async-run

;; async-run function
(defparameter *async-shell* (uiop:launch-program "bash" :input :stream :output :stream))
(defun async-run (command)
  (write-line command (uiop:process-info-input *async-shell*))
  (force-output (uiop:process-info-input *async-shell*))
  (let* ((output-string (read-line (uiop:process-info-output *async-shell*)))
         (stream (uiop:process-info-output *async-shell*)))
    (if (listen stream)
        (loop while (listen stream)
              do (setf output-string (concatenate 'string
                                                  output-string
                                                  '(#\Newline)
                                                  (read-line stream)))))
    output-string))


;; my keyboard layout function
(defun linarcx-keyboard-layout (ml)
  (declare (ignore ml))
  (let ((cmd "xkb-switch -p"))
    (string-trim '(#\Newline) (async-run cmd))))
(add-screen-mode-line-formatter #\L #'linarcx-keyboard-layout)