static S dumbCalc(S s) {
  L<S> tok = javaTok(s);
  int i;
  BigInteger result = null;
  for (S op : litlist("+", "-", "*", "/", "^")) {
    while ((i = matchMetaNoStar(tok, "<number>", op, "<number>")) >= 0) {
      BigInteger a = new BigInteger(tok.get(i)), b = new BigInteger(tok.get(i+4));
      result = mathOp(op, a, b);
      clearAllTokens(tok.subList(i, i+5));
      tok.set(i, "" + result);
      tok = javaTok(tok);
    }
  }
  if (result != null) ret "" + result;
  ret null;
}