これはうまくいくようです:
(defvar my-hex-idle-timer nil)
(defun my-hex-idle-status-on ()
(interactive)
(when (timerp my-hex-idle-timer)
(cancel-timer my-hex-idle-timer))
(setq my-hex-idle-timer (run-with-idle-timer 1 t 'my-hex-idle-status)))
(defun my-hex-idle-status-off ()
(interactive)
(when (timerp my-hex-idle-timer)
(cancel-timer my-hex-idle-timer)
(setq my-hex-idle-timer nil)))
(defun int-to-binary-string (i)
"convert an integer into it's binary representation in string format
By Trey Jackson, from https://stackoverflow.com/a/20577329/."
(let ((res ""))
(while (not (= i 0))
(setq res (concat (if (= 1 (logand i 1)) "1" "0") res))
(setq i (lsh i -1)))
(if (string= res "")
(setq res "0"))
res))
(defun my-hex-idle-status ()
(let ((word (thing-at-point 'word)))
(when (string-prefix-p "0x" word)
(let ((num (ignore-errors (string-to-number (substring word 2) 16))))
(message "In binary: %s" (int-to-binary-string num))))))
入力M-x my-hex-idle-status-on
してオンにします。
前述のように、Trey Jacksonに感謝しint-to-binary-string
ます。