[XeTeX] newcommand with optional arguments

[Sven Siegmund]

Hello guys,

Thanks vor the valuable discussion. In fact I do not understand why
Stephen's code ...

\newcommand{\nuu}[2][]{%
       \textit{#2}\ %
       \ifx#1\empty
       \else
               `#1'
       \fi
}

... does not work if I write \nuu[22]{this} but does work when I write
\nuu[goat]{mudi}. The result of

\nuu{this} \nuu[22]{this} \nuu[goat]{mudi}

is

this this mudi 'goat'

Ross's "bullet proof" codes have simirar bugs as the first solution
suggested by Ulrike.

\makeatletter
\def\myempty@{}
\makeatother
\let\testtheargument\relax

\newcommand{\nuu}[2][]{%
  \def\testtheargument{#1}%
  \textit{#2}%
  \expandafter\ifx\expandafter\myempty@\testtheargument\myempty@
   \typeout{no 1st argument for \string\nuu{#2}}%
  \else
   \ `#1'
  \fi
}

There \nuu{this} \nuu[22]{this} \nuu[goat]{mudi} becomes

this '' this '22' mudi 'goat'

The same result is achieved when using this another Ross's code:

\newcommand{\nuu}[2][]{%
  \def\testtheargument{#1}%
  \textit{#2}%
  \ifx\testtheargument\myempty@
   \typeout{no 1st argument for \string\nuu{#2}}%
  \else
   \ `#1'
  \fi
}

I really do not understand these commands. But practically until now I
don't have nothing better that Stephen's code which works ok except I
want to write something purely numerical as the optional argument. /-:

S.