[texhax] \newif, \csname and \endcsname

[Heiko Oberdiek]

On Mon, Jan 31, 2011 at 08:39:06AM +0100, jfbu wrote:

> >\newif\ifok
> >\newif\ifnotok
> >\newcommand{\printtest}{%
> >\csname ifok\endcsname\csname ifnotok\endcsname print test\fi\fi}

> >\printtest

> >Tex complains that there is an "Extra \fi", why?
> 
> I can not say why, but

Already explained by Uwe Lueck.

> 2. the problem seems to be fixed by that version:
> 
> \newcommand{\printtest}{%
> \expandafter\expandafter\csname ifok\endcsname\csname
> ifnotok\endcsname print test\fi\fi}

Or with one \expandafter only:

\newcommand{\printtest}{%
  \csname ifok\expandafter\endcsname
    \csname ifnotok\endcsname
      print test%
    \fi
  \fi
}

The first \csname is not the problem, but the
second hides an internal conditional (\ifnotok),
that is unhided by \expandafter.

Yours sincerely
  Heiko Oberdiek