{-# LANGUAGE TypeFamilies #-}
module Test where

x = reify (() :: Pred ())

type family Pred a
type instance Pred a = a

class Reify a where
    reify :: a -> ()

instance Reify () where
    reify _ = ()

{-
GHCi, version 6.9.20071015:
*Test> x
()
*Test> reify (() :: Pred ())
()


GHCi, version 6.9.20071103:
*Test> x
()
*Test> reify (() :: Pred ())

<interactive>:1:0:
    No instance for (Reify (Pred ()))
      arising from a use of `reify' at <interactive>:1:0-20
    Possible fix: add an instance declaration for (Reify (Pred ()))
    In the expression: reify (() :: Pred ())
    In the definition of `it': it = reify (() :: Pred ())


GHCi, version 6.8.0.20071002:
*Test> x
()
*Test> reify (() :: Pred ())
()


GHCi, version 6.8.1.20071031:
*Test> x
()
*Test> reify (() :: Pred ())

<interactive>:1:0:
    No instance for (Reify (Pred ()))
      arising from a use of `reify' at <interactive>:1:0-20
    Possible fix: add an instance declaration for (Reify (Pred ()))
    In the expression: reify (() :: Pred ())
    In the definition of `it': it = reify (() :: Pred ())
-}