references-0.2.0.0: Control/Reference/TH/MonadInstances.hs

{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE TypeFamilies, RankNTypes #-}
{-# LANGUAGE FlexibleContexts, FlexibleInstances, MultiParamTypeClasses, UndecidableInstances #-}

-- | A basic set of instances derived using "Control.Reference.TH.Monad".
-- 
-- == Structure defined
--
-- @
--            'ListT' 'IO'
--           /         \\
--         []       'Control.Monad.Trans.Maybe.MaybeT' 'IO'
--         |      /     |
--       'Maybe'         'IO'
--            \\       /
--            'Control.Monad.Trans.Identity.Identity'
-- @
module Control.Reference.TH.MonadInstances () where

import Control.Reference.InternalInterface
import Control.Reference.TH.Monad

import Control.Monad.Identity
import Control.Monad.Trans.Maybe as Trans
import Control.Monad.Trans.List as Trans
import Data.Maybe
import Language.Haskell.TH as TH

$(makeMonadRepr ''Identity          ''Maybe                     [e| return . runIdentity |])
$(makeMonadRepr ''Identity          ''IO                        [e| return . runIdentity |])
$(makeMonadRepr ''Maybe             [t| MaybeT IO |]            [e| MaybeT . return |])
$(makeMonadRepr ''IO                [t| MaybeT IO |]            [e| MaybeT . liftM Just |])
$(makeMonadRepr ''Maybe             TH.ListT                    [e| maybeToList |])
$(makeMonadRepr TH.ListT            [t| Trans.ListT IO |]       [e| Trans.ListT . return |])
$(makeMonadRepr ''IO                [t| Trans.ListT IO |]       [e| Trans.ListT . liftM (:[]) |])
$(makeMonadRepr [t| MaybeT IO |]    [t| Trans.ListT IO |]       [e| Trans.ListT . liftM maybeToList . runMaybeT |])