Hi everyone, I believe I have come to the conclusion that what I would like to do is impossible, but I would like to have that confirmed. I would basically like to be able to have a heterogeneous list without boxing everything in a data type. Below is the sample code, with the code I would like to use commented out. I'm I missing something, or does Haskell simply not support what I am trying for? {-# LANGUAGE ExistentialQuantification #-} data Foo = Foo String class IFoo a where toFoo :: a -> Foo instance IFoo Foo where toFoo = id data A = A String instance IFoo A where toFoo (A a) = Foo a data B = B Int instance IFoo B where toFoo (B b) = Foo $ show b data FooBox = forall t. IFoo t => FooBox t instance IFoo FooBox where toFoo (FooBox f) = toFoo f myPrint :: IFoo t => [(String, t)] -> IO () myPrint = mapM_ myPrint' myPrint' :: IFoo t => (String, t) -> IO () myPrint' (key, value) = let (Foo foo) = toFoo value in putStrLn $ key ++ ": " ++ foo {- What I'd like to do: main = myPrint [ ("one", Foo "1") , ("two", A "2") ] -} main = myPrint [ ("one", FooBox $ Foo "1") , ("two", FooBox $ A "2") ] ---- Thanks