[gecode-users] Parallel conditional combinator

[Guido Tack]

Mauricio Toro wrote:
> I am thinking about implementing the
> parallel conditional combinator as a
> Gecode propagator. Any ideas about
> how to do this efficiently?

I guess by parallel conditional you mean something like (if b1 then a1  
|| if b2 then a2 || ...), where || means parallel composition, and  
with a short-circuit semantics that the first b that is determined to  
be true "wins" and all other branches are discarded?

I think you could just extend the conditional that you already have.   
As soon as one guard is determined, you execute that branch and remove  
the conditional propagator (by returning ES_SUBSUMED).  You have to be  
very careful, though: you can easily program non-monotonic propagators  
this way, which are not allowed in Gecode!  E.g., if you wait for two  
conditions, it may depend on the order of propagation which condition  
is satisfied first, so the constraints added by the parallel  
conditional can be different, depending on the order of propagator  
execution.  Don't do this unless you know exactly what you're doing (I  
cannot see how to use this in a reasonable way).

Remember that Gecode is meant for solving constraint problems, not for  
executing cc programs!

> By the way, where can I find examples
> about using the reflection post and spec
> propagator methods?

Here:
http://www.gecode.org/gecode-doc-latest/PageReflection.html

Cheers,
	Guido