throws Throwable
  public Value execute(Env env)    throws Throwable  {    try {      if (_staticName == null)        _staticName = env.createStaticName();      Var var = env.getStaticVar(_staticName);            env.setValue(_var.getName(), var);      if (! var.isset() && _initValue != null)        var.set(_initValue.eval(env));    }    catch (Throwable t) {      rethrow(t);    }    return null;  }