knitr-like (inline) code formatting

Question

In a LyX/LaTeX document, I am using knitr to include (R) code chunks.

I would like to explain my code in below the chunk, by repeating sections of it inline.

How can I achieve the same formatting of text inline (without evaluation)?

There is a question and answer by Yihui on doing this in rmarkdown and another another answer by him that it should be similar in LaTeX, but when I try using the code from the rmarkdown answer, it throws up errors in LyX.

The error I get is:

Error in if (knitr:::pandoc_to() != "latex") return(code) : 
argument is of length zero

When I remove the if (knitr .... line, I get an output document, but the line code is formatted as normal text.

Any thoughts?

EDIT: upon request a MWE

\documentclass{article}

\begin{document}

<<include=FALSE>>=
local({
  hi_pandoc = function(code) {
    if (knitr:::pandoc_to() != 'latex') return(code)
    if (packageVersion('highr') < '0.6.1') stop('highr >= 0.6.1 is required')
    res = highr::hi_latex(code, markup = highr:::cmd_pandoc_latex)
    sprintf('\\texttt{%s}', res)
  }
  hook_inline = knitr::knit_hooks$get('inline')
  knitr::knit_hooks$set(inline = function(x) {
    if (is.character(x) && inherits(x, 'AsIs')) hi_pandoc(x) else hook_inline(x)
  })
})
@

Test inline R code: \Sexpr{ I("plot(cars, main = 'A scatterplot.')") }.
Normal inline code \Sexpr{pi}.

A code block:

<<>>=
plot(cars, main = 'A scatterplot.')
1 + 2 # a comment
@

\end{document}

Answer 1

The following works for me:

\documentclass{article}

\begin{document}

<<include=FALSE>>=
local({
  hi_pandoc = function(code) {
    if (packageVersion('highr') < '0.6.1') stop('highr >= 0.6.1 is required')
    res = highr::hi_latex(code, markup = highr:::cmd_latex)
    res <- gsub("\\^", "\\\\textasciicircum{}", res)
    sprintf('\\texttt{%s}', res)
  }
  hook_inline = knitr::knit_hooks$get('inline')
  knitr::knit_hooks$set(inline = function(x) {
    if (is.character(x) && inherits(x, 'AsIs')) hi_pandoc(x) else hook_inline(x)
  })
})
@

Test inline R code: \Sexpr{ I("plot(cars, main = 'A scatterplot.')") }.
Normal inline code \Sexpr{pi}.

A code block:

<<>>=
plot(cars, main = 'A scatterplot.')
1 + 2 # a comment
@
% 
And some more inline code \Sexpr{ I("2^3") } and \Sexpr{ 2^3 }

\end{document}

I removed the knitr:::pandoc_to and replaced highr:::cmd_pandoc_latex with highr:::cmd_latex since you are not using pandoc. Result: