[Haskell-cafe] Type families and GADTs in 6.9

[Manuel M T Chakravarty]

Dan,

> I've been playing around with type families off and on in 6.8, but,  
> what with
> the implementation therein being reportedly incomplete, it's hard to  
> know
> what I'm getting right and wrong, or what should work but doesn't  
> and so on.
> So, I finally decided to take the plunge and install 6.9 (which,  
> perhaps,
> isn't yet safe in that regard either, but, such is life :)). But,  
> when I
> loaded up one of my programs, I got a type error. The subject is  
> inductively
> defined tuples:
[..]
> However, proj results in a
> type error:
>
>    Occurs check: cannot construct the infinite type:
>      t = Lookup (t ::: ts) fn
>    In the pattern: v ::: vs
>    In the definition of `proj': proj FZ (v ::: vs) = v

Sorry, but looks like a bug in 6.9 to me.  Could you add it to the GHC  
bug tracker?

Thanks,
Manuel