Change to deriving in 6.7 ??

Conal Elliott conal at
Thu Aug 16 11:50:08 EDT 2007

I'm running ghc-6.7.20070802 and getting a new error message that didn't
show up with ghc-6.6.  Code:

    -- | Pairing for unary type constructors.
    newtype Pair1 f g a = Pair1 {unPair1 :: (f a, g a)}
      deriving (Eq, Ord, Show)

Error message:

    No instances for (Show (g a), Show (f a))
      arising from the 'deriving' clause of a data type declaration
               at src/Data/Tupler.hs:(26,0)-(27,25)
    Possible fix:
      add an instance declaration for (Show (g a), Show (f a))
    When deriving the instance for (Show (Pair1 f g a))

Has there been a change to "deriving"?  Is there a workaround?

Thanks,  - Conal
-------------- next part --------------
An HTML attachment was scrubbed...

More information about the Glasgow-haskell-users mailing list