Monomorphic Pattern Bindings and Error Messages

Not clear to me if the following should be a type error or if it should be allowed to unify properly. In either case, the error message is borked.

{-# OPTIONS -fglasgow-exts #-}

module Test where

data Foo x y = Foo {foo1 :: x, foo2 :: y}
instance Functor (Foo x) where
    fmap f (Foo x y) = Foo x (f y)

bar :: a -> Foo (forall s. s) a
bar a = Foo undefined a

main = print (foo2 (fmap (*2) (bar 2)))

{-
sclv.hs:12:20:
    Cannot match a monotype with `forall s. s'
    When matching `forall s. s'
              and `forall s. s'
      Expected type: Foo (forall s1. s1) a
      Inferred type: Foo (forall s1. s1) a
    In the first argument of `foo2', namely `(fmap ((* 2)) (bar 2))'
-}

*Test> :t bar (2 :: Integer) 
bar (2 :: Integer) :: Foo (forall s. s) Integer
*Test> :t foo2 (bar (2 :: Integer))
foo2 (bar (2 :: Integer)) :: Integer
*Test> :t fmap (*2) (bar (2 :: Integer)) 
fmap (*2) (bar (2 :: Integer)) :: Foo (forall s. s) Integer
*Test> :t foo2 (fmap (*2) (bar (2 :: Integer)))

<interactive>:1:6:
    Cannot match a monotype with `forall s. s'
    When matching `forall s. s'
              and `forall s. s'
      Expected type: Foo (forall s1. s1) Integer
      Inferred type: Foo (forall s1. s1) Integer
    In the first argument of `foo2', namely
        `(fmap ((* 2)) (bar (2 :: Integer)))'

Trac metadata

Trac field	Value
Version	6.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Multiple
Architecture	Multiple