[rules-users] Locating facts via slot values

Given a working memory containing a large number of rather static facts which are from several subclasses (Ape, Bear, Crocodile,...) of some base class (Animal) and a single fact of class Hunter with a field target of type Animal, the shooting of an animal might be written with a rule like this: rule shoot-1 when ?h : Hunter( ?target : target ) ?a : Animal() eval(?target == ?a) then ?h.shoot( ?a ); retract( ?a ); end Avoiding eval (which is said to be inefficient), it could also be written as rule shoot-2 when ?a: Animal() ?h : Hunter( target == ?a ) then ?h.shoot( ?a ); retract( ?a ); end This, however, places the pattern with many instances up front, which is (AFAIK) not so good in a Rete implementation. Which one is to be preferred in Drools? Ideally, one might want to write rule shoot-3 when ?h : Hunter( ?target : target ) ?a == ?target : Animal() ### not valid DRL then ?h.shoot( ?a ); retract( ?a ); end This avoids eval, has the single instance fact up front, but it isn't available. -W