Defining a list environment with multiple optional arguments

Question

I'm trying to define a list environment with multiple optional arguments and with a default values for those arguments. For example, creating a new environment with a name newenv, which accepts two arguments, and if they aren't present uses default values:

\documentclass{article}
\usepackage{array}
\usepackage{multicol}
\usepackage{enumerate}

\begin{document}

\newenvironment{newenv}[2][2]
{\begin{multicols}[#1]\begin{enumerate}[#2]}
{\end{enumerate}\end{multicols}}

\begin{newenv}{2}{2}
  \item a
  \item b
  \item c
  \item d
\end{newenv}

\end{document}

What am I missing?

Answer 1

I would use the enumitem package for this- it eases the syntax and does the heavy lifting for us

The first part is to setup a new list environment

\newlist{newenv}{enumerate}{5}
\setlist[newenv]{label=\arabic*.}

which has a default label of 1., 2., etc

We then setup a new key, columns

\SetEnumitemKey{columns}{before=\begin{multicols}{#1},
                         after=\end{multicols}}

which allows us to use all variety of combinations, as demonstrated in the MWE below

\documentclass{article}
\usepackage{enumitem}
\usepackage{multicol}

\newlist{newenv}{enumerate}{5}
\setlist[newenv]{label=\arabic*.}

\SetEnumitemKey{columns}{before=\begin{multicols}{#1},
                                               after=\end{multicols}}

\begin{document}
\begin{newenv}[label=\roman*),columns=4]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[columns=3]
\item a
\item b
\item c
\end{newenv}

\hrule

\begin{newenv}[label=\roman*)]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[label*=(A\arabic*),columns=3]
\item a
\item b
\item c
\item d
\item e
\item f
\end{newenv}

\end{document}

Answer 2

I agree with Werner that multiple optional arguments should be replaced by a key-value syntax. Here's a way:

\documentclass{article}
\usepackage{enumerate,multicol,xparse}

\ExplSyntaxOn
\NewDocumentEnvironment{newenv}{ O{} }
 {
  \keys_set:nn { aksr/newenv }
   {
    #1           % use the options
   }
  \int_compare:nT { \l__aksr_columns_tl > 1 } % more than one column
   { \begin{multicols}{ \l__aksr_columns_tl } }
  % We must pass the optional argument expanded
  \use:x { \exp_not:N \begin{enumerate}[ \l__aksr_label_tl ] }
 }
 {
  \end{enumerate}
  \int_compare:nT { \l__aksr_columns_tl > 1 }
   { \end{multicols} }
 }

\tl_new:N \l__aksr_columns_tl
\tl_new:N \l__aksr_label_tl

\keys_define:nn { aksr/newenv }
 {
  columns .tl_set:N  = \l__aksr_columns_tl,
  columns .initial:n = 2,
  label   .tl_set:N  = \l__aksr_label_tl,
  label   .initial   = 1.,
 }
\ExplSyntaxOff

\begin{document}
\begin{newenv}
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[columns=1]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[label=i)]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[label=(A),columns=3]
\item a
\item b
\item c
\item d
\item e
\item f
\end{newenv}

\end{document}

It's quite straightforward, once we have some hand with it. The only subtlety is that we must pass the argument to \begin{enumerate} expanded and not the token list variable, so \use:x comes to rescue.

The two keys just store the value in a token list variable for later usage. The defaults are simply established by giving the values before evaluating the optional argument to newenv.

You may consider adopting enumitem rather than enumerate.

---

Here's a different version that works with enumitem and shows the use of "unknown" keys:

\documentclass{article}
\usepackage{enumitem,multicol,xparse}

\ExplSyntaxOn
\NewDocumentEnvironment{newenv}{ O{} }
 {
  % clear the options passed to enumitem
  \tl_clear:N \l__aksr_enumitem_tl
  \keys_set:nn { aksr/newenv }
   {
    #1 % use the options
   }
  \int_compare:nT { \l__aksr_columns_tl > 1 } % more than one column
   { \begin{multicols}{ \l__aksr_columns_tl } }
  % We must pass the optional argument expanded; we append
  % the label key and value to the other possibly set options
  \tl_put_right:Nn \l__aksr_enumitem_tl { label = }
  \tl_put_right:NV \l__aksr_enumitem_tl \l__aksr_label_tl
  \aksr_beginenum:V \l__aksr_enumitem_tl 
 }
 {
  \end{enumerate}
  \int_compare:nT { \l__aksr_columns_tl > 1 }
   { \end{multicols} }
 }
\cs_new_protected:Npn \aksr_beginenum:n #1
 {
  \begin{enumerate}[#1]
 }
\cs_generate_variant:Nn \aksr_beginenum:n {V}

\tl_new:N \l__aksr_columns_tl
\tl_new:N \l__aksr_label_tl
\tl_new:N \l__aksr_enumitem_tl

\keys_define:nn { aksr/newenv }
 {
  columns .tl_set:N  = \l__aksr_columns_tl,
  columns .initial:n = 2,
  label   .tl_set:N  = \l__aksr_label_tl,
  label   .initial:n = \arabic*.,
  %% unknown keys will be passed to enumitem
  unknown .code:n    = \tl_put_right:Nx \l__aksr_enumitem_tl 
                        { 
                         \l_keys_key_tl % the key name
                         \tl_if_empty:nF { #1 } % the value, if not empty
                          { = \exp_not:n { #1 } } , },
 }
\ExplSyntaxOff

\begin{document}
\begin{newenv}
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[columns=1,noitemsep]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[label=\roman*)]
\item a
\item b
\item c
\item d
\end{newenv}

\hrule

\begin{newenv}[label=(\alph*),columns=3]
\item a
\item b
\item c
\item d
\item e
\item f
\end{newenv}

\end{document}

Answer 3

At risk of being reprimanded for the suggestion, you could use different delimiters for the different optionals. The line

\NewDocumentEnvironment{newenv}{ O{2} D<>{(a)} }

Specifies that there are two optional arguments, the first is of type O which is a standard square bracketed optional with default whatever is in the following brace group (here 2). The second optional argument is of type D ("D"elimited) with left delimiter <, right delimiter > and has default whatever is given in the following brace group, here (a).

\documentclass{article}
\usepackage{array}
\usepackage{multicol}
\usepackage{enumerate}
\usepackage{xparse}

\NewDocumentEnvironment{newenv}{ O{2} D<>{(a)} }
{\begin{multicols}{#1}\begin{enumerate}[#2]}
{\end{enumerate}\end{multicols}}

\begin{document}

\begin{newenv}[2]<i.>
  \item a
  \item b
  \item c
  \item d
\end{newenv}

\end{document}