Adding a :redcarpet Haml Filter to Rails 4

haml_filters.rb

# config/initializers/haml_filters.rb

# Thanks to https://gist.github.com/sleepingkingstudios/955676

# config/initializers/haml_filters.rb

# in your haml files do e.g.
# %td.description
#   :markdown
#     #{task.description}

# I put gem 'redcarpet' in my Gemfile

require 'redcarpet' # you might not even need this if it's in your Gemfile

module Haml::Filters

  remove_filter("Markdown") #remove the existing Markdown filter

  module Markdown # the contents of this are as before, but without the lazy_require call

    include Haml::Filters::Base

    def render(text)
      markdown.render(text)
    end

    private

    def markdown
      @markdown ||= Redcarpet::Markdown.new(renderer, extensions)
    end

    def renderer
      @renderer ||= Redcarpet::Render::HTML.new(render_options)
    end

    def render_options
      {
          filter_html: true,
          hard_wrap: true,
          no_styles: true,
          prettify: false,
          safe_links_only: true,
          with_toc_data: false
      }
    end

    def extensions
      {
          autolink: true,
          fenced_code_blocks: false,
          footnotes: false,
          highlight: true,
          no_images: true,
          no_intra_emphasis: true,
          quote: true,
          space_after_headers: false,
          strikethrough: true,
          superscript: true,
          tables: true,
          underline: true
      }
    end
  end

end