David Roundy <droundy <at> darcs.net> writes: > My latest attemp (which won't compile with the HEAD ghc that I just compiled, > probably because I haven't figured out the synatax for guards with indexed > types is: > > class WitnessMonad m where > type W m :: * -> * -> * > (>>=) :: (WitnessMonad m', WitnessMonad m'', > w a b = W m', w b c = W m'', w a c = W m) > => m' x -> (x -> m'' y) -> m y > (>>) :: (WitnessMonad m', WitnessMonad m'', > w a b = W m', w b c = W m'', w a c = W m) > => m' x -> m'' y -> m y > f >> g = f >>= const g > return :: w a a = W m x => -> m x > fail :: String -> m x > > data Witness a b > > instance Monad m => WitnessMonad m where > W m = Witness () () > (>>=) = Prelude.(>>=) > (>>) = Prelude.(>>) > return = Prelude.return > fail = Prelude.fail > > which I think is quite pretty. It allows the Monadlike object to have kind > * -> *, while still allowing us to hide extra witness types inside and pull > them out using the W function.
Did anyone with knowledge of Associated Types pursue this solution? It doesn't work with GHC head, and I can't really do anything about that. Mostly curiosity. Thanks pepe ---------------------------------------------------------------- Everything from here on is to convince GMane that, even if my message contains more quoted text than fresh text, it is a legitimate message and it should be ok to post it. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
