The complete code from my DSL tutorial at http://blog.atechmedia.com/ruby-dsls-for-fun/

dsl.rb

class AddressBook

  def contacts
    @contacts ||= []
  end

  def self.load_from_path(path)
    # Create a new AddressBook instance
    address_book = self.new
    # Create a new AddressBookDSL instance
    address_book_dsl = AddressBookDSL.new(address_book)
    # Loop through every file in the given path
    Dir[File.join(path, '*')].each do |file|
      # Read each file and eval the contents in the address
      # book's DSL instance.
      address_book_dsl.instance_eval(File.read(file), file)
    end
    # Return the finished address book
    address_book
  end

end

class Contact

  # Define the basic information attributes
  attr_accessor :first_name
  attr_accessor :last_name
  attr_accessor :company

  # Define a method to return an array of contact methods for
  # this contact.
  def contact_methods
    @contact_methods ||= []
  end

  # Define a method to return an array of activities for the
  # this contact.
  def activities
    @activities ||= []
  end

end

class ContactMethod

  # When we create a new contact method, we'll store the contact
  # which it is associated with too.
  def initialize(contact)
    @contact = contact
  end

  # Accessor for returning a contact associated with a ContactMethod
  attr_reader :contact

  # Accessors for getting & setting the various properties which
  # are associated with a ContactMethod.
  attr_accessor :type
  attr_accessor :role
  attr_accessor :value

end

class AddressBookDSL

  def initialize(address_book)
    @address_book = address_book
  end

  def contact(&block)
    # Create a new Contact object instance for our new contact
    contact = Contact.new
    # Create a new instance of our Contact DSL (defined in a moment)
    # and pass it our newly instantiated contact.
    contact_dsl = ContactDSL.new(contact)
    # Eval the contacts of the `contact` block within the ContactDSL
    # instance we just created.
    contact_dsl.instance_eval(&block)
    # Add the contact to the array of contacts in our address book
    @address_book.contacts << contact
  end

end

class ContactDSL

  def initialize(contact)
    @contact = contact
  end

  # When the name method is called, we'll accept the first and
  # last names and set them as appropriate on our contact class.
  def name(first_name, last_name)
    @contact.first_name = first_name
    @contact.last_name = last_name
  end

  # When the company is set, we'll just do the same and set that
  # on the contact.
  def company(name)
    @contact.company = name
  end

  # Activities are just passed straight through from the contact
  # itself so we just return the contact's activities array.
  def activities
    @contact.activities
  end

  # When a contact method is defined, we'll need to create a new
  # instance of our ContactMethod class, set the values and then
  # add it to our contact's contact_method array.
  def contact_method(type, role, value)
    method = ContactMethod.new(@contact)
    method.type = type
    method.role = role
    method.value = value
    @contact.contact_methods << method
  end

  def method_missing(name, *values)
    if values.empty?
      # If no values are provided, we'll just let Ruby raise an error
      # as normal.
      super
    else
      # Otherwise, we'll simply call our contact_method method to
      # add our method.
      contact_method(name, *values)
    end
  end

end

address_book = AddressBook.new
address_book_dsl = AddressBookDSL.new(address_book)
address_book_dsl.instance_eval do
  contact do

    name 'Joe', 'Bloggs'
    company 'Bloggs Inc'

    phone :home, '01234 123123'
    phone :work, '01555 123555'
    email :home, "[email protected]"

    activities << 'Piano Playing'
    activities << 'Swag Catching'

  end

  contact do
    name 'Potato', 'Man'
    company 'McCain'
    phone :mobile, '07123 123123'
  end
end

address_book.contacts.each do |contact|
  puts "------------------------------------------------------------------------"
  puts "#{contact.first_name} #{contact.last_name}"
  puts contact.company
  contact.contact_methods.each do |method|
    puts " * #{method.type}:#{method.role} #{method.value}"
  end
end