Writing a multiple option command for a package

Question

I am a newbie at LaTeX programming, so please be patient. :-)

I am writing a .sty file which I want to include a command \dan which is overloaded with three separate versions depending on whether called with zero, one or two arguments.

E.g. I want:

\dan

to generate

Full English

\dan{streaky}

or

\dan{back}

to generate

streaky Bacon

or

back Bacon

respectively, and

\dan{streaky}{fried}

to generate

streaky Bacon with fried Eggs.

"streaky", "fried" etc. are just examples, the users should be able to input any argument.

I have looked into the xparse package, but am finding the documentation inpenetrable. Please can you advise on how to code this?

Answer 1

This is how.

\documentclass[a4paper]{article}
\usepackage{xparse}

\NewDocumentCommand{\dan}{gg}
  {\IfNoValueTF{#2}
     {\IfNoValueTF{#1}
        {Full English}
        {#1 Bacon}%
     }
     {#1 Bacon with #2 Eggs}%
  }

\begin{document}

\dan

\dan{streaky}

\dan{back}

\dan{streaky}{fried}

\end{document}

This said, I advise you against doing so. Users of your package will have a bad time figuring out how to use the commands. Just changing the argument specifier in {oo} instead of {gg} the syntax would be more in line with the LaTeX conventions:

\dan

\dan[streaky]

\dan[back]

\dan[streaky][fried]

If you can be more precise about your intentions, a different strategy may be suggested.

Answer 2

As noted in comments I'd recommend using a more conventional LaTeX syntax. @egreg has given a LaTeX3 version, so here's using a loop from LaTeX2e:

\documentclass{article}

\makeatletter

\newcommand\dan[1][full]{%
\def\dansep{\def\dansep{, }}%
\@for\x:=#1\do{%
\dansep
\@nameuse{dan:\x}}}

\@namedef{dan:full}{Full English}
\@namedef{dan:streaky}{Streaky Bacon}
\@namedef{dan:back}{Back Bacon}
\@namedef{dan:fried}{Fried Egg}
\@namedef{dan:mushrooms}{Grilled Mushrooms}

\makeatother

\begin{document}

a \dan

b \dan[streaky]

c \dan[back]

e \dan[streaky,fried]

f \dan[streaky,fried,mushrooms]

\end{document}

Answer 3

As noted in the comments it is much more preferable to use a key value interface and the answer given by David Carlisle, gives the traditional LaTeX2e way. For more complicated packages, I would lean on using a PGF style of keys. If nothing the amount of users asking questions on this site about TikZ, indicates that there is a large community of users familiar with the PGF style key value interface.

\documentclass{article}
\usepackage[latin]{babel}
\usepackage{pgfkeys}
\begin{document}
%% Step one define family
\pgfkeys{/bacon/.is family}
%% Define your keys
\pgfkeys{/bacon
     type/.store in=\type,
     type/.default=streaky,
     cook/.store in=\cook,
     cook/.default=fried
}
%% Process keys and set defaults, for later use
\def\setdefaults{\pgfkeys{/bacon  
     type,cook
  }%
}
%
\setdefaults
\newcommand{\dan}[2][]{%
  \setdefaults
  \pgfkeys{/bacon #1}
   \def\baconfoods{
      \type\ cook \cook,
   }
  \baconfoods
}
\dan[type=shoulder bacon, cook=well]{}
\dan[type=streaky,cook]{}
\dan[type=streaky]{}
\dan{}
\end{document}

You get tremendous flexibilty with this approach.

Answer 4

Here is a solution using catoptions package:

\documentclass{article}
\usepackage{catoptions}
\makeatletter
\newcommand*\dan[1][full]{%
  \def\do##1{%
    \ifnum\indrisnr>\@ne
      ,\space\iflastindris and\space\fi
    \fi
    \uselivecsn{dan:##1}%
  }%
  \indrisloop{#1}\do
}
% Default inner list parser = , (comma)
% Default outer list parser = ; (semicolon)
\newcommand*\setupdan[2][,;]{%
  \def\reserved@a##1##2##3\@nil{%
    \def\do####1##1####2##1####3\@nil{%
      \csn@edef{dan:\cpttrimspace{####1}}{\cpttrimspace{####2}}%
    }%
    \def\csv@do####1{\do####1##1##1\@nil}%
    \csv@@parse[##2]{#2}%
  }%
  \reserved@a#1,;\@nil
}
\makeatother

% Example:
\setupdan{%
  full,      Full English;
  streaky,   Streaky Bacon;
  back,      Back Bacon;
  fried,     Fried Egg;
  mushrooms, Grilled Mushrooms
}

\commentBegin
% The following is also possible:
\setupdan[=,]{%
  full       =Full English,
  streaky    =Streaky Bacon,
  back       =Back Bacon,
  fried      =Fried Egg,
  mushrooms  =Grilled Mushrooms
}
\commentEnd


\begin{document}
\begin{enumerate}
\item\dan
\item\dan[streaky]
\item\dan[back]
\item\dan[streaky, fried]
\item\dan[streaky, fried, mushrooms]
%\item\dan[xstreaky] % error: undefined
\end{enumerate}
\end{document}