title: How do I know/get the last or first key in a map?
body: <p>I have a mixin, where I loop over a map. Some of my utilities don't apply for the first or last key in the map. </p>
  
  <p>From time to time, is possible that I add new keys to the map. I can use an <code>@if="sm-2"</code> to check directly the value of the key, but I don't want to modify also all 'for/each loops`.</p>
  
  <p>How do I know/get the last or first key in a map ?</p>
  
  <pre><code>@mixin utility_generator {
     @each $bp in map-keys($map) {
     /////////////////////////////////
     // @if not last_key/first_key { 
           @include utility($bp) {
              @content
           }
     ////////////////////////////
     }
  }
  </code></pre>