How to concatenate 2 function in php

I have an application with the following code:

<?php 

if(isset($_GET['function'])){ 
        $_GET['function'](); 
} 

?> 

So if i entered this url: http://localhost/?function=phpinfo

I will see the phpinfo function output on the screen.

can i have a way to concatenate 2 function in the url like this example:

http://localhost/?function=shell_exec('ls') AND phpinfo

So i want to see the first function output..

If you may asking why i need this, is because i am pen testing an web application with this situation..

By the way any suggestion to hack this situation will help.

Thanks for the help..