bug with type families

[Manuel M T Chakravarty]

Stefan Holdermans:
> Peter,
>
>> I've run into a bug that looks to be the same as the one described  
>> here:
>>
>> http://hackage.haskell.org/trac/ghc/ticket/1897
>
> It does not seem like a bug, although the type-error message may be  
> a bit confusing as is the fact that GHC happily infers a type for  
> the signature-less function: these are I guess the real issues here.  
> But, apart from that, the contents of a previous discussion seems to  
> apply here:
>
>  http://www.haskell.org/pipermail/haskell-cafe/2008-April/041385.html
>
> Short version: the type of isValid involves |Depend s| and not |s|.  
> Since |Depend s| does not uniquely determine |s|, it is not possible  
> to resolve which dictionary for Bug to supply for a particular call  
> to isValid.
>
> Or---am I overlooking something?

No, what you are saying is exactly right.  I'll close the ticket.

Manuel