inline_filter.rb

module Inline
  include Haml::Filters::Base

  def self.[](key)
    @@data[key.to_s] rescue nil
  end

  def render(str)
    @@data = Hash[*str.split(/^\s*@@\s*(\w+)\s*\n/m)[1..-1]]
    return nil
  end
end

input.haml

%h1 Inline Filter
.describe= Inline[:describe]
.author created by #{Inline[:author]}

:inline
 @@ describe
 This filter easily separates structure and data.
 You can use in-file-templates like sinatra.

 @@ author
 maiha@wota.jp

output.html

<h1>Inline Filter</h1>
<div class='describe'>
  This filter easily separates structure and data.
  You can use in-file-templates like sinatra.
</div>
<div class='author'>created by maiha@wota.jp</div>