Writing GNU Emacs Extensions

Chapter 9. A Major Mode

In this chapter:

• My Quips File

• Major Mode Skeleton

• Changing the Definition of a Paragraph

• Quip Commands

• Keymaps

• Narrowing

• Derived Modes

Writing a simple major mode is very much like writing a minor mode, which we covered in Chapter 7. We'll just touch on the basic ideas of major modes in this chapter, preparing us for the creation of a substantial major mode—indeed, a whole new application—in the next chapter.

My Quips File

For several years I have been collecting witty quotations from various sources on the Internet, storing them in a file called Quips whose format is the same one used by the old UNIX fortune program. Each quotation is introduced by a line containing the string %%. Here's an example:

%%

I like a man who grins when he fights.

- Winston Churchill

%%

The human race has one really effective weapon, and that is laughter.

- Mark Twain

Apart from the %% lines, the file is completely free-form.

After my Quips file had been growing for a while, I found that I edited it a bit differently from the way I edit ordinary text files. For one thing, I frequently needed to confine my editing to a single quip in order to avoid accidentally straying into a neighboring quip. For another, whenever I needed to fill a paragraph at the beginning of a quip, I first had to separate it from the leading %% with a blank line. Otherwise, the %% would become filled as if it were part of the paragraph:

%%

I like a man who grins when he fights.

- Winston Churchill

%% The human race has one really ...