[Haskell-cafe] Type families versus functional dependencies question

[Alexey Rodriguez]

On Fri, Jul 4, 2008 at 5:03 AM, Manuel M T Chakravarty <chak at cse.unsw.edu.au>
wrote:

> The problem is that blah's type is ambiguous, as f does only occur as an
> argument to the type family.  If you'd define
>
>  class Blah f a where
>    blah :: a -> f -> T f f a
>
> (and change the rest of the program accordingly) then all will be fine.
>  See this thread for a more in-depth discussion of the problem:
>
>  http://www.haskell.org/pipermail/haskell-cafe/2008-April/041385.html
>

Yes, I was afraid that this was the case. However, the question remains on
whether my functional dependencies encoding is correct. A correct encoding
would help me understand this typing problem a bit more. Especially, now
that Claus showed that adding an equality constraint makes this program
work!

Cheers,

Alexey
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