Re: Forall in SWI Prolog

>
> Dear All,
>
> I am running into a problem with forall predicate of SWI-Prolog. I  
> have the following predicate that tries to match all  
> subjectMatch(....) with rSub(...). This makes sure all different  
> combinations of subjectMatch(...) facts with different RID and  
> RValue values are matched. However, forall returns True when the  
> Condition section of forall predicate is not matched. That means if  
> there is no fact matching the condition of forall (that is  
> subjectMatch(P,R,N,RID,RValue)) forall returns True as a default  
> value.
>
> subjectS(P,R,N)  :-  forall(subjectMatch(P,R,N,RID,RValue),
>              rSub(RID,RValue)).
>
> Is there a way to get around this? I mean if the condition of forall  
> is not matched at all, how can I get a false?