[rules-users] Scope of bindings, identical patterns

[Mark Proctor]

Julian Morrison wrote:
> Suppose I have a rule like:
>
> rule "foo"
>     when
>        $a : Cheese(name="Stilton")
>        $b : Cheese(name="Stilton")
>     then
>        # etc
> end
>
> First question: is it possible that a == b ? In other words, can both
> patterns end up matching the same object in one activation? I have been
> assuming this is so, but it isn't covered in the docs so far as I can see.
>   
Yes this is no different from
select * from Cheese a, Cheese b
> Second question: why can't I add as a pattern, $a != $b ? The eclipse
> IDE compiler complains they are undefined. What is the scope of the
> bindings defined by $a and $b ?
>   
$a : Cheese(name=="stilton")
$b : Cheese( this != $a, name == "stilton" )

Or you can use an eval:
eval( $a != $b )