svoid tok_insertCast(LS tok, int i, S type) {
  S expr = tok.get(i);
  S prev = get(tok, i-2), next = get(tok, i+2);
  bool needBrackets = !(
    doubleEq(prev, "=", next, ";")
    || doubleEq(prev, "(", next, ")")
  );
  tok.set(i, roundBracketIf(needBrackets, "(" + type + ") " + expr));
}