title: knitr syntax highlighting: numbers and logical values are not highlighted
body: <p>This is a minimal example for Rwn taken from <a href="http://yihui.name/knitr/demo/minimal/" rel="nofollow">Yihui Xie website</a>. All I did was to add an expression involving logical values and to delete some of the text to make the example a bit shorter.</p>
  
  <pre><code>\documentclass{article}
  \usepackage[sc]{mathpazo}
  \usepackage[T1]{fontenc}
  \usepackage{geometry}
  \geometry{verbose,tmargin=2.5cm,bmargin=2.5cm,lmargin=2.5cm,rmargin=2.5cm}
  \setcounter{secnumdepth}{2}
  \setcounter{tocdepth}{2}
  \usepackage{url}
  \usepackage[unicode=true,pdfusetitle,
  bookmarks=true,bookmarksnumbered=true,bookmarksopen=true,bookmarksopenlevel=2,
  breaklinks=false,pdfborder={0 0 1},backref=false,colorlinks=false]
  {hyperref}
  \hypersetup{
  pdfstartview={XYZ null null 1}}
  
  \begin{document}
  &lt;&lt;setup, include=FALSE, cache=FALSE&gt;&gt;=
  library(knitr)
  # set global chunk options
  opts_chunk$set(fig.path='figure/minimal-', fig.align='center', fig.show='hold')
  options(formatR.arrow=TRUE,width=90)
  @
  \title{A Minimal Demo of knitr}
  \author{Yihui Xie}
  \maketitle
  You can test if \textbf{knitr} works with this minimal demo. OK, let's
  get started with some boring random numbers:
  
  &lt;&lt;boring-random&gt;&gt;=
  set.seed(1121)
  (x=rnorm(20))
  mean(x)
  y &lt;- c(TRUE,FALSE,NA)
  @
  \end{document}
  </code></pre>
  
  <p>The weird thing is that when I knit/compile this minimal example (even when I leave the original example unaltered) the R code highlighting I in my pdf is different to the highlighting scheme of the pdf output that can be found on Yihui Xie website <a href="http://yihui.name/knitr/demo/minimal/" rel="nofollow">here</a>. To be precise: in my pdf neither numbers nor logical values nor function arguments are highlighted. However, R functions, characters and commands (after the #) are properly highlighted.</p>
  
  <p>Has anyone experienced a similar issue, or even better: does anyone know how to fix this?</p>
  
  <p>Greetings, M.</p>
  
  <hr>
  
  <p>UPDATE:</p>
  
  <p>I just ran the example on my computer at work and things worked out the way they should (everything is highlighted as it should be). This is strange, since I'm using the same setup (R, RStudio (updated) , knitr (updated)) at home as I am using at work (so I thought, at least). I think I dont have the newest R version hat home though. Is it possible that the behaviour is caused by an older version of R?</p>