From jan@swi.psy.uva.nl Tue May 16 10:57:58 2000 Received: from gollem.swi.psy.uva.nl (root@gollem [145.18.152.30]) by swi.psy.uva.nl (8.9.3/8.9.3) with ESMTP id KAA24387; Tue, 16 May 2000 10:57:58 +0200 (MET DST) Received: from localhost (localhost [[UNIX: localhost]]) by gollem.swi.psy.uva.nl (8.9.3/8.9.3/SuSE Linux 8.9.3-0.1) id KAA00463; Tue, 16 May 2000 10:58:16 +0200 From: Jan Wielemaker Organization: SWI, University of Amsterdam To: "Marcos Rebelo" , Subject: Re: Need help in a not unifyable Date: Tue, 16 May 2000 10:52:34 +0200 X-Mailer: KMail [version 1.0.28] Content-Type: text/plain References: In-Reply-To: MIME-Version: 1.0 Message-Id: <00051610581602.00382@gollem> Content-Transfer-Encoding: 8bit On Tue, 16 May 2000, Marcos Rebelo wrote: >This is part of a code that I´m doing, when i try check(A,B) prolog gives >no answer, the problem must be in the \== but I have alredy tried \=@=, \=, >=\= and none worked. > >For example if I try to do "c \== _ cf _" gives NO but "c == _ cf _" also >gives no. What is the problem here? > >:-op(950, xfx, cf). >:-op(900, xfx, =>). Operator precedence: 1 ?- op(950, xfx, cf). Yes 2 ?- c \== _ cf _. ERROR: Undefined procedure: (cf)/2 I.e. the precedence of cf > precedence of \== and therefore the term is read as (c\==_) cf _. Always think twice when defining new operators: should they be used in conjunction with built-in's? Are they likely to break other code? As of 3.3, operators are local to a module (unless defined in the user module), so my advice is to use modules if you use local operators to avoid messing up other code. Regards --- Jan