[Haskell-cafe] type and class problems compiling code on GHC 6.6

José Miguel Vilaça jmvilaca at di.uminho.pt
Wed Jan 17 14:42:31 EST 2007

Dear Haskellers,


I had used some code which worked fine on GHC 6.4 and now it don’t compile
on GHC 6.6.

Can anyone please give me some workarounds and/or explanations about these 2


instance InfoKind a b => InfoKind (Maybe a) b where

    blank = Nothing

    check n _ Nothing  = ["No info value stored with "++n]

    check n g (Just a) = check n g a


GHC complains that

Illegal instance declaration for `InfoKind (Maybe a) b'

        (the Coverage Condition fails for one of the functional

    In the instance declaration for `InfoKind (Maybe a) b'



multiListViewGetTSelections :: MultiListView x () -> IO [x]

multiListViewGetTSelections multiListView =

 do { Just ((model, _) :: (Var [x], x -> String)) <-
unsafeObjectGetClientData multiListView

    ; -- more and more code



GHC complains that

    A pattern type signature cannot bind scoped type variables `x'

      unless the pattern has a rigid type context

    In the pattern: (model, _) :: (Var [x], x -> String)


I would really appreciate some help.


Best regards

Miguel Vilaça

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/haskell-cafe/attachments/20070117/2e058a49/attachment.htm

More information about the Haskell-Cafe mailing list