JESS: How to use a Userfunction returning boolean in a LHS of a Jess rule

Hi,

I am beginner in Jess. I have a java application that uses jess.Rete. I want to define a rule in jess that calls a Userfunction in LHS. If the Userfunction returns true, the rule should be fired. I have mainly two problems: 1- how do I write this rule in jess 2- how do I notify my engine that the return value of the function has changed.


1-      How do I write the rule in jess:
I have created a this class that implements Userfunction:

public class ReturnTrue implements Userfunction {
@Override
public Value call(ValueVector arg0, Context arg1) throws JessException {
return new Value(Funcall.TRUE);
}
@Override
public String getName() {return "returnTrue";}
}

My main code, where jess.Rete is initialized and my rules and Userfunctions are loaded:

Rete engine = new Rete();
engine.addUserpackage(new JessTabFunctions());
try {
           //my database is an ontology created with protege
engine.executeCommand("(load-project  file:/M:/MyJessTest/osgi.myjesstest.test/simple-owl.pprj)");
           Batch.batch("myrules.clp", engine);
           engine.addUserfunction(new ReturnTrue());
} catch (JessException e) {
e.printStackTrace();
}

I have write my rule like this, but it does not seem to be working:
(defrule trueFunction
   "True Function"
   (test (returnTrue))
   =>
    ((System.out) println "True"))

What am I doing wrong?


2-  - how do I notify my engine that the return value of the Userfunction has changed


I have found a post that actually talks about this: Userfunction on LHS called only once. In this post ejfried suggests two options: idle-rule or JavaBean which support PropertyChangeEvents. Can some on give more information on how to use PropertyChangeEvents or even better an example code?

Thanks!

Ana