Oh, I guess I missed your point here, thinking that P and Q were
constants.
Your comment implies that the two rules that restrict usage of
patterns—can't fall through past one, and can't combine one (via ',')
with most other labels—could be relaxed slightly in the case of
patterns that have no bindings. I suppose that's formally true, though
I'm not sure it's practically all that useful. (The only non-binding
pattern we have right now is a zero-component record, right? And any
non-binding patterns in the future could be equivalently expressed
with 'when' clauses.)
Here's an example that's not so contrived:
String kind = switch (o) {
case Integer _, Long _, Short _, Character _, Byte _ -> "integral";
case Double _, Float _ -> "floating point";
case Boolean _ -> "boolean";
default -> "something else";
};
Once we have a "don't care" pattern, any pattern can become binding-less.
Looking two steps ahead, we might decide it is not so much that there
can be _no_ bindings, as much as are the bindings unifiable:
case Bag(String x), Box(String x) -> "container of string";
