redcarpet.rb

require 'redcarpet'
class CustomRender < Redcarpet::Render::HTML
  def list_item(text, list_type)
    case text
      when /\[\s?x\s?\]/ 
          "<li><input type='checkbox' value='true' checked>#{text.gsub(/\[\s?x\s?\]/, "").strip}</li>\n"
      when /\[\s?\]/
          "<li><input type='checkbox' value='false'>#{text.gsub(/\[\s?\]/, "").strip}</li>\n"
      else
        "<li>#{text}</li>\n"
    end
  end
end