Error in extending CI_Loader: Class 'CI_Loader' not found

It must not be finding the paths, because I just tried your code here and it works fine

What OS and are you using XAMPP or what?

Did you setup your config base url etc; ?

I'm using Windows 10 Home Edition.
I'm not using XAMPP, I'm using PHP built-in server: php -S localhost:8000 index.php

And yes, I setup my base_url at config.php:

PHP Code:

$config['base_url'] = 'http://localhost:8000/';