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;
static new ThreadLocal<Bool> evalJava_prep_voidMagic; // set to false to avoid looking up standard function return types

static S evalJava_prep(S code, S mainName, S preCode) {
  L<S> tok = javaTok(trim(code));
  
  // =1*2 as in Lua
  if (eqGet(tok, 1, "=")) tok = subList(tok, 2);
  
  // if code is something like "sclass Bla {}", just return as is
  if (tok_isStaticLevelCode(tok))
    ret code;
  
  if (!isFalse(evalJava_prep_voidMagic!) && tok_shouldAddReturn(tok) && eqGet(tok, 3, "(") && isIdentifier(get(tok, 1)) && isKnownVoidFunction(get(tok, 1)))
    tokAppend_reTok(tok, l(tok)-2, ";");
    
  code = tok_addReturn(tok);
  S returnType = containsReturnWithArgument(code) ? "O" : "void";
  S main =
    "static " + returnType + " " + mainName + "(" + unnull(evalJava_prep_args!) + ") throws Exception {\n" 
      + preCode + code + "\n" + "}";
  ret main;
}

Began life as a copy of #1005407