mtl 2.2.2

* `Control.Monad.Identity` now re-exports `Control.Monad.Trans.Identity`
* Fix a bug in which `Control.Monad.State.Class.modify'` was not as strict in
  the new state as its counterparts in `transformers`
* Add a `MonadError () Maybe` instance
* Add `liftEither :: MonadError e m => Either e a -> m a` to
  `Control.Monad.Except{.Class}`
* Add a `MonadWriter w ((,) w)` instance (when built against `base-4.9` or later)

version 2.2.1

version 2.0.1.1

- fix compatibility with base>=4.6

version 2.2.0.1

version 2.2

version 2.1.3.1

2.0.1.0

2.0.0.0

1.1.1.0

1.1.0.2

1.1.0.1 release

1.1.0.0 release

1.0.1 release