[racket] Macro and define question

Dear Stephen,

Works fine, and thanks for the explanation too.

Kind regards,



Tim

On 3 Sep 2013, at 05:32, Stephen Chang <stchang at ccs.neu.edu> wrote:

> If you change datum->syntax's first argument to #'argument, then it
> does what you want.
> 
> In general if you want the identifiers created by datum->syntax to be
> visible to the user, you need to supply a piece of syntax that you got
> from the user. That's why calling "long" directly works but not if
> it's called via "short".
> 
> 
> 
> On Mon, Sep 2, 2013 at 8:08 PM, Tim Jervis <tim at timjervis.com> wrote:
>> Hello,
>> 
>> I have been trying to create a macro to make some arbitrary definitions,
>> with success. The following defines a structure (posn) and a value (val):
>> 
>> (define-syntax (long syntax-object)
>>  (syntax-case syntax-object ()
>>    [(_ argument)
>>     (let ([make-id (lambda (x) (datum->syntax syntax-object x))])
>>       (with-syntax ([posn (make-id 'posn)]
>>                     [val-s (make-id 'val)])
>>         #'(begin (printf "\tfrom the \"long\" macro, defining a structure
>> and a value\n")
>>                  (struct posn (x y))
>>                  (define val-s 12))))]))
>> 
>> 
>> So:
>> 
>> (long argument)
>> 
>> 
>> defines posn and val.
>> 
>> However, if I happen to use this macro indirectly, the definitions aren't
>> visible. For example, if I define:
>> 
>> (define-syntax (short syntax-object)
>>  (syntax-case syntax-object ()
>>    [(_ argument)
>>     #'(long argument)]))
>> 
>> 
>> and then call
>> 
>> (short argument)
>> 
>> 
>> posn and val are not defined, even though the text in the printf buried in
>> the first macro does appear.
>> 
>> I tried this in Dr Racket.
>> 
>> Can anyone tell me where I'm going wrong?
>> 
>> Kind regards,
>> 
>> 
>> 
>> Tim
>> 
>> 
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>>  http://lists.racket-lang.org/users
>> 



Tim Jervis

http://timjervis.com/