title: Filter positions in a list, Haskell
body: <p>I need to print the elements of odd index. Currently is printing index. </p>
  
  <p>I don't understand how I can print elements of this index?</p>
  
  <pre><code>f :: [Int] -&gt; [Int]
  f lst = filter odd [0..length lst]
  
  -- I can't edit this part
  main = do
     inputdata &lt;- getContents
     mapM_ (putStrLn. show). f. map read. lines $ inputdata
  </code></pre>