[racket] local-expand 'module-begin

From: Tero Hasu (tero.hasu at ii.uib.no)
Date: Wed Sep 11 13:50:06 EDT 2013

Hello list,

I'm trying to use local-expand within a custom #%module-begin in order 
to inspect the expansion and its side effects, but this does not appear 
to work in all cases. Am I using local-expand correctly? Are there 
restrictions to its ability to handle a module body?

To demonstrate. This code runs OK

#lang racket
(require (for-meta 2 racket/base))
(define x 0)
   (define x 2)))

but if I instead try to local-expand the same module body with

#lang racket

(module le-lang racket
          (except-out (all-from-out racket) #%module-begin)
          (rename-out [module-begin #%module-begin]))

         (define-syntax (module-begin stx)
           (syntax-case stx ()
             ((_ . bs)
               #'(#%module-begin . bs)
               'module-begin null)))))

(module le-module (submod ".." le-lang)
         (require (for-meta 2 racket/base))
         (define x 0)
           (define x 2))))

then I get the error

module: duplicate definition for identifier
   at: x
   in: (define-values (x) (quote 2))

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