Thanks for everyone's advice. I think I will take it and find another solution. Thanks! -- Chad Albers
On Wed, Aug 28, 2013 at 12:00 AM, Gustavo Massaccesi <gust...@oma.org.ar> wrote: > Generally these kinds of macros are not a good idea, because it's > difficult to combine them with other macros. It's probably better to > use a syntax-parameter like the suggestion in the other message. > > The problem in your macro is that with syntax-case can't search bar > when it's nested at any deep level. It only looks for it in a specific > position. To search at any level of parenthesis nesting you should > create an auxiliary function that analyzes recursively the expression, > and then reconstruct the new version. > > ;---------------- > #lang racket > > (define-syntax (define-foo stx) > (define (replace-bar stx) > (syntax-case stx (bar) > [(bar . body) > (syntax (+ 3 . body))] > [(proc other . rest) > (with-syntax ([new-other (replace-bar #'other)]) > (syntax (proc new-other . rest)))])) > (syntax-case stx () > [(_ (name param) body) > (with-syntax ([new-body (replace-bar #'body)]) > (syntax (define (name param) new-body)))])) > > (define-foo (foof env) > (displayln (bar (+ 1 2)))) > > (foof #f) ;==>6 > > (define-foo (foog env) > (displayln (+ (bar (- 1 (+ 1 2))) 15))) > > (foog #f) ;==>16 > ;---------------- > > This only search for bar in the first argument branch. So > (define-foo (foog env) (+ (bar 1) 2)) ; works but > (define-foo (foog env) (+ 2 (bar 1))) ; don't. > It's not difficult to extend the idea to handle this kind of cases. > > If you want to do more complex transformations with the code between > define-foo and bar (body1 in your code), then you will need a more > complex macro. > > Gustavo > > > On Tue, Aug 27, 2013 at 5:33 AM, Chad Albers <calb...@neomantic.com> wrote: >> I'm still trying to grok macros - which are amazing, but hard. I'd like to >> know if it is possible capture part of the following expression >> >> (display (+ 2 (bar (+ 1 2)))) >> >> if "bar" is a literal in the macro, I would like to capture body0 as (+ 1 2) >> and body1 as (display (+ 2 ...)). >> >> This is a totally artificial example. >> >> Here's what I have: >> >> (define-syntax (define-foo stx) >> (syntax-case stx (bar) >> ([_ (name param) (body1 (bar . body0))] >> (syntax (define (name param) >> (body1 (+ 3 . body0))))))) >> >> (define-foo (foof env) >> (display (bar (+ 1 2)))) >> >> This works...and expands to. >> >> (define (foof env) >> (display (+ 3 (- 1 (+ 1 2))))) >> >> (Note that -1 has been substitute for the "bar" literal"). >> >> This expression fails with "bad syntax" >> >> (define-foo (foog env) >> (display (+3 (bar (- 1 (+ 1 2)))))) >> >> I don't seem be to able to capture (display (+3 )) as separate from (bar (-1 >> (+ 1 2))) >> >> Is this possible to capture? >> >> Thanks for any help and insights into macros >> Chad >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> ____________________ Racket Users list: http://lists.racket-lang.org/users
