definable.rb

module Definable
  def self.redefine(object, method_name, &process)
    original_method = object.method(method_name)

    object.define_singleton_method(method_name) do |*args, &block|
      process[*args, &block]
      original_method[*args, &block]
    end
  end

  def definable(name)
    Definable.redefine(self, :extended) do |object|
      value = Value.new

      object.define_singleton_method(name) { value }

      Definable.redefine(object, :included) do |klass|
        klass.__send__(:define_method, name) { value.eval }
      end
    end
  end

  class Value
    def bind(value)
      @value = value
      @bound = true
    end

    def eval
      raise 'a value is not bound yet' unless @bound
      @value
    end
  end
end

Module.__send__(:include, Definable)

module Nyan
  definable :nyan
end

module UnekoLike
  extend Nyan

  nyan.bind :uneko
end

module EtteLike
  extend Nyan

  nyan.bind :ette
end

class Uneko
  include UnekoLike
end

class Ette
  include EtteLike
end

p Uneko.new.nyan
p Ette.new.nyan