Over-ridables

[MrTAToad]

Whilst CALLBACK allows over-ridables for difference include files, it would be nice if this sort of thing could be done when all the functions are in the same include file

At the moment, the compiler complains if there are more than two functions with the same name.

[Kitty Hello]

you mean over LOADING (2 different argument types).
Call the functions differently:
swapi, swapd, swaps e.g.

[MrTAToad]

Yes - overloading is what I'm after here

Whilst I use different function names, it would be nice to use just one and let the compiler work out the correct function to call...

[Kitty Hello]

it's going to cause a lot of confusion IMO. It's not very "BASIC".