Hi
How many handlers for each type of event in the list of handlers ?
If you have only one handler for each type , it should go in the typeclass,
and you don't need typeable.
If you have more than one maybe you can avoid using type indexing at all,
because it doesn't resolve the handler selection issue.
By the way , it's not clear to me why you don't have a simple Event
datatype describing all the possible events in advance.
Regards
paolino
2012/7/3 Corentin Dupont
Hi all, I read somewhere (here: http://stackoverflow.com/questions/2300275/how-to-unpack-a-haskell-existenti...) that it's bad to try to unbox an existential type using a cast. OK, but without I really can't figure out how to do what I want:
*data NewPlayer = NewPlayer deriving (Typeable, Eq) data NewRule = NewRule deriving (Typeable, Eq)
class (Eq e, Typeable e) => Event e where data EventData e
instance Event NewPlayer where data EventData NewPlayer = P Int
instance Event NewRule where data EventData NewRule = R Int
instance Typeable1 EventData where typeOf1 _ = mkTyConApp (mkTyCon "EventData") []
data EventHandler = forall e . (Event e) => EH e (EventData e -> IO ())
addEvent :: (Event e) => e -> (EventData e -> IO ()) -> [EventHandler] -> [EventHandler] addEvent e h ehs = (EH e h):ehs
triggerEvent :: (Event e) => e -> (EventData e) -> [EventHandler] -> IO () triggerEvent e d ehs = do let r = find (\(EH myEvent _) -> cast e == Just myEvent) ehs case r of Nothing -> return () Just (EH _ h) -> case cast h of Just castedH -> castedH d Nothing -> return ()*
How to remove the casts from triggerEvent? All that I want is to apply the handler found on the data passed in parameter. I tried to add a function apply in the class, without success: *apply :: (EventData e -> IO ()) -> (EventData e) -> IO () apply = ($)*
Thanks! Corentin
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