[texhax] Unexisting commands.

Paul Isambert zappathustra at free.fr
Thu Apr 15 14:39:37 CEST 2010

Joseph, you're right, I've spoken too hastily, the problem comes from 
luaotfload.sty (which loads ifluatex), not from ifluatex. However, the 
questions remains.
As mentionned by Chris and Robin, anybody is free to do whatever s/he 
wants, but there seems to me there isn't any kind of invitation anywhere 
to follow some rules. Actually my question was just the tip of a 
personal iceberg about the desirability of a format-independent API (and 
thus my question perhaps didn't make much sense in itself); this answers 
Philipp's point that "everyone should use packages like etoolbox," a 
good suggestion... except we have no format-independent etoolbox 
(fortunately we still have \newif and friends, which probably satisfy 
everyone, barring \outer-worshippers).

Robin Fairbairns a écrit :
> Philipp Stephani <st_philipp at yahoo.de> wrote:
>> Am 14.04.2010 um 13:33 schrieb Paul Isambert:
>>> Shouldn't we try to all use the same construction to test for the existence of commands?
>> You should normally treat \relax as undefined, but nevertheless take
>> care not to define control sequences with \csname. Everyone should use
>> packages like etoolbox for these tests because they are not trivial. 
> as chris rowley said earlier, what's good and what's obeyed are
> necessarily different things.
>>> If we took e-TeX for granted, then \ifcsname would solve the problem.
>> Even without e-TeX, you can check for the existence of control
>> sequences without visible side effects: 
>> \begingroup\expandafter\expandafter\expandafter\endgroup
>> \expandafter\ifx\csname ...\endcsname\relax ...
> yup.  trips off the toungue like a chunk of finnegan's wake.
> (i wrote that one down, long ago, with a thought of sticking it in the
> faq.  i've still not done that, due to my lack of conviction.)
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