def fibonacci(limit = nil)
  seed1 = 0
  seed2 = 1
  while not limit or seed2 <= limit
    yield seed2
    seed1, seed2 = seed2, seed1 + seed2
 end
end
fibonacci(3) { |x| puts x }

1
1
2
3

1
1
2
3

fibonacci(1) { |x| puts x }

1
1

1
1

fibonacci { |x| break if x > 20; puts x }

1
1
2
3
5
8
13

1
1
2
3
5
8
13

class Range
  def each_slow
    x = self.begin
    while x <= self.end
      yield x
      x = x.succ
    end    
  end
end
(1..3).each_slow {|x| puts x}

1
2
3

1
2
3

class Fixnum
  def double_upto(stop)
    x = self
    until x > stop
      yield x
     x = x * 2
    end
  end
end
10.double_upto(50) { |x| puts x }

10
20
40

10
20
40

def oscillator
  x = 1
  while true
    yield x
    x *= -2
  end
end
oscillator { |x| puts x; break if x.abs > 50; }

1
-2
4
-8
16
-32
64

1
-2
4
-8
16
-32
64

1.5.step(2.0, 0.25) { |x| puts x }

def zeno(start, stop)
  distance = stop - start
  travelled = start
  while travelled < stop and distance > 0
    yield travelled
    distance = distance / 2.0
    travelled += distance
  end
end
steps = 0
zeno(0, 1) { steps += 1 }
steps