Article View: comp.lang.prolog
Article #3961Re: Committed Choice
From: Fernando Pereira
Date: Tue, 21 Mar 1989 02:41
Date: Tue, 21 Mar 1989 02:41
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1564 bytes
In Edinburgh-family Prolog systems, the scope of a cut is the whole clause in which it appears, even it the cut is inside a conditional. This is a very useful control behavior, messy to simulate with cuts that stay inside the scope of conditionals. For example, the following is a common way of terminating a repeat/fail loop: ... repeat, ... ( <exit condition> -> ! ; <continue condition> -> fail ). I will agree with anybody that this is not a pristine example of declarative programming, but such things *are* needed in the imperfect logic-programming languages we have today. I also appreciate that we could move the cut to after the conditional with the same result, but there are more complicated situations, which I don't have the time now to discuss, in which that alternative is not available. Fernando Pereira AI Center SRI International pereira@ai.sri.com
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!agate!labrea!russell!pereira From: pereira@russell.STANFORD.EDU (Fernando Pereira) Newsgroups: comp.lang.prolog Subject: Re: Committed Choice Summary: Cut should cut from inside conditionals Keywords: cut if-then-else Message-ID: <8209@russell.STANFORD.EDU> Date: 21 Mar 89 02:41:44 GMT References: <11500012@hpldola.HP.COM> <733@gould.doc.ic.ac.uk> <1305@murtoa.cs.mu.oz.au> Sender: pereira@russell.Stanford.EDU (Fernando Pereira) Reply-To: pereira@russell.UUCP (Fernando Pereira) Organization: Center for the Study of Language and Information, Stanford U. Lines: 23