[texhax] Passing Underscore

Philip TAYLOR P.Taylor at Rhul.Ac.Uk
Wed Sep 20 01:20:21 CEST 2006

Reinhard Kotucha wrote:

> Nobody forces you to use double quotes.  TeX still works as it did 20
> years ago.  Why do we need a TeX parser to process filenames? 

We don't.  But we do need to know how TeX operates, and in this
context it is a many-layered operation.  Scanning, parsing and
tokenization all take place, as do execution and expansion, and
with (I think) the sole exception of \lowercase and \uppercase
(which are /horribly/ anomalous), each phase is quite distinct
from the other.  What you are suggesting (if I understand you
correctly) would make \input even more anomalous than \...case,
and that would (I believe) be a very retrograde step in the
evolution of (derivates of) TeX.

>  What is the advantage if files are inaccessible?

They are not.  It is not impossible (or even outrageously
difficult) to construct a control sequence that will expand
to "foo<space><space>bar"; what /cannot/ be achieved is for
"foo<space><space>bar" to appear in the input stream with
normal catcodes and for the two spaces to still be there
after the scanner has performed its function.

** Phil.

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