// "$1" is first code token, "$2" second code token etc.
static S jreplaceExpandRefs(S s, L<S> tokref) {
  L<S> tok = javaTok(s);
  for (int i = 1; i < l(tok); i += 2) {
    if (tok.get(i).startsWith("$") && isInteger(tok.get(i).substring(1))) {
      S x = tokref.get(-1+parseInt(tok.get(i).substring(1))*2);
      tok.set(i, x);
    }
  }
  ret join(tok);
}