Sieve of Eratosthenes

eratos.rb

def compute(number)
  sieve((2..number).to_a, [], Math.sqrt(number))
end

def sieve(list, primes, stopper)
  return primes + list if list.first >= stopper
  primes << list.shift
  list.reject! { |n| n % primes.last == 0 }
  sieve(list, primes, stopper)
end

if ($0 == __FILE__)
  puts compute(ARGV.first.to_i).join(', ')
end