Hi all, I was trying to do something very simple with GADTs when I ran into this problem - -- My datatype data T o where Only ∷ o → T o TT ∷ T o1 → (o1 → o2) → T o2 -- Show instance for debugging instance Show o ⇒ Show (T o) where show (Only o) = "Only " ⊕ (show o) show (TT t1 f) = "TT (" ⊕ (show t1) ⊕ ")" When I try to compile this I get the following - Could not deduce (Show o1) arising from a use of `show' from the context (Show o) While I understand why I get this error, I have no idea how to fix it! I cannot put a Show constraint on o1 because that variable is not exposed in the type of the expression. I can work around this by changing my data type declaration to include Show constraints but I don't want to restrict my data type to only Showable things just so I could have a "Show" instance for debugging - Only ∷ Show o ⇒ o → T o TT ∷ (Show o1, Show o2) ⇒ T o1 → (o1 → o2) → T o2 What else can I do to declare a Show instance for my datatype? Thanks, Anupam Jain