Pseudo-class composition in Ruby.

composable_ish.rb

module Composable
  extend self

  def extended klass
    klass.send :attr_reader, :val
  end

  def method_missing klass
    f, g = self, const_get(klass)

    Class.new do
      define_method(:initialize) do |n|
        @val = f.new(g.new(n).val).val
      end
    end.extend Composable
  end
end

class Succ
  extend Composable

  def initialize n
    @val = n.succ
  end
end

class Twice
  extend Composable

  def initialize n
    @val = n * 2
  end
end

(Twice . Succ . Twice).new(10).val # => 42