How to use \edef to wrap an existing macro with @inmatherr?

Question

I have a handful of existing macros that I want to wrap in some custom processing. Here's an example of the kind of thing I'm aiming to do:

\makeatletter
\let\olddag\textdagger
\renewcommand\textdagger{\@inmatherr\textdagger \olddag}
\makeatother

Then if were to try to use $\textdagger$, I'd get a error, rather than the existing behavior of typesetting nothing appropriate. However, \textdagger in regular text mode will fall through to its existing definition.

My question is, how can I achieve the same effect but without making the assignment to the intermediate command \olddag? I suspect there would be some voodoo using \edef and/or \expandafter that would enable me to expand:

{\@inmatherr\textdagger \textdagger}

or perhaps:

{\noexpand\@inmatherr\noexpand\textdagger \textdagger}

at definition time, so that when I invoke \textdagger in the body of my document, I don't get a TeX stack overflow. But I haven't yet been able to find what it is.

These other questions (and answers) may be relevant:

• A: How do I reuse a command name two or more times?
• How to use \noexpand in an \edef?
• When to use \edef, \noexpand, and \expandafter?
• What is the difference between \let and \edef?
• How to control whether and when a macro gets expanded during another definition?
• Problem with nested \noexpand and \edef

But I haven't yet been able to piece together a solution from them. I guess it's no news that LaTeX's order-of-evaluation rules aren't that transparent.

Answer 1

\documentclass{article}

\makeatletter

\expandafter
\renewcommand
\expandafter\textdagger
\expandafter{%
\expandafter\@inmatherr
\expandafter\textdagger
\textdagger}

\makeatoher

\begin{document}

\textdagger $\textdagger$

\end{document}

The above shows the general technique but in this case you already get a warning, \textdagger by default makes

LaTeX Warning: Command \textdagger invalid in math mode on input line 8.

so an alternative would be to redefine that warning command to be an error.

Answer 2

The behavior of \textdagger is shared by all commands that are defined with \OMS-cmd, so a way to get errors when they're used in math mode is to change \@inmathwarn in the definition of \OMS-cmd with \@inmatherr. See Why does \textbackslash render as "n" in math mode? for more information about the issue.

\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\expandafter\patchcmd\csname OMS-cmd\endcsname{\@inmathwarn}{\@inmatherr}{}{}
\makeatother
\begin{document}
$\textdagger$
\end{document}

This gives

! LaTeX Error: Command \textdagger invalid in math mode.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.7 $\textdagger
                $