Mixin experiment

gistfile1.hs

import Data.IORef
import Control.Applicative

data CounterRep = CounterRep { x :: IORef Int }

newCounterRep = CounterRep <$> newIORef 0 

data Counter = Counter { get :: IO Int,
                         set :: Int -> IO () }

counterClass = \rep -> Counter { get = readIORef $ x rep,
                                 set = writeIORef (x rep) }

doubleMixin into = \rep -> let super = into rep in
                               Counter { get = get super,
                                         set = set super . (*2) }

plusOneMixin into = \rep -> let super = into rep in
                                Counter { get = get super,
                                          set = set super . (+1) }              

newCounter = counterClass <$> newCounterRep
newDoubleCounter = doubleMixin counterClass <$> newCounterRep
newDDCounter = (doubleMixin . doubleMixin) counterClass <$> newCounterRep
newDPlusCounter = (plusOneMixin . doubleMixin) counterClass <$> newCounterRep