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Tue, 3 Nov 1998 12:11:48 +0100 |
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At 09:53 +0000 1998/11/03, David Carlisle wrote:
>This works for a few more cases, but only a few. What if the quote is
>inside a font change, or a section head, or any other command, you still
>have the potential problem of the lookahead coping with {}.
I was able to make a \leturelet to detect {}:
% Make a definition that uses \futurelet to check the next token,
% and then pick up all arguments until the next token is a } or a \par.
\newtoks\@tget
\def\get{\@tget={}\@get}
\def\@get{\futurelet\@next\@getA}
\def\@getA{%
\ifx\@next\@sptoken%
\let\@@next\@getspace%
\else\ifcat\noexpand\@next{%
\let\@@next\@getarg%
\else\ifcat\noexpand\@next}%
\let\@@next\@getend%
\@tget=\expandafter{\the\@tget\@get@end}%
\else%
\let\@@next\@gettoken%
\fi\fi\fi%
\@@next%
}
It is the funny section
\else\ifcat\noexpand\@next{%
\let\@@next\@getarg%
\else\ifcat\noexpand\@next}%
that makes it possible. I have no idea why it works; TeX seemed to accept it.
>Of course you can follow the above to its logical conclusion of
>implementing _everything_ via active characters and implementing your
>own parsing routines _in_ TeX rather than using the parser built into
>tex-the-program. This is certainly possible (some people have done
>exactly that) but TeX isn't really the best language for implementing a
>parser, and certainly isn't the fastest.
It is extremely difficult to implement any general type of parser; TeX is
not suitable for that.
>If more involved contextual
>analysis is required in the input stream then it probably makes more
>sense to look to an extended system that can provide such extended
>functionality. (Something like omega's OTP processes.) They may not be
>quite what you want here, but the principle is the same, to make a
>controlled extension of the underlying system rather than try to build a
>tower of macros on the rather fragile sand that is tex-the-program.
One needs a successor to TeX, or perhaps a TeX preprocessor.
Hans Aberg
* Email: Hans Aberg <mailto:[log in to unmask]>
* Home Page: <http://www.matematik.su.se/~haberg/>
* AMS member listing: <http://www.ams.org/cml/>
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