> I've been using "cabal haddock" to run haddock on my package. I also
> get the same error using haddock directly:
>
> > $ haddock -odir=tmp --debug --verbose --html
> Generics/EMGM.hs
> > haddock: internal Haddock or GHC error: Maybe.fromJust: Nothing

Have you filed a ticket for this in the haddock trac so that he doesn't
forget?
http://trac.haskell.org/haddock/

There seemed to be perhaps one or two tickets related, but I wasn't sure if any exactly matched the issue, so I created a new one with a minimal testcase.

http://trac.haskell.org/haddock/ticket/68

Regards,
Sean