Increasing nesting level for parameters and global xparse macros?

Question

This is kind of a double question but closely connected in my case. Inspired by https://tex.stackexchange.com/a/55769/14159 I tried to make an improved version which allows additional parameters for the defined symbols.

This is my current code:

\documentclass{article}
\usepackage{xparse}
\usepackage{nomencl}
\usepackage{xcolor}

% colorize to distinguish original and renewed command
\NewDocumentCommand{\defsym}{mmmmm} {%
    \NewDocumentCommand{#1}{#2}{%
        \RenewDocumentCommand{#1}{#2}{\textcolor{blue}{#4}}
        \nomenclature{$#1$}{#5}
        \textcolor{red}{#3}
    }
}

\defsym\Uk{O{k}}{U_{#1}}{U_{##1}}{Some variable}

\makenomenclature

\begin{document}
\noindent$\Uk[j]$,$\Uk,$ $\Uk[p], \Uk[q]$ and $\Uk[r]$
\printnomenclature
\end{document}

---

---

Now to the two problems I have are

1. The double definition #3 and #4 is very ugly, is there some macro which increases the nesting level, i.e. which adds one # to each parameter? So that I could write \incnest{#3} instead of #4
2. The \RenewDocumentCommand definition is not global so all U's except the \Uk[q] are red. Is there some equivalent to \global or \gdef in xparse. I found something similar for \renewcommand in \global\renewcommand equivalent of \global\def but it's a bit hacky.

Any tricks or workarounds to get it working are welcome.

Answer 1

This problem of global redefinition can't be solved with \RenewDocumentCommand; with deeper expl3 programming, it can be done by setting a switch (a boolean).

\documentclass{article}
\usepackage{xparse}
\usepackage{nomencl}
\usepackage{xcolor}

% colorize to distinguish original and renewed command
\ExplSyntaxOn
% #1 = command name
% #2 = definition
% #3 = default optional argument
% #4 = description
\NewDocumentCommand{\defsym}{mmmm}
  {
   \bool_new:c { g_buergi_sym_ \cs_to_str:N #1 _bool }
   \bool_gset_false:c { g_buergi_sym_ \cs_to_str:N #1 _bool }
   \buergi_defsym:nnnn { #1 } { #2 } { #3 } { #4 }
  }
\cs_new_protected:Npn \buergi_defsym:nnnn #1 #2 #3 #4
 {
  \NewDocumentCommand{#1}{O{#3}}
   {
    \bool_if:cTF  { g_buergi_sym_ \cs_to_str:N #1 _bool }
     { \textcolor{blue}{#2} }
     {
      \textcolor{red}{#2}
      \nomenclature{$#1$}{#4}
      \bool_gset_true:c { g_buergi_sym_ \cs_to_str:N #1 _bool }
     }
   }
 }
\ExplSyntaxOff

\defsym\Uk{U_{#1}}{k}{Some variable}
\defsym\Ak{A(#1)}{k}{Another}

\makenomenclature

\begin{document}
\noindent $\Uk[j]$, $\Uk$, $\Uk[p]$, $\Uk[q]$ and $\Uk[r]$

\noindent $\Ak$, $\Ak[n]$
\printnomenclature
\end{document}

As you see, you can give in the second argument any token list with #1 representing the optional argument, that I've placed third. Just personal preference, if you want to switch the second and third arguments, just change the first definition into

\NewDocumentCommand{\defsym}{mmmm}
  {
   \bool_new:c { g_buergi_sym_ \cs_to_str:N #1 _bool }
   \bool_gset_false:c { g_buergi_sym_ \cs_to_str:N #1 _bool }
   \buergi_defsym:nnnn { #1 } { #3 } { #2 } { #4 }
  }

The command \defsym first defines a boolean switch with a name based on the first argument and sets it to false; then executes the core function which does the required \NewDocumentCommand; so \Uk is defined to do its normal job in blue color if the boolean is true, while it does its job in red color. annotates in the nomenclature file the usage and globally sets the boolean to true.