Defining a command that starts with "@"

Question

Context: I've inherited a mess of latex notes from another faculty member; these are processed by using a home-brew system that does lots of clever stuff ... but that means that I must work on them using the linux systems at the office, and also means that finding bugs ends up being a binary-search process, because the clever processing eats up all the error messages and mangles them.

Here's the thing: a typical file looks like this:

@course{coursehead}
@lec{17}{\textit{(Provisional)} Analysis, Combinatorics}
@cs{coursebegin}
@localnotes{obj}

@localnotes{racket/text/stars-and-stripes}
@localnotes{racket/text/analysis}

which turns out to mean (in real LaTeX) just this:

\include{../../latex/coursehead}
\title{Lecture 17 \textit{(Provisional)} Analysis, Combinatorics}
\include{../../latex/coursebegin}
\include{obj}

\include{racket/text/stars-and-stripes}
\include{racket/text/analysis}

So if I could just "define" "@localnotes" to mean "\include", I'd be about 90% of the way to being able to work with the notes without breaking anything from the other system.

Question: Is there a way to make something like "@localnotes" act as a latex macro? Perhaps equally important: is it certain that there is no way to do so? {If it can't be done, I'd like to stop looking for ways to do it!}.

I'm not very tex-savvy. At about the point where I see "makeatletter", I know that I'm about to not understand whatever follows. But if there's a solution that somehow uses this, I'll slog through it until I understand it.

Thanks in advance.

Answer 1

Just change @ to be the same as the backslash, after giving the appropriate definitions.

TeX doesn't bother what characters have category code 0, it just follows instructions. ;-) And it's immaterial what category code 0 character has been used for defining the macro.

\documentclass{article}

\newcommand\course[1]{\input{../../latex/#1}}
\newcommand\lec[2]{Lecture #1 #2}
\newcommand\cs[1]{\input{../../latex/#1}}
\newcommand\localnotes[1]{\input{#1}}

\begin{document}

\catcode`@=0

@course{coursehead}
@lec{17}{\textit{(Provisional)} Analysis, Combinatorics}
@cs{coursebegin}
@localnotes{obj}

@localnotes{racket/text/stars-and-stripes}
@localnotes{racket/text/analysis}

\end{document}

In the document environment, after \catcode`@=0, you can use @cs or \cs with exactly the same result.

Answer 2

Here is a very simplified implementation of what you can do:

First: 123; Second: 456

\documentclass{article}

\usepackage{filecontents}
\begin{filecontents*}{inputfile.tex}
@somemacro{123}{456}
\end{filecontents*}

\newcommand{\somemacroprocess}[2]{First: #1; Second: #2}

\begin{document}

\begingroup
\catcode`@=0
\newcommand{@somemacro}{\somemacroprocess}
\input{inputfile}
\endgroup

\end{document}

The idea is to make @ act just like \ by changing its category code via

\catcode`@=0

That way you can define a macro called @somemacro that matches whatever you have in your input file. I've created a macro \somemacroprocess to be the replacement for @somemacro locally (inside a group), while defining \somemacroprocess in the usual way (outside the group).