Re: clpfd constraints not taking effect

Hi James,

James Hogan <[email protected]> writes:

> Ah, I think I get it, so in the apply_preargs example, SWI's shallow
> look at apply_preargs sees the latter two functors as taking the same
> argument types, so it has to remember it in case the first fails or
> other solutions required.

Yes, with your current version, the second argument of both clauses is a
term of the form [_|_] (functor '.', arity 2), so SWI's current, shallow
indexing cannot distinguish them, and choice-points are left behind.
Relatedly, tail call optimization cannot be applied as a consequence.

>>    ?- person(enosh).
>>    true ;
>>    true ;
>>    false.
>
> yes, I've been trying to get rid of these cases, especially the final
> false (which now makes much more sense).

It probably makes sense to precompute the definition of person/1 before
your actual constraint solving: You can use setof/3 to collect
everything you consider a person, using the various rules you defined,
and then use assertz/1 to create a single clause for each person. This
makes further uses of person/1 deterministic when the argument is bound.

All the best,
Markus