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. John
smime.p7s
Description: S/MIME cryptographic signature
_________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
