print highlighted source of a function

printfun.Rnw

\documentclass{article}

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

\begin{document}

This is ordinary printing:

<<ordinary-print>>=
fivenum
@

We insert the source of fivenum into knitr and print it in the chunk fivenum-source:

<<insert-fivenum, echo=FALSE>>=
insert_fun('fivenum')
<<fivenum-source, eval=FALSE>>=
@

\end{document}