conduit json parsing

example.hs

avgForClient :: Purchase -> Double
avgForClient (Purchase _ products) =
  let n      = fromIntegral $ DT.length products
      totals = sum $ price <$> products
  in  totals / n

-- outputs nullnullnullnull...  unless the json is on a single line. 
-- how to make this work for multi-line json? 

main :: IO ()
main =
  runConduitRes
    $  B.sourceFile "ch10.json"
    .| B.lines
    .| L.map LB.fromStrict -- ?? L.foldMap (id . LB.fromStrict) to read all the files in memory at once? 
    .| L.map (\x -> (fmap avgForClient $ decode x))
    .| L.map (LB.toStrict . encode)
    .| B.sinkFile "ch10.out.json"