[plt-scheme] Foreign Function Interface...

I have been working with the Foreign Function
Interface  to ImageMagick.  It appears that c-pointer
cannot be passed to a scheme function.  It that
correct?  Is it possible to create a c-pointer
parameter so that it may  be passed?

Am I even asking the right questions? :-)

Thanks for the help.

Sincerely,

Dan

(define (average r g b)
  (/ (+ r g b) 3))

(define (wand->number wand)
    (average
          (car  (test (MagickGetImageChannelMean wand
'RedChannel)))
          (car  (test (MagickGetImageChannelMean wand
'GreenChannel)))
          (car  (test (MagickGetImageChannelMean wand
'BlueChannel)))))

(define w (test (MagickReadImage "test.jpg")))
> w
#<cpointer:MagickWand>
>  (wand->number w)
. .
../../../../../../usr/local/plt/collects/ffi/magick.ss::16917:
MagickWand: (CoderError) Application transferred too
few scanlines `test.jpg'
> 


 
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