[Haskell-cafe] Existentially-quantified constructors, Eq and Show

Folks, Is there a less verbose way of doing this: data State a = Start | Stop | (Show a, Eq a) => State a instance Eq a => Eq (State a) where (State a) == (State b) = a == b Start == Start = True Stop == Stop = True instance Show a => Show (State a) where show (State a) = show a show Start = "Start" show Stop = "Stop" Thanks, Joel -- http://wagerlabs.com/