scale.rb

class Scale
  IONIAN_HALF_STEPS = [2, 2, 1, 2, 2, 2, 1]

  class << self
    [   
      :ionian,
      :dorian,
      :phrygian,
      :lydian,
      :mixolydian,
      :aeolian,
      :locrian
    ].each_with_index do |name, i|
      define_method(name) do
        half_steps = IONIAN_HALF_STEPS.dup
        i.times { half_steps.push(half_steps.shift) }
        from_half_steps(half_steps)
      end 
    end 
  end 

  def self.from_half_steps(*half_steps)
    values = half_steps.flatten[0..-2].inject([0]) { |a, x|
      a + [(a.last + x) % 12] 
    }.uniq
    new(values)
  end 

  attr_reader :values

  def initialize(values)
    @values = values
  end 
end

puts Scale.ionian.values.inspect
puts Scale.dorian.values.inspect
puts Scale.ionian.values.inspect