[plt-scheme] undefined identifiers after generating (require (all-except)) statement

From: Danny Yoo (dyoo at hkn.eecs.berkeley.edu)
Date: Tue Jul 25 22:23:47 EDT 2006

On Tue, 25 Jul 2006, Kimberley Burchett wrote:

> I'm have a macro that generates (require (all-except)) statements, but
> they don't seem to actually import any identifiers.  That is, I get
> "unbound variable in module" errors when referencing identifiers that
> should have been imported.

Hi Kimberley,

Those identifiers should have the same color as the input stx. I think 
what's going on is that REQUIRE is trying to use the whole syntax object 
to introduce the identifiers non-hygienically, but that's not working out 
because the syntax object here:

>     [(_ (all-except mod id ...))
>      #`(require (all-except mod id ...))]

has a different color than the input stx, since that syntax object is 
freshly created by the macro.  If I make a change to explicitely color 
that syntax, using a combination of SYNTAX-OBJECT->DATUM and 
DATUM->SYNTAX-OBJECT, then things appear to work out:

(module m2 mzscheme
  (define-syntax (my-require stx)
    (syntax-case stx (all-except)
      [(_ (all-except mod id ...))
         #'(require (all-except mod id ...))))]
      [(_ mod)  ;; require entire module
       #'(require mod)]))
  (my-require (all-except m1 foo))
  (display bar))

This does look a little weird to me though.  I have to admit that I'm 
still newbie enough that I'm not quite sure if this is the right way to 
approach the macro.

Best of wishes!

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