[racket] Question on (quote var) in macros

And that did it! Thanks so much ^_^


On Tue, Jan 15, 2013 at 9:27 PM, Jon Rafkind <rafkind at cs.utah.edu> wrote:

>  Untested but I think this will work
>
>
> (define-syntax (my-macro stx)
>   (syntax-case stx ()
>     [(_ (id1 id2 ...) body ...)
>      #'(lambda (expr)
>            (match expr [(list 'id1 id2 ...) body ...]))]))
>
>
> On 01/15/2013 10:22 PM, Paul Meier wrote:
>
> Hi friends,
>
>  I'm working on a macro that expands into a match statement. It looks
> something like
>
>  (define-syntax (my-macro stx)
>    (syntax-case stx ()
>     [(_ (id1 id2 ...) body ...)
>      (with-syntax ([match-pattern
>                           (datum->syntax stx (cons 'list (syntax->datum
> #'(id1 id2 ...))))])
>      #'(lambda (expr)
>          (match expr
>             [match-pattern body ...])))))
>
>  So in effect, it expands
>
>  (my-macro (push i) (printf "~v" i)
>
>  into
>
>  (lambda (expr)
>   (match expr
>     [(list push i) (printf "~v" i)]))
>
>  Here is the problem: I'd like the first entry of the match list to be
> quoted (e.g. 'push) rather than unquoted, as it is above, since 'match'
> will interpret this as a free variable, meaning
>
>  ((my-macro (push i) i) '(dont-push 45)) will evaluate to 45, rather than
> fail to match (the desired behavior).
>
>  Unfortunately, trusty (quote (syntax->datum stx id1)) and or any
> variation thereof will do what it's supposed to: quote whatever expression
> will evaluate into whatever I want quoted.
>
>  I could just write the quotes into the expressions using the macro, a la
> (my-macro ('push i) ...), but Shirly there's a way around this?
>
> Any help would be appreciated. Thanks for your time; I'm loving my
> explorations into Racket ^_^
>
>  -Paul
>
>
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