title: let vs def in clojure
body: <p>I want to make a local instance of a Java <code>Scanner</code> class in a clojure program.  Why does this not work:</p>
  
  <pre><code>; gives me:  count not supported on this type: Symbol 
  (let s (new Scanner "a b c"))
  </code></pre>
  
  <p>but it will let me create a global instance like this:</p>
  
  <pre><code>(def s (new Scanner "a b c"))
  </code></pre>
  
  <p>I was under the impression that the only difference was scope, but apparently not.  What is the difference between <code>let</code> and <code>def</code>?</p>