Well one problem is expander application his its own mark to deal with, so you can't cancel the mark on x.
https://github.com/plt/racket/blob/master/racket/collects/racket/match/parse-helper.rkt#L157 Another problem is expecting the implementation of match-define to not have any inner macros that would change syntax-local-introduce to a less helpful extent. What would be ideal is if racket/match could change some "parameter" so that syntax-local-introduce used the introducer defined in the above link, since the generated temporary does not have x's mark that x has annihilated. Instead x's mark will be added to tmp after the transformer returns, and there's nothing you can do about it :( -Ian ----- Original Message ----- From: "Alexander D. Knauth" <[email protected]> To: "J. Ian Johnson" <[email protected]> Cc: "racket users list" <[email protected]> Sent: Friday, August 1, 2014 6:31:59 PM GMT -05:00 US/Canada Eastern Subject: Re: [racket] getting one macro to tell another macro to define something Well, if the match-expander is invoked in the “dynamic extent” of the match-define form, then would syntax-local-introduce apply that syntax-mark? On Aug 1, 2014, at 6:20 PM, J. Ian Johnson <[email protected]> wrote: > Well that's a pickle. I can tell you that (mac . args) gets expanded as > (X[mac^m] . X[args^m])^m where m is a fresh mark and X expands a form. If m > is applied to something with m already, they annihilate each other (see > Syntactic Abstraction in Scheme for how this totally works). > The syntax-local-introduce form allows you to apply the macro application's > mark to an arbitrary piece of syntax, so later on the application's mark will > annihilate it and voila`, it's like it was textually given to the macro > application itself. > > Here, however, a match expander is not treated as a macro invocation. There > is no mark for that match-expander use to introduce. There is, however, the > mark from match-define that you'll want to introduce to this temporary you've > generated. I think. I haven't quite worked out how to make this work. > -Ian > ----- Original Message ----- > From: "Alexander D. Knauth" <[email protected]> > To: "racket users list" <[email protected]> > Sent: Friday, August 1, 2014 5:55:57 PM GMT -05:00 US/Canada Eastern > Subject: Re: [racket] getting one macro to tell another macro to define > something > > > > > > On Aug 1, 2014, at 5:37 PM, J. Ian Johnson < [email protected] > wrote: > > > It's best to expand into a begin-for-syntax that does the desired mutation, > rather than mutate within the transformer. You currently _cannot_ do this > outside top level forms. > > > > The reason I can’t do that is because in the real program, sender is actually > a match-expander. > > > You are also right about the marks. The call to receiver adds additional > marks to the definitions that it pulls out, so you'll need to apply > syntax-local-introduce. ... > > > > > On Aug 1, 2014, at 5:39 PM, Ryan Culpepper < [email protected] > wrote: > > > Use syntax-local-introduce when putting syntax into a side-channel or getting > it back out across macro calls. This only matters when the syntax represents > a definition or more generally contains binders whose references are not all > in the same syntax. > ... > > > Thanks, the syntax-local-introduce got it working for that example, but for > some reason it’s not working when sender is a match-expander. > > I’m still not very clear on when to use syntax-local-introduce and when not > to, or even what it does (other than get that example working), so could > someone point me in the right direction? > > > > #lang racket > (require racket/stxparam > (for-syntax syntax/parse > racket/syntax > racket/set)) > ;; current-defs : (syntax-parameter-of (or/c set-mutable? #f)) > (define-syntax-parameter current-defs #f) > (define-match-expander sender > (lambda (stx) > (syntax-parse stx > [(sender x) > #:with tmp (generate-temporary #'x) > (define defs (syntax-parameter-value #'current-defs)) > (set-add! defs (syntax-local-introduce #'(define x tmp))) > #'tmp]))) > (define-syntax reciever > (lambda (stx) > (syntax-parse stx > [(reciever) > (define defs (syntax-parameter-value #'current-defs)) > (with-syntax ([(def ...) (map syntax-local-introduce (set->list defs))]) > #'(begin def ...))]))) > > > (syntax-parameterize ([current-defs (mutable-set)]) > (match-define (sender x) 1) > (reciever) > x) > > > ;x3: unbound identifier; > ; also, no #%top syntax transformer is bound in: x3 > > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
