Functors for creating modules that mint unique identifiers.
An abstract unique identifier based on ordinary OCaml integers. Be careful, this may
easily overflow on 32-bit platforms! Int63 is a safer choice for portability.
Int is useful when one is passing unique ids to C and needs a guarantee as to their
representation. Int is always represented as an integer, while Int63 is either an
integer (on 64-bit machines) or a pointer (on 32-bit machines).
The generated ids will therefore be fast to generate and not use much memory. If you do not have very stringent requirements on the size, speed, and ordering of your IDs then you should use the UUIDM library instead, which will give you a truly unique id, even amongst different runs and different machines.