🚀 go-pugleaf

In article <1992Sep11.201211.29920@constellation.ecn.uoknor.edu> wszczepo@wildcat.ecn.uoknor.edu (Witold Szczeponik) writes:

> I ran into the same problem some days ago.  Here's a piece of the
> code that tests whether the first argument is empty or not:
>     {\setbox0=\hbox{\ignorespaces#1\unskip\relax}%
>     \ifdim \wd0=0pt%
> % do whatever you want if the argument is empty
>     \else%
> % do whatever you want if it isn't
>     \fi%
>    }%


This works and is more general than the above solution (it does not
falsely declare an argument null if the argument produces no text.)

Almost certainly there are better solutions.

			mike


\def\makeatletter{\catcode`\@=11\relax}
\def\makeatother{\catcode`\@=12\relax}
\makeatletter
\def\ifnullarg#1\ifnullarg#2#3{%
\begingroup
	\def\@flag{\relax\relax\relax}
	\def\@na@yes{#2}%
	\def\@na@no{#3}%
	\ifx\@flag#1\@flag\let\@na@chosen=\@na@yes
	\else\let\@na@chosen=\@na@no\fi
	\relax
	\@na@chosen
\endgroup
}
\makeatother

% Testing -- Cut here --

\def\iw#1{\immediate\write16{#1}}

\def\usenullchk#1{%
	\ifnullarg#1\ifnullarg{\iw{Null}}%
			{\iw{Not Null}}}
	
\usenullchk{}
\usenullchk{foo}
\usenullchk{\relax}

\end