www.delorie.com/gnu/docs/emacs-lisp-intro/emacs-lisp-intro_245.html

search

	Buy the book!

Programming in Emacs Lisp

16.11 A Simple Extension: line-to-top-of-window

Here is a simple extension to Emacs that moves the line point is on to the top of the window. I use this all the time, to make text easier to read.

You can put the following code into a separate file and then load it from your `.emacs' file, or you can include it within your `.emacs' file.

Here is the definition:

;;; Line to top of window; ;;; replace three keystroke sequence C-u 0 C-l (defun line-to-top-of-window () "Move the line point is on to top of window." (interactive) (recenter 0))

Now for the keybinding.

Nowadays, function keys as well as mouse button events and non-ASCII characters are written within square brackets, without quotation marks. (In Emacs version 18 and before, you had to write different function key bindings for each different make of terminal.)

I bind line-to-top-of-window to my F6 function key like this:

(global-set-key [f6] 'line-to-top-of-window)

For more information, see section `Rebinding Keys in Your Init File' in The GNU Emacs Manual.

If you run two versions of GNU Emacs, such as versions 20 and 21, and use one `.emacs' file, you can select which code to evaluate with the following conditional:

(cond ((string-equal (number-to-string 20) (substring (emacs-version) 10 12)) ;; evaluate version 20 code ( ... )) ((string-equal (number-to-string 21) (substring (emacs-version) 10 12)) ;; evaluate version 21 code ( ... )))

For example, in contrast to version 20, version 21 blinks its cursor by default. I hate such blinking, as well as some other features in version 21, so I placed the following in my `.emacs' file(12):

(if (string-equal "21" (substring (emacs-version) 10 12)) (progn (blink-cursor-mode 0) ;; Insert newline when you press `C-n' (next-line) ;; at the end of the buffer (setq next-line-add-newlines t) ;; Turn on image viewing (auto-image-file-mode t) ;; Turn on menu bar (this bar has text) ;; (Use numeric argument to turn on) (menu-bar-mode 1) ;; Turn off tool bar (this bar has icons) ;; (Use numeric argument to turn on) (tool-bar-mode nil) ;; Turn off tooltip mode for tool bar ;; (This mode causes icon explanations to pop up) ;; (Use numeric argument to turn on) (tooltip-mode nil) ;; If tooltips turned on, make tips appear promptly (setq tooltip-delay 0.1) ; default is one second ))

(You will note that instead of typing (number-to-string 21), I decided to save typing and wrote `21' as a string, "21", rather than convert it from an integer to a string. In this instance, this expression is better than the longer, but more general (number-to-string 21). However, if you do not know ahead of time what type of information will be returned, then the number-to-string function will be needed.)