pi_digits = Enumerator.new do |y|
  q, r, t, k, n, l = 1, 0, 1, 1, 3, 3
  loop do
    if 4*q+r-t < n*t
      y << n
      nr = 10*(r-n*t)
      n = ((10*(3*q+r)) / t) - 10*n
      q *= 10
      r = nr
    else
      nr = (2*q+r) * l
      nn = (q*(7*k+2)+r*l) / (t*l)
      q *= k
      t *= l
      l += 2
      k += 1
      n = nn
      r = nr
    end
  end
end

print pi_digits.next, "."
loop { print pi_digits.next }