From: Florian Gross <flgr@...>
Date: 2004-08-21T07:55:49+09:00
Subject: Re: ruby, actors, continuations, Kernel#callcc

--------------080201020302010204060603
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit

zuzu wrote:

> but i still can't quite seem to grok continuations, at least in terms
> of interpreting it for ruby, w/r/t closures and Kernel#callcc.  this
> after reading dan "parrot" sugalski's weblog

I find that Continuations are easy to work with once you've got the 
confusing stuff wrapped away. I've attached Continuation.create which 
allows you to do such things:

cc, counter = Continuation.create(10)
puts counter
cc.call(counter - 1) if counter > 0

Or a custom version of Enumerable#inject: (Won't work with Enumerables 
containing nil values and is way less efficient than the built-in one.)

module Enumerable
   def cc_inject(initial_state = nil, &block)
     obj = self.to_a.clone
     initial_state = obj.shift if initial_state.nil?
     cc, state, item = Continuation.create(initial_state, obj.shift)
     unless item.nil?
       state = yield(state, item)
       cc.call(state, obj.shift)
     end
     return state
   end
end

Can't say anything about the whole actor thing, but I hope I was at 
least of some help. :)

Regards,
Florian Gross


--------------080201020302010204060603
Content-Type: text/plain;
 name="simplecc.rb"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
 filename="simplecc.rb"

def Continuation.create(*args, &block)
  args = [args] if not args.nil? and not args.is_a? Array # 1.6.8 compatibility
  cc = nil; result = callcc {|c| cc = c; block.call(cc) if block and args.empty?}
  result ||= args
  return *[cc, *result]
end

--------------080201020302010204060603--