    -- | The multi-valued version of mtl's MonadState
    module Control.Monad.Trans.MultiState.Class
      (
      -- * MonadMultiState class
        MonadMultiGet(..)
      , MonadMultiState(..)
      )
    where

    import Control.Monad.Trans.MultiGet.Class

    import Control.Monad.Trans.Class  ( MonadTrans
                                      , lift )

    -- The idea is: Any monad stack is instance of @MonadMultiState a@, iff
    -- the stack contains a @MultiStateT s m@ with /a/ element of /s/,
    -- or a @MultiRWST r w s m@ with /a/ element of /s/.
    class (MonadMultiGet a m) => MonadMultiState a m where
      mSet :: a -> m ()

    instance (MonadTrans t, Monad (t m), MonadMultiState a m)
          => MonadMultiState a (t m) where
      mSet :: a -> t m ()
    mSet = m () -> t m ()
    forall (t :: (* -> *) -> * -> *) (m :: * -> *) a.
    (MonadTrans t, Monad m) =>
    m a -> t m a
    lift (m () -> t m ()) -> (a -> m ()) -> a -> t m ()
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . a -> m ()
    forall a (m :: * -> *). MonadMultiState a m => a -> m ()
    mSet