> I got the GADT > > data DataBox where > DataBox :: (Show d, Eq d, Data d) => d -> DataBox > [snip] > > but I can't figure out how to implement gunfold for DataBox. > > The error message is > > Text/XML/Generic.hs:274:23: > Ambiguous type variable `b' in the constraints:
I had a similar difficultly in Atom making a GADT a member of Eq. At one point I had my head wrapped around the reason for the problem, but now it escapes me. However, I remember the solution: I created a function to convert the GADT into another, unGADT type, which was then used to compute (==). _______________________________________________ Haskell-Cafe mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell-cafe
