require 'fiber'

class Fiber
  def inject *sval, &blk
    ival = sval.empty? ? resume : sval.first
    loop do
      ival = blk.call ival, resume
    end
  rescue FiberError
    ival
  end
end

f = Fiber::new do
  5.times do |i| Fiber::yield i end
end

p f.inject{ |s, i| s+i }

def fibo limit = nil
  a = b = 1
  Fiber::new do
    loop do
      a, b = b, a+b
      raise FiberError if limit && a > limit
      Fiber::yield a
    end
  end
end

p fibo(20).inject{ | s, i | p [s, i];i + s }