title: F# how to abstract Console.ReadLine() as string seq
body: <p>I want to write a function to abstract Console.ReadLine() into a string seq</p>
  
  <p>the seq should break when line = null</p>
  
  <pre><code>ConsoleLines(): unit -&gt; string seq
  </code></pre>
  
  <p>To be used like this:</p>
  
  <pre><code>for line in ConsoleLines() do
      DoSomething line
  </code></pre>
  
  <p>How do you write this function?</p>
  
  <p>Thanks</p>