Monad.hs

{-# LANGUAGE ScopedTypeVariables, Rank2Types #-}
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies #-}
-- .$Header: c:/Source/Haskell/Wrapper/Data/Flex/RCS/Monad.hs,v 1.3 2011/09/20 23:37:34 dosuser Exp dosuser $
module Data.Flex.Monad (
    -- * Common flexible Monad instance selection types and classes
    -- ** Analysis class for @'Monad'@ instance selection
    FWMonad,
    -- ** Instance selectors
    FWDefaultMonad(..),
    -- ** Function identifier types for @'Apply'@
    FWReturn(..),
    FWBind(..),
    -- ** Polymorphic function wrappers
    WrapReturn(..),
    WrapBind(..),
    -- ** Constructor aliases
    wrapReturn,
    wrapBind
) where

-- import Data.Flex.Applicative (WrapPure(..))

-- | Analysis class for @'Monad'@ instance selection
-- You need a specific instance of this for any instance selectors
-- you may define.
class FWMonad (m :: * -> *) r | m -> r

-- | Instance selector type for the default @'Monad'@
-- instances
data FWDefaultMonad = FWDefaultMonad

-- | Function identifier type for @'Apply'@.
-- You need a corresponding instance of @'Apply'@ for any
-- instance selectors you may define.
data FWReturn t (m :: * -> *) = FWReturn

-- | Polymorphic function wrapper for @'return'@
newtype WrapReturn m = WrapReturn {unwrapReturn :: forall a. a -> m a}
wrapReturn :: (forall a. a -> m a) -> WrapReturn m
wrapReturn = WrapReturn
{- GHC 6.6.1 can't cope with this version of unwrapReturn
type WrapReturn = WrapPure
wrapReturn :: (forall a. a -> m a) -> WrapReturn m
wrapReturn = WrapPure
unwrapReturn :: WrapReturn m -> (forall a. a -> m a)
unwrapReturn = unwrapPure
-}

-- | Function identifier type for @'Apply'@.
-- You need a corresponding instance of @'Apply'@ for any
-- instance selectors you may define.
data FWBind t (m :: * -> *) = FWBind

-- | Polymorphic function wrapper for @'>>='@
newtype WrapBind m =
    WrapBind {unwrapBind :: forall a b. m a -> (a -> m b) -> m b}

wrapBind :: (forall a b. m a -> (a -> m b) -> m b) -> WrapBind m
wrapBind = WrapBind

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