General ⇒ ifmtarg | Unexpected Behaviour

[mojo]

This is almost certainly a limitation of the user, but I can't get the ifmtarg to do what I expect.

I have a macro that adds some text to its arg. I'd like for the macro to output nothing if the arg is empty.

Something like

Code: Select all

\newcommand{\hexaddr}[1]{%
\texttt{\#0#1h}%
}

I'd like to avoid having "#0h" emitted when the arg is empty.

It sounds like ifmtarg should do the trick, but it doesn't work for me.

Here's a simplistic example, using code in the ifmtarg docs:

Code: Select all

\documentclass{article}
\usepackage{ifmtarg}
\newcommand{\isempty}[1]{%
  \@ifmtarg{#1}{YES}{NO}}

\begin{document}
Should be empty: \isempty{}

Not empty: \isempty{notempty}
\end{document}

The result looks like:

Should be empty: ifmtargYESNO
Not empty: ifmtargnotemptyYESNO

I'm using pdflatex on a typical MiKTeX 2.9 install.

Clearly, I'm not using the package correctly. Can someone help me understand what I'm doing wrong?
Thanks.


todd.

[josephwright]

You need to make @ a 'letter' to access code internals:

Code: Select all

\documentclass{article}
\usepackage{ifmtarg}
\makeatletter
\newcommand{\isempty}[1]{%
  \@ifmtarg{#1}{YES}{NO}}
\makeatother

\begin{document}
Should be empty: \isempty{}

Not empty: \isempty{notempty}
\end{document}

[mojo]

Excellent! Thanks.