title: Syntax for if/else condition in SCSS mixin
body: <p>Hi I'm trying to learn SASS/SCSS and am trying to refactor my own mixin for clearfix</p>
  
  <p>what I'd like is for the mixin to be based on whether I pass the mixin a width.</p>
  
  <p>thoughts so far (pseudo code only as I will be including other mixins)</p>
  
  <pre class="lang-sass prettyprint-override"><code>@mixin clearfix($width) {
  
     @if !$width {
  
      // if width is not passed, or empty do this
  
     } @else {
  
          display: inline-block;
          width: $width;
     }
  }
  </code></pre>
  
  <p>here's how I thought I might call it, but it's not working.</p>
  
  <p><code>@include clearfix();</code></p>
  
  <p>or</p>
  
  <p><code>@include clearfix(100%)</code></p>
  
  <p>or</p>
  
  <p><code>@include clearfix(960px)</code></p>
  
  <p>I'd appreciate any help on the best or right way to do this!</p>