sclass NLLogic_MultiThreadedEngine {
  bool unsafeEvals, showFailed;
  F0<NLLogicChecker_v2> makeLogicChecker;
  Pair<L<IfThen>, LS> rulesAndFacts;
  MultiMap<Int, ExecutedRule> executedRules = treeMultiMap();
  new MultiThreadStepper stepper;
  new LinkedHashSet<S> inputs;
  
  *(Pair<L<IfThen>, LS> *rulesAndFacts) {}
  
  void processInput(S input) {
    if (!inputs.add(input)) ret;

    temp tempSetTL(nlLogic_processInputOrFact_steppable_allowUnsafeEvals, unsafeEvals);
    stepper.add(nlLogic_processInputOrFact_steppable(makeLogicChecker(), input, false /*inputAsFact*/, 
      rulesAndFacts, new Collector<ExecutedRule>() {
        bool add(ExecutedRule r) {
          if (!showFailed && r.isFailed()) true;
          executedRules.put(ai_executedRuleScorer().get(r), r);
          for (S s : unnull(r.newInput))
            processInput(s);
          true;
        }
      }));
  };
  
  void seedInput(S input) { processInput(input); }
  
  void fullRun {
    stepAllWithStats_multiThreaded(stepper);
  }
  
  NLLogicChecker_v2 makeLogicChecker() {
    ret makeLogicChecker != null ? callF(makeLogicChecker) : new NLLogicChecker_v2;
  }
  
  L<ExecutedRule> executedRules() { ret executedRules.allValues(); }
}