readInt64 :: ReadValue Int64
readInt64 = readIntegral f
  where f (I64LIT x) = Just x
        f _          = Nothing
readInt64 :: ReadValue Int64
readInt64 = readIntegral f
  where f (I64LIT x) = Just x
        f _          = Nothing
readInt64 = readIntegral f
  where f (I64LIT x) = Just x
        f _          = Nothing