ReflectBark.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}
module ReflectBark where
import Control.Applicative
import Data.Aeson
import Data.Proxy
import Data.Reflection
 
data Bark = Bark | Woof | Yelp | Yap deriving Show
newtype B s = B { getDog :: String }
 
instance Reifies s Bark => FromJSON (B s) where
    parseJSON _ = B <$> (pure . show $ reflect (Proxy :: Proxy s))
 
testdog :: Bark -> Maybe String
testdog s = reify s $ \r -> fmap (getDog . isProxyFor r) $ decode "{}"
    where isProxyFor :: Proxy s -> f s -> f s
          isProxyFor = flip const