Hello Haskellers, I'm having trouble writing a Read Instance for my GATD. Arg this GATD!! It causes me more problems that it solves ;) Especially with no automatic deriving, it adds a lot of burden to my code.
data Obs a where ProposedBy :: Obs Int -- The player that proposed the tested rule Turn :: Obs Turn -- The current turn Official :: Obs Bool -- whereas the tested rule is official Equ :: (Eq a, Show a, Typeable a) => Obs a -> Obs a -> Obs Bool Plus :: (Num a) => Obs a -> Obs a -> Obs a Time :: (Num a) => Obs a -> Obs a -> Obs a Minus :: (Num a) => Obs a -> Obs a -> Obs a And :: Obs Bool -> Obs Bool -> Obs Bool Or :: Obs Bool -> Obs Bool -> Obs Bool Not :: Obs Bool -> Obs Bool Konst :: a -> Obs a
instance Read a => Read (Obs a) where readPrec = (prec 10 $ do Ident "ProposedBy" <- lexP return (ProposedBy)) +++ (prec 10 $ do Ident "Official" <- lexP return (Official)) (etc...)
Observable.lhs:120:8: Couldn't match expected type `Int' against inferred type `Bool' Expected type: ReadPrec (Obs Int) Inferred type: ReadPrec (Obs Bool) Indeed "ProposedBy" does not have the same type that "Official". Mmh how to make it all gently mix altogether? Best, Corentin