virtual boost::any eval(void)
{
    boost::any lresult = left->eval(), rresult = right->eval();

    if (lresult.type() == typeid(char))
    {

    }
    else if (lresult.type() == typeid(int))
    {

    }
    else if (lresult.type() == typeid(double))
    {

    }
    else if (lresult.type() == typeid(std::string))
    {

    }
    else if (lresult.type() == typeid(void))
    {

    }
    else
    {

    }
}