-- This example is basically the same as in Simplest.hs, only it uses

-- GHC's builtin generics instead of explicit instances of ToJSON and

-- FromJSON.

-- We enable the DeriveGeneric language extension so that GHC can

-- automatically derive the Generic class for us.

{-# LANGUAGE DeriveGeneric #-}

{-# LANGUAGE OverloadedStrings #-}

module Main (main) where

import Prelude ()

import Prelude.Compat

import Data.Aeson (FromJSON, ToJSON, decode, encode)

import qualified Data.ByteString.Lazy.Char8 as BL

import GHC.Generics (Generic)

-- To decode or encode a value using the generic machinery, we must

-- make the type an instance of the Generic class.

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

             deriving (Show, Generic)

-- While we still have to declare our type as instances of FromJSON

-- and ToJSON, we do *not* need to provide bodies for the instances.

-- Default versions will be supplied for us.

instance FromJSON Coord

instance ToJSON 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)