foo should be in scope at this macro's definition, otherwise you'll have to
unhygienically introduce it.
(define-syntax my-macro-aux
(syntax-rules ()
[(_ (exprs ...) v) (let ([v foo]) exprs ...)]
[(_ (exprs ...) v k e rest ...) (my-macro-aux (exprs ... [k e v]) v rest
...)]
[(_ any ...) (raise-syntax-error #f "Expected even number of inputs to
my-macro")]))
(define-syntax my-macro
(syntax-rules ()
[(_ kv ...) (my-macro-aux () x kv ...)]))
As for #2, I have no idea why you would want to do that, seeing as those
identifiers would be unbound and thus cause a syntax error. But here's a way
anyhow.
(define-syntax my-macro-zip
(syntax-rules ()
[(_ () () x (exprs ...)) (let ([x foo]) exprs ...)]
[(_ (k ks ...) (e es ...) x (exprs ...)) (my-macro-zip (ks ...) (es ...) x
((k e x) exprs ...))]))
(define-syntax (my-macro2 stx)
(syntax-case stx ()
[(_ ks es)
(with-syntax ([freshks (generate-temporaries #'(ks ...))])
#'(my-macro-zip freshks es x ())]
[(_ (ks ...) (es ...) k e rest ...) (syntax/loc stx (my-macro2-aux (k ks
...) (e es ...) rest ...))]
[(_ any ...) (raise-syntax-error #f "Expected even number of inputs to
my-macro")]))
(define-syntax my-macro2
(syntax-rules ()
[(_ kv ...) (my-macro2-aux () () kv ...)]))
-Ian
----- Original Message -----
From: "Răzvan Rotaru" <razvan.rot...@gmail.com>
To: users@racket-lang.org
Sent: Sunday, December 4, 2011 10:41:48 AM GMT -05:00 US/Canada Eastern
Subject: [racket] beginner question about macros
Hi,
I currently learning scheme macros, and trying to figure out how to do
two particulars things:
1/
(my-macro a 1 b 2 c 3)
should generate:
(let ((x foo))
(a 1 x)
(b 2 x)
(c 3 x))
The order is important.
2/
I need to transform somehow the symbols:
(my-macro a 1 b 2 c 3)
should generate:
(let ((x foo))
(new-a 1 x)
(second-b 2 x)
(another-c 3 x))
I'd like to ask for some hints about how to achieve these two goals.
I'm currently not able to decide whether to use syntax-rules or
syntax-case.
Thanks,
Razvan
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