[texhax] The details of \csname, in this specific case

Reinhard Kotucha reinhard.kotucha at web.de
Mon Feb 25 21:46:06 CET 2013

On 2013-02-25 at 19:35:22 +0100, Uwe Lück wrote:

 > > 4) How exactly does TeX come to interpret the #1 as a "character
 > > token," aren't things above value 127 by default labeled "invalid?"
 > I guess the same, and I had to care for this in the fifinddo package 
 > by a loop turning the character codes into "other". 
 > Your code may work due to earlier context that does the same. 
 > I have seen such a loop in the graphics package. From a glance at 
 > inputenc.sty (LaTeX) I guess that it turns them into "active" 
 > instead.
 > I cannot find an answer in The TeXbook quickly about TeX's 
 > (INITEX's) default (would require reading many pages). 
 > AFAIK The TeXbook originally was written 
 > when TeX took 7-bit characters. I would not be surprised 
 > if the default were left to the installation.
 > After what I have experienced and seen, I would say that 
 > it is safe (at least) to "fix" those catcodes before 
 > trying your code.

$ tex -ini \\relax
This is TeX, Version 3.1415926 (TeX Live 2012) (INITEX)

*\showthe\catcode 222
> 12.
<*> \showthe\catcode 222

See also TeXbook, page 39, 4th paragraph.  BTW, the TeXbook already
describes TeX 3, which is an 8-bit engine.


Reinhard Kotucha                                      Phone: +49-511-3373112
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Microsoft isn't the answer. Microsoft is the question, and the answer is NO.

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