title: Higher Order Function in Haskell
body: <p>I have written the following code. I know that a higher order function is a function that takes in another function and returns a function as a result. But I can't clearly distinguish a function if it is higher order or not. Is <code>sort</code> a higher order function? How do I find out if a function is higher order or not?</p>
  
  <pre><code>sortString :: String -&gt; [String]
  sortString x = sort (convertStringIntoList x)
  </code></pre>