> On Apr 27, 2016, at 2:38 PM, Matthew Butterick <m...@mbtype.com> wrote:
>
> For the first time, I used `syntax-local-introduce` to solve a problem. But I
> don't understand whether I'm using it correctly or just relying on a spooky
> side effect. (I did the read the docs, but I'm looking for a higher-level
> "why this exists and what its idiomatic use is")
>
> The problem I had was how to make two macros cooperate: one macro defines a
> variable, and another macro uses it. One can re-introduce the variable
> unhygienically each time. Or, apparently, you can use
> `syntax-local-introduce` once at the moment of binding. (Sample code below
> shows these two options.)
>
> I understand that the two options are not the same in terms of the use site.
> Introducing a binding unhygienically makes it available to other code at the
> use site as if it had been defined there; `syntax-local-introduce` does not.
>
> I suppose I'm wondering if a) this "cooperation" among macros I'm enjoying is
> simply a lucky side effect of both being in the same module
Well, it's not even that. This doesn't work:
(let ()
(define-sli-foo)
(let ()
(invoke-sli-foo)))
I had expected that changing invoke-sli-foo to this would help:
(define-simple-macro (invoke-sli-foo)
#:with sli-foo (syntax-local-introduce #'foo)
(slo-foo))
But it didn't. Hm. Although this definition of invoke-sli-foo works with
define-sli-foo: (which uses syntax-local-introduce)
(define-simple-macro (invoke-sli-foo)
#:with sli-foo (datum->syntax this-syntax 'foo)
(sli-foo))
And it works with with and without that let.
I'm not sure why (datum->syntax this-syntax 'foo) would work and
(syntax-local-introduce #'foo) wouldn't.
Alex Knauth
> and thus sharing a 'local' environment into which the identifier is being
> 'introduced', and if so b) there's a better way to go about this than
> `syntax-local-introduce`.
>
>
>
> <Screen Shot 2016-04-27 at 11.30.20 AM.gif>
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> #lang racket
> (provide (all-defined-out))
>
> (define-syntax (define-sli-foo stx)
> (syntax-case stx ()
> [(_)
> (with-syntax ([sli-foo (syntax-local-introduce #'foo)])
> #`(begin
> (define (sli-foo) 'sli-worked)))]))
>
> (define-syntax-rule (invoke-sli-foo)
> (foo))
>
> (define-syntax (define-ds-foo stx)
> (syntax-case stx ()
> [(_)
> (with-syntax ([ds-foo (datum->syntax stx 'foo)])
> #`(begin
> (define (ds-foo) 'ds-worked)))]))
>
> (define-syntax (invoke-ds-foo stx)
> (syntax-case stx ()
> [(_)
> (with-syntax ([ds-foo (datum->syntax stx 'foo)])
> #'(ds-foo))]))
>
>
> (module+ test
> (require rackunit)
> (check-equal?
> (let ()
> (define-sli-foo)
> (invoke-sli-foo)) 'sli-worked)
> (check-equal?
> (let ()
> (define-ds-foo)
> (invoke-ds-foo)) 'ds-worked))
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