title: Drools with eval function rule won't fire
body: <p>I have the following rule:</p>
  
  <pre><code>rule "AddSource"
  when
      $model : MFMModel ()
      Node( type == "source", funName : name )
      $ffs : Structure( ffsName : name )
      WholePart( structure == ffsName, ffunction == funName )
      eval (Test.checkExsit($model,$ffs))
  
  
  then
      System.out.println( ffsName + ":" + funName);
      Source s = new Source( funName );
      insert (s);
      $ffs.addToStructure( s );
      System.out.println(Test.checkExsit($model,$ffs));
  end
  </code></pre>
  
  <p>The rule fires when I delete the eval function in the when part, and the printout says Test.checkExsit($model,$ffs) return true. </p>
  
  <p>But with the eval function, the rule will never fire. </p>
  
  <p>Anyone knows what the problem is?</p>