Re: [Haskell-cafe] Type families versus functional dependencies question

On Fri, Jul 4, 2008 at 5:03 AM, Manuel M T Chakravarty 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