[racket] Strange macro behavior with set! and syntax-local-introduce

Wow, sorry for the auto correct fail in my earlier message! ("is" => "id"
and "sucks" => "a").

Robby

On Thursday, May 15, 2014, Matthias Felleisen <matthias at ccs.neu.edu> wrote:

>
> Yes, being forced to use 'stx' as context is suspicious, too. It injects
> the identifier into the scope and a program may accidentally see it then.
>
>
>
> On May 15, 2014, at 7:20 PM, Robby Findler wrote:
>
> We have a work around. (In the larger program there is one is that comes
> from the input and one that doesn't. We can just bind it to a pair instead.)
>
> This program seems quite suspicious. I can't quite bring myself to call it
> a bug because it is sucks widely used part of things tho!
>
> Robby
>
> On Thursday, May 15, 2014, Matthias Felleisen <matthias at ccs.neu.edu>
> wrote:
>
>
>
> On May 15, 2014, at 5:56 PM, Robby Findler wrote:
>
> How does this help us understand the original, strange program?
>
>
> I am providing a work-around because I recognize the idiom.
> I can't explain the original.
>
>
>
> On May 15, 2014, at 6:23 PM, Spencer Florence wrote:
>
> I'm not sure how gensym fixes this:
>
>
>
> Not #f, stx:
>
> (define-syntax (make-funny-set! stx)
>   (syntax-parse stx
>     [(_ v) #`(define #,(begin (set! funny (datum->syntax stx (gensym)))
> funny) v)]))
>
>
>
>
>
>
>
>
>
>
>
>
>
> #lang racket
>
> (require (for-syntax syntax/parse racket/syntax racket/format))
>
> (define-for-syntax funny #f)
>
> (define-syntax (make-funny-set! stx)
>   (syntax-parse stx
>     [(_ v) #`(define #,(begin (set! funny (datum->syntax #f (gensym)))
> funny) v)]))
>
> (define-syntax (funny-ref stx)
>   (syntax-parse stx
>     [(_) funny]))
>
> (define-syntax (funny-set! stx)
>   (syntax-parse stx
>     [(_ v) #`(set! #,funny v)]))
>
> (make-funny-set! 2)
> (void (void (void (funny-set! 3))))
> (funny-ref)
>
> errors with:
>
>   g27591: unbound identifier;
>    also, no #%top syntax transformer is bound in: g27591
>
> regardless of how many calls to void there are (inclusive of 0). This
> makes sense, as the syntax marks don't add up. The calls to
> "syntax-local-introduce" in the original program aught to solve this, but
> as we saw... `/me points to robby's email`
>
>
>
> And removing the datum->syntax errors with:
>
>   funny-ref: received value from syntax expander was not syntax
>     received: 'g27876
>
> Which also makes sense: a symbol is not Syntax.
>
>
>
>
> On Thu, May 15, 2014 at 4:56 PM, Robby Findler <
> robby at eecs.northwestern.edu> wrote:
>
> How does this help us understand the original, strange program?
>
> Robby
>
> On Thu, May 15, 2014 at 4:51 PM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
> >
> > Then use gensym instead of g and "~a" instead.
> >
> >
> >
> > On May 15, 2014, at 5:38 PM, Matthias Felleisen <matthias at ccs.neu.edu>
> wrote:
> >
> >>
> >> Did you want this:
> >>
> >> #lang racket
> >>
> >> (require (for-syntax syntax/parse racket/syntax))
> >>
> >> (define-for-syntax funny #f)
> >>
> >> (define-syntax (make-funny-set! stx)
> >>  (syntax-parse stx
> >>    [(_ v) #`(define #,(begin (set! funny (form
>
>
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