Huh. Somehow that rep trick never occurred to me either.
One of my big motivations for first-class macros was to be able to organize my code in any order. If there's no external constraints it increases the odds that a given snapshot will have some reasonable organization that's easy for newcomers to understand. Any constraints just increase the odds of stale organization. I've ranted before about this: http://arclanguage.org/item?id=15587 (footnote 1); https://github.com/akkartik/wart/blob/master/001organization. If macros can be written in any order, that reduces a lot of my need for first-class macros.
Sorry to say, but I don't believe any of this actually lets you use macros before they're defined. Calling the macro's rep will just succeed at expanding the macro, not executing the resulting code (and not suppressing expansion and execution of the arguments).
