<div dir="ltr">Oh yea,<div><br></div><div style>An example of use:</div><div style>Define a layout of field types and lengths, then when creating a text line parser you give it the fields you want, and you get a (: Orderline-parser (String -> Orderline)) where Orderline is an implicitly created struct:</div> <div style><br></div><div style><br></div><div style><div>(define-fixed-layout Orderline-layout</div><div> (order C 11)</div><div> (order-sub C 5)</div><div> (line C 7)</div><div> (account C 10)</div><div> (address-seq C 7)</div> <div> (create-date D 10)</div><div> (order-type S 1)</div><div> (location C 4)</div><div> (dept C 2)</div><div> (class C 3)</div><div> (sku C 20)</div><div> (vendor C 2)</div><div> (entered-sku C 20)</div><div> (source C 2)</div> <div> (list-price N 9)</div><div> (sku-price N 10)</div><div> (cost N 10)</div><div> (uom C 2)</div><div> (pack-qty I 7)</div><div> (order-qty I 7)</div><div> (ship-qty I 7)</div><div> (misc-charge S 1)</div><div> (sub-flag S 1)</div><div> (contract-pp C 9)</div><div> (contract-pp-seq C 5)</div><div> (commission N 9)</div><div> (contract-addendum C 1))</div><div><br></div><div>(define-static-parser-for-layout (Orderline-parser Orderline-layout)</div> <div> (order sku create-date order-type dept class))</div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Jan 16, 2013 at 10:56 AM, Ray Racine <span dir="ltr"><<a href="mailto:ray.racine@gmail.com" target="_blank">ray.racine@gmail.com</a>></span> wrote:<br> <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">On the topic of "state" propagation across macros by extending the expansion environment (or whatever the terminology would be). I have an example where a macro is used to define a layout of a fixed offset text file. Then a second macro expands into a mini field parser based on the layout definition. Frankly my first macro beyond a basic syntax-rules sort, so it's rough and assuredly less than optimal. It can be found here.<div> <br></div><div><a href="https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/layout-types.rkt" target="_blank">https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/layout-types.rkt</a><br></div><div><a href="https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/layout.rkt" target="_blank">https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/layout.rkt</a><br> </div><div><a href="https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/parser.rkt" target="_blank">https://github.com/RayRacine/racketlib/blob/mapred/RpR/format/parser.rkt</a><br></div></div><div class="HOEnZb"> <div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote"> On Wed, Jan 16, 2013 at 10:33 AM, Danny Yoo <span dir="ltr"><<a href="mailto:dyoo@hashcollision.org" target="_blank">dyoo@hashcollision.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> <div>On Wed, Jan 16, 2013 at 7:24 AM, Tim Brown <<a href="mailto:tim.brown@cityc.co.uk" target="_blank">tim.brown@cityc.co.uk</a>> wrote:<br> > Folks,<br> ><br> > I would like to write a module that uses a macro to transform "define"s<br> > and accumulate a value based on those transformations.<br> ><br> > In a fairly simple way, I want to do something like the below. However, it<br> > seems the module-begin is being transformed before the my-defines. How do<br> > I get counter to be incremented before I need it?<br> <br> </div>The transformation happens top-down, so you'll see that the body of<br> your program expands in the following steps (to a first<br> approximation):<br> <br> <br> (#%your-module-begin (your-define woo 2))<br> <br> ==><br> <br> (#%racket-module-begin (your-define woo 2)<br> (define defines-counter 0)<br> (provide defines-counter))<br> <br> ==><br> <br> (#%racket-module-begin (racket-define woo 2)<br> (define defines-counter 0)<br> (provide defines-counter))<br> <br> <br> One possible workaround is the the following: add one level of<br> indirection in installing the value of the defines-counter. You can<br> do something like:<br> <br> (define-syntax (get-counter stx)<br> (datum->syntax stx counter))<br> <br> and use (get-counter) in place of #,counter in your module-begin.<br> This way, we delays the lookup of counter until the macro expander<br> finally reaches that expression, and by that time, it should have hit<br> all the defines already.<br> <br> <br> If you need to control the order of expansion more explicitly, you may<br> need to look into local-expand:<br> <br> <a href="http://docs.racket-lang.org/reference/stxtrans.html#(def._((quote._~23~25kernel)._local-expand))" target="_blank">http://docs.racket-lang.org/reference/stxtrans.html#(def._((quote._~23~25kernel)._local-expand))</a><br> <br> ----<br> <br> Modified code below:<br> <br> #lang racket/base<br> <div><br> (provide (except-out (all-from-out racket) #%module-begin define)<br> (rename-out (module-begin #%module-begin) (my-define define)))<br> <br> </div> (require (for-syntax racket/base<br> <div> syntax/parse))<br> (define-for-syntax counter 0)<br> <br> (define-syntax (my-define stx)<br> (syntax-parse<br> stx<br> [(_ i v) (set! counter (add1 counter)) #`(define i v)]<br> [(_ (i args ...) v ...+) (set! counter (add1 counter))<br> #`(define (i args ...) v ...)]))<br> <br> </div> (define-syntax (get-counter stx )<br> (datum->syntax stx counter))<br> <div><br> (define-syntax (module-begin stx)<br> (syntax-parse<br> stx<br> [(_ expr ...)<br> #`(#%module-begin expr ...<br> </div> (define defines-count (get-counter))<br> (provide defines-count))]))<br> <div><div>____________________<br> Racket Users list:<br> <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a><br> </div></div></blockquote></div><br></div> </div></div></blockquote></div><br></div>