haml_in_code.rb

# coding: utf-8
=begin
## Haml

http://haml.info/docs/yardoc/frames.html#!http%3A//haml.info/docs/yardoc/
http://haml.info/docs/yardoc/file.REFERENCE.html#options

=end

require 'haml'
require 'haml/template/options'
require 'date'

# set options
Haml::Template.options[:format] = :xhtml
Haml::Template.options[:autoclose] = [/.*/]

template = File.read('test.xml.haml')
haml_engine = Haml::Engine.new(template, Haml::Template.options)

output = haml_engine.render
puts output

result.xml

<?xml version='1.0' encoding='utf-8' ?>
<charactors>
  <created_at>2013-04-03</created_at>
  <charactor>
    <name>博麗霊夢</name>
    <ability>空を飛ぶ程度の能力</ability>
  </charactor>
  <charactor>
    <name />
    <nickname>大妖精</nickname>
    <ability />
  </charactor>
</charactors>

test.xml.haml

!!! XML

%charactors
  %created_at= Date.today
  %charactor
    %name 博麗霊夢
    %ability 空を飛ぶ程度の能力
  %charactor
    %name
    %nickname 大妖精
    %ability