Re: [TED] Action-188, ISSUE: production rule systems have "difficulty" with recursive rules in RIF Core

Christian de Sainte Marie wrote:

>
> You may also try to compute all the factorials until the memory is 
> full by asking :- factorial(?in ?out) to your LP system, no? 
> Similarly, you might compute the factorial of 4 with your PR engine by 
> executing step by step, checking after each cycle if you have your 
> answer and stopping when you have it.
>
Good points.  In prolog, I could add the builtin predicate "novar(?in)" 
as the *first* predicate in the recursive factorial rule body to avoid 
the infinite loop.  :- factorial(?in ?out) would just return with no 
answers.  Good for a prolog dialect.  I'm not sure how I would convey 
the need to execute step by step to a PR engine, though.

BTW, is "novar" a builtin, a constraint, or could never be in CORE 
because it is too operational?  I'm thinking something like "novar" 
could be a hint that a translation to PR had better be careful, lest it 
attempts to generate too many facts.