On Sun, Sep 20, 2009 at 06:43:53PM -0700, Alexander Solla wrote: > > data Add a b = Add a b > > instance ( Evaluate a > > , Evaluate b > > ) => Evaluate (Add a b) where
Okay. > > data Value (Sum a b) = SumValue (Sum a b) Hmmm, have you tried > data Value (Add a b) = AddValue (Value a) (Value b) Now your 'value' function would be > value (AddValue va vb) = value va + value vb because you're holding 'Value a' and 'Value b', not 'a' and 'b'. It may help to think as if this class represented a container. For value, do you need the whole container or just one of its elements? I know other will give a better explanation, but maybe this is enough to get you in the right track :). HTH, -- Felipe. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
