The macro application (foo 3) expands into
#'(begin
(_foo n0)
(foo n ...))
The expansion of (_foo n0) then defines foo3, but
the scope will only include the piece of code above.
To make definitions made by sub-macros available
at the original macro application site, you can use
syntax-local-introduce:
(define-syntax (foo stx)
(syntax-case stx ()
[(_) #'(begin)]
[(_ n0 n ...) (syntax-local-introduce
#'(begin
(_foo n0)
(foo n ...)))]))
Note that I changed the pattern variable to _ in order not to
show shadow the binding of foo.
This might not be strictly necessary here, but if you do
run into such a case, it will be hard to spot the error.
/Jens Axel
2016-05-20 23:36 GMT+02:00 Kevin Forchione <lyss...@gmail.com>:
> Hi guys,
> I’ve been interested in having a macro build a series of defines. So I
> decided to start small, trying to get to a macro that would do something
> like the following to begin with:
>
> >(foo 3)
> (define foo1 1)
> (define foo2 2)
> (define foo3 3)
>
> I start with a macro that appears to do a single define:
>
> (require (for-syntax racket/syntax))
>
> (define-syntax (_foo stx)
> (syntax-case stx ()
> [(_ n) (with-syntax ([id (format-id stx "foo~a" (syntax-e #'n))])
> #'(define id n))]))
>
>
> And this appears to work for (_foo 3) for instance.
>
> Then I create a macro that calls this macro:
>
> (define-syntax (foo stx)
> (syntax-case stx ()
> [(foo n0) #'(_foo n0)]
> [(foo n0 n ...) #'(begin
> (_foo n0)
> (foo n ...))]))
>
> thinking that I could do something like (foo 1 2 3) as an intermediary
> step. So I test it with (foo 3) for instance, expecting it to define foo3
> and the macro debugger tells me that it’s created (define foo3 3), but that
> foo3 is bound as foo3.0, which is a mystery to me as I thought building the
> id using with-syntax and format-id would have sorted the binding for this.
>
> Looks like I’m at a learning moment…. any explanation why executing (_foo
> 3) at the real works and (foo 3) does not?
>
> Thanks!
> -Kevin
>
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--
Jens Axel Søgaard
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