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Programming in Emacs Lisp

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16.4 Text and Auto Fill Mode

Now we come to the part that `turns on' Text mode and Auto Fill mode.

 
;;; Text mode and Auto Fill mode
; The next three lines put Emacs into Text mode
; and Auto Fill mode, and are for writers who
; want to start writing prose rather than code.

(setq default-major-mode 'text-mode)
(add-hook 'text-mode-hook 'text-mode-hook-identify)
(add-hook 'text-mode-hook 'turn-on-auto-fill)

Here is the first part of this `.emacs' file that does something besides remind a forgetful human!

The first of the two lines in parentheses tells Emacs to turn on Text mode when you find a file, unless that file should go into some other mode, such as C mode.

When Emacs reads a file, it looks at the extension to the file name, if any. (The extension is the part that comes after a `.'.) If the file ends with a `.c' or `.h' extension then Emacs turns on C mode. Also, Emacs looks at first nonblank line of the file; if the line says `-*- C -*-', Emacs turns on C mode. Emacs possesses a list of extensions and specifications that it uses automatically. In addition, Emacs looks near the last page for a per-buffer, "local variables list", if any.

See section `How Major Modes are Chosen' in The GNU Emacs Manual.

See section `Local Variables in Files' in The GNU Emacs Manual.

Now, back to the `.emacs' file.

Here is the line again; how does it work?

 
(setq default-major-mode 'text-mode)

This line is a short, but complete Emacs Lisp expression.

We are already familiar with setq. It sets the following variable, default-major-mode, to the subsequent value, which is text-mode. The single quote mark before text-mode tells Emacs to deal directly with the text-mode variable, not with whatever it might stand for. See section Setting the Value of a Variable, for a reminder of how setq works. The main point is that there is no difference between the procedure you use to set a value in your `.emacs' file and the procedure you use anywhere else in Emacs.

Here are the next two lines:

 
(add-hook 'text-mode-hook 'text-mode-hook-identify)
(add-hook 'text-mode-hook 'turn-on-auto-fill)

In these two lines, the add-hook command first adds text-mode-hook-identify to the variable called text-mode-hook and then adds turn-on-auto-fill to the variable.

turn-on-auto-fill is the name of a program, that, you guessed it!, turns on Auto Fill mode. text-mode-hook-identify is a function that tells toggle-text-mode-auto-fill which buffers are in Text mode.

Every time Emacs turns on Text mode, Emacs runs the commands `hooked' onto Text mode. So every time Emacs turns on Text mode, Emacs also turns on Auto Fill mode.

In brief, the first line causes Emacs to enter Text mode when you edit a file, unless the file name extension, first non-blank line, or local variables tell Emacs otherwise.

Text mode among other actions, sets the syntax table to work conveniently for writers. In Text mode, Emacs considers an apostrophe as part of a word like a letter; but Emacs does not consider a period or a space as part of a word. Thus, M-f moves you over `it's'. On the other hand, in C mode, M-f stops just after the `t' of `it's'.

The second and third lines causes Emacs to turn on Auto Fill mode when it turns on Text mode. In Auto Fill mode, Emacs automatically breaks a line that is too wide and brings the excessively wide part of the line down to the next line. Emacs breaks lines between words, not within them.

When Auto Fill mode is turned off, lines continue to the right as you type them. Depending on how you set the value of truncate-lines, the words you type either disappear off the right side of the screen, or else are shown, in a rather ugly and unreadable manner, as a continuation line on the screen.

In addition, in this part of my `.emacs' file, I tell the Emacs fill commands to insert two spaces after a colon:

 
(setq colon-double-space t)


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