git.iko.soy/typeable/aeson
on 0.11.3.0 help sign in
typeable/aeson/examples/Simplest.hs
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1{-# LANGUAGE OverloadedStrings, RecordWildCards #-}
3import Control.Applicative ((<$>), (<*>), empty)
4import Data.Aeson
5import Data.Monoid
6import qualified Data.ByteString.Lazy.Char8 as BL
8data Coord = Coord { x :: Double, y :: Double }
9 deriving (Show)
11-- A ToJSON instance allows us to encode a value as JSON.
13instance ToJSON Coord where
14 toJSON (Coord xV yV) = object [ "x" .= xV,
15 "y" .= yV ]
17 toEncoding Coord{..} = pairs $
18 "x" .= x <>
19 "y" .= y
21-- A FromJSON instance allows us to decode a value from JSON. This
22-- should match the format used by the ToJSON instance.
24instance FromJSON Coord where
25 parseJSON (Object v) = Coord <$>
26 v .: "x" <*>
27 v .: "y"
28 parseJSON _ = empty
30main :: IO ()
31main = do
32 let req = decode "{\"x\":3.0,\"y\":-1.0}" :: Maybe Coord
33 print req
34 let reply = Coord 123.4 20
35 BL.putStrLn (encode reply)