[texhax] question about \if

[Vafa Khalighi]

Thanks heaps, Heiko

On Fri, Nov 12, 2010 at 10:57 PM, Heiko Oberdiek <
heiko.oberdiek at googlemail.com> wrote:

> On Fri, Nov 12, 2010 at 10:30:17PM +1100, Vafa Khalighi wrote:
>
> > To be more specific, this is what I have in mind:
> >
> > \newcommand{\setmaindir}[1]{\if#1RTL\pagedir TRT\else \if#1LTR\pagedir
> > TLT\fi\fi}
> >
> > so that
> >
> > \setmaindir{RTL} gives  \pagedir TRT and
> > \setmaindir{LTR} gives \pagedir TLT
>
> \makeatletter
> \newcommand*{\my at pagedir@RTL}{\pagedir TRT}
> \newcommand*{\my at pagedir@LTR}{\pagedir TLT}
> \newcommand*{\setmaindir}[1]{%
>  \ifcsname my at pagedir@#1\endcsname
>    \csname my at pagedir@#1\expandafter\endcsname
>  \else
>    \PackageError{...}%
>      {Invalid argument `#1' for \string\setmaindir}%
>      \@ehc
>  \fi
> }
> \makeatother
>
> Without e-TeX replace \ifcsname by
>  \expandafter\ifx\csname ...\endcsname\relax
> or without the side effect of defining undefined
> commands with meaning \relax:
>  \RequirePackage{ltxcmds}
>  ...
>  \newcommand*{\setmaindir}[1]{%
>    \ltx at IfUndefined{}{%
>      \csname my at pagedir@#1\endcsname
>    }{%
>      \PackageError{...}{...}\@ehc
>    }%
>  }%
> or without the package
>  \newcommand*{\setmaindir}[1]{%
>    \begingroup\expandafter\expandafter\expandafter\endgroup
>    \expandafter\ifx\csname my at pagedir@#1\endcsname\relax
>      \csname my at pagedir@#1\expandafter\endcsname
>    \else
>      \PackageError...
>    \fi
>   }
>
> Yours sincerely
>  Heiko Oberdiek
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I prefer the most bloodcurdling death to living with humility. The only
country I am faithful to, is IRAN. Do not denigrate my last moments...
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