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{-# LANGUAGE TemplateHaskell, OverloadedStrings, FlexibleInstances, TypeSynonymInstances #-}
import Network.URI (URI, parseURI)
import Network.HTTP
import Control.Applicative
import Data.Aeson
import qualified Data.ByteString.Lazy as BL
import Data.Maybe (fromJust)
redditURL = fromJust . parseURI $ ""
getJSON :: URI -> IO BL.ByteString
getJSON url = simpleHTTP (defaultGETRequest_ url) >>= getResponseBody
data Votes = Votes
{ ups :: Int
, downs :: Int
, likes :: Maybe Bool
} deriving Show
instance FromJSON Votes where
parseJSON (Object o) = Votes <$> o .: "ups"
<*> o .: "downs"
<*> o .:? "likes"
data Link = Link
{ link_votes :: Votes
} deriving Show
instance FromJSON Link where
parseJSON v@(Object _) = do
vote <- parseJSON v
-- parseJSON again for each of your types:
-- cinfo <- parseJSON o
-- ...
return $ Link vote
Since the data for each Link starts deep in the json
at {"data":{"children":[{"data": <here>}]}} we use this
function to unwrap things first. It requires enabling
a few extensions to be able to write a FromJSON instance for
[Link], but this way other FromJSON instances like Votes
can just act on the nested object without having to unwrap again.
instance FromJSON [Link] where
parseJSON (Object o) = do
children <- o .: "data" >>= (.: "children")
datas <- mapM (.: "data") children
mapM parseJSON datas
main = do
bs <- getJSON redditURL
case decode bs of
Nothing -> return ()
Just links -> print $ map link_votes links
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