title: HAML filters in a helper
body: <p>Helper functions can receive a block which they <code>yield</code> to render the block. Sometimes I'd want that block to be spec'd with a filter. So for example:</p>
  
  <pre><code>= doc_page title: 'FAQ' do
    :markdown
      # Welcome to the *FAQ*
  </code></pre>
  
  <p>This is not so DRY as we are always writing doc_page and markdown together. Can I make the helper method accept a block and pass it through a HAML filter. Something like:</p>
  
  <pre><code>= doc_page title: 'FAQ' do
    # Welcome to the *FAQ*
  </code></pre>
  
  <p>In this fantasy, <code>doc_page</code> is a helper method that does some setup stuff and then passes the content through markdown, saving us the need to declare <code>:markdown</code> everywhere and making the world a DRYer place.</p>