title: Sudden "unused argument" error
body: <p>I have no idea why but I am quite sure the following did produce a plot a while back. Can you tell me what's wrong here?</p>
  
  <pre><code>library(ggplot2)
  qplot(c(0, 2), stat="function", fun=exp, geom="line") 
  </code></pre>
  
  <p>This returns "Error in c(0, 2) : unused argument (2)." Why?</p>
  
  <p><strong>Edit:</strong> This is a general problem:</p>
  
  <pre><code>a &lt;- c(0, 2)
  </code></pre>
  
  <p>gives the same error. What's going on here?</p>