title: Square numbers in list and then add them up
body: <p>I am trying to create a function that squares the numbers of an ML list and then adds those numbers up</p>
  
  <pre><code>fun sqsum(lst) = map (fn x =&gt; x*x) lst;
  </code></pre>
  
  <p>What I have there takes a list and returns a list of the square of each number but I can't figure out the adding part.</p>