gistfile1.hs

{-#LANGUAGE OverloadedStrings#-}

import Data.Aeson.Types
import Data.Aeson
import qualified Data.Vector as V
import qualified Data.ByteString.Lazy as L 
import Data.HashMap.Strict
import qualified Data.Text as T

-- this is backward maybe -- also doesn't crack open the Values
data Invoice = Invoice (V.Vector Value) | Invoices (HashMap T.Text Value)

parseInvoices  :: L.ByteString -> Either String Invoice
parseInvoices s = case parseObjects s of 
    Left err -> Left err
    Right (Left obj) -> Right (Invoices obj)
    Right (Right hmap) -> Right (Invoice hmap)
 where
  parseObjects :: L.ByteString -> Either String (Either Object Array)
  parseObjects s = do
      result <- eitherDecode s
      flip parseEither result $ \obj -> do
          d <- (obj .: "invoices") >>= (.: "invoice")
          case d of
              Object v -> return (Left v)
              Array v  -> return (Right v)
              -- other constructors?