static LS tok_groupPhrase(LS tok, S phrase) {
  LS tokPhrase = dropFirstAndLast(javaTok(phrase));
  L<Int> l = indicesOfSubListIC(tok, tokPhrase);
  for (int i : l) {
    int j = i+l(phrase);
    S pre = get(tok, i-1), post = get(tok, j+1);
    if (endsWith(pre, "{") && startsWith(post, "}"))
      continue;
    tokPrepend(tok, i, "{");
    tokAppend(tok, j, "}");
  }
  ret join(tok);
}

sS tok_groupPhrase(S s, S phrase) {
  ret tok_groupPhrase(javaTok(s), phrase);
}