Couldn't match type `Window' with `Button'
    Expected type: IO Button
      Actual type: IO Window
    In the return type of a call of `bind'
    In the second argument of `(<*>)', namely `bind castToButton "b"'
    In a stmt of a 'do' block:
      MyDialog <$> bind castToWindow "w" <*> bind castToButton "b"

    Couldn't match type `Button' with `Window'
    Expected type: GObject -> Window
      Actual type: GObject -> Button
    In the first argument of `bind', namely `castToButton'
    In the second argument of `(<*>)', namely `bind castToButton "b"'
    In a stmt of a 'do' block:
      MyDialog <$> bind castToWindow "w" <*> bind castToButton "b"