I was surprised to see that the linked "real world" implementation actually defines a bunch of macros with very generic names like "in", "out" and "end". The "

I was surprised to see that the linked "real world" implementation actually defines a bunch of macros with very generic names like "in", "out" and "end". The "standard" way of doing these things would be to name them MILL_IN etc. Not as pretty, but less likely to cause problems down the road.