enumerator.cr

require "big_int"

class Enumerator(T)
  include Enumerable(T)

  struct Yielder(T)
    def initialize
      @channel = Channel(T).new(20)
    end

    def <<(value : T)
      @channel.send value
    end

    def receive
      @channel.receive
    end
  end

  def initialize(&block : Yielder(T) ->)
    @yielder = Yielder(T).new
    spawn do
      block.call(@yielder)
    end
  end

  def next
    @yielder.receive
  end

  def each
    loop do
      yield self.next
    end
  end
end

fib = Enumerator(BigInt).new do |y|
  a = b = 1.to_big_i
  loop do
    y << a
    a, b = b, a + b
  end
end

100.times do
  puts fib.next
end