (and (eval-feature-expression (cadr form)) > (eval-feature-expression (cons 'and (cddr form)))))) > ((eq (car form) 'or) > (if (not (cdr form)) > nil > (or (eval-feature-expression (cadr form)) > (eval-feature-expression (cons 'or (cddr form)))))) > (t (error "Invalid feature expression: %s" form)))) Just for fun, here's a version using pcase: (defun eval-feature-expression (form) (pcase form ((pred atom) (featurep form nil)) (`(not ,x) (not (eval-feature-expression x))) (`(and) t) (`(and ,form1 . ,forms) (and (eval-feature-expression form1) (eval-feature-expression (cons 'and forms)))) (`(or) nil) (`(or ,form1 . ,forms) (or (eval-feature-expression form1) (eval-feature-expression (cons 'or forms)))) (t (error "Invalid feature expression: %s" form))))) -- Stefan