No instance for <type family result type> in ghci command line

In the following code, Pred () no longer matches the instance for () from the GHCi command line, even though Pred () ~ ().

In 6.9.20071015 it still works, in 6.9.20071103 it no longer does.

{-# 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 _ = ()

The exact results:

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 ())

And, just for completeness, 6.8 shows the same regression:

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 ())

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	rturk@science.uva.nl
Operating system	Unknown
Architecture	Unknown