I have grasp the problem i have expanded the file and narrow the region
concerned and get :
(define-values
(struct:person person1 person? person-name person-nickname) ;
define here
(let-values (((struct: make- ? -ref -set!)
(let-values ()
(let-values ()
(#%app
make-struct-type
'person
'#f
'2
'0
'#f
(#%app list (#%app cons prop:insiders
person-name)) ; accessed here
(#%app current-inspector)
'#f
'(0 1)
'#f
'person)))))
(#%app
values
struct:
make-
?
(#%app make-struct-field-accessor -ref '0 'name)
(#%app make-struct-field-accessor -ref '1 'nickname))))
We see that person-name is accessed before it definition.
So i rewrite the macro :
(define-syntax (struct-abc stx)
(syntax-case stx ()
[(_ sname (name args ...) props ...)
(with-syntax ([sname-name (format-id #'sname "~a-~a" #'sname
#'name)])
#`(struct sname (name args ...) props ...
#:property prop:insiders sname-name))]))
to :
(define-syntax (struct-abc stx)
(syntax-case stx ()
[(_ sname (name args ...) props ...)
(with-syntax ([sname-name (format-id #'sname "~a-~a" #'sname
#'name)])
#`(struct sname (name args ...) props ...
#:property prop:insiders (lambda () sname-name)))]))
I don't know if there is another way to do this sort of recursive
binding without a lambda.
Thanks for you reply it helps me point out the problem.
On 03/09/2013 18:36, J. Ian Johnson wrote:
The struct form generates names unhygienically, but predictably. You will have
to have a handle on both the struct name and field name to produce an
identifier equal to the generated field accessor.
In your case, if you can commit to name always being given first (there are
ways around this that involve more parsing), then the following will allow you
to write your macro correctly:
(require (for-syntax racket/syntax))
(define-syntax (struct-abc stx)
(syntax-case stx ()
[(_ sname (name args ...) props ...)
(with-syntax ([sname-name (format-id #'sname "~a-~a" #'sname #'name)])
#`(begin
(+ 1 1)
(struct sname (name args ...) props ...
#:property prop:insiders sname-name)))]))
-Ian
----- Original Message -----
From: "antoine" <[email protected]>
To: [email protected]
Sent: Tuesday, September 3, 2013 12:23:17 PM GMT -05:00 US/Canada Eastern
Subject: [racket] Binding undefined with a macro
Hello,
With this macro:
(define-syntax (struct-abc stx)
(syntax-case stx ()
[(_ name (args ...) props ...)
#`(begin
(+ 1 1)
(struct name (args ...) props ...
#:property prop:insiders person-name))]))
(define-values (prop:insiders insiders? insiders-ref)
(make-struct-type-property 'insider))
When i do :
(struct-abc person (name nickname))
I get :
person-name: undefined;
cannot reference an identifier before its definition
But i know that person-name is defined the problem come from 'begin' in
the macro, if i rewrite like this :
(define-syntax (struct-abc stx)
(syntax-case stx ()
[(_ name (args ...) props ...)
#`(struct name (args ...) props ...
#:property prop:insiders person-name)]))
It works as expected.
So my question are:
Could you explain (point out) me why the person-name is unknown at this
point?
And how can i change the begin with something like '#,@'?
Thank you.
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