static F1<ExecutedRule, Int> ai_executedRuleScorer() {
  ret func(ExecutedRule r) -> Int {
    int n = r.failureLevel();
    if (n == 0)
      ret nempty(r.output) ? 0 : nempty(r.facts) ? 1 : 2;
    else
      ret n < 0 ? 10 : Int.MAX_VALUE-n;
  };
}