Passing a macro as the argument to an arbitrary arg-spec

Question

MWE:

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\ExplSyntaxOn
\tl_new:N \g__mymodule_env_name_tl
\tl_new:N \g__mymodule_env_args_tl
% Defaults
\tl_set:Nn \g__mymodule_env_name_tl { matrix }
\keys_define:nn { mymodule/math } {
    ,env     .tl_set:N = \g__mymodule_env_name_tl
    ,env-args .tl_set:N = \g__mymodule_env_args_tl
}
\NewDocumentCommand{\mat}{ O{} m }{
    \keys_set:nn { mymodule/math } { #1 }
    \begin{\g__mymodule_env_name_tl}\g__mymodule_env_args_tl
        #2
    \end{\g__mymodule_env_name_tl}
}
\NewDocumentEnvironment{funnymatrix}{ s O{} m }{
    \begin{matrix}
    \text
    {
        (Star:~\bool_if:nTF { #1 } { T } { F })
        (Optional:~#2)
        (Mandatory:~#3)
    }
}{
    \end{matrix}
} 
\ExplSyntaxOff
\section{Current output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\mat[env=matrix*,env-args=[l]]{1}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\mat[env=funnymatrix,env-args=*[optional]{mandatory}]{1}\]
\section{Desired output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\begin{matrix*}[l]
    1
\end{matrix*}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\begin{funnymatrix}*[optional]{mandatory}
    1
\end{funnymatrix}\]
\end{document}

Edit

Skillmon and egreg's solutions work very nicely, but they both seem to give a fatal error when compiling \mat[env=NiceArray,env-args={cc|cc}[baseline=line-3]]{1 & 1 & 1 & 1} (with the package nicematrix). How can either solution be modified such that this works?

I think in general it would be nice to have versions of the optional arg specs that do a \romannumeral-style expansion ahead before peeking for the optional [ (or the corresponding character). — plante
– plante, Commented 23 hours ago
@Grass: Your example \mat[env=NiceArray,env-args={cc|cc}[baseline=line-3]]{1 & 1 & 1 & 1}, has two problems: line-3 does not exist because your matrix has only one row and you should also add braces for the whole value : \mat[env=NiceArray,env-args={{cc|cc}[baseline=line-3]]{1 & 1 & 1 & 1}} to protect the inner-most = — F. Pantigny
– F. Pantigny, Commented 2 hours ago

Skillmon · Accepted Answer · 2025-11-01 18:57:27Z

Expand the macro before the environment searches for any trailing arguments.

As @egreg pointed out in his answer in the meantime you should pay attention to naming conventions. g indicates a globally changed variable but your usage is local, so your variables should be named l. Also you should either group the assignments to your key-variables or reset them to defaults.

\documentclass{article}

\usepackage{mathtools}

\ExplSyntaxOn
\tl_new:N \l__mymodule_env_name_tl
\tl_new:N \l__mymodule_env_args_tl
% Defaults
\tl_set:Nn \l__mymodule_env_name_tl { matrix }
\keys_define:nn { mymodule/math } {
    ,env     .tl_set:N = \l__mymodule_env_name_tl
    ,env-args .tl_set:N = \l__mymodule_env_args_tl
}
\NewDocumentCommand{\mat}{ O{} m }{
  \group_begin:
    \keys_set:nn { mymodule/math } { #1 }
    \use:e
      {
        \exp_not:n { \begin { \l__mymodule_env_name_tl } }
          \exp_not:V \l__mymodule_env_args_tl
      }
        #2
    \end { \l__mymodule_env_name_tl }
  \group_end:
}
\NewDocumentEnvironment{funnymatrix}{ s O{} m }{
    \begin{matrix}
    \text
    {
        (Star:~\bool_if:nTF { #1 } { T } { F })
        (Optional:~#2)
        (Mandatory:~#3)
    }
}{
    \end{matrix}
}
\ExplSyntaxOff

\begin{document}
\section{Current output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\mat[env=matrix*,env-args=[l]]{1}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\mat[env=funnymatrix,env-args=*[optional]{mandatory}]{1}\]
\section{Desired output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\begin{matrix*}[l]
    1
\end{matrix*}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\begin{funnymatrix}*[optional]{mandatory}
    1
\end{funnymatrix}\]
\end{document}

Advertisement: you could have much simpler code if you used a key=value system that doesn't use assignments (disclaimer: I'm the author of expkv-cs), at least for small things with few keys this works out pretty nicely:

\documentclass{article}

\usepackage{mathtools}
\usepackage{expkv-cs}

\NewDocumentCommand\mat{O{} m}{\matKV{#1}{#2}}
\ekvcSplitAndForward\matKV\matDO
  {
     env = matrix
    ,env-args = {}
  }
\newcommand\matDO[3]{\begin{#1}#2#3\end{#1}}

\NewDocumentEnvironment{funnymatrix}{ s O{} m }{%
    \begin{matrix}
      \text
        {%
          (Star: \IfBooleanTF{#1}{T}{F})
          (Optional: #2)
          (Mandatory: #3)
        }%
  }{%
    \end{matrix}%
  }

\begin{document}
\section{Current output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\mat[env=matrix*,env-args=[l]]{1}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\mat[env=funnymatrix,env-args=*[optional]{mandatory}]{1}\]
\section{Desired output}
Environment \verb|matrix|:
\[\mat{1}\]
Environment \verb|matrix*| with optional argument:
\[\begin{matrix*}[l]
    1
\end{matrix*}\]
Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\begin{funnymatrix}*[optional]{mandatory}
    1
\end{funnymatrix}\]
\end{document}

Woah, thanks! This seems like exactly what I want! I'll inspect it a bit tmr and accept the answer. — Grass
– Grass, Commented 23 hours ago
Hm this doesn't seem to work in all cases: compiling \mat[env=NiceArray,env-args={cc|cc}[baseline=line-3]]{1 & 1 & 1 & 1} gives a fatal error. — Grass
– Grass, Commented 13 hours ago
@Grass You need env-args={{cc|cc}[baseline=line-3]} so as to hide the =. At least, with my solution this works. — egreg
– egreg, Commented 5 hours ago
@egreg same here with the L3 based one. With expkv-cs it works even without the extra braces unless you also use , in the argument to env-args. — Skillmon
– Skillmon, Commented 3 hours ago

egreg · Accepted Answer · 2025-11-01 17:10:05Z

Use variants!

Also, the construction should be grouped and the variables should have the \l prefix rather than \g.

\documentclass{article}
\usepackage{mathtools}

\ExplSyntaxOn

\keys_define:nn { grass_matrix/math }
  {
    env      .tl_set:N  = \l__grass_matrix_env_name_tl ,
    env-args .tl_set:N  = \l__grass_matrix_env_args_tl ,
    env      .initial:n = matrix,
  }

\NewDocumentCommand{\mat}{ O{} m }
  {
    \group_begin:
    \keys_set:nn { grass_matrix/math } {#1}
    \__grass_matrix_do:VVn \l__grass_matrix_env_name_tl \l__grass_matrix_env_args_tl {#2}
    \group_end:
  }

\cs_new_protected:Nn \__grass_matrix_do:nnn
 {
  \tl_if_blank:nTF {#2} { \begin{#1} } { \begin{#1}#2 } #3 \end{#1}
 }
\cs_generate_variant:Nn \__grass_matrix_do:nnn {VV}

\ExplSyntaxOff

\NewDocumentEnvironment{funnymatrix}{ s O{} m }{%
  \begin{matrix}
  \text{%
    (Star:~\IfBooleanTF { #1 } { T } { F })
    (Optional:~#2)
    (Mandatory:~#3)
  }
}{\end{matrix}}

\begin{document}

\section{Current output}

Environment \verb|matrix|:
\[\mat{1 \\ 11 \\ 111}\]

Environment \verb|matrix*| with optional argument:
\[\mat[env=matrix*,env-args=[l]]{1 \\ 11 \\ 111}\]

Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\mat[env=funnymatrix,env-args=*[optional]{mandatory}]{1 \\ 11 \\ 111}\]

\section{Desired output}

Environment \verb|matrix|:
\[\mat{1 \\ 11 \\ 111}\]

Environment \verb|matrix*| with optional argument:
\[\begin{matrix*}[l]
    1 \\ 11 \\ 111
\end{matrix*}\]

Environment \verb|funnymatrix| with a star, mandatory and optional argument:
\[\begin{funnymatrix}*[optional]{mandatory}
    1 \\ 11 \\ 111
\end{funnymatrix}\]

\end{document}

Note that this wouldn't work if you plan to nest your \mat commands. For this case, change the main commands into

\keys_define:nn { grass_matrix/math }
  {
    env      .tl_set:N  = \l__grass_matrix_env_name_tl ,
    env-args .tl_set:N  = \l__grass_matrix_env_args_tl ,
  }

\NewDocumentCommand{\mat}{ O{} m }
  {
    \group_begin:
    \keys_set:nn { grass_matrix/math } {env=matrix,env-args=,#1}
    \__grass_matrix_do:VVn \l__grass_matrix_env_name_tl \l__grass_matrix_env_args_tl {#2}
    \group_end:
  }

so as to always reinitialize at a fixed state.

Stack Exchange Network

Passing a macro as the argument to an arbitrary arg-spec

Edit

2 Answers 2

You must log in to answer this question.

Hot Network Questions

Passing a macro as the argument to an arbitrary arg-spec

Edit

2 Answers 2

You must log in to answer this question.

Related

Hot Network Questions