[plt-scheme] defmacro problem in Swindle?

On Jun  2, michael rice wrote:
> Don't know what's going on here. Scheme code (206p1
> w/Swindle) just below doesn't work. Similar Common
> Lisp code further down works fine. Any ideas?
> 
> (define sum 
>   (lambda (nums)
>     (if (null? nums)
>         0
>         `(+ ,(car nums) ,(sum (cdr nums))))))
> 
> (defmacro (mac1 nums)
>   `(+ 4 ,(sum nums)))
> 
> > (sum '(1 2 3))
> (+ 1 (+ 2 (+ 3 0)))
> > (mac1 (1 2 3))
> . reference to undefined identifier: sum

You're running into the phase separation problem: in MzScheme macros
work in their own level, so they cannot use any run-time values.  Se
the MzScheme documentation.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!