Hi I am struggling with an ambiguity problem. I have the following code:
> foo :: Constr -> Int > foo = numChildren . fromConstr > > numChildren :: (Data a) => a -> Int > numChildren x = sum $ gmapQ (\_ -> 1) x which I thought would work, but the GHC-6.4 says: > Ambiguous type variable `a' in the constraint: > `Data a' arising from use of `numChildren' at AutoForm.hs:87:6-16 > Probable fix: add a type signature that fixes these type variable(s) I cannot see why I need to add (Data a), as fromConstr signatur is: fromConstr :: forall a. (Data a) => Constr -> a I do not know where to add it either. Hope, somebody can enlighten me. Greetings, Mads Lindstrøm _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
