That's a rather clever step at it, but wrong as far as I can tell. This gives us the parent of the slot currently being evaluated.

E.g.

```ruby
Shoes.app do
  my_flow = flow do ; end
  stack do
    my_flow.parent
  end
end
```

Probably returns the wrong value now.

Plus the app has no parent. It's the parent of ALL THE THINGS.
Returning self here might fix things temporarily... but I'm not sure about that.