How to rewrite a native defun in Emacs?

1
votes

Premises:

My Emacs has a small bug (cannot go up from inside of "") in one of its original defun (up-list). This defun is vital to one of my frequently used command (backward-up-list) which is bound to C-M-u.

Therefore, I wanted to achieve below objectives:

  1. Write a NEW defun named my-up-list which has the bug fix;
  2. RE-write the native defun backward-up-list to call the above new defun (instead of the native buggy up-list). (By RE-writing under the same defun name, I intend to preserve its original convenient key bindings.)

By following the Emacs Tutorial Here, I implemented it as below:

  1. I wrote a new defun my-up-list inside .emacs file; (see code in the end)
  2. I rewrote the defun backward-up-list under a the same name inside .emacs file; (see code in the end).

However, when wI tested it out by trying it in "|" (| is the cursor position), I encounter below error:

backward-up-list: Wrong number of arguments: (lambda nil (interactive) (let ((s (syntax-ppss))) (if (nth 3 s) (progn (goto-char (nth 8 s))))) (condition-case nil (progn (up-list)) (error nil))), 1 [2 times]

Question:

  • Is it the correct way to re-write a native defun just by putting the new implementation with the same name in .emacs file?
  • What may went wrong in my code?

Reference: (The my-up-list is from here)

;; I only changed "up-list" to "my-up-list" -modeller
(defun backward-up-list (&optional arg)
  "Move backward out of one level of parentheses.
With ARG, do this that many times.
A negative argument means move forward but still to a less deep spot.
This command assumes point is not in a string or comment."
  (interactive "^p")
  (my-up-list (- (or arg 1))))

;; copied from solution to another question - modeller
(defun my-up-list ()
  (interactive)
  (let ((s (syntax-ppss)))
    (when (nth 3 s)
      (goto-char (nth 8 s))))
  (ignore-errors (up-list)))
2
emacs
If the aim of redefining the function is to retain its keybindings, Emacs has you covered with command remapping. See C-h i g (elisp) Remapping Commands RET. Here you can use (global-set-key [remap backward-up-list] 'my-backward-up-list). – phils
@phils thanks for the tips. It is great to learn an alternative way for doing the trick. – modeller
It's not clear (to me at least) why you even want to do this. Vanilla up-list takes you out of the string, just past it. And invoking it again then takes you exactly where my-up-list takes you. So without my-up-list you just need to hit the up-list key twice to get the same effect. And as a bonus you can use up-list whenever you just want to get past the string. If you bind a command such as (my-)up-list to a key then you typically want it to be a simple, repeatable key anyway. – Drew
@Drew, I got a "scan error: unbalanced parentheses" from the vanilla version up-list. I uses (self-compiled Emacs 23.4 64-bit). Please see code here: lpaste.net/109513 – modeller
Ah yes, there is an up-list bug in Emacs 23 and 24 (including the latest 24.4 pretest), and there is a different bug in Emacs 22 and prior. You could just pick up the definition from a recent Emacs 24.4 development snapshot, where the Emacs 23-24 bug has been fixed. – Drew

2 Answers

1
votes

I guess your my-up-list function needs to accept the same arguments as the original up-list, and call up-list with them?

0
votes

The simplest way to do this is with the "advice" system. This provides some simple ways to wrap and extend existing functions. There's a whole section in the elisp manual explaining how to do it.