Injecting variables into closures.

["Kjetil S. Matheussen" <k.s.matheussen@notam02.no>]

Hi,

I need (well) to inject variables into closures, and have
come up with the following macro to do so:

(define-macro (inject-variable name value)
   (define env (gensym))
   (define closure (gensym))
   (define vars (gensym))
   (define secondname (gensym))
   (define secondval (gensym))
   (define first-env (gensym))
   `((procedure->macro (lambda (,(gensym) ,env)
                         (cond ((null? (cdr ,env))
                                (let ((,closure (car ,env)))
                                  (set-car! ,env (cons ',name ,value))
                                  (set-cdr! ,env (list ,closure))))
                               ((null? (null? (cdr (car ,env))))
                                (let* ((,vars (car ,env))
                                       (,secondname (car vars))
                                       (,secondval (cdr vars)))
                                  (set-car! ,env
                                            (list (list ',name firstname)
                                                  ,value ,secondval))))
                               (else
                                (let ((,first-env (car ,env)))
                                  (set-cdr! ,first-env
                                            (cons ,value (cdr ,first-env)))
                                  (set-car! ,first-env
                                            (cons ',name (car ,first-env)))
                                  (set-car! ,env ,first-env))))))))


(let ()
   (display (defined? 'gakk))
   (inject-variable gakk 90)
   gakk)
=> #f90


Now I wonder, is this safe and portable? Or are there
other and better ways to do this?

Thanks for any answers.

Kjetil.



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