>From your question I assume you want functions like htonl / ntohl.
I think the cleanest approach is to always have yours Ints, etc in host order, and place
the endianness stuff in serialization / deserialization code, ie. on the Number <-> Byte
sequence boundary.

Having htonl/ntohl as pure functions in Haskell would be a bit ugly, because
they would be defined differently on different platforms, and putting them in the
IO monad would make them barely usable.

Best regards
Tomasz