Emacs Redux

Return to the Essence of Text Editing

A Crazy Productivity Boost: Remap Return to Control

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People have always complained about the awkward positioning of the two Control keys on modern keyboards. That’s a fact! Effective Emacs usage is heavily dependent on the Control keys (yep, both of them). That’s also a fact!

A great many Emacs users remap the infrequently used CapsLock key to Control to alleviate partially the problem with the accessibility of the control keys. That, while useful, is not sufficient for the optimal typing experience, since that way you’re breaking the key symmetry on both sides of your keyboard. Also - your right pinky has to go much further than your left one, while you’re typing. Many people seem to be using only the left Control and I guess they’re not particularly bothered by this, but touch typists like me are generally quite bothered by such things.

A much better idea would be to leverage a little knows capability of keyboard input systems and map the Return key to Control only when it’s held down (it will behave like a normal Return key in all other situations). This sounds a bit crazy, but please bear with me for a while.

This radical approach has several advantages. First and foremost - it’s much easier to hit Return with your right pinky than it is to hit the regular right Control (especially if you’re using a US layout keyboard - these have long single row Return keys, compared to the short 2 row Returns found on European keyboards). Second, if you’ve already remapped CapsLock to Control (like you should have done) you’re getting a pretty symmetrical mapping on the opposite side of your keyboard. Last, but not least - it’s a great option for people using compact keyboards with no left Control key.

Obviously you’ll need some keyboard remapping software to make this trick work. OSX users can use KeyRemap4MacBook to do that. In its settings look up the Change Return section and under it Return to Control_R (+ When you type Return only, send Return). As far as I know this remapping can be done on GNU/Linux systems with xcape (though I haven’t checked that myself), but I have no idea if it’s a viable option for Windows users.

All in all - remapping Return to Control should be a big productivity win for some (the touch typists) of you and should make your right pinky’s life easier.

Highlight Matching Delimiters With Smartparens

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Some time ago I wrote about highlighting matching parentheses with show-paren-mode. This is definitely useful, but it’s kind of restrictive, since parentheses are just a specific kind of paired delimiter. Single and double quotes are also paired delimiters (at least in most programmming languages). In the Ruby programmming language, for instance, do and end also constitute paired delimiter.

smartparens offers extremely customizable handling of paired delimiters and comes with an extra minor mode called show-smartparens-mode to highlight them. This mode totally replaces show-paren-mode and language specific modes like hirb (which highlights Ruby blocks).

Assuming you’re already using smartparens, enabling show-smartparens-mode is trivial:

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(show-smartparens-global-mode +1)

Here’s a glimpse of it in action:

In Prelude show-paren-mode was replaced by show-smartparens-mode some time ago.

Instant Access to Your Shell Init File

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A while ago I showed you a way to instantly edit your Emacs init file. Today we’ll adapt the original idea for shell init files like .bashrc and .zshrc. The code required is fairly short and simple:

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(defun find-shell-init-file ()
  "Edit the shell init file in another window."
  (interactive)
  (let* ((shell (car (reverse (split-string (getenv "SHELL") "/"))))
         (shell-init-file (cond
                           ((string-equal "zsh" shell) ".zshrc")
                           ((string-equal "bash" shell) ".bashrc")
                           (t (error "Unknown shell")))))
    (find-file-other-window (expand-file-name shell-init-file (getenv "HOME")))))

The shell init file is deduced from your SHELL env variable. While there are different shell init files for most shell (e.g. .bash_profile, .zshenv, .zprofile), here we’re assuming you’re using the most commonly used files. find-file-other-window will open the file in a window adjacent to the one you’re currently in.

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(global-set-key (kbd "C-c S") 'find-shell-init-file)

find-shell-init-file is available in Prelude(but with a prelude- prefix).

Removing/Altering Key Bindings From Minor Mode Keymaps

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Often minor modes don’t respect standard keybinding conventions and use some user reserved keys (like C-c a). Occasionally two minor modes would have conflicting keybindings or a minor mode would keybindings conflicting with a major mode. I guess you can imagine similar problems. Dealing with them is fairly straight-forward - we have to either unbind or rebind the offending binding:

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;; remove keybinding
(define-key minor-mode-map (kbd "C-c c") nil)

;; change keybinding
(define-key minor-mode-map (kbd "C-c c") (kbd "C-c C-c"))

Generally speaking you can use define-key to alter the keymap of a major mode as well, but those are rarely offenders when it comes to picking appropriate keybindings for their keymaps.

Normally you’d want to invoke the above code right after the related minor (or major) mode is loaded:

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(eval-after-load "minor-mode"
  '(define-key minor-mode-map (kbd "C-c c") nil))

Making a minor mode have different keymaps in different major modes is tricky, but possible. Here’s an example that disables some keybindings in the minor prelude-mode, that are conflicting with the major org-mode:

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(defun my-org-mode-hook ()
  (let ((oldmap (cdr (assoc 'prelude-mode minor-mode-map-alist)))
        (newmap (make-sparse-keymap)))
    (set-keymap-parent newmap oldmap)
    (define-key newmap (kbd "C-c +") nil)
    (define-key newmap (kbd "C-c -") nil)
    (make-local-variable 'minor-mode-overriding-map-alist)
    (push `(prelude-mode . ,newmap) minor-mode-overriding-map-alist))
)

(add-hook 'org-mode-hook 'my-org-mode-hook)

Dired Jump

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Most Emacs users know that they can start dired (Emacs’s file browser) with M-x dired or C-x d. That would display a prompt in the minibuffer asking which directory to open with dired (the current directory will be suggested as a default).

More often than not you’ll probably want dired to display the directory of file you’re currently editing. You might even want to have the cursor positioned over that very same file in the dired buffer. There’s a cool command that does exactly that - dired-jump. To use it you have to first load the built-in library dired-x:

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(require 'dired-x)

You can run the command with C-x C-j (M-x dired-jump). No prompts, no wasted time. You’re instantly teleported to the currently edited file’s position in a dired buffer.

This command works out-of-the-box in Prelude.

A Proper Replacement for Flet

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The popular flet macro was deprecated in Emacs 24.3 and replaced with two similar macros - cl-flet and cl-letf.

flet was used to temporarily override function definitions. This was an analogue of a dynamically scoped let that operates on the function cell of symbols rather than their value cell.

The ability to dynamically rebind a functions was very useful for stubbing purposes in unit tests (you do write unit tests, don’t you?).

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(flet ((projectile-project-root () "/path/to/project")
       (projectile-project-name () "project"))
  ...)

projectile-project-root and projectile-project-name are impure functions (they depend on the current directory) and testing functions that use them internally would normally be problematic. However, flet gives us the ability to override their actual definitions in our tests. flet’s official replacement cl-flet is lexically bound and this is no longer possible with it.

Fortunately Nic Ferrier created a true drop-in flet replacement (with some extra magic baked in) - noflet. If you’re missing flet, I suggest you to give noflet a try.

Version Checks

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Often the code you’re writing would be depending on the version of some external tool (say git) or Emacs itself. Version checks in Emacs are pretty easy - just use the built-in functions version=, version<= or version=.

Let’s illustrate this with an example. Prelude requires at least GNU Emacs 24.1 to run and on startup it performs the following check:

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(when (version< emacs-version "24.1")
  (error "Prelude requires at least GNU Emacs 24.1"))

Simple and effective. The version functions are pretty smart and recognize most popular version formats correctly. Note that version string “1” is equal to “1.0”, “1.0.0”, “1.0.0.0”, etc. That is, the trailing “.0”s are insignificant. Also, version string “1” is higher (newer) than “1pre”, which is higher than “1beta”, which is higher than “1alpha”. Also, “-CVS” and “-NNN” are treated as alpha versions.

If you’re writing an Emacs package you can also add an explicit Emacs version dependency in the packge metadata:

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;; Package-Requires: ((emacs "24.1"))

That way users of older Emacsen would not see a version of your package targeting newer Emacsen.

Search Youtube

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Some time ago I showed you how to do Google queries from Emacs. The approach used in that articles is pretty generic and can be used for the creation of various similar commands. Let’s create a command that searches in YouTube:

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(defun youtube ()
  "Search YouTube with a query or region if any."
  (interactive)
  (browse-url
   (concat
    "http://www.youtube.com/results?search_query="
    (url-hexify-string (if mark-active
                           (buffer-substring (region-beginning) (region-end))
                         (read-string "Search YouTube: "))))))

This command will display the query results in your default browser.

I’d suggest binding the command to C-c y if you plan to use it regularly.

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(global-set-key (kbd "C-c y") 'youtube)

youtube is available in Prelude(but with a prelude- prefix).

Color Themes: Redux

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Prelude

This is a slightly refreshed version of an article originally published on my personal blog.

If there is something that people love as much as tweaking their editing configurations it’s probably the selection of color themes. A good color theme can make your work much more pleasant and a bad one that literally impair your vision. It’s a fact of life that I’m a firm supporter of low-contrast color themes with dark backgrounds - I find them easy on the eyes and I feel that they don’t strain the eyes as much as most themes. I’ve even ported a couple of popular themes to Emacs - Zenburn and Solarized.

In this short article we’ll see how color theming has changed in Emacs 24 and I’ll share with you a few tips on theme creation and distribution.

Increment and Decrement Integer at Point

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While editing you often have to increment or decrement some number (usually an integer) by some step. Obviously this is trivial when the number is something like 10, but not pretty pleasant when the number is 2343566 and you want to increment it by 943. Most of the time, however, you’ll probably be incrementing or decrementing by 1.

A long time ago I found a bit of code by Ryan Thompson to help us deal with such tasks. Here’s a slightly modified version of the original code:

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(require 'thingatpt)

(defun thing-at-point-goto-end-of-integer ()
  "Go to end of integer at point."
  (let ((inhibit-changing-match-data t))
    ;; Skip over optional sign
    (when (looking-at "[+-]")
      (forward-char 1))
    ;; Skip over digits
    (skip-chars-forward "[[:digit:]]")
    ;; Check for at least one digit
    (unless (looking-back "[[:digit:]]")
      (error "No integer here"))))
(put 'integer 'beginning-op 'thing-at-point-goto-end-of-integer)

(defun thing-at-point-goto-beginning-of-integer ()
  "Go to end of integer at point."
  (let ((inhibit-changing-match-data t))
    ;; Skip backward over digits
    (skip-chars-backward "[[:digit:]]")
    ;; Check for digits and optional sign
    (unless (looking-at "[+-]?[[:digit:]]")
      (error "No integer here"))
    ;; Skip backward over optional sign
    (when (looking-back "[+-]")
        (backward-char 1))))
(put 'integer 'beginning-op 'thing-at-point-goto-beginning-of-integer)

(defun thing-at-point-bounds-of-integer-at-point ()
  "Get boundaries of integer at point."
  (save-excursion
    (let (beg end)
      (thing-at-point-goto-beginning-of-integer)
      (setq beg (point))
      (thing-at-point-goto-end-of-integer)
      (setq end (point))
      (cons beg end))))
(put 'integer 'bounds-of-thing-at-point 'thing-at-point-bounds-of-integer-at-point)

(defun thing-at-point-integer-at-point ()
  "Get integer at point."
  (let ((bounds (bounds-of-thing-at-point 'integer)))
    (string-to-number (buffer-substring (car bounds) (cdr bounds)))))
(put 'integer 'thing-at-point 'thing-at-point-integer-at-point)

(defun increment-integer-at-point (&optional inc)
  "Increment integer at point by one.

With numeric prefix arg INC, increment the integer by INC amount."
  (interactive "p")
  (let ((inc (or inc 1))
        (n (thing-at-point 'integer))
        (bounds (bounds-of-thing-at-point 'integer)))
    (delete-region (car bounds) (cdr bounds))
    (insert (int-to-string (+ n inc)))))

(defun decrement-integer-at-point (&optional dec)
  "Decrement integer at point by one.

With numeric prefix arg DEC, decrement the integer by DEC amount."
  (interactive "p")
  (increment-integer-at-point (- (or dec 1))))

The code is based on the popular built-in library thing-at-point and extends it to make it aware of integer numbers. The commands increment-integer-at-point and decrement-integer-at-point operate with a step of 1 by default, but with a prefix argument you can select any step you desire. Unlike other similar commands floating in the Internet, these two handle correctly numbers like -3434 and +343.

I’d suggest binding these commands to C-c + and C-c -:

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(global-set-key (kbd "C-c +") 'increment-integer-at-point)
(global-set-key (kbd "C-c -") 'decrement-integer-at-point)

Both commands are available in Prelude(but with a prelude- prefix).