I'll be interesting to have two parameters, the `StatefulInterface` Object and the `TransitionEvent` when we write an anonymous function callback:
```php
$callback($object, $e);
```
Then we can do :
```php
$loader       = new Finite\Loader\ArrayLoader([
    ...
    'callbacks' => [
        'before' => [
            [
                'from' => '-proposed',
                'do'   => function($object, \Finite\Event\TransitionEvent $e) {
                   echo $object->display()."\n";
                   echo 'Applying transition '.$e->getTransition()->getName(), "\n";
                }
            ],
        ]
    ]
]);
```