XParse: Command, which creates a command

Question

SE, lately I'm playing around with expl3 and xparse a little and I encountered following problem: I want to create a command which creates a new command -- similar to this post. This is not as hard, as long the second command doesn't have any arguments; trying to create a command, which accepts arguments is a little more tricky.

What I got so far:

\documentclass{article}
\usepackage{xparse}

\NewDocumentCommand\test{ m}
{
    \NewDocumentCommand#1 {m}
        {My name is \string#1, king of kings}
}

\begin{document}
\test{\ozymandias}
\ozymandias{\manthano}
\end{document}

This outputs My name is ozymandias, king of kings, which gives the correct sonnet, but not what I wanted. I know where the problem is, I just don't know how to fix it atm :)

Answer 1

I wonder about the \string#1 inside.

The new command inside can be constructed with

\expandafter\NewDocumentCommand\csname #1\endcsname{...}{....}

i.e. the name of the new sequence must be constructed first with \expandafter (first the name is given, then \NewDocumentCommand comes into action). The same approach has to be taken for the traditional \newcommand or \renewcommand etc.

However, the \test command must be used as \test{ozymandias}, without \!

Please note, that it is necessary to use ##1 to access the first argument of the inner macro (if this is wanted at all), subsequent arguments are numbered with ##2 etc.

\documentclass{article}
\usepackage{xparse}

\NewDocumentCommand{\manthano}{}{Manthano}

\NewDocumentCommand\test{ m}
{%
  \expandafter\NewDocumentCommand\csname #1\endcsname{m}{%
   My name is ##1, king of kings%
   }
}

\begin{document}
\test{ozymandias}
\ozymandias{\manthano}
\end{document}

EDIT: To use \test with \, you have to adapt the command to

\makeatletter
\NewDocumentCommand\test{ m}
{%
  \expandafter\NewDocumentCommand\csname\expandafter\@gobble\string #1\endcsname{m}{%
   My name is ##1, king of kings%
   }
}
\makeatother