{-# LANGUAGE DataKinds #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverloadedStrings #-}

module Proxy where

-- import Control.Applicative ((<$>), (<*>))
import Control.Monad (mzero)
import Data.Aeson
import qualified Data.Aeson as A
import qualified Data.ByteString.Lazy as BL
import Data.Proxy (Proxy(Proxy))
import GHC.TypeLits (symbolVal)

instance ToJSON (Proxy "foo") where
    toJSON p = object [ "type" .= symbolVal p ]

instance FromJSON (Proxy "foo") where
    parseJSON (Object v) = v .: "type" >>= handleType
      where
        handleType (A.String "foo") = return (Proxy :: Proxy "foo")
        handleType _ = mzero
    parseJSON _      = mzero

jsonString :: BL.ByteString
jsonString = "{\"type\": \"foo\"}"