Does this, and should this type check on GHC 6.10.x ?

[Ahn, Ki Yung]

Ahn, Ki Yung wrote:
> 
> Another problem, which I haven't mentioned, I have when I tried to make 
> additional type family instance declarations  that latest (stable) 

Typo: I mean type class instance declaration of course.

> distributions of GHC 6.10.x does not let me declare instances of 
> (Expandable (Tuple (Map ((,) t2) ys))).  When you try declaring such an 
> instance something like this:
> 
>  > instance Expandable (Tuple (Map ((,) t2) ys)) where
>  > ...
> 
> GHC will give me an error message that type synonyms are not allowed in 
> instance declarations:
> kyagrd at kyavaio:~/tmp$ ghci -fglasgow-exts -XUndecidableInstances 
> Review3.lhs
> GHCi, version 6.10.3: http://www.haskell.org/ghc/  :? for help
> Loading package ghc-prim ... linking ... done.
> Loading package integer ... linking ... done.
> Loading package base ... linking ... done.
> [1 of 1] Compiling Main             ( Review3.lhs, interpreted )
> 
> Review3.lhs:62:2:
>     Illegal type synonym family application in instance:
>         Tuple (Map ((,) t2) ys)
>     In the instance declaration for `Expandable (Tuple (Map ((,) t2) ys))'
> Failed, modules loaded: none.
> 
> So, my impression is that there is little hope even I try fixing this by 
> adding more instance declarations, even if this was an incomplete code 
> because of space restrictions of the review.  But I still wanted to 
> double check and discuss this matter with mailing list readers since 
> there were few reports (which we fail to reproduce) that this type 
> checks in their installation of GHC.