static F1<S, Double> f1_scoreRegexpIC(Cl<S> plusExamples, Cl<S> minusExamples) {
  ret func(S regexp) -> double {
    new Scorer scorer;
    fOr (S s : plusExamples)
      scorer.add(regexpICFind(regexp, s));
    fOr (S s : minusExamples)
      scorer.add(!regexpICFind(regexp, s));
    ret scorer!;
  };
}