title: How to summarize the index of odd numbers in haskell?
body: <p>Amount of items with odd number 
  Define the function f4, which represents the sum of elements of a unique index in a list! Indexing is exceptional!</p>
  
  <pre><code>f4 :: [Int] -&gt; Int
  f4 [] == 0
  f4 [4] == 4
  f4 [4.2] == 4
  f4 [4,2,3] == 7
  f4 [4,2,3,5] == 7
  f4 [5,4,2,3,8,3,9,5,2] == 26
  
  f4 :: [Int] -&gt; Int
  f4 [] = 0
  f4 [x] = x
  f4 (x:xs) = odd (x:xs) 
  </code></pre>