proc_composition.rb

class Proc
  def <<(other)
    case other
    when Proc
      Proc.new do |*args|
        call(other.call(*args))
      end
    else
      call(other)
    end
  end

  def >>(other)
    raise TypeError unless Proc === other
    Proc.new do |*args|
      other.call(call(*args))
    end
  end
end

times6 = ->(i){ i * 2 } << ->(i){ i * 3 }
times2plus1 = ->(i){ i * 2} >> ->(i){ i + 1 }

puts times6.call(3)
puts times2plus1.call(3)