[Haskell-cafe] Re: Re: [Haskell] ANNOUNCE: reference 0.1
uzytkownik2 at gmail.com
Wed Sep 8 04:19:03 EDT 2010
On Wed, 2010-09-08 at 09:53 +0200, Alberto G. Corona wrote:
> Ah, ok. I though that your intention was to restrict the class
> definition for the IO monad . Goood.
> Maybe in the long term, it make sense to include this type class in
> some monad related package such is mtl, since references are part of
> many user monads. I think also that some default instances can be
> defined for transformed monads.
Yes - they can.
instance (MonadTrans t, Monad (t m),
Reference r m) => Reference r (t m) where
newRef = lift . newRef
readRef = lift . readRef
writeRef r = lift . writeRef r
instance (MonadIO m, Reference r IO) => Reference r m where
newRef = liftIO . newRef
readRef = liftIO . readRef
writeRef r = liftIO . writeRef r
> It is pleasant for me to read and write something like
> x <- readRef rx
> rather than
> x<- readMyMonadRef sx
> Such generalizatiopns may be also good for extracting more common
> patterns among different monads.
Actually the primary need was to create mutable single-linked list for
iteratee-parsec. I didn't wanted to restrict myself to ST or IO so I
choose to add class for them.
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