Hit an web API with http-streams and aeson

api.hs

{-# LANGUAGE OverloadedStrings #-}

import           Control.Applicative
import           Control.Monad
import           Data.Aeson            (FromJSON, parseJSON, (.:))
import qualified Data.Aeson            as AE
import           Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Lazy  as LBS
import           Network.Http.Client   (Response, concatHandler, get)
import           OpenSSL               (withOpenSSL)
import           System.IO.Streams     (InputStream, toList)

data User = User
    { userId   :: String
    , userName :: String
    } deriving Show

instance FromJSON User where
    parseJSON (AE.Object v) = User <$>
                           v .: "id" <*>
                           v .: "name"
    parseJSON _          = mzero

jsonHandler :: FromJSON a => Response -> InputStream ByteString -> IO (Maybe a)
jsonHandler r i = (AE.decode . LBS.fromChunks) <$> toList i

main :: IO ()
main = withOpenSSL $ do
     user <- get "http://graph.facebook.com/dfujimura" jsonHandler :: IO (Maybe User)
     print user

$ ghc --make -threaded api.hs
[1 of 1] Compiling Main             ( api.hs, api.o )
Linking api ...
$ ./api
Just (User {userId = "100001730250658", userName = "\34276\26449 \22823\20171"})