title: How to use ST Monad with monad transformers
body: <p>The haskell <code>transformers</code> library provides <code>MonadIO</code> class and <code>liftIO</code> to lift IO operations in a monad transformer stack.  It seems to me that the same could be done for the ST monad, but I couldn't find it in any monad transformer library.  Is there a reason for this omission?  How do I use ST monad with e.g., <code>MaybeT</code> or <code>ReaderT</code>?</p>