On Sun, May 27, 2001 at 10:46:37PM -0500, Jay Cox wrote:
data S m a = Nil | Cons a (m (S m a)) ... instance (Show a, Show (m (S m a))) => Show (S m a) where show Nil = "Nil" show (Cons x y) = "Cons " ++ show x ++ " " ++ show y ... show s s = Cons 3 [Cons 4 [], Cons 5 [Cons 2 [],Cons 3 []]]
Anyway, is my instance declaration still a bit mucked up?
Hmm. To try to deduce Show (S [] Integer), the type checker reduces it by your instance declaration to Show [S [] Integer], which reduces to Show (S [] Integer), which reduces to... ghci or hugs could, in theory, be slightly smarter and handle this case.
Also, could there be a way to give a definition of show for S [] a?
Yes. You could drop the generality: instance (Show a) => Show (S [] a) where show Nil = "Nil" show (Cons x y) = "Cons " ++ show x ++ " " ++ show y Really, the context you want is something like instance (Show a, forall b. Show b => Show (m b)) => Show (S m b) ... if that were legal. --Dylan