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@bos
31 lines (23 sloc) 0.858 kb
{-# LANGUAGE OverloadedStrings #-}
import Control.Applicative ((<$>), (<*>), empty)
import Data.Aeson
import qualified Data.ByteString.Lazy.Char8 as BL
data Coord = Coord { x :: Double, y :: Double }
deriving (Show)
-- A ToJSON instance allows us to encode a value as JSON.
instance ToJSON Coord where
toJSON (Coord xV yV) = object [ "x" .= xV,
"y" .= yV ]
-- A FromJSON instance allows us to decode a value from JSON. This
-- should match the format used by the ToJSON instance.
instance FromJSON Coord where
parseJSON (Object v) = Coord <$>
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)
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