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 fibonacci(1) { |x| puts x } # 1 # 1 fibonacci { |x| break if x > 20; puts x } # 1 # 1 # 2 # 3 # 5 # 8 # 13