[racket] Another Canonical Use of Macros?

I'm preparing a 10-minute lightning talk on hygienic macros in rust (preview: I'm barely going to *mention* hygiene), and in the process, I've been surveying some of the Rust macros, and roughly categorizing them in terms of the "three canonical categories" that Matthias described--apologies if I'm misrepresenting him/you:
- changing evaluation order,
- implementing a data sublanguage, and
- creating new binding forms.

Some of the Rust macros seem to fall into a fourth category, which arises from the fact that certain things are not expressions:

- abstracting over things that are not expressions.

For instance:

cmp_impl!(impl Eq, eq, ne)
cmp_impl!(impl TotalEq, equals)
cmp_impl!(impl Ord, lt, gt, le, ge)
cmp_impl!(impl TotalOrd, cmp -> cmp::Ordering)

Each of these expands into a top-level "impl" declaration, extending implementations of, e.g., Ord, from type T to type Ratio<T>. 

More generally, it seems to me that every time you constrain first-class-ness by making things not-first-class (e.g. module-level stuff in Racket), you will be required to use macros to abstract over these things.

Thoughts?

Back to writing my talk...

John