sclass NLLogicChecker_v1 {
  S input;
  new L<S> facts;
  
  sclass Matching {
    SS matches; // var -> match
    new L<Exp> output;
  }
  
  bool checkRule(IfThen rule, Matching m) {
    if (rule == null) false;
    if (!checkExpression(rule.in, m)) false;
    m.output.add(rule.out);
    true;
  }
  
  bool checkExpression(Exp e, Matching m) {
    if (e cast And)
      ret checkExpression(e.a, m) && checkExpression(e.b, m);
    if (e cast Func) {
      if (eq(e.name, "input"))
        ret match(join(((Sentence) e.arg).tok), input);
      else if (eq(e.name, "fact")) {
        S pat = join(((Sentence) e.arg).tok);
        for (S fact : facts)
          if (match(pat, fact))
            true;
      }
    }
    false;
  }
}