Writing GNU Emacs Extensions

Quip Commands

What else should Quip mode be able to do?

• It should allow the user to move forward and backward a quip at a time.

• It should allow the user to restrict editing operations to a single quip.

• It should be able to report the number of quips in the file, and the number of the quip that point is on.

• Apart from that, it should work by and large the same way Text mode works. After all, the contents are mostly plain text.

Let's pause a moment to consider the different kinds of cursor motion commands in Emacs. There's forward-char and backward-char for moving one character at a time. There's forward-word and backward-word. There's forward-line and previous-line. There are also commands for moving forward and backward in units of sentences, paragraphs, sexps, and pages.

What's a page? Conventionally, a new page begins at a formfeed character (control-L), because in the ancient days of teletypes and line printers, the way to begin a new page was to send a control-L to the device. In true Emacs style, however, we can redefine what constitutes a "page" by changing the regexp in page-delimiter.

(make-local-variable 'page-delimiter)
(setq page-delimiter "^%%$")

This single insight—making a "page" equal a "quip"—solves most of the requirements we've stipulated for Quip mode! Now Emacs's many built-in page commands will operate on quips:

• backward-page and forward-page, normally bound to C-x [ and C-x ], allow moving back and forth a quip at a time

• narrow-to-page, bound to C-x n p, confines ...