content: {-# LANGUAGE CPP #-}
  #if __GLASGOW_HASKELL__ >= 702
  {-# LANGUAGE Safe #-}
  #endif
  #if __GLASGOW_HASKELL__ >= 706
  {-# LANGUAGE PolyKinds #-}
  #endif
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Control.Monad.Signatures
  -- Copyright   :  (c) Ross Paterson 2012
  -- License     :  BSD-style (see the file LICENSE)
  --
  -- Maintainer  :  R.Paterson@city.ac.uk
  -- Stability   :  experimental
  -- Portability :  portable
  --
  -- Signatures for monad operations that require specialized lifting.
  -- Each signature has a uniformity property that the lifting should satisfy.
  -----------------------------------------------------------------------------
  
  module Control.Monad.Signatures (
      CallCC, Catch, Listen, Pass
    ) where
  
  -- | Signature of the @callCC@ operation,
  -- introduced in "Control.Monad.Trans.Cont".
  -- Any lifting function @liftCallCC@ should satisfy
  --
  -- * @'lift' (f k) = f' ('lift' . k) => 'lift' (cf f) = liftCallCC cf f'@
  --
  type CallCC m a b = ((a -> m b) -> m a) -> m a
  
  -- | Signature of the @catchE@ operation,
  -- introduced in "Control.Monad.Trans.Except".
  -- Any lifting function @liftCatch@ should satisfy
  --
  -- * @'lift' (cf m f) = liftCatch ('lift' . cf) ('lift' f)@
  --
  type Catch e m a = m a -> (e -> m a) -> m a
  
  -- | Signature of the @listen@ operation,
  -- introduced in "Control.Monad.Trans.Writer".
  -- Any lifting function @liftListen@ should satisfy
  --
  -- * @'lift' . liftListen = liftListen . 'lift'@
  --
  type Listen w m a = m a -> m (a, w)
  
  -- | Signature of the @pass@ operation,
  -- introduced in "Control.Monad.Trans.Writer".
  -- Any lifting function @liftPass@ should satisfy
  --
  -- * @'lift' . liftPass = liftPass . 'lift'@
  --
  type Pass w m a =  m (a, w -> w) -> m a
  