[texhax] [TeXhax] Latex: dumbing down ?

Yuri Robbers yuri.robbers at gmail.com
Sun Sep 3 11:57:50 CEST 2006

I see this discussion going back and forth and many people repeating what
they said before only slightly more extensively, or with slightly more
examples. This has turned into a textbook example of basic logic. A random
case from a random person (anonymized , albeit rather too simplistically,
because it is no more than an example) is this one:

Let me explain why I think that LateX and plain tex cannot be
> combined and why I use \@ifundefined as an example.
> The definition of \@ifundefined is
>     \expandafter \ifx \csname #1\endcsname \relax \expandafter
>     \@firstoftwo \else \expandafter \@secondoftwo \fi
> Hence, if someone says \@ifundefined{foo}{}{} and tries later
> \ifx\foo\undefined this will always succeed because \@ifundefined sets
> undefined cotrol sequences to \relax.
> You cannot safely use \ifx in LaTeX.

One example is not going to prove a general point ever. Nor are two, ten, or
10000 examples. Perhaps it is bad, bad, bad to use plain TeX in those
examples, but perfectly safe to use plain TeX in all other cases.

The same of course holds the other way round: no amount of examples, be they
two, ten or 10000, showing ways in which plain TeX does work in LaTeX will
prove the general point that it does. Maybe it works fine in those examples,
but wreaks havoc in any other case.

By now we have seen that there are many cases in which a) using plain TeX in
LaTeX creates a horrible problem, and b) using plain TeX in LaTeX is the
best thing since sliced bread. Isn't the most sensible conclusion that
sometimes it works, sometimes it doesn't. If you know what you're doing,
you're not likely to need advice and if you don't know what you're doing
then either don't try it all (probably best for most inexperienced users) or
by all means do try it but take the responsibility when it comes to bite you
in the behind (probably best for inexperienced users that want to learn
something about the internals of teh system and don't mind things going
wrong from time to time)?

Just my two pence,

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