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From: px@fctunl.rccn.pt (Joaquim Baptista [pxQuim])
Newsgroups: comp.lang.prolog
Subject: Re: Prolog's pitfalls
Message-ID: <PX.90Jul13144444@zen.fctunl.rccn.pt>
Date: 13 Jul 90 13:44:44 GMT
References: <1396@quintus.UUCP> <5135@castle.ed.ac.uk>
Sender: news@fctunl.rccn.pt (USENET News System)
Organization: Universidade Nova de Lisboa -- Lisbon, Portugal
Lines: 47
In-Reply-To: jha@lfcs.ed.ac.uk's message of 12 Jul 90 11:39:15 GMT

In article <5135@castle.ed.ac.uk> jha@lfcs.ed.ac.uk (Jamie Andrews) writes:

	This reminds me of something I've been wondering about for
   a while.  Built-in "if-then-else" and "case" constructs are
   often touted as a way of getting around using cuts.  What is the
   current wisdom about this?  I know that not all uses of cut can
   be replaced by if-then-else, but what proportion of them can?
   (I seem to remember hearing some figure like 70% at one point --
   don't know how this was measured, though.)

	On a related point, what proportion of instances of
   negation can be eliminated by using if-then-elses?  (The
   problems of negation wouldn't be eliminated, of course, but if
   we could replace negation by if-then-else there would be more
   uniformity with other programming languages.)

Do you know the work reported in:

%T UNL Prolog User's Guide Manual, version 1.0, draft
%A Antonio Porto
%A Luis Moniz Pereira
%A Luis Trindade
%P 11
%I Dept Informatica, UNL
%C Lisboa
%D May 1987
%R ALPES WP 9
%K =UNL-Prolog =Prolog Manual
%X The system described here is UNL Prolog version 1.0 running on top of
O'Keefe's Edinburgh C-Prolog version 1.5b.edai under the Ultrix operating
system.
   If you heard about Two-Level Prolog, conceived by Antonio Porto, there are
a lot of things that you will recognize in UNL Prolog. UNL Prolog results
from the experience acquired in the use of the first system, which it aims
at improving.
   One of the main intentions in the design of the system was to replace the
anarchical use of the cut with constructs or system predicates, that
express in a better way the intention of that use.
   UNL Prolog accepts standard Edinburgh Prolog clauses for the sake of
compatibility. But if you want to start to use UNL Prolog, you should
do without standard Prolog, which is allways possible as there is no loss
of power with respect to Prolog.
--
Joaquim Manuel Soares Baptista, aka px@fctunl.rccn.pt, px@unl.uucp
Snail: CRIA, UNINOVA, FCT/UNL, 2825 Mt Caparica, Portugal

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