[Haskell-cafe] Re: GUI programming

[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/


Regards,
Heinrich Apfelmus

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