[texhax] Defining a command which runs differently based ioninput argument

[Ulrike Fischer]

Am Tue, 28 Dec 2010 10:43:04 +0100 schrieb Lars Madsen:

> Mike B. wrote:
>> Hi all,
>> 
>> How can I define a command which runs differently based on if an input argument was provided or not?. For example:
>> 
>> \mycommand
>> would introduce a vsapce of 1cm
>> 
>> whereas 
>> \mycommand{xyz}
>> would print xyz

> that is sadly not possible. You cannot make macros that can run as 
> \macro and \macro{...}

Sure it is possible. The LaTeX-kernel defines \input differently
depending on if a brace follows or not:

\def\input{\@ifnextchar\bgroup\@iinput\@@input}

You only need to copy this:

\documentclass[12pt]{article}

\begin{document}

\makeatletter
\def\mymacro{\@ifnextchar\bgroup\@mymacroi\@mymacroii}

\def\@mymacroi#1{BLA -- \textbf{#1} -- BLA }
\def\@mymacroii{blubb -- }

\mymacro \mymacro{abc}
\end{document}

-- 
Ulrike Fischer