drools, globals and lhs method calls

[eng1]

hi. i'm using drools for the first time and i'm running into a problem using a global in the lhs. here's the situation

i have a service object set as a global
i want to call a method on this object that returns a boolean
i can use it in the rhs no problem but in the lhs i get compilation errors

so for example, i can do this no problem:

rule checkExistingSub
when
$s : SubscriberModel()
$c : CollectiveModel()
then
collectiveService.isMember($s, $c);
end

however when i try this:
rule checkExistingSub
when
$s : SubscriberModel()
$c : CollectiveModel()
collectiveService.isMember($s, $c);
then
end
i get this:
[23,29]: unknown:23:29 Unexpected token '$s'

i've experimented a bit but just can't get it to work. so my questions are:

is this possible?
if so, what am i missing?

[eng1]

for any body interested, wrapping the service call in eval() works like so:

rule checkExistingSub
when
$s : SubscriberModel()
$c : CollectiveModel()
eval (collectiveService.isMember($s, $c));
then
end

pretty sure i had tried this before posting but guess not