[rules-users] Checking for a lack of an object

[Chris Richmond]

How do I fire a rule if an object with certain characterstics does not 
exists.

For example my class Foo, if I have a rule:

rule "Identify Foos with values"

when
         Foo(stringProp=="blah", intProp==5)
then
         System.err.println("A Foo was found!");
end


So how do I check for lack of existence of an object with certain 
characteristics

I tried:
rule "Flag missing Foos with values"

when
         not(Foo(stringProp=="blah", intProp==5))
then
         System.err.println("A proper foo does not exist");
end

I also tried:
rule "Flag missing Foos with values"

when
         not(exists(Foo(stringProp=="blah", intProp==5)))
then
         System.err.println("A proper foo does not exist");
end