[rules-dev] modify (expr) catch 22

[Mark Proctor]

On 08/04/2011 12:39, Geoffrey De Smet wrote:
> Related to the modify expression,
> I 've always wondered about this code:
>
> rule "MyRule"
>     when
>       $p : Person(name = "Yoda")
>     then
>       modify ($p) {
>         setAge(300)
>       }
> end
>
> Doesn't this create an infinite loop? (In my experience it does or at
> least it takes a lot longer)
> Because the modify ($p) schedules any rule using a Person back on the
> agenda to be re-evaluated,
> so also that rule, which is evaluated and executed again, modifying $p
> again, ... hence the infinite loop?
It would, unless you have slot specific - which Jess does. Slot specific 
is something I really want to add, I think it will resolve a lot of 
recursion problems and make Drools a lot easier to use. I took the slot 
specific problem and genericsed it further for "slot listeners". I 
discussed this here:
http://blog.athico.com/2010/07/slot-specific-and-refraction.html. I 
think Laune added some refinements to this in a mailing list entry  
somewhere.

Mark