On Wed, Sep 7, 2011 at 1:37 PM, John Clements <cleme...@brinckerhoff.org> wrote: > > On Sep 6, 2011, at 8:12 PM, Sam Tobin-Hochstadt wrote: > >> On Tue, Sep 6, 2011 at 8:05 PM, John Clements <cleme...@brinckerhoff.org> >> wrote: >>> >>> On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: >>> >>>> >>>> Yes, I understand why this happens. As I see it, there are a few >>>> possibilities: >>>> >>>> 1. The expander should check for duplicates, in some fashion. >>>> 2. This idiom is problematic, in the case where `stx' is both the >>>> input and used for the syntax properties of the output. >>>> 3. Macros may freely duplicate syntax properties. >>>> >>>> All of these have drawbacks, but (3), which you are suggesting, means >>>> either that syntax properties can only be used to specify idempotent >>>> information or that the non-idempotent ones need to have some >>>> *explicit* means by which equal elements can be distinguished, which >>>> must be part of the API of that syntax property. >>>> >>>> If we think this is how syntax properties ought to work, then we >>>> should add something to the documentation making this clear, and we >>>> should recognize that it's a limitation. >>> >>> Would syntax-property guards solve this problem? >> >> I don't really see how. What are you thinking of? > > A guard could keep track of duplicates. Keep in mind that syntax-property > guards are purely a > figment of my imagination.
What, in your imagination, is a syntax-property guard? --Carl _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
