title: Sass variable type handling
body: <p>How can I get this to work as I expect?</p>
  
  <pre><code>// https://github.com/thoughtbot/bourbon/blob/master/app/assets/stylesheets/addons/_size.scss
  @mixin size($size) {
      $height: nth($size, 1);
      $width: $height;
      @if length($size) &gt; 1 {
          $height: nth($size, 2);
      }
      @if $height == auto or (type-of($height) == number and not unitless($height)) {
          height: $height;
      }
      @if $width == auto or (type-of($width) == number and not unitless($width)) {
          width: $width;
      }
  }
  
  $height:10;
  
  .sample {
      @include size(10px $height + px)
  }
  </code></pre>
  
  <p>I expect the output to be:</p>
  
  <pre><code>.sample {
      height: 10px;
      width: 10px;  
  }
  </code></pre>
  
  <p><a href="http://sassmeister.com/gist/2bc77fdb2d5a7d656cf6" rel="nofollow">http://sassmeister.com/gist/2bc77fdb2d5a7d656cf6</a></p>