[texhax] Some puzzling TeX

Uwe Lueck uwe.lueck at web.de
Fri Feb 18 21:37:50 CET 2011

>"Rod Harries" <rod at harries.net.nz>, 17.02.2011 00:44:25:
>> I am trying to understand why  one would write
>> \def\:{\let\@sptoken= } \: %
>> instead of just \let\@sptoken=   %
>> or \def\@sptoken{ }

I wrote 17.02.2011 13:20:53:
> Isn't this one of the (rather rare) cases where the documentation of latex.ltx 
> -- source2e.pdf, ltdefns.dtx -- is quite comprehensive? 

In order to explain why \def\@sptoken{ } is useless, I should have pointed 
to the explanation of \@ifnch _preceding_ the explanation of \@sptoken in 
source2e.pdf (ltdefns.dtx):

    \@ifnch is a tricky macro to skip any space tokens that may appear before the
character in question. If it encounters a space token, it calls xifnch.

259 \def\@ifnch{%
260   \ifx\@let at token\@sptoken

\@sptoken in the first instance is a part of implementing the functionality 
of LaTeX's internal \@ifnextchar.

RTFM! - ) -- Uwe.

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