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 <[email protected]> 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 < > [email protected]> wrote: > > How does this help us understand the original, strange program? > > Robby > > On Thu, May 15, 2014 at 4:51 PM, Matthias Felleisen > <[email protected]> wrote: > > > > Then use gensym instead of g and "~a" instead. > > > > > > > > On May 15, 2014, at 5:38 PM, Matthias Felleisen <[email protected]> > 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 (format-id stx "g")) 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) > >> > >> [I had to write such a macro a while back, and the above is roughly > what I remember doing. Note the lexical context] > >> > >> > >> On May 15, 2014, at 5:25 PM, Spencer Florence <[email protected]> > wrote: > >> > >>> I'm attempting to write a macro which introduces a new id, then > another macro that set!s that id. > >>> Example: > >>> > >>> #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 unmarked (generate-temporary)) > >>> (set! funny (syntax-local-introduce unmarked)) > >>> #`(define #,unmarked v)])) > >>> (define-syntax (funny-ref stx) > >>> (syntax-parse stx > >>> [(_) > >>> funny])) > >>> (define-syntax (funny-set! stx) > >>> (syntax-parse stx > >>> [(_ v) > >>> #`(set! #,(syntax-local-introduce funny) v)])) > >>> > >>> (make-funny-set! 2) > >>> (funny-set! 3) > >>> (funny-ref) > >>> > >>> This program works as I expect, evaluating to 3. However if I change > (funny-set! 3) to (void (funny-set! 3)) I get the error: "set!: unbound > identifier in module in: g1" > >>> > >>> I do not get this error if I change (funny-ref) to (void (funny-ref)). > >>> > >>> If I look at the expansion of the (void (funny-set! 3)) program in > drracket's macro stepper the the g1 in (define g1 2) and the g1 in (void > (set! g1 3)) have the > > >
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