Hi Chris! On Aug 24, 2006, at 7:28 PM, Chris Kuklewicz wrote:
class Ref m r | m->r where newRef readRef writeRef
instance Ref IO IORef writeRef r x = writeIORef r $! x
instance (Ref m r) => Ref (WriterT m) r where writeRef = lift . writeRef
and so on...
The code snippet above looks like a very good idea. The monad dependent operations combined with "lift" seem more complicated than necessary. "lift" in particular often seems like plumbing that should not be necessary. Best Wishes, Greg
Well, lift is the common plumbing that lets you build writeRef and liftIO. So it is an intermediate invention. In fact it is the only thing in MonadTrans:
class MonadTrans (t::(* -> *) -> * -> *) where lift :: forall (m::* -> *) a. Monad m => m a -> t m a -- Imported from Control.Monad.Trans
You are supposed to make higher level shorthand and abstractions from it.
But it helps to learn how the plumbing works.
I have no objection to good plumbing (I have some in my house). I just usually like it to be out of sight in the wall or under the floor. Which does lead to a mess in the case of leaks.... ;-) Metaphorically, Greg
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe