So I have turned my hand to ExpressionEngine and while the backend crud was easy enough getting the frontend working with template syntax is proving difficult, even at the "hello world" level.

expressionengine/third_party/rest/mod.rest.php

class Rest
{
    var $return_data    = '';

    function Rest()
    {
        $this->EE =& get_instance();
        return $this->return_data = 'HAI';
    }
}
// END REST Class

/* End of file REST.php */
/* Location: ./application/libraries/REST.php */

Then im calling it directly in a new empty template:

{exp:rest}

So I'm expecting to see "HAI" but I get:

Error

The following tag cannot be processed:

{exp:rest}

Please check that the ‘rest’ module is installed and that ‘rest’ is an available method of the module

Any ideas? The module is installed and the backend is running fine.