-- We can use Template Haskell (TH) to generate instances of the

-- FromJSON and ToJSON classes automatically.  This is the fastest way

-- to add JSON support for a type.

{-# LANGUAGE OverloadedStrings #-}

{-# LANGUAGE TemplateHaskell #-}

module Main (main) where

import Prelude ()

import Prelude.Compat

import Data.Aeson (decode, encode)

import Data.Aeson.TH (deriveJSON, defaultOptions)

import qualified Data.ByteString.Lazy.Char8 as BL

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

             deriving (Show)

-- This splice will derive instances of ToJSON and FromJSON for us.

$(deriveJSON defaultOptions ''Coord)

main :: IO ()

main = do

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

  print req

  let reply = Coord { x = 123.4, y = 20 }

  BL.putStrLn (encode reply)