Hi there,
 Do you have any idea why the following code is not valid?

class Guess g where
 makeGuess :: g -> String

instance Guess GuessLetter where
 makeGuess = ...

instance Guess GuessWord where
 makeGuess = ...

-- | This function is nod valid
nextGuess :: Guess g => String -> g
nextGuess = ...



Thank you.

-Haisheng