I also have reason to believe that, if we do generalized patterns
property, we won't need to do this as a language feature, we can
do it as a library feature. So, let's come back to this later.
Exhaustiveness is hard to emulate in a library.
Understood, but I would happily trade non-exhaustive, library-based
switches on all kinds of non-constants for adding YET ANOTHER weird,
bespoke, ad-hoc form of switch. Or even the possibility of same in the
future for another weird thing now. (Anyway, this is a topic for later.)
