Applying defadvice to Several Functions at Once

One of the distinguishing—and most useful—features of Lisp is the macro. Sadly, we don’t often see them discussed in the Emacs blogosphere so I was happy to see Bozhidar Batsov over at Emacs Redux give a beautiful example of macro use. The problem he addresses is to save the current buffer whenever you switch to a different window¹. You can switch windows in a number of ways, of course, so several functions need to be advised to first save the current buffer.

The result is that six statements of the form

(defadvice switch-to-buffer (before switch-to-buffer-auto-save activate)
  (prelude-auto-save))

are replaced with the single statement

(advise-commands "auto-save"
                 (switch-to-buffer other-window windmove-up windmove-down windmove-left windmove-right)
                 (prelude-auto-save))

using the advise-commands macro that Batsov wrote.

This neatly illustrates one of the main uses of macros: rather than writing almost identical code over and over, you abstract the common code into a macro. Be sure to read Batsov’s post to see the concept in action.

Update: Inserted missing “of.”