Fixnum/Bignum to_en function - convert numbers to English. Useful for testing your Euler 17 solution (hint, hint)

to_en.rb

# Fixnum and Bignum :to_en function
# For Ruby Hack Night, May 7, 2012
# By David Andrews, Ryatta Group

class Unit
  UNITS = [ "thousand",  "million",  "billion",  "trillion",  "quadrillion",  "quintillion",  "sextillion", "septillion", "octillion", "nonillion", "decillion", "undecillion", "duodecillion", "tredecillion", "quattuordecillion", "quindecillion", "sexdecillion", "septendecillion", "octodecillion", "novemdecillion", "vigintillion" ]
  HUNDRED = "hundred and"

  def self.how_big(zeroes)
    return HUNDRED if zeroes == 2
    return "" if zeroes < 3 || zeroes % 3 > 0 # if it ain't hundred, or a power of three, there's no name for it
    zeroes /= 3
    throw "toobig!" if zeroes >= UNITS.length
    "#{UNITS[zeroes-1]},"
  end
end

class Bignum
  def to_en # handles massively large (possibly negative) values
    return "negative #{(-self).to_en}" if self < 0
    as_chars = self.to_s.split("")
    chunk = self.to_s.length % 3
    chunk = 3 if chunk == 0
    text = ""
    while as_chars.length > 0 # eat "chunks" until there are none left
      text << "#{as_chars.shift(chunk).join.to_i.hundreds_to_en} #{Unit.how_big(as_chars.length)} "
      chunk = 3
    end
    text
  end
end

class Fixnum
  ONES = [ "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven", "twelve",  "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen", "twenty" ]
  TENS = [ "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" ]

  def to_en
    9999999999999999999.coerce(self).first.to_en # a cheap way of achieving DRY -> defer to Bignum's to_en
  end

  def hundreds_to_en # handles the range [0, 999]
    case self.to_s.length
    when 3 # a number in the hundreds
      "#{ONES[self/100]} #{Unit.how_big(2)} #{(self % 100).hundreds_to_en}"
    when 2 # tens
      return ONES[self] if self < ONES.length # teens
      return "#{TENS[self/10-1]}-#{ONES[self % 10]}" if self % 10 > 0 # a compound name, if not a power of 10
      TENS[self/10-1]
    when 1 # ones
      ONES[self]
    end
  end
end

puts "Gimme some numbers and I'll print them in English"
ARGF.each do |line|
  puts line.to_i.to_en
end