static Set<S> mapLike tok_allGroups_recursive(O tokenizer, S s) {
  new Set<S> set;
  tok_allGroups_recursive_collect(tokenizer, s, set);
  ret set;
}

svoid tok_allGroups_recursive_collect(O tokenizer, S s, Set<S> set) {
  if (empty(s)) ret;
  LS tok = cast callF(tokenizer, s);
  for ping (int i = 1; i < l(tok); i += 2) {
    S t = tok.get(i);
    if (isCurlyBraced(t)) {
      t = unCurly(t);
      set.add(t);
      tok_allGroups_recursive_collect(tokenizer, t, set);
    }
  }
}

Began life as a copy of #1021295