Re: Preserving query data in foreign interface

On 11/08/2013 11:39, Abramo Bagnara wrote:

> I'm calling from Java a Prolog query and I need to avoid that returned
> data is lost.

The "high level" interface does that for you

> I'm using low-level interface to avoid term_t <-> Term copying and the
> very deep stack recursion that this implies when handling long lists.

Then you'll have to implement your own non-recursive term_t <-> Term 
copying - please donate this to JPL :-)

> If I use Prolog.close_query the binding is lost and we have no
> Prolog.cut_query available.

Hmm, if your hypothetical Prolog.cut_query retains the binding, then 
we can't reuse the engine until you explicitly close it; I don't think 
this is the way to go...

> That apart, I also have noted that in both java interface and C
> interface it is missing an helper to do deep copy of answers so to
> preserve multiple results of nondet queries.

JPL has this; Query#allSolutions returns an array of maps from 
variable names to copied bindings

> I've missing something? There are other ways to do what above?

Until term_t <-> Term copying is reimplemented non-recursively (or 
otherwise ingeniously), the best workaround for copying long lists is 
to use a Prolog-side wrapper for long-list-returning predicates which 
converts them to trees (or atoms?), then convert them again Java-side.

Paul Singleton