title: How do I declare a map type in Reason ML?
body: <p>One advantage of Reason ML over JavaScript is that it provides a <code>Map</code> type that uses structural equality rather than reference equality. </p>
  
  <p>However, I cannot find usage examples of this. </p>
  
  <p>For example, how would I declare a type <code>scores</code> that is a map of strings to integers? </p>
  
  <pre><code>/* Something like this */
  type scores = Map&lt;string, int&gt;; 
  </code></pre>
  
  <p>And how would I construct an instance?</p>
  
  <pre><code>/* Something like this */
  let myMap = scores();
  
  let myMap2 = myMap.set('x', 100);
  </code></pre>