[OS X TeX] PDF Sync and different fonts/encodings?

[Morten Høgholm]

On Mon, 06 Feb 2006 20:19:23 +0100, Frank STENGEL <fstengel at mac.com> wrote:

>
> Le 6 févr. 06 à 18:54, Morten Høgholm a écrit :
>
>>
>> Careful, the above will most likely lead to an error like
>>   ! TeX capacity exceeded, sorry [input stack size=5000].
>>
>> What we want here is to insert \@PDFSYNC unexpanded into \everymath  
>> while making sure we do not get an infinite loop with \everymath  
>> calling itself. Hence the above code should be
>>   \expandafter\everymath\expandafter{\expandafter\@PDFSYNC\the 
>> \everymath}
>
> Thanks. To test the line I posted, I had actually tried adding something  
> to pdfsync's \everymath, and that worked: the thing I had added was non  
> expandable. I am not surprised the reverse would fail... By the way, why  
> doesn't the following work?
>
> \expandafter\everymath\expandafter{\noexpand\@PDFSYNC\the\everymath}

First expansion results in \noexpand being expanded which leaves \@PDFSYNC  
as it is[*] and \the\everymath untouched. Then the assignment takes places  
and you now have
   \everymath{\@PDFSYNC\the\everymath}

Only use \noexpand when doing an \edef or \xdef or when you rely on  
something so dirty that \noexpand will work for you.

And here comes the *:
\begin{dirtyusesofnoexpand}
   \noexpand temporarily turns the next token into \relax if it was  
expandable so actually \@PDFSYNC temporarily had meaning \relax above but  
that fizzled before anything else happened.

   This means that sometimes you can use a test like  
\expandafter\ifx\noexpand<token><token> which would return <true> if  
<token> was unexpandable like \def and <false> if it was expandable like  
\expandafter. The soon to be released new version of xspace uses such a  
test (watch this space for announcement).

You can also define a macro
   \def\IgnoreOneSpace{\romannumeral`\x\noexpand}
where the \romannumeral will expand until it finds a space or an  
unexpandable token. The \noexpand in itself is an expandable command but  
since it turns a following expandable token into \relax this will stop the  
scanning because \relax is also unexpandable. Try the following small  
document:

\documentclass{minimal}
\def\IgnoreOneSpace{\romannumeral`\a\noexpand}
\def\test#1{``#1''}
\begin{document}
\test{abc}, \test{ abc}
\end{document}

This method is used in the rather new (an unfinished) l3keyval module in  
the LaTeX3 experimental code (available at  
<http://www.latex-project.org/cgi-bin/cvsweb/experimental/expl3/>).

\end{dirtyusesofnoexpand}


-- 
Morten
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