12 days of Rubymas. Based on clojure implementation by @syntacticsugar

rubymas.rb

class Fixnum
  def ordinal
    %w[first second third fourth fifth sixth seventh eighth ninth tenth eleventh twelfth][self - 1]
  end

  # Use #to_word rather than #to_s, so it doesn't break any other printing of numbers.
  def to_word
    %w[one two three four five six seven eight nine ten eleven twelve][self - 1]
  end
end

GIFTS = {
   1 => "an embarrassing garbage collector with a stutter",
   2 => "#ruby slippers",
   3 => "hash rockets => => =>",
   4 => "unplayed games",
   5 => "Sinatra songs",
   6 => "segfaulting extensions",
   7 => "pragmatic hackers",
   8 => "lucky stiffs",
   9 => "scintillating beardies",
  10 => "leet Macbooks",
  11 => "gazillion tests",
  12 => "Rails hipsters",
}

def gift(day)
  # Memoise it because it is hip and we have hips.
  # Completely pointless, but 'memoisation' is fun to type and fun to say!
  # Don't let nasty spell-checkers make you 'memorise' it though D:
  $gifts ||= Hash.new do |hash, key|
    hash[key] = case key
    when 1     then GIFTS[1]
    when 2..12 then "#{key.to_word} #{GIFTS[key]}"
    else raise "an exquisite eyebrow"
    end
  end

  $gifts[day]
end

def list_of_gifts_recursive(day)
  # Put the gifts in a big pile, ready for the courier service.
  case day
  when 1     then "#{gift 1}"
    # Could recurse this next case, but it is as no simpler than just doing it
    # this way (list_of_gifts(1) vs. gift(1)).
  when 2     then "#{gift 2} and #{gift 1}"
  when 3..12 then "#{gift(day)}, #{list_of_gifts_recursive(day - 1)}"
  end
end

def list_of_gifts_functionalish(day)
  # Put all but the last gift in a big pile, ready for the courier service.
  gifts = day.downto(2).map(&method(:gift)).join(", ")

  # And it was looking so functional...
  gifts << " and " unless day == 1

  gifts + gift(1)
end

def list_of_gifts_functional(day)
  # Put the gifts in a big pile, ready for the courier service.
  # As we know, #injecting gives you cooties, so stay in school #with_object!
  day.downto(1).with_object("") do |current_day, str|
    str << gift(current_day)

    case current_day
    when 3..12 then str << ", "
    when 2     then str << " and "
    # when 1 then do nowt!
    end
  end
end

def chorus(day, algorithm)
  list_of_gifts = send "list_of_gifts_#{algorithm}", day
  puts "On the #{day.ordinal} day of Rubymas, my true love gave to me: #{list_of_gifts}."
  puts
end

# Use three different algorithms to generate the same output.
[:recursive, :functionalish, :functional].each do |algorithm|
  puts "=" * 40
  puts "Now let's be a good little #{algorithm} Al Gore Rhythm!"
  puts
  (1..12).each {|day| chorus day, algorithm }
end