Bug report.

Started getting:

ghc-6.2.1.20040313: panic! (the `impossible' happened, GHC version 
6.2.1.20040313):
        mkTyVar a1 {- tv a75q -}

Please report it as a compiler bug to glasgow-haskell-bugs@xxxxxxxxxxx,
or http://sourceforge.net/projects/ghc/.

today... definitely a but to do with class inference, as it started appearing
aftyer changing some instance constraints and fundeps on classes.

Can't really be a lot more specific as code is big. Let me know if you want
me to produce a small code extract which triggers it.

        Regards,
        Keean.