Tuesday, November 6, 2007

Effective .emacs

Tip #0: Use Emacs 22
Emacs 22 is super stable. About half of my .emacs file (before I cleaned it up) was loading stuff that's now part of Emacs 22 and has autoloads.

Tip #1: Never quit Emacs
Okay, this has nothing to do with your .emacs file, but I have to put it in here. Just because your .emacs file should load quickly doesn't imply that you should quit and restart all the time. Figure it out!

Tip #2: (require 'cl)
I put this at the top of my .emacs. It's a no-brainer. It adds in a ton of compatibility with CL, so that you can just use the CL functions you know and love (well, most of them, anyway), without a second thought.

Tip #3: Never LOAD, never REQUIRE
Your .emacs file shouldn't contain any calls to LOAD or REQUIRE (which are slow and often cause errors on startup). The only possible exceptions are loading files that contain nothing but autoloads (or similar stuff). How do you avoid loads and requires? First try removing each call to LOAD or REQUIRE to see if it's needed at all. Often (e.g., if you follow Tip #0) Emacs already has autoloads in place for the library already (e.g., "cc-mode"). For other libraries, where that's not true, put your own autoloads in your .emacs file. For example, rather than load SLIME in my .emacs (so I can bind the F1 key to SLIME-SELECTOR), instead I have:
(autoload 'slime-selector "slime" t)
The only call to LOAD in my .emacs file is for "erlang-start", but if you look inside the file you can see it contains only autoloads (and morally equivalent stuff). I also load the custom file, but that's different, see Tip #7. I don't have a single call to REQUIRE (beyond that mandated by Tip #2).

Tip #4: Understand and use EVAL-AFTER-LOAD
Another reason why you might have strewn needless REQUIRE and LOAD calls throughout your .emacs file is that you need to call a function from a specific library. For example, let's say you want to set your default SQL database type to MySQL:
(sql-set-product 'mysql)
If you put this in your .emacs, you'll get an error because the SQL library isn't loaded so SQL-SET-PRODUCT isn't yet defined. But before you add a LOAD or REQUIRE, stop! Instead do:
(eval-after-load "sql"
(sql-set-product 'mysql)
;; any other config specific to sql
As the name suggests, this will defer calling that code until the SQL module is actually loaded. This saves startup time and prevents errors!

Tip #5: Time your .emacs
You really ought to know how much time it's taking to load your .emacs file. Use the following in your .emacs:
(require 'cl) ; a rare necessary use of REQUIRE
(defvar *emacs-load-start* (current-time))

;; rest of your .emacs goes here

(message "My .emacs loaded in %ds" (destructuring-bind (hi lo ms) (current-time)
(- (+ hi lo) (+ (first *emacs-load-start*) (second *emacs-load-start*)))))
After Emacs finishing initializing, you can switch to the *Messages* buffer and see how much of that time was taken by loading your .emacs. Mine now contributes less than one second!

Tip #6: Set background colors
Don't just stand for the default colors! Set them to what you really want. In my case I want a reverse video effect:
(set-background-color "black")
(set-face-background 'default "black")
(set-face-background 'region "black")
(set-face-foreground 'default "white")
(set-face-foreground 'region "gray60")
(set-foreground-color "white")
(set-cursor-color "red")

Tip #7: Separate custom file
It's annoying to have your .emacs file modified by Emacs' "custom" library, especially if you check in your .emacs to a source code control system such as Subversion (which you should do) and synchronize it on multiple machines. Keep those customizations in a separate file:
(setq custom-file "~/.emacs-custom.el")
(load custom-file 'noerror)

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