[Oz] Filtering of values of constraint variables

[Benko Tamas]

Dear Mozart users,

I'm from the Prolog world, and I'm interested in solving constraint
problems.  There is a technique called filtering which I use quite often,
but I don't see how I could implement it in Mozart.

Filtering is used in (or before) the labeling phase and it means that
before committing to a possible value we try to exclude values by
tentatively instantiating it to a value and watching if it fails.

In Prolog it looks like this:

% Try to filter out value V from variable X.
filter(X, V) :-
        (   \+ X = V -> X #\= V
        ;   true
        ).

This kind of filtering is useful if the constraint system is unable infer
that X can't have the value V, but it can detect the inconsistency if X is
instantiated to V.

In Mozart the constraint posting and the search phases are nicely
separated, and I don't know to which phase filtering belongs.


Another (completely unrelated) question: is it possible to program
constraint propagators in Mozart without using the C++ interface?  For
prototyping purposes it would be fast enough for me.

Cheers,
Tamás Benkõ
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