automatically checking your spelling

When I'm typing fast, it's easy to make spelling mistakes (as you may have noticed reading Emacs-Fu). It's not so much that I don't know how to write things, but sometimes there seems to be a bit of a disconnect between brain and fingers.

One tool that helps me to make fewer mistakes is automatic spelling checking, and in particular on-the-fly spelling checking. Spell-checking in emacs is taken care of by the ispell-package. Traditionally, this was a way to interface emacs with the ispell-program on Unix, but nowadays it's often used with other programs, such as aspell.

aspell is GNU's intended replacement for ispell, and has been for a long time. In the meantime, other spelling checkers have come up; in the Free Software world, the most prominent one is probably hunspell, which is used by e.g. Mozilla and OpenOffice. As I said, Emacs supports all of those; I'm using aspell, which works well for me. To use aspell for spelling-checking, I have the following in my .emacs:

(setq ispell-program-name "aspell"
  ispell-extra-args '("--sug-mode=ultra"))

Please consult the aspell documentation for the details.

You can spell-check your text with ispell-buffer and friends, which are also available through the menu (Tools/Spell Checking/...). This works fine, but it makes spelling checking a separate step you have to go through and you may forget. So, I like to do the spelling-checking on-the-fly, that is, while I am typing. This can be done using flyspell-mode (you can also use flyspell-prog-mode, to do spell checking inside comments in computer programs, but I find that a bit over the top).

When flyspell-mode is enabled, it will mark misspelt eh misspelled words by painting them in a different color while you are typing -- the common way many word processing programs do it. A common way to enable flyspell-mode is to put it the the mode-hook for the modes where you want to use it. For example, to enable flyspell-mode for all your org-mode buffers, you can add something like the following to your .emacs:

(add-hook 'org-mode-hook
    (flyspell-mode 1)))

Note, you can use the middle mouse button to get alternatives for a misspelled word.

By default, it uses the English dictionary, but it's easy to switch to another using M-x ispell-change-dictionary. To make it easier, I have defined the C-c N key binding to activate Dutch-language ("nederlands") spelling checking, and update the buffer.

(global-set-key (kbd "C-c N") 
    (ispell-change-dictionary "nederlands")

Now, there's another category of mistakes – their-they're-there, its-it's or to-too-two that require a spelling checker that's a bit smarter. There are some free implementations in OpenOffice and Abiword; it'd be interesting to see if those could be integrated with emacs as well.

Now, laugh about the sweet irony of the spelling errors that I failed to notice :)


yo said...

For grammar checking there is the command line diction program and the emacs mode diction.el.

rico said...

the auto lang mode
checks the text and sets the dict on the fly

kiwonum said...

Sometimes, flyspell-mumamo-mode works well, e.g. for TeX-mode.

oylenshpeegul said...

Nice! I think the org-mode-hook example needs another close paren.

djcb said...

@oylenshpeegul: thanks, fixed.

Roland Smith said...

I like to do the following;

cat foo.tex | ispell -t -l -W 4 -C -d nederlands | sort | uniq | less

This gives me a list that ispell thinks are wrong. I can then pick out the really misspelt words.

jyby said...

I often write documents with a mix of English and Spanish (such as, changing language every paragraph). Would it be possible to configure aspell so that it looks into two dictionaries in parallel?

I assume it already does, given that it has a personal dictionary and the distribution one, so it is only a matter of interface.

Sergio said...

Great tip Dirk as usual

Anonymous said...

@jyby check out http://www.dur.ac.uk/p.j.heslin/Software/Emacs/Download/flyspell-babel.el