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 Sender: Mailing list for the LaTeX3 project <[log in to unmask]> Subject: Re: \InputTranslation From: Lars Hellström <[log in to unmask]> Date: Wed, 13 Jun 2001 14:57:54 +0200 In-Reply-To: Reply-To: Mailing list for the LaTeX3 project <[log in to unmask]> Parts/Attachments: text/plain (63 lines) ```At 00.10 +0200 2001-06-11, I wrote: >The main problem I see with context labels is that of when they should be >attached, since one cannot do any context-dependent processing before the >context is determined. I can think of at least three different models: [snip] >3. Have command-like markup for context-switching, but attach labels as >part of the tokenization. This has the merit of looking like current LaTeX >markup and allowing LaTeX to keep all ICR strings fully context-labeled, >but it would also mean that processing of markup is a two-step process >(first all language markup is processed, then all the rest). That doesn't >feel right. Here I was thinking of having the processing done by OCPs or something similar. The problem with this is of course that these OCPs would have to parse the input rather thoroughly to actually determine that a certain command is markup for a context switch and not part of something else. In particular one would need one such interpreting OCP for every set of catcodes being used, since they otherwise almost certainly would get things wrong. This is rather unrealistic, and having OCPs doing the interpretation would probably also in effect be an invitation to syntax inconsistencies. There is however another way of doing it, by introducing a mechanism which generalizes \outer (thus I'm still in the game of imagining extensions to TeX). Let's say a macro is `exceptional' if it uses this mechanism. Like outer macros, an exceptional macro causes TeX to stop if it occurs in a place where TeX is "absorbing tokens at high speed" (TeXbook p. 206), but unlike outer tokens it doesn't make TeX report an error. Instead TeX should make notes of everything it was currently doing an push that onto some stack, after which it starts executing the replacement text of the macro; in particular, it must be possible to make assignments. What the macro is expected to do is to grab its arguments (with whatever catcodes, input OCPs, language context, etc. in force that are needed for this) and then return (using some new primitive) the resulting token list to TeX, after which TeX resumes whatever processing was interrupted by the exceptional macro. With such a mechanism, one could in the infamous example   \newcommand{\foo}{\languageIC{manadrin}{\unichar{}}} have \languageIC being such an exceptional macro, and thus have the \unichar{} tagged as being mandarin *even in the replacement text of \foo*! More fun one could have with this mechanism would be to define a \verb command that _can_ be used in the arguments (or even replacement texts) of commands! I suspect such a feature could be a useful argument in convincing users untroubled by multilinguality problems to switch to a new typesetting engine. The crux of the matter is of course how much TeX would have to be changed to allow such a mechanism. Seeing the exceptional macros wouldn't be a problem, as TeX is already looking for outer macros. The mechanisms for expanding the next token are already fairly reentrant, so I wouldn't expect many problems there either. What could be tricky is actually executing commmands (since TeX's main_control procedure is never called recursively), but even that doesn't look like such a problem if we stay away from doing typesetting; it seems after_token (related to \afterassignment) is the only global variable that definitely must be saved away! Could perhaps someone with experience of implementing and/or extending TeX please comment on these ideas? Lars Hellström ```