(use coops)
(use coops-primitive-objects)

(define-class <color> ()
  ((red 0)
   (green 0)
   (blue 0)))

(define-method (set-color (color <color>) (red <integer>) (green <integer>) (blue <integer>))
  (set! (slot-value color 'red) red)
  (set! (slot-value color 'green) green)
  (set! (slot-value color 'blue) blue))

(define-method (print-object (color <color>))
  (fprintf port "#<'<color>', ~X ~X ~X>" (slot-value color 'red) (slot-value color 'green) (slot-value color 'blue)))


; Result:

CSI> (define clr (make <color>))
#<unspecified>
CSI> clr
#<no print-method defined for: #<coops instance of `<color>'>>
CSI>