title: knitr changing my reverse assignment operator -> to <-
body: <p>I am having trouble when using "reverse" assignment operators (->) in a knitr .Rnw file. For example, I have the following simple .Rnw file</p>
  
  <pre><code>\documentclass{article}
  \begin{document}
  &lt;&lt;test&gt;&gt;=
      options(tidy=FALSE, width=50)
      1:5 -&gt; a
  @
  \end{document} 
  </code></pre>
  
  <p>When I use knitr to compile into a pdf, the operator -> has been reversed so the output actually has </p>
  
  <pre><code>1:5 &lt;- a 
  </code></pre>
  
  <p>in it!</p>
  
  <p>how can I change this?</p>