Make every place where binding variables currently appear allow arbitrary match patterns about rhombus-prototype HOT 4 OPEN

I like the use of _ (recognized by free-identifier=?) in match, syntax-case, syntax-rules, and syntax-parse as an explicit way of communicating "I'm not going to use this thing". I often wish define-values and lambda understood it in the same way: I have at least once had a bug from accidentally shadowing _ by using it as a placeholder in a binding form that didn't treat it specially. I'm conflicted, though, about how deeply it should be built in: I value that Racket's heritage has no "reserved words". Maybe the solution is a #%plain-define-values, but I'm still trying to think of what other pitfalls "_-everywhere" might bring.

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@LiberalArtist Related, I am constantly annoyed that I can't do this:

(define-values (_ _ value-I-actually-want _ _) (something))

...because it complains that this introduces duplicate bindings for _. Yes, you're technically correct there compiler. The worst kind of correct.

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I emphatically think this should NOT be a match pattern, but a more general sort of binding-expander, like Remix's def-expanders. We don't want to push people to use a single system, match, when there are many available options.

For your second point, Remix's def+ is an attempt to provide that feature and is a relevant place to look for inspiration for an RFC.

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Yeah, I find myself always using match-define-values instead of define-values for this reason.

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