title: Map function applied to specific elements of the list
body: <p>I have a function:</p>
  
  <pre><code>mapAtOriginal :: (a -&gt; a) -&gt; [Int] -&gt; [a] -&gt; [a]
  mapAtOriginal f is xs = helper 0 is xs
    where
      helper _ [] xs = xs
      helper c (i:is) (x:xs)
        | c &lt; i     =   x : helper (c+1) (i:is) xs
        | otherwise = f x : helper (c+1)    is  xs
  </code></pre>
  
  <p>It works like this:</p>
  
  <pre><code>mapAtOriginal (*2) [0,3] [1,2,3,4]   -- == [2,2,3,8]
  </code></pre>
  
  <p>So I want to rewrite it but using a <strong><code>map</code></strong> function. I understand that <em><code>map</code></em> applies to every element of the list, however, I need it applied only for specific indices.</p>
  
  <p>How can I do it? </p>