I am looking to define a command (actually, an environment, but that shouldn't matter for the purposes of this question) that does some default behavior, and if an optional argument is passed, does something else.
For example,
\newcommand{mycommand}[1]{%
if (#1 != NULL){%
The argument #1 was passed}
else {%
No argument was passed.}}
Obviously this is not valid LaTeX, but hopefully this makes it clear what I am trying to do. Is there a way to do this with ordinary LaTeX? Is it worth switching to LuaLaTeX to accomplish behavior like this?
Best Answer
You can do it easily with
xparse
:This will print
For an environment it's similar
Other code common to the two cases can be added at will. As you see,
xparse
also allows (but it's not mandatory) to use the argument specifiers also in the end part.