[plt-scheme] Inspectors in mzscheme

Lo, on Thursday, January 22, Felix Klock's PLT scheme proxy did write:

> Also, as I discovered today, this approach will not work for code that 
> has macros that expand into define-struct definitions.  

... like the define-tokens form from Scott's parser-tools collection.

> You have to do something more clever for that; if you need that, let
> us know and Richard and Ryan will post the solution that they came up
> with to the list.

  (define-syntax with-public-inspector
    (lambda (stx)
      (syntax-case stx ()
        [(kw defns ...)
         (with-syntax ([old-inspector (datum->syntax-object #'kw (gensym))])
           #'(begin 
               (define old-inspector (current-inspector))
               (current-inspector (make-inspector))
               defns ...
               (current-inspector old-inspector)))])))

Use as follows:

(with-public-inspector
  (define-struct loc (x y))
  (define-struct foo (bar baz)))

The whole (datum->syntax-object #'kw (gensym)) garbage is necessary when
you define the macro in one module but use it in another; you have to
break hygiene and then patch it back the old-fashioned way, or define
complains.  I personally think this is a really awful hack, so if anyone
has any alternatives, please let me know.

Richard