Emacs Tip #35: framemove

Ever wanted to easily navigate between frames? Perhaps using arrow keys? Surprisingly, this didn't exist before (AFAIK).

I wrote the package framemove to have the same usage as Emacs' built in windmove package. And, even better, it can integrate with windmove so that when you run out of windows to move between, you'll jump to the next frame in that direction.

To install framemove on its own:

    (require 'framemove)
    (framemove-default-keybindings) ;; default prefix is Meta

But you might want to use this in conjunction with windmove, in which case this is the integration code to add to your .emacs:

    (require 'framemove)
    (windmove-default-keybindings)
    (setq framemove-hook-into-windmove t)

With the integration with windmove, you just do SHIFT-right to move focus to the window to the right of the current, and when there are no more, focus will shift to the frame to the right.

Switching frames is a little more challenging than switching windows - mostly because windows are simply rectangular divisions of a window - it is easy to tell what window (if any) is to the right of the point. For frames, the answer is ambiguous because the placements of frames is free-form, and frames can overlap. I think this initial implementation does a reasonable job of choosing which frame to select. It first tries the frame directly in line with the point, and if one doesn't exist, it then uses the distance between the point (projected onto the edge of the current frame) and the frames in the given direction, and after that it just tries any frame that extends beyond the current frame in that direction.

Check it out.

Currently, when focus shifts to a new frame - the point does not change inside the frame.

Emacs Tip #34: line-beginning-position, line-end-position

Such a simple thing - finding the position of the beginning or end of the current line. I've been completely oblivious to the existence of the functions line-beginning-position and line-end-position.

They return the position of the beginning or end of the current line.
They both accept an optional argument, which has the same
meaning as the argument to beginning-of-line or end-of-line.

They were first introduced in Emacs 20, in the middle of 2006. Which means I've been unnecessarily typing this for 4 years:

(save-excursion
   (beginning-of-line)
   (point))

Emacs Paper from 1981

It's been a while since I read RMS's paper on Emacs. Back in 1981, I still had another 2 years before I even saw my first computer. Reading the paper gives some insight into some of the issues they were trying to solve (real time display, extensibility, portability).

The first thing that came to mind when I first read this paper was that (to an outsider at least) Emacs really hasn't changed fundamentally since 1981 - the basic structures have held up well. I don't see any mention of subprocesses in the original paper, so that's something pretty fundamental that is new (since 1981). Of course the other obvious additions are MULE, image support, fonts, and the graphical interface.

Amusingly, vi was not mentioned in the Other Interesting Editors section. From reading the wikipedia article on vi, it certainly was available (it's a part of the Unix standard).

But what really struck me as interesting and powerful was the decision to use dynamic binding. I'd remembered playing with the differences between dynamic and lexical scoping in my SICP class in college, but never saw a reason to use it. Well, it totally fits when you want to customize Emacs' behavior.

The paper is certainly worth the 10 minutes it takes to read.

Emacs Tip #33: paredit

I recently found paredit. It is a mode which allows you to edit s-expressions (sexps) in a structured way.

Essentially it forces you to maintain balanced parentheses by always inserting/deleting matched pairs. It is very easy to modify the current sexp to: enclose (wrap) the next element, to merge it up one level (aka splice, i.e. remove a set of parentheses), to split the current sexp, etc.

It works with round parens (), square brackets [], curly braces {}, and angle braces <>. It also handles string quotes " the same way.

Deleting and killing of text also works nicely. For example, C-k is bound to 'paredit-kill which has the following behavior (note: | represents the cursor position):

(foo bar)|     ; Useless comment!
 ->
(foo bar)|

(|foo bar)     ; Useful comment!
 ->
(|)            ; Useful comment!

|(foo bar)     ; Useless line!
 ->
|

(foo "|bar baz"
    quux)
 ->
(foo "|"
    quux)

It's taking a little getting used to, but I'm finding myself thinking less about where the current block of code ends than I used to. The parentheses just take care of themselves...

This is how I enabled it:

(defun turn-on-paredit-mode ()
 (paredit-mode +1))

;; I didn't like C-j being overridden, I want it to still work the old way in lisp-interaction
(eval-after-load "paredit"
 '(progn
    (define-key paredit-mode-map (read-kbd-macro "C-j") nil)))

(add-hook 'emacs-lisp-mode-hook 'turn-on-paredit-mode)

The cheat sheet is probably the best way to get an idea of what is possible. Check it out here. Also, the command documentation is very complete (see the above which was grabbed right from the C-k documentation, so it's easy to remind yourself what is possible.

About the only problem I've had is when I've yanked code that has unbalanced parens. So I wrote a little advice which at least warns you and allows you to abort if the yanked text is unbalanced. It's not perfect, but it is a reasonable first implementation:

(defun paredit-check-region-for-yank ()
  "run after yank and yank-pop to verify balanced parens"
  (when paredit-mode
    (save-excursion
      (save-restriction
        (narrow-to-region (point) (mark))
        (condition-case nil
            (check-parens)
          (error
           (if (not (y-or-n-p "The text inserted has unbalanced parentheses, continue? "))
               (delete-region (point-min) (point-max)))))))))

(defadvice yank (after yank-check-parens activate)
  (paredit-check-region-for-yank))
(defadvice yank-pop (after yank-pop-check-parens activate)
  (paredit-check-region-for-yank))

Somewhat meta: blogs on reddit

Recently, doing a vanity search, I saw a link to this blog from reddit. I'm not a reddit user, but found it interesting that some of my posts had made it on there (as you can see here: trey-jackson.blogspot.com on reddit.com).

What I find curious about reddit as it applies to blogs is that it ends up taking the conversation away from the blog. This works well for reddit users, but ends up fracturing the audience. I don't get many comments (I have very few readers) and would have appreciated the reading the comments made on reddit.

For what it's worth, I did update a post to fix a coding bug noticed by someone on reddit (ironically, their fix had syntax problems at the same spot as well).

Emacs Tip #32: completion-ignore-case and Emacs 23

Everyone is all a-buzz over the new release of Emacs. I've started using it, and I do like the font support.

There was one surprise. I had the old setting

(setq completion-ignore-case t)

because I hate typing capital letters when I can avoid it. Enter Emacs 23.1, and I now have to type capital letters for buffer names and file names (which is 90% of what I use minibuffer completion for). It turns out, there are two new variables, one for each of the types of completion:

(setq read-buffer-completion-ignore-case t)
(setq read-file-name-completion-ignore-case t)

Everything else in the upgrade has been smooth.

Emacs Tip #31: kill-other-buffers-of-this-file-name

A friend mentioned he wanted a way to get rid of all the other buffers visiting files that of the same file name. I instantly realized this was something I'd wanted for a long time without knowing it.

My usage is that I'm often viewing different versions of the same file, usually in different sandboxes. And, I might also have older versions checked out, whose file names are the same, but end with ".~1.12~" (or whatever version number was checked out).

I'm still old-school and don't use anything fancy for my buffer switching like `ido` or `icicles` or `iswitchb` or any of the other myriad of choices. And, as a result, it's a pain to switch because I have to now discern between the variants. Well, do that once, type `C-x K`, and that'll be the only buffer left for that file name.

(global-set-key (kbd "C-x K") 'kill-other-buffers-of-this-file-name)
(defun kill-other-buffers-of-this-file-name (&optional buffer)
"Kill all other buffers visiting files of the same base name."
(interactive "bBuffer to make unique: ")
(setq buffer (if buffer (get-buffer buffer) (current-buffer)))
(cond ((buffer-file-name buffer)
      (let ((name (file-name-nondirectory (buffer-file-name buffer))))
        (loop for ob in (buffer-list)
              do (if (and (not (eq ob buffer))
                          (buffer-file-name ob)
                          (let ((ob-file-name (file-name-nondirectory (buffer-file-name ob))))
                            (or (equal ob-file-name name)
                                (string-match (concat name "\\(\\.~.*\\)?~$") ob-file-name))) )
                     (kill-buffer ob)))))
     ((message "This buffer has no file name."))))

Edited Sept. 30, 2009 to fix coding error.