readWord64 :: ReadValue Word64
readWord64 = readIntegral f
  where f (U64LIT x) = Just x
        f _          = Nothing
readWord64 :: ReadValue Word64
readWord64 = readIntegral f
  where f (U64LIT x) = Just x
        f _          = Nothing
readWord64 = readIntegral f
  where f (U64LIT x) = Just x
        f _          = Nothing