Jukebox.rb:47:in `initialize': uninitialized constant SongList::WordIndex (NameError)
	from Jukebox.rb:123:in `new'
	from Jukebox.rb:123
	from Jukebox.rb:122:in `open'
	from Jukebox.rb:122

## Jukebox.rb [ruby]
class Song
  @@plays = 0
  def initialize(name, artist, duration)
    @name      = name
    @artist    = artist
    @duration  = duration
    @plays     = 0
  end

  attr_reader :name, :artist, :duration
  attr_writer :duration

  def play
    @plays  += 1
    @@plays += 1
    "This song: #{@plays} plays. Total #{@@plays}."
  end

  def to_s
    "Song: #{@name}--#{@artist} (#{@duration})"
  end

  def duration_in_minutes
    @duration / 60.0 # force floating point
  end

  def duration_in_minutes=(new_duration)
    @duration = (new_duration*60).to_i
  end

end

class KaraokeSong < Song
  def initialize(name, artist, duration, lyrics)
    super(name, artist, duration)
    @lyrics = lyrics
  end

  def to_s
    super + " [#{@lyrics}]"
  end
end

class SongList
  def initialize
    @songs = Array.new
    @index = WordIndex.new
  end

  def append(song)
    @songs.push(song)
    @index.add_to_index(song, song.name, song.artist)
    self
  end

  def lookup(word)
    @index.lookup(word)
  end

  def delete_first
    @songs.shift
  end

  def delete_last
    @songs.pop
  end

  def [](index)
    @songs[index]
  end

  def with_title(title)
    @songs.find {|song| title == song.name }
  end

  MAX_TIME = 5*60   # 5 minutes

  def SongList.is_too_long(song)
    return song.duration > MAX_TIME
  end
end

class MyLogger
  private_class_method :new
  @@logger = nil

  def MyLogger.create
    @@logger = new unless @@logger
    @@logger
  end
end

class Accounts
  def initialize(checking, savings)
    @checking = checking
    @savings = savings
  end

  private
  def debit(account, amount)
    account.balance -= amount
  end
  def credit(account, amount)
    account.balance += amount
  end

  public
  def transfer_to_savings(amount)
    debit(@checking, amount)
    credit(@savings, amount)
  end
end

class Account
  attr_reader :balance # accessor method 'balance'
  protected :balance
  def greater_balance_than(other)
    return @balance > other.balance
  end
end

File.open("songdata") do |song_file|
  songs = SongList.new
  song_file.each do |line|
    file, length, name, title = line.chomp.split(/\s*\|\s*/)
    name.squeeze!(" ")
    mins, secs = length.scan(/\d+/)
    songs.append(Song.new(title, name, mins.to_i*60+secs.to_i))
  end
  puts songs[1]
end

class WordIndex
  def initialize
    @index = {}
  end

  def add_to_index(obj, *phrases)
    phrases.each do |phrase|
      phrase.scan(/\w[-\w']+/) do |word|    # extract each word
        word.downcase!
        @index[word] = [] if @index[word].nil?
        @index[word].push(obj)
      end
    end
  end

  def lookup(word)
    @index[word.downcase]
  end
end

songs = SongList.new
song_file.each do |line|
  file, length, name, title = line.chomp.split(/\s*\|\s*/)
  name.squeeze!(" ")
  mins, secs = length.scan(/\d+/)
  songs.append(Song.new(title, name, mins.to_i*60+sec.to_i))
end