yay Enumerator

fibs.rb

fibs = Enumerator.new do |y|
  recent = [0,1]
  loop do
    y << recent.last
    recent = (recent << recent[0..1].inject(:+)).pop(2)
  end
end


fibs.first(20) #=> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765]