Created
February 17, 2015 00:44
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{-# LANGUAGE FunctionalDependencies #-} | |
{-# LANGUAGE GeneralizedNewtypeDeriving #-} | |
{-# LANGUAGE MultiParamTypeClasses #-} | |
{-# LANGUAGE TemplateHaskell #-} | |
module Stack where | |
import Control.Applicative | |
import Control.Lens | |
import Control.Monad.State | |
data OuterData = OuterData | |
{ _outerDataName :: String | |
} | |
data InnerData = InnerData | |
{ _innerDataName :: String | |
} | |
makeClassy ''OuterData | |
makeClassy ''InnerData | |
newtype InnerT m a = InnerT { unInnerT :: StateT InnerData m a } | |
deriving (Functor, Applicative, Monad) | |
newtype OuterT m a = OuterT { unOuterT :: StateT OuterData (InnerT m) a } | |
deriving (Functor, Applicative, Monad) | |
instance HasOuterData (InnerData, OuterData) where | |
outerData = _2 | |
instance HasInnerData (InnerData, OuterData) where | |
innerData = _1 | |
instance Monad m => MonadState (InnerData, OuterData) (OuterT m) where | |
getOuterName :: (MonadState s m, HasOuterData s) => m String | |
getOuterName = use outerDataName | |
getInnerName :: (MonadState s m, HasInnerData s) => m String | |
getInnerName = use innerDataName | |
a :: OuterT Identity String | |
a = getInnerName |
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