Fun with Enumerator

fax.rb

require_relative 'libfax'

puts "Sending fax..."
attempts = mock_fax('555-555-5555', "Here's a fax!")
attempts.each_with_index do |status, i|
  case status
  when :sent
    puts "Fax sent!"
    break
  when :busy
    puts "Line busy!"
    if i < 10
      sleep 2
      next
    else
      puts "Tried 10 times; aborting."
      break
    end
  else
    puts "Error!"
    break
  end
end

guess.rb

require_relative 'libguess'

puts "Let's plan Infinite Questions!"
turns = guessing_game
turns.each do
  print "Guess the word: "
  gets.chomp
end
puts "You win!"

puts "Let's play 20 Questions!"
turns = guessing_game
won = turns.each_with_index do |_,i|
  break if i+1 > 20
  print "Guess the word: "
  gets.chomp
end
puts won ? "You won!" : "You lose :("

libfax.rb

# Returns an Enumerator in which each iteration will attempt to send the fax. A status is handed to the caller's "each" block, and it decides how to proceed.
# NOTE The domain and API are completely fictitious, but similar enough to some real ones.
def fax(number, body)
  Enumerator.new do |y|
    # Try (or retry) to send the fax
    loop do
      # POST the fax to the API
      resp = JSON.parse(RestClient.post("https://fax.example.com/api/fax", number: number, body: body))
      # Keep polling the status until it's no longer "pending"
      status = resp['status'].to_sym
      while status == :pending
        sleep 2
        status = JSON.parse(RestClient.get("https://fax.example.com/api/fax/#{resp['id']}"))['status'].to_sym
      end
      # Inform the caller of the final status
      y << status
    end
  end
end

# A mock implementation of the fax method. This one will actually run, since it doesn't depend on non-existent APIs.
def mock_fax(number, body)
  Enumerator.new do |y|
    y << :busy
    y << :busy
    y << :busy
    y << :sent
  end
end

libguess.rb

def guessing_game
  answer = ANSWERS[rand(ANSWERS.size)]
  Enumerator.new do |y|
    guess = nil
    # Keep yielding to the caller for new guess until one matches
    until guess == answer
      guess = y.yield
    end
    true
  end
end

ANSWERS = %w(
  rectangle
  america
  megaphone
  monday
)