title: Which is more preferable? Guard or case?
body: <p>Style 1:</p>
  
  <pre><code>a(X) when X&gt;1 -&gt; 
      ...omitted;
  a(X) when X -&gt;
      ...omitted.
  </code></pre>
  
  <p>Style 2</p>
  
  <pre><code>a(X) -&gt;
      case X&gt;1 of
          true-&gt; ...ommited;
          false-&gt; ...ommited
      end.
  </code></pre>
  
  <p>====Update===</p>
  
  <p>As @rviding said, I update the comparison as following:</p>
  
  <p>Style 1:</p>
  
  <pre><code>a(X) when X&gt;1 -&gt; 
      ...omitted;
  a(X) -&gt;
      ...omitted.
  </code></pre>
  
  <p>Style 2</p>
  
  <pre><code>a(X) -&gt;
      case X&gt;1 of
          true-&gt; ...ommited;
          false-&gt; ...ommited
      end.
  </code></pre>