As I know the ST monad doesn't provide getState/setState functions. In order to get this kind of overloading we need to put all functions that deal with references in type class:
class MonadRef m r where readRef :: r a -> m a writeRef :: a -> r a -> m () I guess that this is an overkill since we can just define IO as type IO a = ST RealWorld a Krasimir --- Keean Schupke <[EMAIL PROTECTED]> wrote: > Krasimir Angelov wrote: > > >ered on top of ST and the stToIO is > >the lifting function. What does 'automatically be > >lifted' mean? > > > > Krasimir > > > > > For example with the state monad you can define: > > instance (MonadState st m,MonadT t m) => MonadState > st (t m) where > update = up . update > setState = up . setState > getState = up $ getState > > This makes any monad transformer applied to the > StateMonad transformer > an instance of the StateMonadTransformer. When you > use getState, you > do not have to prefix the lifting, the type checker > unwinds the > instance, and > for each transformer it removes adds a lift. > > If is only possible to define the above for some > monad-transformers. In > other > cases the lifts must be specific to the > monad-transformer being lifted > through, > in which case you would define: > > instance Monad m => MonadTransX (MonadState m) where > ... > > This would be for lifting functions of MonadTransX > through MonadState > specifically. > > Keean. > > > > _______________________________________________ > Haskell mailing list > [EMAIL PROTECTED] > http://www.haskell.org/mailman/listinfo/haskell > __________________________________ Do you Yahoo!? Check out the new Yahoo! Front Page. www.yahoo.com _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
