How reuse latex code for later expansion?

Question

I would like to make a command to help me writing lines like:

The \LaTeX~code is: \verb@e^{i\pi} - 1 = 0@, and the result is: $e^{i\pi} - 1 = 0$.

I thought of using a newcommand as:

\newcommand{\eqn}[1]{The \LaTeX~code is: \verb@#1@, and the result is: $#1$.}

to use as:

\eqn{e^{i\pi} - 1 = 0}

which doesn't work.

Trying to pull out the verbatim out as:

\newcommand{\eqn1}[1]{The \LaTeX~code is: #1, and the result is: $#1$.}

to use as:

\eqn1{\verb@e^{i\pi} - 1 = 0@}

also doesn't work.

My question is, is there a way to achieve this in latex?

Thank you. PS: unfortunately the thread bellow seems to indicate that it's not possible :( Wrapping code (listings, verbatim, or other method) inside a newcommand

Regarding the second definition, there are two things which would cause errors: LaTeX commands cannot contain numbers (so \eqn1 generates a Missing \begin{document} error); and your eqn1 command takes math and pastes it into the document inside textmode, so you'll get a bunch of errors from that (e.g. ^ is not allowed in textmode). — Arun Debray, Dec 18 '15 at 05:17
Also related: How to put \verb command inside of \textbf block? — Werner, Dec 18 '15 at 05:47

score 6 · Answer 1 · answered Dec 18 '15 at 18:43

6

Absorb the argument verbatim and rescan it when you need the real output:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\eqn}{v}
 {
  The~\LaTeX{}~code~is:~\texttt{#1},~and~the~
  result~is:~\tl_rescan:nn { } { $#1$ }.
 }
\ExplSyntaxOff

\begin{document}

\eqn{e^{i\pi} - 1 = 0}

\end{document}

answered Dec 18 '15 at 18:43

egreg

1,121,712

1

Nice! I really need to look more into expl3 programming. – Håkon Marthinsen Dec 18 '15 at 18:49

score 2 · Answer 2 · edited Apr 13 '17 at 12:35

2

With inspiration from this answer by Ulrich Schwarz, we can solve this using \meaning:

\documentclass{article}

\makeatletter
\newcommand\meaningbody[1]{%
  {\ttfamily
    \expandafter\strip@prefix\meaning#1}%
}
\newcommand\eqn[1]{%
  {\def\@foo{$#1$}The \LaTeX~code is \meaningbody\@foo, and the result is: $#1$.}%
}
\makeatother

\begin{document}

\eqn{e^{i\pi} - 1 = 0}

\end{document}

The result is:

One potential problem is that the output from \meaning is not exactly the same as the input code. There is an extra space after \pi in this example.

edited Apr 13 '17 at 12:35

Community

1

answered Dec 18 '15 at 18:26

Håkon Marthinsen

1,132

(This is just detokenize in e-TeX.) – user202729 Apr 03 '22 at 07:55

How reuse latex code for later expansion?

2 Answers2