Hi Tyson, I also needed something like this a while ago so I knocked up a really simple module and put it on hackage: If you have any suggestions for improvement they are most welcome. Patches even more so. Josef 2009/2/2 Tyson Whitehead <twhitehead at gmail.com>: > I have a situation in which I believe I need a parameterizable version of the > strict ST monad. My computation type is "StateT s' (STT s (ErrorT e m)) a" > (i.e., fails or succeeds and has an internal state involving a state thread). > > > > (I'm guessing on the UNPACK paragmas here) with > > runSTT :: (Monad m) => (forall s. STT s m a) -> m a > runSTT m = case m of STT m' -> do STTBox _ x <- m' realWorld# > return x > > (writing this as "runSTT (STT m') = ..." doesn't typecheck with ghc 6.8.2) > > instance Monad m => Monad (STT s m) where > return x = STT $ \s -> return $ STTBox s x > (STT m) >>= k = STT $ \s -> do STTBox s' x <- m s > case k x of STT k' -> k' s' > > plus all the assorted instances for Functor, MonadPlus, MonadFix, MonadTrans, > MonadReader, MonadState, etc. For example, > > instance MonadWriter w m => MonadWriter w (STT s m) where > tell = lift . tell > listen (STT m) = STT $ \s -> do (STTBox s' x,w) <- listen $ m s > return $ STTBox s' (x,w) > pass (STT m) = STT $ \s -> pass $ do STTBox s' (x,f) <- m s > return (STTBox s' x,f) > > I was looking for any comments, wondering if there is a reason for this not > existing in the library already, and what I should do in terms of paragmas and > such for speed? I see the GHC-ST file has a mix of INLINE and NOINLINE. > > > > In particular, return, >>=, >>, and runST are marked INLINE, but there is a > "regrettably delicate" comment that goes with the runST method. Also, what > about the Functor, MonadPlus, MonadFix, MonadTrans, MonadReader, etc. methods? > > Thanks! -Tyson > > PS: I would be happy to provide the whole works to be added to the library if > it is something that should be there. > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users at haskell.org > > >