(use coops)

(define-class <window> (<standard-object>)
  ((size reader: size initform: '#(800 600))))

(define-method (initialize-instance
                after:
                ((obj <window>)))
  (unless (vector? (slot-value obj 'size))
    (abort "Size must be a vector")))

#|
Error: during expansion of (lambda112 ...) - in `lambda' - lambda-list expected: (lambda (((obj <window>))) (unless (vector? (slot-value obj (quote size))) (abort "Size must be a vector")))

	Call history:

	<syntax>	  (define-method (initialize-instance after: ((obj <window>))) (unless (vector? (slot-value obj (quote......
	<syntax>	  (##core#begin (ensure-generic-procedure107 () initialize-instance) ((slot-value108 initialize-instan......
	<syntax>	  (ensure-generic-procedure107 () initialize-instance)
	<syntax>	  (void113)
	<syntax>	  ((slot-value108 initialize-instance (quote109 add-new-after-method110)) (list111) (lambda112 (((obj ......
	<syntax>	  (slot-value108 initialize-instance (quote109 add-new-after-method110))
	<syntax>	  (quote109 add-new-after-method110)
	<syntax>	  (##core#quote add-new-after-method110)
	<syntax>	  (list111)
	<syntax>	  (lambda112 (((obj <window>))) (unless (vector? (slot-value obj (quote size))) (abort "Size must be a...	<--
|#