From: "Hans Jörg Hessmann" <hessmann@...>
Date: 2003-03-17T03:29:28+09:00
Subject: Iterator using Continuations

Hi,

Im am preparing a small presentation for ruby. Therefore I was searching for a 
continuation example. I tried to make a Java like iterator for any ruby class 
with an each() method. This is the solution I found:

class Iterator
  def initialize(enum)
    @enum = enum
    @current = nil
    @back = nil

    @enum.each do |el|
      @current = el
      callcc do |cc|
        @next = cc
        if @back then @back.call else return end
      end
    end
    @current = nil
    @back.call if @back
  end

  def hasNext?
    @current != nil
  end

  def next
    last = @current
    callcc do |cc|
      @back = cc
      @next.call if @current
    end
    last
  end
end

iter = Iterator.new(1..5)
while iter.hasNext?
  puts iter.next
end

What do you think of this approach? Is there an easier way to do it?

Best regards,
Hans J�rg Hessmann