title: Drools Expert output object in Scala
body: <p>I'm a novice in both Scala and Drools Expert, and need some help getting information out of a Drools session. I've successfully set up some Scala classes that get manipulated by Drools rules. Now I want to create an object to store a set of output facts for processing outside of Drools. Here's what I've got. </p>
  
  <p>I've got a simple object that stores a numeric result (generated in the RHS of a rule), along with a comment string:</p>
  
  <pre><code>class TestResults {
      val results = new MutableList[(Float, String)]()
  
      def add(cost: Float, comment: String) {
          results += Tuple2(cost, comment)
      }
  }
  </code></pre>
  
  <p>In the DRL file, I have the following:</p>
  
  <pre><code>import my.domain.app.TestResults
  
  global TestResults results
  
  rule "always"
      dialect "mvel"
      when
          //
      then
          System.out.println("75 (fixed)")
          results.add(75, "fixed")
  end
  </code></pre>
  
  <p>When I run the code that includes this, I get the following error:</p>
  
  <pre><code>org.drools.runtime.rule.ConsequenceException: rule: always
      at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:39)
  ...
  Caused by: [Error: null pointer or function not found: add]
  [Near : {... results.add(75, "fixed"); ....}]
                                                         ^
  [Line: 2, Column: 9]
      at org.mvel2.optimizers.impl.refl.ReflectiveAccessorOptimizer.getMethod(ReflectiveAccessorOptimizer.java:997)
  </code></pre>
  
  <p>This looks to me like there's something goofy with my definition of the TestResults object in Scala, such that the Java that Drools compiles down to can't quite see it. Type mismatch, perhaps? I can't figure it out. Any suggestions? Thank you!</p>