文档如下：
<?php
// +----------------------------------------------------------------------
// | ThinkPHP [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2006-2014 http://thinkphp.cn All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: liu21st <liu21st@gmail.com>
// +----------------------------------------------------------------------

// 应用入口文件

$ module=isset($ _GET['m'])?$ _GET['m']:'Index';
$ action=isset($ _GET['a'])?$ _GET['a']:'Index';
$ do=new $ module;
$ do->$ action;
class index{
function __construct(){
echo'index控制器的index方法';
}
function Index(){
echo'index方法';
}
}


这问题出在哪里呢？$这个符号也已尝试修改很多次了，求助