1-- We can use Template Haskell (TH) to generate instances of the
2-- FromJSON and ToJSON classes automatically.  This is the fastest way
3-- to add JSON support for a type.
4{-# LANGUAGE NoImplicitPrelude #-}
5{-# LANGUAGE OverloadedStrings #-}
6{-# LANGUAGE TemplateHaskell #-}
7
8module Main (main) where
9
10import Prelude.Compat
11
12import Data.Aeson (decode, encode)
13import Data.Aeson.TH (deriveJSON, defaultOptions)
14import qualified Data.ByteString.Lazy.Char8 as BL
15
16data Coord = Coord { x :: Double, y :: Double }
17             deriving (Show)
18
19-- This splice will derive instances of ToJSON and FromJSON for us.
20
21$(deriveJSON defaultOptions ''Coord)
22
23main :: IO ()
24main = do
25  let req = decode "{\"x\":3.0,\"y\":-1.0}" :: Maybe Coord
26  print req
27  let reply = Coord { x = 123.4, y = 20 }
28  BL.putStrLn (encode reply)
29