[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)

;; 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 :).


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