On Thu, Mar 12, 2009 at 17:02, Bernd Brassel <bbr@informatik.uni-kiel.de> wrote:

José Pedro Magalhães wrote:
> Hi Bernd,
>
> I guess this might be the same issue reported some time ago (
> http://thread.gmane.org/gmane.comp.lang.haskell.generics/53/focus=54): the
> derived instances of Data do not define dataCast1. If you define your own
> instance of Data for MyMaybe and add the definition of dataCast1 you will
> get the expected behavior.

Your link pointed me in the right direction to fix the bug for my
application. Many thanks! Did you submit a bug report?