macros
I would like to define a new command comp with two arguments where the second (and last) argument is optional, using 'ifthenelse'. I tried :
\newcommand{\comp}[2]{%
\ifthenelse{\isempty{#2}}%
{{#1}^{c}}% if #2 is empty
{#2 \backslash #1}% if #2 is not empty
}
but \comp{Y}{X} gives Y\X instead of X\Y as wanted and \comp{Y} gives Y\ instead of the result of Y^c as wanted.
Try the new xparse package, which is built on top of LaTeX3. With this package you can specify arbitrary combinations of mandatory and optional arguments. This case would be as easy as
\DeclareDocumentCommand \sfsx { m m o } { \wrapper{#1}{#2}{#3} }
If you want to have your own default value, use O{value} instead of o.
You can profit of xparse and LaTeX3 functions.
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\outline}{ m o }
{
\par\noindent\textbf{#1}
\IfNoValueTF { #2 }
{
\par\vspace{\topsep} % no list of items
}
{
\egreg_outline_items:n { #2 } % there are items
}
}
\seq_new:N \l_egreg_outline_items_seq
\cs_new_protected:Npn \egreg_outline_items:n #1
{
% split the \\ separated list of items
\seq_set_split:Nnn \l_egreg_outline_items_seq { \\ } { #1 }
% make an itemize with them
\begin{itemize}
\seq_map_inline:Nn \l_egreg_outline_items_seq
{
\item ##1
}
\end{itemize}
}
\ExplSyntaxOff
\begin{document}
\section{First}
\outline{Some text for the outline}
Here is something in the section.
\section{Second}
\outline{Here I have more}[
something \\
something else \\
again
]
Here is something in the section.
\end{document}
Best Answer
Optional arguments are usually set first and specified in brackets
[]rather than braces{}.With your code, if you type
$\comp{Y}=Z$, the second argument is taken to be=, because of how TeX decides what the argument to a command is. Indeed, withthe required arguments are two.
In my opinion, the optional argument should be the first, so you read
as “the complement in X of Y” or “the complement of Y” respectively.
How to define that?
or