I have this simple code:

```
class Main {

    protected $setting;

    public function __construct($setting = false)
    {
        $this->setting;
    }

    public function call($param)
    {
        //do some stuff
        //$this->setting
    }

    public function groupA()
    {
        return new GroupA();
    }
}

class GroupA {

    public function methodA()
    {
        //how to call call('method') at Main function
    }
}

$obj = new Main();
$obj->groupA()->methodA();

```

How can I run function call() at Main class at method MethodA at GroupA class?
How to access to this function?