// returns (function, isSplitRule)
static Pair<O, Bool> gazelle_parseInstruction(S s) {
  new Matches m;
  if "simplify with *"
    ret pairWithFalse((O) $1);
  else if "drop after word *" {
    fS word = $1;
    ret pairWithFalse((O) func(S s) { tok_dropStartingWithWord(word, s) });
  } else if "group words *" {
    fS words = $1;
    ret pairWithFalse((O) func(S s) { tok_groupPhrase(s, words) });
  } else if "split with *" {
    ret pairWithTrue((O) $1);
  }
  null;
}