# Redefining the knitr code chunk delimeter in LaTeX to compile .Rnw files as .tex files

I am trying to define some LaTeX commands/environments to handle the raw text in an Rnw file (R + LaTeX document compiled with R package `knitr`). The goal is to allow someone to rename a .Rnw file to a .tex file and be able to compile the document so that LaTeX puts placeholders for the code chunks. It is a different approach to the root problem discussed in How to export changes from a .tex file back to the source .Rnw file.

There are two things that need to happen: `\Sexpr{}` needs to be redefined and the code block sequence

``````<< chunk-name, option1 = TRUE, option2 = FALSE, ...>>=
... R code ...
@
``````

Needs to be redefined. Redefining `\Sexpr{}` was easy:

``````\newcommand{\Sexpr}[1]{\textbf{\#\#}}
``````

However, I am struggling with how to define a control sequence (expansion?) to process `<<`chunk name, options`>>`R code`@`.

Technically, I can skip over all the errors and end up with a LaTeX document that has the code chunks as plain text. I can accept this, but it would be better to output a placeholder, e.g. a box containing the chunk name but definitely not the R code.

EDIT This looks to be in the right direction, but I'm having trouble understanding what is going on: https://tex.stackexchange.com/a/80370/82573

EDIT EDIT So actually the main issue seems to be that underscores `_` in R code (such as in function names) are what actually cause the errors, so some way to ignore the code or wrap it in a `verbatim` environment is needed.