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From: rbj@dsys.ncsl.nist.GOV (Root Boy Jim)
Newsgroups: comp.emacs
Subject: gnu emacs lisp question
Message-ID: <8907271852.AA18438@dsys.ncsl.nist.gov>
Date: 27 Jul 89 18:52:19 GMT
Sender: news@bbn.COM
Organization: National Institute of Standards and Technology
	formerly National Bureau of Standards
Lines: 83

? From: Jimmy Aitken <mcvax!ukc!pyrltd!jimmy@uunet.uu.net>

? This is my first attempt at a lisp routine for GNU emacs so excuse the
? sloppyness/incorrectness.  What I'm trying to do is toggle certain
? vlaaues of variables/states in GNU emacs so that they can be changed
? via a single keystroke rather than setting the variable manually.  I
? wrote the function by looking at the code for other lisp functions in
? the lisp directory of GNU.  Things seem to work OK for the readonly
? funtion, but for the clt-arrow, wrap, and mode changes the effect of
? changing the variable doesn't appear until I redraw the screen.  Can
? anybody explain why and, more importantly, how to fix it?  Also if

Yeah. If you need to redraw the screen, do so in your lisp code.

? there are any style improvements I'll gladly accept criticism.

Consider these gentle criticisms of style.

? many thanks,

? Jimmy
? Here's the code:
? (defun toggle ()
?   "Toggle the values of certain variables."
?   (interactive)
?   (message
?    "toggle: srwct (control^ searchanycase readonly textmode wrap)")
?   (let ((char (read-char)))

The (let), (message), and (read-char) can be done inside (interactive):

	(defun toggle (what)
	  "Toggle ..."
	  (interactive "cToggle: ")

This has the advantage of allowing your function to be called as
(toggle ?c) from other elisp code. BTW, toggle is too generic a name

?     (if (char-equal char (string-to-char "c"))

Characters are denoted as a `?' followed by the character desired.
Thus, (if (char-equal char ?c) ...)
?\C-x is C-x, ?\M-x is M-x, ?\M-C-x is M-C-X, ?\n is \n, ?\e is ESC

In elisp, characters are numbers, and numbers can be compared with
(eq) as well as (=). But if you prefer (char-equal), that's fine,
as it will be more portable and you're saying what you mean.

This sequence of (if)'s should really be coded as a cond. A cond is a
good way to implement a case statement, which is what you are doing.
The format is

	(cond				C language equivalent
		((c1) (e1))	if (c1) { e1; } else
		((c2) (e2))	if (c2) { e2; } else
		....		...
		(t    (en))	{ en; }
	)

?         (set 'ctl-arrow (not ctl-arrow)))

Why don't you use setq instead of set? Perhaps it makes a difference
if a variable is a local one?

?     (if (char-equal char (string-to-char "r"))
?         (toggle-read-only))
?     (if (char-equal char (string-to-char "s"))
?         (setq case-fold-search (not case-fold-search)))
?     (if (char-equal char (string-to-char "t"))
?         (if (eq major-mode 'fundamental-mode)
?             (text-mode)
?           (fundamental-mode)))
?     (if (char-equal char (string-to-char "w"))
?         (setq truncate-lines (not truncate-lines)))
?     ))
? -- 
?       -m-------  Jimmy Aitken                Phone : +44 252 373035
?     ---mmm-----  Pyramid Technology Ltd      PSS   : 234248300152
?   -----mmmmm---  Concept 2000, Farnboro' Rd. Telex : 859056
? -------mmmmmmm-  Farnboro', Hants GU14 7NA   ...!mcvax!ukc!pyrltd!jimmy

	Root Boy Jim
	Have GNU, Will Travel.