[texhax] Unexisting commands.

[Paul Isambert]

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).
Paul


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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