On Thu, Jun 10, 2010 at 11:14:42PM +0200, Daniel Fischer wrote:
Show can work (should with the constraint on Equ), Eq is hairy.
instance Show t => Show (Obs t) where show (Equ a b) = show a ++ " `Equal` " ++ show b show (Plus a b) = ... show (Konst x) = "Konst " ++ show x ...
For an Eq instance, you have the problem that
Equ (Konst True) (Konst False) and Equ Player Turn
both have the type Obs Bool, but have been constructed from different types, so you can't compare (Konst True) and Player. I don't see a nice way to work around that.
I didn't test, but something like this could work: Equ :: (Show a, Eq a, Typeable a) => Obs a -> Obs a -> Obs Bool (Equ a b) == (Equ c d) = eqTypeable (a,b) (c,d) eqTypeable :: (Typeable a, Eq a, Typeable b, Eq b) => a -> b -> Bool eqTypeable x y = case cast y of Just y' -> x == y' Nothing -> False Maybe not ;). Cheers, -- Felipe.