class Haml::Generators::ApplicationLayoutGenerator

def convert

with some error checking.
and creates app/views/layouts/application.html.haml
Converts existing application.html.erb to haml format, 
def convert
  app_layout_from = ::Rails.root.join(HTML_LAYOUT_PATH).to_s
  app_layout_to   = ::Rails.root.join(HAML_LAYOUT_PATH).to_s
  if File.exist?(app_layout_from)
    if !File.exist?(app_layout_to)
      `html2haml #{app_layout_from.shellescape} #{app_layout_to.shellescape}`
      puts "Success! app/views/layouts/application.html.haml is created.\n" \
           "Please remove the erb file: app/views/layouts/application.html.erb"
    else
      puts "Error! There is a file named app/views/layouts/application.html.haml already."
    end
  else
    puts "Error! There is no file named app/views/layouts/application.html.erb."
  end
end