Goodbye to FUNCTORs
I added FUNCTORs because we thought they might be useful, and BrianH provided an elegant implementation for them (in one line).
Functors are essentially objects, but with a single entry point. They can be used for things like event processing, which holds state, but only has a single entry (method): the event action itself.
However, I don't want to pollute R3. It's always difficult to decide what is and what is not useful. (And, functors are probably not alone.)
So, in A51, they're gone. If I'm wrong in this choice, I'm sure you will tell me.
Also, we can put them into an "R3/Plus" and you can import that as a module.