On Wed, Feb 3, 2010 at 4:11 PM, Heinrich Apfelmus
Victor Nazarov wrote:
data Behaviour a = forall b. BBind (Behaviour b) (b -> Behaviour a) | BIO (IO a) | forall obj. GObjectClass obj => BWaitEvent (Event obj) (Behaviour a)
instance Monad Behaviour where action >>= generator = BBind action generator return a = BIO (return a)
instance MonadIO Behaviour where liftIO action = BIO action
runBehaviour :: Behaviour a -> IO a runBehaviour (BBind (BWaitEvent event after) f) = runBehaviour (BWaitEvent event (after >>= f)) runBehaviour (BBind (BIO a) f) = a >>= \x -> runBehaviour (f x) runBehaviour (BBind (BBind a f) g) = runBehaviour (a >>= (\x -> f x >>= g))
Just a minor note: you can somewhat clean up your code by using a generic monad, as implemented in my cabal package operational
http://hackage.haskell.org/package/operational
and described in
Heinrich Apfelmus. The Operational Monad Tutorial. In http://themonadreader.wordpress.com/2010/01/26/issue-15/
Thank you. It seems relevant. I'll have a look at it. Speaking about packages. What is current community status of monad transformers packages. I'm using MonadIO class and there are mtl, monads-fd, monads-tf packages that provide it. I personally prefer type families to functional dependencies. Should I use monads-tf, or should I stick to mtl? -- Victor Nazarov