Extracting Code of R function to be used in knitr with controlled width

Question

We can use formatR::usage(lm) to get the arguments of lm function and can use the following command to redirect the output to knitr:

<<test, code=formatR::usage(lm), eval=FALSE>>=
@

I wonder if there is such function to get the lm function code to redirect to knitr.

Edited

Got the code of lm function to be used in knitr using the following code (as suggested by @JoshO'Brien):

<<test, code=lm, eval=FALSE>>=
@

But could not figure out how to control the width of knitr output.

Answer 1

To embed a 'tidy' definition of some function see Yihui's self-explanatory existing code,

<<insert-fun, echo=FALSE>>=
insert_fun = function(name) {
  read_chunk(lines = capture.output(dump(name, '')), labels = paste(name, 'source', sep = '-'))
}
@

<<insert-lm, echo=FALSE>>=
insert_fun('lm')
@

<<lm-source, eval=FALSE, tidy=TRUE, tidy.opts=list(width.cutoff=30)>>=
@

Example Rnw and Rmd Gist

---

When output is going to latex, there are sometimes have issues with getting line breaks to stay within the page margins. Its a known issue with multiple fixes that have various drawbacks. Like this one where you get the full function within the margins but without the pretty coloring... It is all a matter of trade-offs and/or effort you put into a solution. :)

\documentclass{article}

\usepackage{listings}
\usepackage{inconsolata}

<<echo=FALSE>>=
options(width=60)

listing <- function(x, options) {
  paste("\\begin{lstlisting}[language=R,basicstyle=\\ttfamily,breaklines=true]\n",
    x, "\\end{lstlisting}\n", sep = "")
}
knit_hooks$set(source=listing, output=listing)

insert_fun = function(name) {
  read_chunk(lines = capture.output(dump(name, '')), labels = paste(name, 'source', sep = '-'))
}

@

<<insert-lm, echo=FALSE>>=
insert_fun('lm')
@

\begin{document}

<<lm-source, eval=FALSE, tidy=TRUE, tidy.opts=list(width.cutoff=50)>>=
@

\end{document}