title: Why does "isset($a[0]) and unset($a[0]);" cause syntax error?
body: <p>My Code:</p>
  
  <pre><code>$a = [];
  isset($a[0]) and unset($a[0]);
  </code></pre>
  
  <p>it shows <strong><code>"syntax error, unexpected 'unset' (T_UNSET)"</code></strong></p>
  
  <p>but </p>
  
  <pre><code>$a = [];
  isset($a[0]) and exit();
  </code></pre>
  
  <p>it <strong>works!</strong></p>
  
  <p>Both of <code>exit()</code> and <code>unset()</code> are returning no value. Why does one work but not the other?</p>