[texhax] question about \if

Heiko Oberdiek heiko.oberdiek at googlemail.com
Fri Nov 12 11:22:12 CET 2010

On Fri, Nov 12, 2010 at 05:31:13PM +1100, Vafa Khalighi wrote:

> \newcommand{\test}[1]{\if#1t True\fi}
> \test{t}
> gives "True" as expected.
> I want to change that so that \test{txys} gives "True" but I do not know
> how?

And what do you want to test?
* argument starts with `t',
* after expansion the first token is `t',
* the argument contains `t',
* ...
The context is important, are assigments allowed or is the
test restricted to expandable contexts?

Variant without expansion:

  \expandafter\ifx\expandafter t\@car#1XX\@nil

Yours sincerely
  Heiko Oberdiek

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