Writing GNU Emacs Extensions

Chapter 2. Simple New Commands

In this chapter:

• Traversing Windows

• Line-at-a-Time Scrolling

• Other Cursor and Text Motion Commands

• Clobbering Symbolic Links

• Advised Buffer Switching

• Addendum: Raw Prefix Argument

In this chapter we'll develop several very small Lisp functions and commands, introducing a wealth of concepts that will serve us when we tackle larger tasks in the chapters to follow.

Traversing Windows

When I started using Emacs, I was dissatisfied with the keybinding C-x o, other-window. It moves the cursor from one Emacs window into the next. If I wanted to move the cursor to the previous window instead, I had to invoke other-window with -1 as an argument by typing C-u - 1 C-x o, which is cumbersome. Just as cumbersome was pressing C-x o repeatedly until I cycled through all the windows and came back around to what had been the "previous" one.

What I really wanted was one keybinding meaning "next window" and a different keybinding meaning "previous window." I knew I could do this by writing some new Emacs Lisp code and binding my new functions to new keybindings. First I had to choose those keybindings. "Next" and "previous" naturally suggested C-n and C-p, but those keys are bound to next-line and previous-line and I didn't want to change them. The next best option was to use some prefix key, followed by C-n and C-p. Emacs already uses C-x as a prefix for many two-keystroke commands (such as C-x o itself), so I chose C-x C-n for "next window" and C-x C-p for "previous window." ...