title: instance variable in blocks
body: <p>How to pass an instance variable as an <em>argument</em> to a block?</p>
  
  <p>This doesn't work in Ruby 1.9 (<strong>formal argument cannot be an instance variable</strong>).</p>
  
  <pre><code>awesome do |foo, @bar|
    puts 'yay'
  end
  </code></pre>