How to name command arguments

Question

Is there a way to give a "name" to the arguments of a command and use them in its definition? What I'd like to do is to be able to get the value of an argument with a "label" like #myargname instead of #<number>. For example, I'd like to define a \foocommand like

\newcommand{\foocommand}[#normal,#bold,#italics,#smallcaps,#emphasis]%
           {#normal \textbf{#bold} \textit{#italics} \textsc{#smallcaps} \emph{#emphasis}}

instead of

\newcommand{\foocommand}[5]%
           {#1 \textbf{#2} \textit{#3} \textsc{#4} \emph{#5}}

Answer 1

You can. Here's a proof of concept.

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\newparametercommand}{smO{}m}
 {
  \IfBooleanTF { #1 }
   {
    \ntakwetet_newparametercommand:Nnnn \cs_set_nopar:cV { #2 } { #3 } { #4 }
   }
   {
    \ntakwetet_newparametercommand:Nnnn \cs_set:cV { #2 } { #3 } { #4 }
   }
 }
\tl_new:N \l__ntakwetet_replacement_tl
\int_new:N \l__ntakwetet_index_int
\cs_generate_variant:Nn \cs_set:Nn { cV }
\cs_generate_variant:Nn \cs_set_nopar:Nn { cV }
\cs_new_protected:Nn \ntakwetet_newparametercommand:Nnnn
 {
  \tl_set:Nn \l__ntakwetet_replacement_tl { #4 }
  % double the #
  \regex_replace_all:nnN { \cP. } { \cP#\cP# } \l__ntakwetet_replacement_tl
  % index for the parameters
  \int_zero:N \l__ntakwetet_index_int
  % substitute any item in the list of parameters with #<n>
  \clist_map_inline:nn { #3 }
   {
    \int_incr:N \l__ntakwetet_index_int
    \exp_args:Nne \regex_replace_all:nnN
     { ##1 } % search
     { \exp_not:n { \cP# } \int_eval:n { \l__ntakwetet_index_int } } % replace
     \l__ntakwetet_replacement_tl
   }
  % define a temporary macro with #1=\cs_set:cV or \cs_set_nopar:cV
  #1 {__ntakwetet_temp:\prg_replicate:nn { \l__ntakwetet_index_int } { n } } % name
   \l__ntakwetet_replacement_tl % replacement
  \cs_new_eq:Nc #2 {__ntakwetet_temp:\prg_replicate:nn { \l__ntakwetet_index_int } { n } }
 }
\ExplSyntaxOff
\newparametercommand\foo[#abc,#def]{#abc,#def}
\newparametercommand*\baz[#abc,#def]{#abc--#def}
\newparametercommand{\foocommand}[#normal,#bold,#italics,#smallcaps,#emphasis]{%
  #normal \textbf{#bold} \textit{#italics} \textsc{#smallcaps} \emph{#emphasis}%
}
\begin{document}
\foo{a}{b}
\baz{a}{b}
\foocommand{normal}{bold}{italics}{smallcaps}{emphasis}
\end{document}

Each item in the comma separated list is searched for in the replacement text and substituted with #<n> for the current index.

Limitation: a keyword cannot have another keyword as initial segment. So #a and #aa would not work. Also one cannot use more than nine arguments, of course.

Answer 2

Not automatic, but simple and easy.

\documentclass{article}
\newcommand{\foo}[2]% #1=\first, #2=\second
{\bgroup% make definitions local
  \def\first{#1}%
  \def\second{#2}%
  Arguments are \first{} and \second.
\egroup}
\begin{document}
\foo{A}{B}
\end{document}

---

Alternate, but prone to errors.

\documentclass{article}
\newcommand{\foo}[1]% #1 = TeX definitions
{\bgroup% make definitions local
  #1
  Arguments are \first{} and \second.
\egroup}
\begin{document}
\foo{\def\first{A}\def\second{B}}
\end{document}

Answer 3

EDITED to remove the deficiency of the prior approach.

If you don't mind changing your syntax in the following ways:

1. Change your symbolic-argument identifier from # to something that is not cat 6, here done with !

2. Define the new command with \symbolicnewcommand, since \newcommand is already defined with a different syntax.

Thus, the syntax is something like:

\symbolicnewcommand{\foocommand}%
  [!normal,!bold,!italics,!smallcaps,!emphasis,!boxed]%
  {!normal{} \textbf{!bold} \textit{!italics} 
   \textsc{!smallcaps} \emph{!emphasis} \fbox{!boxed}}

Unlike my prior approach, this approach doesn't merely mimic the \newcommand behavior, but recreates it, by converting the symbolic arguments into explicit #1, #2, etc., (i.e., NOT placed inside a \def).

Here is the MWE. Note that in the \meaning of the defined macro, the symbolic arguments, for example, !normal, is converted into an explicit #1.

\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{listofitems,tokcycle}
\newtoks\mytoks
\newtoks\tmptoks
\def\OPENSgroup{\OPENSgroup}% quark
\def\CLOSEgroup{\CLOSEgroup}% quark
\def\SPACEquark{\SPACEquark}% quark
\newcommand{\addtotoks}[2]{#1\expandafter{\the#1#2}}
\newcommand{\xaddtotoks}[2]{%
  \expandafter\addtotoks\expandafter#1\expandafter{#2}}
\makeatletter
\long\def\symbolicnewcommand#1[#2]#3{%
  \readlist\arglist{#2}%
  \stripgroupingtrue%
  \tokcycle{\addcytoks{##1}}%
    {\addcytoks{\OPENSgroup}\processtoks{##1}\addcytoks{\CLOSEgroup}}%
    {\addcytoks{##1}}{\addcytoks{\SPACEquark}}{#3}%
  \mytoks\expandafter{\the\cytoks}%
  \foreachitem\z\in\arglist[]{%
    \expandafter\setsepchar\expandafter{\z}%
    \expandafter\def\expandafter\tmp\expandafter{\the\mytoks}%
    \readlist\cmdlist{\tmp}%
    \mytoks{}%
    \foreachitem\zz\in\cmdlist[]{%
      \ifnum\zzcnt=1\relax\else%
        \tmptoks{&}%
        \xaddtotoks\tmptoks{\zcnt}%
        \xaddtotoks\mytoks{\the\tmptoks}%
      \fi%
      \xaddtotoks\mytoks{\zz}%
    }%
  }%
%
  \setsepchar{&}%
  \expandafter\readlist\expandafter\cmdlist\expandafter{\the\mytoks}%
  \mytoks{}%
  \foreachitem\z\in\cmdlist[]{%
    \ifnum\zcnt=1\relax\else\addtotoks\mytoks{####}\fi%
    \xaddtotoks\mytoks{\z}%
  }%
%
  \expandafter\addBracesSpaces\expandafter{\the\mytoks}%
%
  \def\tmp{\newcommand{#1}[\arglistlen]}%
  \expandafter\tmp\expandafter{\the\mytoks}%
}
\newcommand\addBracesSpaces[1]{\mytoks{}\fooaux#1\endfoo}
\def\fooaux#1{%
  \tctestifx{\endfoo#1}{}
  {\tctestifx{\OPENSgroup#1}{\Z}
  {\tctestifx{\SPACEquark#1}{\addtotoks\mytoks{ }}
  {\addtotoks\mytoks{#1}}\fooaux}}%
}
\makeatother
\def\Z#1\CLOSEgroup{\addtotoks\mytoks{{#1}}\fooaux}
\symbolicnewcommand{\foocommand}%
  [!normal,!bold,!italics,!smallcaps,!emphasis,!boxed]%
  {!normal{} \textbf{!bold} \textit{!italics} 
   \textsc{!smallcaps} \emph{!emphasis} \fbox{!boxed}}
\begin{document}
\meaning\foocommand
\foocommand{To be,}{or not}{to be?}{That}{is the question.}{123}
\end{document}