static S evalJava_prep(S code) {
  ret evalJava_prep(code, "calc");
}

static S evalJava_prep(S code, S mainName) {
  ret evalJava_prep(code, mainName, "");
}

static new ThreadLocal<S> evalJava_prep_args;

sS evalJava_prep(S code, S mainName, S preCode) {
  new EvalJavaPrep prep;
  LS tok = evalJava_prePrep(code, prep);
  code = tok_addReturn(tok);
  S returnType = containsReturnWithArgument(code) ? "Object" : "void";
  S main =
    lines(prep.global)
    + "static " + returnType + " " + mainName + "(" + unnull(evalJava_prep_args!) + ") throws Exception {\n" 
      + preCode + code + "\n" + "}";
  ret main;
}

Began life as a copy of #1005407