Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!pt.cs.cmu.edu!rochester!ferguson
From: ferguson@cs.rochester.edu (George Ferguson)
Newsgroups: comp.lang.prolog
Subject: Re: different Prologs?
Message-ID: <1989Oct11.142859.23324@cs.rochester.edu>
Date: 11 Oct 89 14:28:59 GMT
References: <111000002@uxa.cso.uiuc.edu>
Reply-To: ferguson@cs.rochester.edu.UUCP (George Ferguson)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 28

In article <111000002@uxa.cso.uiuc.edu>, ddgg0881@uxa.cso.uiuc.edu writes:
> I have two questions about Prolog implementations:
> One of the main selling points of Prolog
> is the efficient way that it backtracks upon failure.  Are there any
> implementations of Prolog that allow 'get' or 'get0' to backtrack
> and unread characters?

WUP (Waterloo Unix Prolog) claimed to implement both _logical_ (ie. back-
trackable) I/O predicates based (I think) on streams as well as the
standard non-logical I/O predicates.

The best reference I can find is the User's manual which reads:

	WUP Version 3.0 User's Manual
	David J. McClurkin
	Logic Programming and AI Group
	Department of Computer Science
	University of Waterloo
	Waterloo, Ontario, Canada
	[ version of August 6, 1987 ]

Perhaps you can track it down if you're interested, I never used the
system myself.

-- 
George Ferguson			ARPA: ferguson@cs.rochester.edu
University of Rochester		UUCP: {decvax,rutgers}!rochester!ferguson
Rochester  NY  14627		VOX:  (716) 275-2527