I have re-defined blink-cursor-timer-function for the cursor to change colour. How can I modify this without re-defining the build-in function?

(defvar ramona-indicator-colour
  (list "#FFA500" "#8A8AFF" "#FF6161" "#61FF61"
        "#FFFF00" "#E859E8" "#FFFFFF" "#FFC370" "#C370FF")
  "Define list of cursor colours.")

(defvar ramona-indicator-point 0
  "Set colour of cursor defined by position in indicator colour list.")

(defun blink-cursor-timer-function ()
  "Blinks the cursor"

  (let ( (i ramona-indicator-point)
         (n (length ramona-indicator-colour)) )

    (when (not (internal-show-cursor-p))
      (when (>= i n) (setq i 0))
      (set-cursor-color (nth i ramona-indicator-colour))
      (setq i (+ 1 i))
      (setq ramona-indicator-point i))
    (internal-show-cursor nil (not (internal-show-cursor-p))) ))
  • If the purpose is to change the behavior of an original function that has already been defined, then a common approach is to redefine that function in order to achieve the desired modified behavior. There is no need to modify the source code containing the original function -- all that is needed is to ensure the library containing the original function has been loaded, and thereafter evaluate the new/modified function. Emacs will use the redefined function instead of the original once the aforementioned has occurred.
    – lawlist
    Commented Nov 30, 2022 at 16:03
  • What if others want to use the original? What can they do, besides commenting it out?
    – Dilna
    Commented Nov 30, 2022 at 16:43
  • One approach would be to define a variable that the user can customize and bind the variable to a default function, which the user can set to a different function if so desired. The code that uses the variable would use something like (funcall VARIABLE) For example, have a look at the variable initial-major-mode -- M-x find-variable RET initial-major-mode RET. It is bound to the function lisp-interaction-mode.
    – lawlist
    Commented Nov 30, 2022 at 16:58
  • Right. I fail to see what to do in my case though. If I need to call a different function, then I cannot use my implementation because I change the original function.
    – Dilna
    Commented Nov 30, 2022 at 17:20
  • Alternatives to redefining a function, include, but are not limited to advice. To temporarily let-bind a function to something different, you might be interested in cl-letf: stackoverflow.com/a/39564067
    – lawlist
    Commented Nov 30, 2022 at 17:23

1 Answer 1


If you only want to add a changing cursor color, then, as mentioned already by @lawlist, it is probably best to advice the function as follows:

(defvar ramona-indicator-colour
  (list "#FFA500" "#8A8AFF" "#FF6161"
        "#61FF61" "#FFFF00" "#E859E8"
        "#FFFFFF" "#FFC370" "#C370FF")
  "List of cursor colours.")

(defun ramona-blink-timer-advice ()
  (when (= blink-cursor-blinks-done 2) 
    (let* ((current-color (frame-parameter nil 'cursor-color))
           (next-color (cadr (member current-color ramona-indicator-colour))))
       (or next-color (car ramona-indicator-colour))))
    (setq blink-cursor-blinks-done 0)))

(advice-add 'blink-cursor-timer-function :before #'ramona-blink-timer-advice)

We reset the blink-cursor-blinks-done to 0 on each second call of the function, as the function is called twice for a single blink.

  • Cursor starts blinking but then it stops.
    – Dilna
    Commented Dec 1, 2022 at 7:15
  • Ah okay, I did not know that this was Emacs standard behavior. I have updated the answer. Commented Dec 1, 2022 at 8:07

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