Emil Axelsson reports: I attach a program Test.hs which I suspect demonstrates a bug in GHC. The important lines are:

   showType :: forall a . Expr a -> String
   showType (Lit _) = show (typeOf (undefined :: a))

   test1 = showType (mk     :: Expr BOOL) -- Prints "Bool" (wrong?)
   test2 = showType (Lit mk :: Expr BOOL) -- Prints "Main.BOOL" (correct)

test1 and test2 give different results, even though showType shouldn't be able to tell them apart. It seems that the Typeable context packed with the Lit constructor is wrong in test2.