From: Patrick Roemer <sangamon@...>
Date: 2004-04-11T19:44:13+09:00
Subject: Continuation usage

Once again I've been trying to get a grip on continuations, however, I'm
quite unsure whether I've really got it this time. Could anybody please
take a look at the example 'server' below. It seems to work when called
from irb, but I'm unclear on how to test such a beast programmatically,
so I suspect I somehow must have got it wrong again.

TIA,
Patrick

class ContServer
  def initialize()
    @blocks={}                  # named services
    @mains={}                   # top-level continuations by session id
    @conts={}                   # service continuations by session id
  end

  def add(name,&block)
    @blocks[name]=block
  end

  def service(id,name='',inp='')
    callcc do |cc|
      @mains[id]=cc             # remember top-level continuation
      if(@conts.key?(id))       # already in session?
        @conts[id].call(inp)    # return to service continuation
      else
        ret=@blocks[name].call(id,self)   # enter new session
        @conts.delete(id)                 # finish session
        ret
      end
    end
  end

  def io(id,out)
    callcc do |cc|
      @conts[id]=cc             # remember service continuation
      @mains[id].call(out)      # return to top-level continuation
    end
  end

  def ContServer::init
    cs=ContServer.new
    cs.add('guess') do |id,server|
      target=rand(100)
      inp=server.io(id,"Please enter a number between 1 and 100.").to_i
      round=1
      while(inp!=target)
        inp=server.io(id,(inp < target ? "Higher" : "Lower")).to_i
        round += 1
      end
      "You found it in #{round} rounds."
    end
    cs
  end
end