[racket] Another Canonical Use of Macros?

What is the source of  "three canonical categories"?

Thanks,
Ben


On Sat, Nov 23, 2013 at 2:46 PM, John Clements <clements at brinckerhoff.org>wrote:

> 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
>
>
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