title: Why does my Mac (OS X 10.7.3) have an old version (2.3) of Gnu Bison?
body: <p>The version of GNU Bison on my mac is 2.3 but I know that Bison 2.5 was released long ago. The book <em>Flex &amp; Bison</em> uses version 2.5.</p>
  
  <p>Should I upgrade to 2.5 myself? Is it necessary?</p>
  
  <p>What's the difference between 2.3 and 2.5?</p>