    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Control.Monad.Signatures
    -- Copyright   :  (c) Ross Paterson 2012
    -- License     :  BSD-style (see the file LICENSE)
    --
    -- Maintainer  :  ross@soi.city.ac.uk
    -- Stability   :  experimental
    -- Portability :  portable
    --
    -- Signatures for monad operations that require specialized lifting.
    -----------------------------------------------------------------------------

    module Control.Monad.Signatures (
        CallCC, Catch, Listen, Pass
      ) where

    -- | Signature of the @callCC@ operation,
    -- introduced in "Control.Monad.Trans.Cont".
    type CallCC m a b = ((a -> m b) -> m a) -> m a

    -- | Signature of the @catchE@ operation,
    -- introduced in "Control.Monad.Trans.Except".
    type Catch e m a = m a -> (e -> m a) -> m a

    -- | Signature of the @listen@ operation,
    -- introduced in "Control.Monad.Trans.Writer".
    type Listen w m a = m a -> m (a, w)

    -- | Signature of the @pass@ operation,
    -- introduced in "Control.Monad.Trans.Writer".
    type Pass w m a =  m (a, w -> w) -> m a