hockey_client.rb

require 'ostruct'

class HockeyClient
  def listen_for_hockey_scores
    return enum_for(:listen_for_hockey_scores) unless block_given?
    sleep 1
    yield score "Blues", "Cracknell"
    sleep 0.1
    yield score "Red Wings", "Salei"
    sleep 0.1
    yield score "Red Wings", "Helm"
    sleep 1
    yield score "Red Wings", "Kronwall"
    sleep 0.1
    yield score "Blues", "Backes"
    sleep 0.2
    yield score "Blues", "D'Agostini"
    sleep 0.2
    yield score "Red Wings", "Datsyuk"
    sleep 0.1
    yield score "Red Wings", "Abdelkader"
  end

  private

  def score(team, scorer)
    OpenStruct.new :team => team, :scorer => scorer
  end
end

if $0 == __FILE__
  hockey_client = HockeyClient.new
  puts "Listening to the game..."
  hockey_client.listen_for_hockey_scores do |goal|
    puts "#{goal.scorer} scored a goal for #{goal.team}"
  end
  puts "The game is over."
end

red_wings_fan.rb

require './hockey_client'

module Enumerable
  def lazy_select(&block)
    Enumerator.new do |yielder|
      self.each do |element|
        yielder << element if yield(element)
      end
    end
  end

  def lazy_map(&block)
    Enumerator.new do |yielder|
      self.each do |element|
        yielder << yield(element)
      end
    end
  end
end

class RedWingsFan
  def initialize(hockey_client)
    @hockey_client = hockey_client
  end

  def red_wings_goal_scorers
    @hockey_client.listen_for_hockey_scores.lazy_select do |goal|
      goal.team == "Red Wings"
    end.lazy_map do |goal|
      goal.scorer
    end
  end
end

red_wings_fan = RedWingsFan.new(HockeyClient.new)
puts "Red Wings scorers:"
red_wings_fan.red_wings_goal_scorers.each do |scorer|
  puts scorer
end