slowbox.dtx: Delete spurious `{'.
[mdwtools] / at.dtx
1 % \begin{meta-comment}
2 %
3 % $Id: at.dtx,v 1.1 2002/02/03 20:49:02 mdw Exp $
4 %
5 % Allow @-commands
6 %
7 % (c) 1995 Mark Wooding
8 %
9 % \end{meta-comment}
10 %
11 % \begin{meta-comment} <general public licence>
12 %%
13 %% at package -- support for `@' commands'
14 %% Copyright (c) 1996 Mark Wooding
15 %%
16 %% This program is free software; you can redistribute it and/or modify
17 %% it under the terms of the GNU General Public License as published by
18 %% the Free Software Foundation; either version 2 of the License, or
19 %% (at your option) any later version.
20 %%
21 %% This program is distributed in the hope that it will be useful,
22 %% but WITHOUT ANY WARRANTY; without even the implied warranty of
23 %% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
24 %% GNU General Public License for more details.
25 %%
26 %% You should have received a copy of the GNU General Public License
27 %% along with this program; if not, write to the Free Software
28 %% Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
29 %%
30 % \end{meta-comment}
31 %
32 % \begin{meta-comment} <Package preamble>
33 %<+package>\NeedsTeXFormat{LaTeX2e}
34 %<+package>\ProvidesPackage{at}
35 %<+package> [1996/05/02 1.3 @-command support (MDW)]
36 % \end{meta-comment}
37 %
38 % \CheckSum{355}
39 %% \CharacterTable
40 %% {Upper-case \A\B\C\D\E\F\G\H\I\J\K\L\M\N\O\P\Q\R\S\T\U\V\W\X\Y\Z
41 %% Lower-case \a\b\c\d\e\f\g\h\i\j\k\l\m\n\o\p\q\r\s\t\u\v\w\x\y\z
42 %% Digits \0\1\2\3\4\5\6\7\8\9
43 %% Exclamation \! Double quote \" Hash (number) \#
44 %% Dollar \$ Percent \% Ampersand \&
45 %% Acute accent \' Left paren \( Right paren \)
46 %% Asterisk \* Plus \+ Comma \,
47 %% Minus \- Point \. Solidus \/
48 %% Colon \: Semicolon \; Less than \<
49 %% Equals \= Greater than \> Question mark \?
50 %% Commercial at \@ Left bracket \[ Backslash \\
51 %% Right bracket \] Circumflex \^ Underscore \_
52 %% Grave accent \` Left brace \{ Vertical bar \|
53 %% Right brace \} Tilde \~}
54 %%
55 %
56 % \begin{meta-comment} <driver>
57 %
58 %<*driver>
59 \input{mdwtools}
60 \describespackage{at}
61 \def\atsign{@}
62 \def\athyphen{@\mbox{-}}
63 \aton
64 \atlet p=\package
65 \atdef at{\package{at}}
66 \atdef={\mbox{-}}
67 \atdef-{@@@=}
68 \atlet.=\syntax
69 \mdwdoc
70 %</driver>
71 %
72 % \end{meta-comment}
73 %
74 % \section{User guide}
75 %
76 % The @at\ package is an attempt to remove a lot of tedious typing that
77 % ends up in \LaTeX\ documents, by expanding the number of short command
78 % names available. The new command names begin with the `|@|' character,
79 % rather than the conventional `|\|', so you can tell them apart.
80 %
81 % The package provides some general commands for defining @-commands, and
82 % then uses them to define some fairly simple ones which will be useful to
83 % most people.
84 %
85 % The rules for @-command names aren't terribly complex:
86 % \begin{itemize}
87 % \item If the first character of the name is a letter, then the command name
88 % consists of all characters up to, but not including, the first
89 % nonletter. Spaces following the command name are ignored.
90 % \item If the first character of the name is a backslash, then the @-command
91 % name consists of the control sequence introduced by the backslash.
92 % \item Otherwise, the command name consists only of that first character.
93 % Spaces following the name are not ignored, unless that character
94 % was itself a space character.
95 % \end{itemize}
96 %
97 % Usually, digits are not considered to be letters. However, the
98 % \package{at} package will consider digits to be letters if you give it the
99 % \textsf{digits} option in the |\usepackage| command. (Note that this
100 % only affects the \package{at} package; it won't change the characters
101 % allowed in normal command names.)
102 %
103 % \DescribeMacro{\atallowdigits}
104 % \DescribeMacro{\atdisallowdigits}
105 % You can enable and disable digits being considered as letters dynamically.
106 % The |\atallowdigits| command allows digits to be used as letters;
107 % |\atdisallowdigits| prevents this. Both declarations follow \LaTeX's
108 % usual scoping rules. Both of these commands have corresponding
109 % environments with the same names (without the leading `|\|', obviously).
110 %
111 % \subsection{Defining \athyphen commands}
112 %
113 % \DescribeMacro{\newatcommand}
114 % \DescribeMacro{\renewatcommand}
115 % The |\newatcommand| command will define a new @-command using a syntax
116 % similar to |\newcommand|. For example, you could define
117 % \begin{listing}
118 %\newatcommand c[1]{\chapter{#1}}
119 % \end{listing}
120 % to make @.{"@c{"<name>"}"} equivalent to @.{"\\chapter{"<name>"}"}.
121 %
122 % A |\renewatcommand| is also provided to redefine existing commands, should
123 % the need arise.
124 %
125 % \DescribeMacro{\atdef}
126 % For \TeX\ hackers, the |\atdef| command defines @-commands using a syntax
127 % similar to \TeX's built-in |\def|.
128 %
129 % As an example, the following command makes @.{"@/"<text>"/"} write its
130 % argument \<text> in italics:
131 % \begin{listing}
132 %\atdef/#1/{\textit{#1}}
133 % \end{listing}
134 % The real implementation of the |@/|\dots|/| command is a bit more
135 % complex, and is given in the next section.
136 %
137 % You can use all of \TeX's features for defining the syntax of your
138 % command. (See chapter~20 of @/The \TeX book/ for more details.)
139 %
140 % \DescribeMacro{\atlet}
141 % Since |\atdef| is provided to behave similarly to |\def|, @at\ provides
142 % |\atlet| which works similarly to |\let|. For example you can say
143 % \begin{listing}
144 %\atlet!=\index
145 % \end{listing}
146 % to allow the short |@!| to behave exactly like |\index|.
147 %
148 % Note that all commands defined using these commands are robust even if you
149 % use fragile commands in their definitions. Unless you start doing very
150 % strange things, @-commands never need |\protect|ing.
151 %
152 % \subsection{Predefined \athyphen commands}
153 %
154 % A small number of hopefully useful commands are provided by default.
155 % These are described in the table below:
156 %
157 % \bigskip \begin{center} \begin{tabular}{lp{3in}} \hline
158 % \bf Command & \bf Meaning \\ \hline
159 % @.{"@@"} & Typesets an `@@' character. \\
160 % @.{"@/"<text>"/"} & In text (LR or paragraph) mode, typesets its
161 % argument emphasised. In maths mode, it
162 % always chooses italics. \\
163 % @.{"@*"<text>"*"} & Typesets its argument \<text> in bold. \\
164 % @.{"@i{"<text>"}"} & Equivalent to `@.{"\\index{"<text>"}"}'. \\
165 % @.{"@I{"<text>"}"} & As for |@i|, but also writes its argument
166 % to the document. \\ \hline
167 % \end{tabular} \end{center} \bigskip
168 %
169 % Package writers should not rely on any predefined @-commands -- they're
170 % provided for users, and users should be able to redefine them without
171 % fear of messing anything up. (This includes the `standard' commands
172 % provided by the @at\ package, by the way. They're provided in the vague
173 % hope that they might be useful, and as examples.)
174 %
175 % \implementation
176 %
177 % \section{Implementation}
178 %
179 % \begin{macrocode}
180 %<*package>
181 % \end{macrocode}
182 %
183 % \subsection{Options handling}
184 %
185 % We need a switch to say whether digits should be allowed. Since this
186 % is a user thing, I'll avoid |\newif| and just define the thing by hand.
187 %
188 % \begin{macrocode}
189 \def\atallowdigits{\let\ifat@digits\iftrue}
190 \def\atdisallowdigits{\let\ifat@digits\iffalse}
191 % \end{macrocode}
192 %
193 % Now define the options.
194 %
195 % \begin{macrocode}
196 \DeclareOption{digits}{\atallowdigits}
197 \DeclareOption{nodigits}{\atdisallowdigits}
198 \ExecuteOptions{nodigits}
199 \ProcessOptions
200 % \end{macrocode}
201 %
202 % \subsection{How the commands work}
203 %
204 % Obviously we make the `@@' character active. It inspects the next
205 % character (or argument, actually -- it can be enclosed in braces for
206 % longer commands, although this is a bit futile), and builds the command
207 % name from that.
208 %
209 % The |\at| command is equivalent to the active `@@' character always.
210 %
211 %
212 % \subsection{Converting command names}
213 %
214 % We need to be able to read an @-command name, and convert it to a normal
215 % \TeX\ control sequence. First, we declare some control sequences for
216 % braces, which we need later.
217 %
218 % \begin{macrocode}
219 \begingroup
220 \catcode`\<1
221 \catcode`\>2
222 \catcode`\{12
223 \catcode`\}12
224 \gdef\at@lb<{>
225 \gdef\at@rb<}>
226 \gdef\at@spc< >
227 \endgroup
228 % \end{macrocode}
229 %
230 % I'll set up some helper routines now, to help me read the command
231 % names. The way this works is that we |\futurelet| the token into
232 % |\@let@token|. These routines will then sort out what to do next.
233 %
234 % \begin{macro}{\at@test}
235 %
236 % Given an |\if|\dots\ test, does its first or second argument.
237 %
238 % \begin{macrocode}
239 \def\at@test#1\then{%
240 #1\expandafter\@firstoftwo\else\expandafter\@secondoftwo\fi%
241 }
242 % \end{macrocode}
243 %
244 % \end{macro}
245 %
246 % \begin{macro}{\at@ifcat}
247 %
248 % Checks the category code of the current character. If it matches the
249 % argument, it does its second argument, otherwise it does the third.
250 %
251 % \begin{macrocode}
252 \def\at@ifcat#1{\at@test\ifcat#1\noexpand\@let@token\then}
253 % \end{macrocode}
254 %
255 % \end{macro}
256 %
257 % \begin{macro}{\at@ifletter}
258 %
259 % This routine tests the token to see if it's a letter, and if so adds
260 % it to the token list and does the first argument; otherwise it does the
261 % second argument. It accepts digits as letters if the switch is turned
262 % on.
263 %
264 % There's some fun later, so I'll describe this slowly. First, we compare
265 % the category code to a letter, and if we have a match, we know we're done;
266 % we need to pick up the letter as an argument. If the catcode is `other',
267 % we must compare with numbers to see if it's in range.
268 %
269 % \begin{macrocode}
270 \def\at@ifletter#1#2{%
271 \at@ifcat x%
272 {\at@ifletter@ii{#1}}%
273 {\at@ifcat 0%
274 {\at@ifletter@i{#1}{#2}}%
275 {#2}%
276 }%
277 }
278 % \end{macrocode}
279 %
280 % Right. It's `other' (so it's safe to handle as a macro argument) and we
281 % need to know if it's a digit. This is a little tricky: I use |\if| to
282 % compare two characters. The first character is~`1' or~`0' depending on the
283 % `digit' switch; the second is~`1' or~`x' depending on whether it's actually
284 % a digit. They'll only match if everything's worked out OK.
285 %
286 % \begin{macrocode}
287 \def\at@ifletter@i#1#2#3{%
288 \at@test\if%
289 \ifat@digits1\else0\fi%
290 \ifnum`#3<`0x\else\ifnum`#3>`9x\else1\fi\fi%
291 \then%
292 {\at@ifletter@ii{#1}{#3}}%
293 {#2#3}%
294 }
295 % \end{macrocode}
296 %
297 % Right; we have the character, so add it to the list and carry on.
298 %
299 % \begin{macrocode}
300 \def\at@ifletter@ii#1#2{\toks@\expandafter{\the\toks@#2}#1}
301 % \end{macrocode}
302 %
303 % \end{macro}
304 %
305 % Now we define the command name reading routines. We have @/almost/ the
306 % same behaviour as \TeX, although we can't support `|%|' characters for
307 % reasons to do with \TeX's tokenising algorithm.
308 %
309 % \begin{macro}{\at@read@name}
310 %
311 % The routine which actually reads the command name works as follows:
312 % \begin{enumerate}
313 % \item Have a peek at the next character. If it's a left or right brace,
314 % then use the appropriate character.
315 % \item If the character is not a letter, just use the character (or whole
316 % control sequence.
317 % \item Finally, if it's a letter, keep reading letters until we find one
318 % that wasn't.
319 % \end{enumerate}
320 %
321 % First, we do some setting up and read the first character
322 %
323 % \begin{macrocode}
324 \def\at@read@name#1{%
325 \let\at@next=#1%
326 \toks@{}%
327 \futurelet\@let@token\at@rn@i%
328 }
329 % \end{macrocode}
330 %
331 % Next, sort out what to do, based on the category code.
332 %
333 % \begin{macrocode}
334 \def\at@rn@i{%
335 \def\@tempa{\afterassignment\at@rn@iv\let\@let@token= }%
336 \at@ifletter%
337 {\futurelet\@let@token\at@rn@iii}%
338 {\at@ifcat\bgroup%
339 {\toks@\expandafter{\at@lb}\@tempa}%
340 {\at@ifcat\egroup%
341 {\toks@\expandafter{\at@rb}\@tempa}%
342 {\at@ifcat\at@spc%
343 {\toks@{ }\@tempa}%
344 {\at@rn@ii}%
345 }%
346 }%
347 }%
348 }
349 % \end{macrocode}
350 %
351 % Most types of tokens can be fiddled using |\string|.
352 %
353 % \begin{macrocode}
354 \def\at@rn@ii#1{%
355 \toks@\expandafter{\string#1}%
356 \at@rn@iv%
357 }
358 % \end{macrocode}
359 %
360 % We've found a letter, so we should check for another one.
361 %
362 % \begin{macrocode}
363 \def\at@rn@iii{%
364 \at@ifletter%
365 {\futurelet\@let@token\at@rn@iii}%
366 {\@ifnextchar.\at@rn@iv\at@rn@iv}%
367 }
368 % \end{macrocode}
369 %
370 % Finally, we need to pass the real string, as an argument, to the
371 % macro. We make |\@let@token| relax, since it might be something which will
372 % upset \TeX\ later, e.g., a |#| character.
373 %
374 % \begin{macrocode}
375 \def\at@rn@iv{%
376 \let\@let@token\relax%
377 \expandafter\at@next\csname at.\the\toks@\endcsname%
378 }
379 % \end{macrocode}
380 %
381 % \end{macro}
382 %
383 % \begin{macro}{\at@cmdname}
384 %
385 % Given a control sequence, work out which @-command it came from.
386 %
387 % \begin{macrocode}
388 \def\at@cmdname#1{\expandafter\at@cmdname@i\string#1\@@foo}
389 % \end{macrocode}
390 %
391 % Now extract the trailing bits.
392 %
393 % \begin{macrocode}
394 \def\at@cmdname@i#1.#2\@@foo{#2}
395 % \end{macrocode}
396 %
397 % \end{macro}
398 %
399 % \begin{macro}{\at@decode}
400 %
401 % The |\at@decode| macro takes an extracted @-command name, and tries to
402 % execute the correct control sequence derived from it.
403 %
404 % \begin{macrocode}
405 \def\at@decode#1{%
406 \at@test\ifx#1\relax\then{%
407 \PackageError{at}{Unknown @-command `@\at@cmdname#1'}{%
408 The @-command you typed wasn't recognised, so I've ignored it.
409 }%
410 }{%
411 #1%
412 }%
413 }
414 % \end{macrocode}
415 %
416 % \end{macro}
417 %
418 % \begin{macro}{\@at}
419 %
420 % We'd like a measure of compatibility with @p{amsmath}. The @-commands
421 % provided by @p{amsmath} work only in maths mode, so this gives us a way of
422 % distinguishing. If the control sequence |\Iat| is defined, and we're in
423 % maths mode, we'll call that instead of doing our own thing.
424 %
425 % \begin{macrocode}
426 \def\@at{%
427 \def\@tempa{\at@read@name\at@decode}%
428 \ifmmode\ifx\Iat\not@@defined\else%
429 \let\@tempa\Iat%
430 \fi\fi%
431 \@tempa%
432 }
433 % \end{macrocode}
434 %
435 % \end{macro}
436 %
437 %
438 % \subsection{Defining new commands}
439 %
440 % \begin{macro}{\at@buildcmd}
441 %
442 % First, we define a command to build these other commands:
443 %
444 % \begin{macrocode}
445 \def\at@buildcmd#1#2{%
446 \expandafter\def\csname\expandafter
447 \@gobble\string#1@decode\endcsname##1{#2##1}%
448 \edef#1{%
449 \noexpand\at@read@name%
450 \expandafter\noexpand%
451 \csname\expandafter\@gobble\string#1@decode\endcsname%
452 }%
453 }
454 % \end{macrocode}
455 %
456 % \end{macro}
457 %
458 % \begin{macro}{\newatcommand}
459 % \begin{macro}{\renewatcommand}
460 % \begin{macro}{\provideatcommand}
461 % \begin{macro}{\atdef}
462 % \begin{macro}{\atshow}
463 %
464 % Now we define the various operations on @-commands.
465 %
466 % \begin{macrocode}
467 \at@buildcmd\newatcommand\newcommand
468 \at@buildcmd\renewatcommand\renewcommand
469 \at@buildcmd\provideatcommand\providecommand
470 \at@buildcmd\atdef\def
471 \at@buildcmd\atshow\show
472 % \end{macrocode}
473 %
474 % \end{macro}
475 % \end{macro}
476 % \end{macro}
477 % \end{macro}
478 % \end{macro}
479 %
480 % \begin{macro}{\atlet}
481 %
482 % |\atlet| is rather harder than the others, because we want to allow people
483 % to say things like @.{"\\atlet"<name>"=@"<name>}. The following hacking
484 % does the trick. I'm trying very hard to duplicate |\let|'s behaviour with
485 % respect to space tokens here, to avoid any surprises, although there
486 % probably will be some differences. In particular, |\afterassignment|
487 % won't work in any sensible way.
488 %
489 % First, we read the name of the @-command we're defining. We also open
490 % a group, to stop messing other people up, and make `@@' into an `other'
491 % token, so that it doesn't irritatingly look like its meaning as a control
492 % sequence.
493 %
494 % \begin{macrocode}
495 \def\atlet{%
496 \begingroup%
497 \@makeother\@%
498 \at@read@name\atlet@i%
499 }
500 % \end{macrocode}
501 %
502 % Put the name into a scratch macro for later use. Now see if there's an
503 % equals sign up ahead. If not, this will gobble any spaces in between the
504 % @-command name and the argument.
505 %
506 % \begin{macrocode}
507 \def\atlet@i#1{%
508 \def\at@temp{#1}%
509 \@ifnextchar=\atlet@ii{\atlet@ii=}%
510 }
511 % \end{macrocode}
512 %
513 % Now we gobble the equals sign (whatever catcode it is), and peek at the
514 % next token up ahead using |\let| with no following space.
515 %
516 % \begin{macrocode}
517 \def\atlet@ii#1{\afterassignment\atlet@iii\global\let\at@gnext=}
518 % \end{macrocode}
519 %
520 % The control sequence |\at@gnext| is now |\let| to be whatever we want the
521 % @-command to be, unless it's picked up an `@@' sign. If it has, we've
522 % eaten the |@| token, so just read the name and pass it on. Otherwise,
523 % we can |\let| the @-command directly to |\at@gnext|. There's some
524 % nastiness here to make |\the\toks@| expand before we close the group and
525 % restore its previous definition.
526 %
527 % \begin{macrocode}
528 \def\atlet@iii{%
529 \if @\noexpand\at@gnext%
530 \expandafter\at@read@name\expandafter\atlet@iv%
531 \else%
532 \expandafter\endgroup%
533 \expandafter\let\at@temp= \at@gnext%
534 \fi%
535 }
536 % \end{macrocode}
537 %
538 % We've read the source @-command name, so just copy the definitions over.
539 %
540 % \begin{macrocode}
541 \def\atlet@iv#1{%
542 \expandafter\endgroup%
543 \expandafter\let\at@temp=#1%
544 }
545 % \end{macrocode}
546 %
547 % \end{macro}
548 %
549 %
550 % \subsection{Robustness of \athyphen commands}
551 %
552 % We want all @-commands to be robust. We could leave them all being
553 % fragile, although making robust @-commands would then be almost impossible.
554 % There are two problems which we must face:
555 %
556 % \begin{itemize}
557 %
558 % \item The `|\@at|' command which scans the @-command name is (very)
559 % fragile. I could have used |\DeclareRobustCommand| for it (and in
560 % fact I did in an earlier version), but that doesn't help the other
561 % problem at all.
562 %
563 % \item The `name' of the @-command may contain active characters or control
564 % sequences, which will be expanded at the wrong time unless we do
565 % something about it now.
566 %
567 % \end{itemize}
568 %
569 % We must also be careful not to introduce extra space characters into any
570 % files written, because spaces are significant in @-commands. Finally,
571 % we have a minor problem in that most auxiliary files are read in with
572 % the `@@' character set to be a letter.
573 %
574 % \begin{macro}{\at}
575 %
576 % Following the example of \LaTeX's `short' command handling, we'll define
577 % |\at| to decide what to do depending on what |\protect| looks like. If
578 % we're typesetting, we just call |\@at| (above) and expect it to cope.
579 % Otherwise we call |\at@protect|, which scoops up the |\fi| and the |\@at|,
580 % and inserts other magic.
581 %
582 % \begin{macrocode}
583 \def\at{\ifx\protect\@typeset@protect\else\at@protect\fi\@at}
584 % \end{macrocode}
585 %
586 % \end{macro}
587 %
588 % \begin{macro}{\at@protect}
589 %
590 % Since we gobbled the |\fi| from the above, we must put that back. We then
591 % need to do things which are more complicated. If |\protect| is behaving
592 % like |\string|, then we do one sort of protection. Otherwise, we assume
593 % that |\protect| is being like |\noexpand|.
594 %
595 % \begin{macrocode}
596 \def\at@protect\fi#1{%
597 \fi%
598 \ifx\protect\string%
599 \expandafter\at@protect@string%
600 \else%
601 \expandafter\at@protect@noexpand%
602 \fi%
603 }
604 % \end{macrocode}
605 %
606 % \end{macro}
607 %
608 % \begin{macro}{\at@protect@string}
609 %
610 % When |\protect| is |\string|, we don't need to be able to recover the
611 % original text particularly accurately -- it's for the user to look at.
612 % Therefore, we just output a $|@|_{11}$ and use |\string| on the next
613 % token. This must be sufficient, since we only allow multi-token command
614 % names if the first token is a letter (code~11).
615 %
616 % \begin{macrocode}
617 \def\at@protect@string{@\string}
618 % \end{macrocode}
619 %
620 % \end{macro}
621 %
622 % \begin{macro}{\at@protect@noexpand}
623 %
624 % This is a little more complex, since we're still expecting to be executed
625 % properly at some stage. However, there's a cheeky dodge we can employ
626 % since the |\at| command is thoroughly robustified (or at least it will be
627 % by the time we've finished this). All |\@unexpandable@protect| does
628 % is confer repeated robustness on a fragile command. Since our command
629 % is robust, we don't need this and we can get away with just using a
630 % single |\noexpand|, both for the |\@at@| command and the following token
631 % (which we must robustify, because no-one else can do it for us -- if
632 % anyone tries, they end up using the |@\protect| command which is rather
633 % embarassing).
634 %
635 % I'll give the definition, and then examine how this expands in various
636 % cases.
637 %
638 % \begin{macrocode}
639 \def\at@protect@noexpand{\noexpand\@at@ @\noexpand}
640 \def\@at@#1{\at}
641 % \end{macrocode}
642 %
643 % A few points, before we go into the main examination of the protection.
644 % I've inserted a $|@|_{11}$ token, which is gobbled by |\@at@| when the
645 % thing is finally expanded fully. This prevents following space tokens
646 % in an |\input| file from being swallowed because they follow a control
647 % sequence. (I can't use the normal $|@|_{13}$ token, because when files
648 % like the |.aux| file are read in, |@| is given code~11 by
649 % |\makeatletter|.)
650 %
651 % \setbox0\hbox{|@at@|}
652 % Now for a description of why this works. When |\at| is expanded, it works
653 % out that |\protect| is either |\noexpand| or |\@unexpandable@protect|, and
654 % becomes |\at@protect@noexpand|. Because of the |\noexpand| tokens, this
655 % stops being expanded once it reaches $\fbox{\box0}\,|@|_{11}\,x$ (where
656 % $x$ is the token immediately following the $|@|_{13}$ character). If this
657 % is expanded again, for example in another |\edef|, or in a |\write| or a
658 % |\mark|, the |\@at@| wakes up, gobbles the following |@| (whatever catcode
659 % it is -- there may be intervening |\write| and |\input| commands) and
660 % becomes |\at|, and the whole thing can start over again.
661 %
662 % \end{macro}
663 %
664 %
665 % \subsection{Enabling and disabling @-commands}
666 %
667 % \begin{macro}{\aton}
668 %
669 % We define the |\aton| command to enable all of our magic. We store
670 % the old catcode in the |\atoff| command, make `@@' active, and make it
671 % do the stuff.
672 %
673 % \begin{macrocode}
674 \def\aton{%
675 \ifnum\catcode`\@=\active\else%
676 \edef\atoff{\catcode`\noexpand\@\the\catcode`\@}%
677 \catcode`\@\active%
678 \lccode`\~`\@%
679 \lowercase{\let~\at}%
680 \fi%
681 }
682 % \end{macrocode}
683 %
684 % \end{macro}
685 %
686 % \begin{macro}{\atoff}
687 %
688 % The |\atoff| command makes `@@' do the stuff it's meant to. We remember
689 % the old catcode and revert to it. This is largely unnecessary.
690 %
691 % \begin{macrocode}
692 \def\atoff{\catcode`\@12}
693 % \end{macrocode}
694 %
695 % \end{macro}
696 %
697 % \begin{macro}{\makeatother}
698 %
699 % Now we make our active `@@' the default outside of package files.
700 %
701 % \begin{macrocode}
702 \let\makeatother\aton
703 % \end{macrocode}
704 %
705 % \end{macro}
706 %
707 % And we must make sure that the user can use all of our nice commands.
708 % Once the document starts, we allow @-commands.
709 %
710 % \begin{macrocode}
711 \AtBeginDocument{\aton}
712 % \end{macrocode}
713 %
714 % \begin{macro}{\dospecials}
715 % \begin{macro}{\@sanitize}
716 %
717 % We must add the `@@' character to the various specials lists.
718 %
719 % \begin{macrocode}
720 \expandafter\def\expandafter\dospecials\expandafter{\dospecials\do\@}
721 \expandafter\def\expandafter\@sanitize\expandafter{%
722 \@sanitize\@makeother\@}
723 % \end{macrocode}
724 %
725 % \end{macro}
726 % \end{macro}
727 %
728 % \subsection{Default \athyphen commands}
729 %
730 % We define some trivial examples to get the user going.
731 %
732 % \begin{macrocode}
733 \expandafter\chardef\csname at.@\endcsname=`\@
734 \atdef*#1*{\ifmmode\mathbf{#1}\else\textbf{#1}\fi}
735 \atdef/#1/{\ifmmode\mathit{#1}\else\emph{#1}\fi}
736 \atlet i=\index
737 \atdef I#1{#1\index{#1}}
738 %</package>
739 % \end{macrocode}
740 %
741 % \hfill Mark Wooding, \today
742 %
743 % \Finale
744 %
745 \endinput