title: Functional way to check if array of numbers is sequential
body: <p>Let's say that an array is sequential when each successful element has the value of previous element <code>+ 1</code>. Suppose I have an array of numbers like <code>{5,6,7,8}</code> (sequential) or <code>{1,2,5}</code> (not sequential).  </p>
  
  <p>Is there a nice functional way to check if the array is sequential? I can do it with the following code: </p>
  
  <pre><code>bool IsSequential(int[] array)
  {
      for (int i = 1; i &lt; array.Length; i++)
         if (array[i] != array[i - 1] + 1)
              return false;
      return true;
  }
  </code></pre>
  
  <p>I'm trying to determine if a poker hand is straight.</p>