title: Need help to make a func such as ('a -> 'b) option -> 'a option -> 'b option
body: <p>I'm currently learning Ocaml on my cursus and i've been trying to solve this exercise for a long time, but I can't for the life of me find the answer..</p>
  
  <p>How do i make a function that applies an optional function to an optional value, and if one of these is missing, we return None.</p>
  
  <pre><code>val apply_opt : ('a -&gt; 'b) option -&gt; 'a option -&gt; 'b option
  </code></pre>
  
  <p>I hope you guys can help me cause i can't find any example of this </p>