Ruby implementation to find out the easter day date for a specific year (based on Anonymous Gregorian algorithm)

easter_day.rb

require "date"

# anonymous gregorian algorithm (http://en.wikipedia.org/wiki/Computus#Anonymous_Gregorian_algorithm)
def easter_day(year)
  if year.is_a?(Integer)
    y = year
    # calculation
    a = y % 19
    b = y / 100
    c = y % 100
    d = b / 4
    e = b % 4
    f = (b + 8) / 25
    g = (b - f + 1) / 3
    h = (19 * a + b - d - g + 15) % 30
    i = c / 4
    k = c % 4
    l = (32 + 2 * e + 2 * i - h - k) % 7
    m = (a + 11 * h + 22 * l) / 451;
    # date
    month = (h + l - 7 * m + 114) / 31;
    day = ((h + l - 7 * m + 114) % 31) + 1;

    Date.new(year,month,day).to_s
  else
    nil
  end
end