Couldn't match type `GObject -> widget0' with `WidgetClass w'
    Expected type: WidgetClass w => (GObject -> w) -> String -> IO w
      Actual type: (GObject -> widget0) -> String -> IO widget0
    In the pattern:
      bind :: WidgetClass w => (GObject -> w) -> String -> IO w
    In a stmt of a 'do' block:
      bind :: WidgetClass w =>
              (GObject -> w) -> String -> IO w <- widgetBinder file
    In the expression:
      do { bind :: WidgetClass w =>
                   (GObject -> w) -> String -> IO w <- widgetBinder file;
           MyDialog <$> bind castToWindow "w" <*> bind castToButton "b" }

    Couldn't match type `Window' with `Button'
    Expected type: IO Button
      Actual type: IO w
    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 `Window' with `Button'
    Expected type: GObject -> w
      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"