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From: raf@bu-cs.UUCP
Newsgroups: comp.lang.prolog
Subject: Re: cut for meta-interpreter
Message-ID: <6867@bu-cs.BU.EDU>
Date: Wed, 22-Apr-87 19:01:21 EST
Article-I.D.: bu-cs.6867
Posted: Wed Apr 22 19:01:21 1987
Date-Received: Fri, 24-Apr-87 03:51:18 EST
References: <6681@bu-cs.BU.EDU> <1861@druhi.UUCP>
Organization: Boston U. Comp. Sci.
Lines: 31
Keywords: cut,ancestor cut,meta-interperter
Summary: a possible solution

In response to my question  for meta-circular interpreter
which includes cut (without the use of ancesstor cut 
in the implementation!) Karen A. Morrissey proposes 
the "solution" which is just a regular meta-interpeter,
but DOES NOT incorporate cut!

Here is a possible solution which does incorporate cut and
is based on the assumption (which is true for C-prolog)
that cut cuts the goal choice-point rather then the 
disjunctive choice-point:

%-------------------------------------------------------
%  /* meta-circular interpreter with cut  */
%-------------------------------------------------------
%  Author: Rafail Ostrovsky                4/20/1987
%-------------------------------------------------------
%
solve(G) :- solve(G,_).
solve(!,X) :- var(X);X=cut.
solve((A,B),C) :- solve(A,C),solve(B,C).
solve(A,C) 
    :-  C==cut;
        (system_pred(A),!,A);
        (clause(A,B),solve(B,C1),(var(C1);C1==cut,!,fail)).
%-------------------------------------------------------

I do not know how to implement ancesstor cut (see Shapiro and
Sterling book) without the use of ancesstor cut at the meta-level,
and how to implement meta-circular interpreter with cut 
without the use of the above assumption. 
/raf