From: Kristof Bastiaensen <kristof@...>
Date: 2004-04-12T09:34:26+09:00
Subject: Re: Continuation usage

Hi,

On Sun, 11 Apr 2004 12:41:50 +0200, Patrick Roemer wrote:

> 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.
> 

This looks very solid to me.  Maybe you could make every
Service a subclass of ContSession, and every session an 
instance of that session.  It would look something like this:

class ContSession
  def start(*args)
    callcc do |cc|
      @main = cc
      session(*args)
    end
  end

  def service(arg)
    callcc do |cc|
      @main = cc
      @cont.call(arg)
    end
  end

  def io(out)
    callcc do |cc|
      @cont = cc
      @main.call(out)
    end
  end
  private :io
end

class Guess < ContSession
  def session
    target = rand(100)
    inp = io("Please enter a number between 1 and 100.").to_i
    round = 1
    while(inp != target)
      inp = io(inp < target ? "Higher" : "Lower").to_i
      round += 1
    end
    "You found it in #{round} rounds."
  end
  private :session
end

irb(main):002:0> g = Guess.new  
#<Guess:0x402a7484>
irb(main):003:0> g.start
"Please enter a number between 1 and 100."
irb(main):004:0> g.service(50)
"Lower"
irb(main):005:0> g.service(25)
"Higher"
irb(main):006:0> g.service(37)
"Lower"
irb(main):007:0> g.service(31)
"Higher"
irb(main):008:0> g.service(34)
"You found it in 5 rounds."