I just released the monad-peel library to Hackage. http://hackage.haskell.org/package/monad-peel MonadPeelIO is a simple class that allows lifting monadic control operations, such as those in Control.Exception and Foreign.Marshal.Alloc, through layers of monad transformers. It comes with instances for every transformer in the transformers package except ContT, and uses no Haskell extensions. class MonadTrans t => MonadTransPeel t where peel :: (Monad m, Monad n, Monad o) => t n (t m a -> m (t o a)) class MonadIO m => MonadPeelIO m where peelIO :: m (m a -> IO (m a)) I’ve included a wrapped version of Control.Exception with types generalized to all monads in MonadPeelIO, for example: catch :: (MonadPeelIO m, Exception e) => m a -> (e -> m a) -> m a catch a handler = do k <- peelIO join $ liftIO $ Control.Exception.catch (k a) (\e -> k $ handler e) I’m hoping this package can become a suitable replacement for MonadCatchIO, whose implementation of ‘finally’ was recently shown to be broken with certain monads (see “MonadCatchIO, finally and the error monad” on this list). The home page has links to a Git repository and has references to older mailing list threads providing some background: http://andersk.mit.edu/haskell/monad-peel/ Thanks to everyone who contributed to those threads and helped shape the ideas that led to this package (and if it turns out more ideas are needed, thanks for those too!). Anders