LinuxQuestions.org - Common Lisp: CLOS and with-slots

Hi. I'm a newbie to Common Lisp, and I'm using GNU Clisp. In working through a tutorial on CLOS, I set up a simple class and an instance:

Code:

(defclass rect () (l w))



(setf rect-a (make-instance 'rect))

One of the exercises challenged me to create a setter function, using with-slots. So, I wrote this:

Code:

(defun set-rect-values (rect l w)

  (with-slots ((l-old l) (w-old w))

              rect

              (setf 'l-old l)

              (setf 'w-old w)))

But I get this error when trying to use it:

Code:

> (set-rect-values rect-a 2 2)



*** - SLOT-VALUE: The slot L of #<RECT #x0003348AC408> has no value

Please advise.