gistfile1.hs

bookResource :: Controller ()
bookResource = do
  gid <- ((fromString . unpack . fromJust) <$> getParam "gid") >>= (\gid' -> gid' `onNothing` "Invalid BBID")
  maybeBook <- model $ getBook gid
  case maybeBook of
    Nothing -> generic404 "The request book could not be found"
    Just book -> do
      book <- model $ loadAuthorCredit book
      book <- model $ set lBookAuthorCredit book <$> (loadForAuthorCredits $ bookAuthorCredit book)
      editions <- model $ findBookEditions book
      output $ showBook book editions
  where onNothing (Just a) _ = return a
        onNothing Nothing message = throwError message
        set field on = \val -> setL field val on