bug in scoping for higher order terms

[Lee Naish]

Fergus Henderson <fjh at cs.mu.OZ.AU> writes:

> > The standard Prolog solution is to treat as quantified all variables
> > appearing in the first argument of setof.  [...]

>Actually it's more complicated than that.

>(Perhaps that's what you mean by saying that it is
>"not done properly and its all not quite logical" ;-)

Yes.

>My point here is that Prolog sometimes locally quantifies the arguments and
>sometimes doesn't, depending on the instantiation of variables at runtime,
>so it doesn't set any clear precedent.

I believe its normally a mistake to use variables in the first argument
of setof/3 or '^'/2 (existential quantification in DEC10 Prolog) which
also appear in a wider scope.  The quantification problems are just one
of many reasons why setof/3 is not logical.  If you are interested, see

@inproceedings{naish:solns:85,
        author =        {Naish, Lee},
        title  =        {All solutions predicates in {Prolog}},
        booktitle =     {Proceedings of the Second IEEE Symposium on
                                Logic Programming},
        address =       {Boston, Massachusetts},
        year   =        {July 1985},
        pages  =        {73--77},
        comment = {Technical report 84/4, Department of Computer Science,
                University of Melbourne}
}


> > Its cleaned up in NU-Prolog's solutions/3,

>Actually this is only true of the NU-Prolog compiler.
>The NU-Prolog interpreter

... has various (documented) bugs and limitations.  Perhaps this is a
precedent for a Mercury "bug in scoping for higher order terms"!  Or
perhaps its just irrelevant.

	lee