Re: callbacks in slot writer

  (defun sans (plist &rest keys)
    "Returns PLIST with keyword arguments from KEYS removed."
    ;; stolen from Usenet posting <3247672165664225@naggum.no> by
    ;; Erik Naggum
    (let ((sans ()))
      (loop
        (let ((tail (nth-value 2 (get-properties plist keys))))
          ;; this is how it ends
          (unless tail
            (return (nreconc sans plist)))
          ;; copy all the unmatched keys
          (loop until (eq plist tail) do
                (push (pop plist) sans)
                (push (pop plist) sans))
          ;; skip the matched key
          (setq plist (cddr plist))))))