static O gazelle_parseInstruction(S s) {
  new Matches m;
  if "simplify with *"
    ret $1;
  else if "drop after word *" {
    fS word = $1;
    ret func(S s) { tok_dropStartingWithWord(word, s) };
  } else if "group words *" {
    fS words = $1;
    ret func(S s) { tok_groupPhrase(s, words) };
  }
  null;
}