Rebinding M-q in `define-minor-mode`

Question

I'm trying to define a minor mode that rebinds M-q to a modified version of fill-paragraph. What I've written so far:

(defun myfun ()
  (message "myfun called"))
(define-minor-mode mymode
  "Test for minor mode keymap."
  :lighter " MM"
  :keymap '(([M-q] . myfun)))

doesn't work, as M-q is still bound to fill-paragraph when mymode is active. Can anyone spot the issue with my code and tell me how to rebind that key properly?

Answer 1

Contrast M-f1 for a function key with ?\M-f for a character. You've bound myfun to [M-q] which means the one-key sequence where the key is the function key called q (which does not exist) with the modifier whose prefix is M (which is meta). Instead of referencing a function key q, you need to reference the character q. You can write this [?\M-q], or in string notation "?\M-q". You can also use the ESC prefix (written \e as a character) instead of the meta modifier: "\eq" or [?\e \q].

(Do not use [escape q], because that would override the default redirection of the escape function key to the escape character ?\e, and so pressing Escape key would no longer be equivalent to Meta+key.)

Answer 2

I'd consider calling (define-key mymode-map [remap fill-paragraph] #'myfun) from mymode-hook rather than defining it in the minor mode.

(defun remap-fill-paragraph ()
  (define-key mymode-map [remap fill-paragraph] #'myfun))

(add-hook 'mymode-hook #'remap-fill-paragraph)

This means you don't have to remember to change the minor-mode mapping if you ever change the default mapping for fill-paragraph.

Unfortunately (based on a single quick test) it seems that the expansion of the define-minor-mode Lisp macro is not smart enough to handle a [remap ...] within the :keymap form, hence the need to use the more verbose approach.

Answer 3

There are two problems in the code above:

1. The code was bound to the non-existing q function key (see Gilles' answer).
2. In order to be added to a keymap, functions must be commands (i.e. interactive).

The following code works and solves both problems:

(defun myfun ()
  (interactive)
  (message "myfun called"))
(define-minor-mode mymode
  "Test for minor mode keymap."
  :lighter " MM"
  :keymap '([?\M-q] . myfun))