json.hs

{-# LANGUAGE OverloadedStrings #-}

import Data.Aeson
import Data.Maybe
import Data.ByteString.Lazy
import Control.Applicative

main = do
  res <- liftA show (liftA decodeOriginal (Data.ByteString.Lazy.readFile "./a.json"))
  Prelude.putStrLn res
    
interpretResult :: Maybe String -> String
interpretResult Nothing = "Error."
interpretResult x = fromJust x

data TotalLine1 = TotalLine1 {
  timestamp :: Integer,
  value :: Integer
} deriving (Eq, Show)

data Original = Original {
  totals :: [TotalLine1]
} deriving (Eq, Show)

instance FromJSON Original where
  parseJSON (Object o) = Original <$>
                         (parseJSON =<< (o .: "visitors.total"))

instance FromJSON TotalLine1 where
  parseJSON (Object o) = TotalLine1 <$>
                         o .: "timestamp" <*>
                         o .: "value"

decodeOriginal :: ByteString -> Maybe Original
decodeOriginal response = decode response