{-# LANGUAGE OverloadedStrings #-}

{-# LANGUAGE RecordWildCards #-}

module Main (main) where

import Prelude ()

import Prelude.Compat

import Control.Applicative (empty)

import Data.Aeson

import Data.Monoid

import qualified Data.ByteString.Lazy.Char8 as BL

data Coord = Coord { x :: Double, y :: Double }

             deriving (Show)

-- A ToJSON instance allows us to encode a value as JSON.

instance ToJSON Coord where

  toJSON (Coord xV yV) = object [ "x" .= xV,

                                  "y" .= yV ]

  toEncoding Coord{..} = pairs $

    "x" .= x <>

    "y" .= y

-- A FromJSON instance allows us to decode a value from JSON.  This

-- should match the format used by the ToJSON instance.

instance FromJSON Coord where

  parseJSON (Object v) = Coord <$>

                         v .: "x" <*>

                         v .: "y"

  parseJSON _          = empty

main :: IO ()

main = do

  let req = decode "{\"x\":3.0,\"y\":-1.0}" :: Maybe Coord

  print req

  let reply = Coord 123.4 20

  BL.putStrLn (encode reply)