title: How is this fibonacci-function memoized?
body: <p>By what mechanism is this fibonacci-function memoized?</p>
  
  <pre><code>fib = (map fib' [0..] !!)                 
       where fib' 1 = 1                                                        
             fib' 2 = 1                                                        
             fib' n = fib (n-2) + fib (n-1)                    
  </code></pre>
  
  <p>And on a related note, why is this version not?</p>
  
  <pre><code>fib n = (map fib' [0..] !! n)                                               
       where fib' 1 = 1                                                        
             fib' 2 = 1                                                        
             fib' n = fib (n-2) + fib (n-1)                    
  </code></pre>