Question

Suppose I have a class called board:

(defclass board ()
 ((blocker    :accessor blocker    :initarg :blocker    :initform  0))

According to this book I can define a custom setf for blocker by:

(defmethod (setf blocker) (new-blocker (b board))
  (setf (slot-value b 'blocker) new-blocker))

However, steel bank common lisp will say function not defined, even though I have evaluated it. Does anyone know what’s wrong here?

Answer 1

That looks correct. Note that you are redefining the already existing setf method that you created by specifying :accessor blocker. SBCL will give you a style-warning about that.

Your mistake is somewhere else. Are you in a different package, perhaps? Try to show the steps you have taken in your IDE to compile and load those forms, and to attempt to run that method invocation.