Aha. Maybe the following question won't make any sense after I've digested the implications, but to ask anyway:
I'm completely sold on "keeping it clean", and for example using syntax parameters when possible. That leaves at least one use case, which is what I'll call (not knowing a better phrase) defining-things macros. Like what `struct` does when defining field accessors, and like my toy hyphen-define example does. This seems like a really, really common use case for macros. Is there a generically safe/sane way to write such macros? Could some mechanism be devised to help do this -- much like syntax-parameters enables you to write anaphoric-if and friends safely/sanely? On Tue, Oct 1, 2013 at 2:48 PM, Sam Tobin-Hochstadt <sa...@cs.indiana.edu> wrote: > On Tue, Oct 1, 2013 at 2:42 PM, Greg Hendershott > <greghendersh...@gmail.com> wrote: >> >> 2. Plus it seems like it would be really unfortunate if carefully >> choosing one of #'a or #'b were required -- because that would mean >> `inner` couldn't be written to be usable by other macros independent >> of knowing the origin of what they give to `inner`, right? I mean, >> without knowing if a comes from `outer` or from the usage of `outer`, >> and likewise for b, and therefore which of a or b to choose carefully. > > Carefully choosing one _is_ required, and it _is_ really unfortunate. > > This is, in essence, why unhygenic macros are bad for composition. You > have to pick something as the lexical context of your identifiers, and > your choices are limited to (a) one of the syntax objects in your > input or (b) whatever the previous expansion step was (that's what > syntax-local-introduce does). Therefore, it's hard to compose them > because they have to have a specific protocol for choosing identifier > contexts, and if the protocols don't line up, everything becomes much > more painful. > > Sam ____________________ Racket Users list: http://lists.racket-lang.org/users
