stumpwm : grenumber

;; Extension code for the Stump Window Manager
;; https://stumpwm.github.io/

(defcommand grenumber (new-number &optional (screen (current-screen))) ((:number "Number: "))
  "Change the current group's number to the specified number. If another group
is using the number, then the groups swap numbers. Defaults to current screen."
  (let* ((this-group (current-group screen))
         (current-number (group-number this-group))
         (other-group (find-if
                       #'(lambda (grp) (= (group-number grp) new-number))
                       (screen-groups screen))))
    ;; If another group has the new number, change it to the number of the
    ;; current group.
    (when other-group
      (setf (group-number other-group) current-number))
    ;; Now, set the current group to the new number.
    (setf (group-number this-group) new-number)))