As a result of an answer in a previous question of mine I am trying to translate M-RET in C-u C-RET using the following code:

(define-key key-translation-map (kbd "M-RET") (kbd "C-u C-RET"))

I have used the same code to translate other functions and it worked flawlessly so I don't know what is wrong with it. Does anyone?

2 Answers 2


I don't know what is wrong with using key-translation-map (I hope somebody else will chime in). My guess is that it makes Emacs look up the binding of C-u C-RET, not C-RET with a prefix argument.

This alternative seems to work, though:

(global-set-key (kbd "M-RET") (kbd "C-u C-<return>"))
  • Ok that works fine! Thank you. Let's wait for someone to explain why my solution didn't work...
    – Adam
    Nov 23, 2014 at 0:18

The input translation maps (input-decode-map, local-function-key-map, function-key-map, key-translation-map) apply only within a key sequence. While you can specify multiple keys in the output of the translation, they'll only be counted towards binding.

For example, consider:

(define-key key-translation-map [f12] [?\C-x ?\C-f ?a])
(define-key key-translation-map [f11] [?\C-u C-return])
(define-key key-translation-map [f10] "abc")

F12 is translated to C-x C-f a. The key sequence C-x C-f is bound to find-file, so pressing F12 will invoke find-file, and the extra a input event will be discarded. Similarly, F11 is translated to C-u C-return, which invokes universal-argument and discards the extraneous event C-return. Pressing F10 invokes the command bound to a, which is self-insert-command; the character c is actually inserted, because self-insert-command inserts the character based on the last input event.

If you want M-RET to be equivalent to C-u C-return in all contexts where M-RET is not bound, then you can bind it in the global keymap. In keymaps other than the translation maps, if the binding for a key is an array of events (such as constructed by kbd) or a string, then the binding is interpreted as a sequence of events to replay — a macro. Note that C-RET isn't normally generated; Ctrl+Return is C-return.

(global-set-key (kbd "M-RET") (kbd "C-u C-<return>"))

Given that C-return is not globally bound by default, it would probably make more sense to define M-RET in the mode where you want to use it. It would be clearer to bind M-RET to a function which does whatever you want — if C-return invokes foo-frobnicate then you might do something like

(defun foo-frobnicate-harder ()
  (frobnicate t))
(define-key foo-mode-map (kbd "M-RET") 'foo-frobnicate-harder)

If you really want M-RET to be equivalent to C-u C-return in every context, you can stuff events into unread-command-events — see Simulating mouse operations with keyboard for an example.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.