[plt-scheme] Evaluating code in namespace of calling module

At Thu, 17 Mar 2005 09:30:38 +0100, Erich Rast wrote:
> However, I'm still curious whether there generally is some way to 
> evaluate code in one module as if it was evaluated in the calling 
> module---something like a macro that expands in the namespace of the 
> module it is used in, not in the module in which it is defined.

Like this?

 (module m mzscheme
   ;; Defines `minus1' to use the `-' in the environment
   ;; of the macro use:
   (define-syntax (minus1 stx)
     (syntax-case stx ()
       [(_ v) (with-syntax ([- (datum->syntax-object stx '-)]) 
                #'(- v 1))]))
   (provide minus1))

 (module n mzscheme
   (require m)
   (define (f -)
     (minus1 10))
   (provide f))

 (require n)
 (f +) ; => 11

> (Of course, this would somewhat defeat the whole purpose of modules
> and might also raise security issues.)

For various reasons, you always have a trust a module if you use a
macro that it provides. But a macro-providing module doesn't have to
trust its users.

Matthew