On Tue, 19 Jul 2005, Ben Lippmeier wrote: > An example, using some arbitrary data type "Thingo": > > > class ShallowEq a where > > shallowEq :: a -> a -> Bool > > > data Thingo a b > > = TOne a > > | TTwo a b Int Char Float > > | TThree Int Char b b > > Questions: > 1) Does anyone know a better/existing way to implement ShallowEq that > doesn't involve enumerating all the constructors in the data type?
A more general approach are projection functions like getTOne :: Thingo a b -> Maybe a getTOne (TOne x) = Just x getTOne _ = Nothing Then you can map the values to be compared into a Maybe and you need only a shallowEq for Maybe. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
