[racket] macros whose meaning is dependent on context?

From: John Clements (clements at brinckerhoff.org)
Date: Tue Oct 16 18:18:42 EDT 2012

This seems like a straightforward question; apologies if I just haven't dug deep enough to find the answer.

I want to define a macro whose meaning depends on its context. More specifically, I want to define an "outer" macro that gives a particular meaning to the "inner" macro. 

I can see how to get the job done in a yucky way, using mutation:

#lang racket

;; I want m's meaning to depend on its context
(define-syntax (m stx)
  #`#,(unbox the-box))

(define-syntax (deeper stx)
  (syntax-case stx ()
    [(_ arg)
     ;; I want to change the meaning of m, here:
     (set-box! the-box 16)
     #'arg]))

;; yucky mutation-based way to get the job done
(define-for-syntax the-box (box 13))


(deeper (m 134))


… but it seems like there must be a simple way for the outer binding to say "whatever meaning the inner macro wants it to have".

Don't tell me, it's define-for-inner-syntax/local-expand. I just made that up, so I hope it's wrong :).

John

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4800 bytes
Desc: not available
URL: <http://lists.racket-lang.org/users/archive/attachments/20121016/8cd3eb85/attachment.p7s>

Posted on the users mailing list.