static Pair<LS, O> prepareEvalWithDollarVars(S code) {
  L<S> tok = javaTok(code);
  new LinkedHashSet<S> vars;
  for (int i = 1; i < l(tok); i += 2) {
    S t = tok.get(i);
    if (isDollarVar(t))
      vars.add(t);
  }
  temp tempSetThreadLocal(evalJava_prep_args, joinWithComma(map(func(S var) -> S { "S " + var }, vars)));
  S src = evalJava_prep(code);
  O c = evalJava_prep2(src);
  ret pair(asList(vars), c));
}