From: Carlos <angus@...>
Date: 2004-03-10T22:17:15+09:00
Subject: Re: Why there is no Continuation.new ?

[gabriele renzi <surrender_it@rc1.vip.ukl.yahoo.com>, 2004-03-10 13.34 CET]
> I understand hat callcc calls the block passing the continuation to
> it,  I did'nt meant to replace it.
> I just asked why the process by witch |$cc| is initialized is not
> available to us.
> 
> 
>  I just knew of scheme's call/cc till some time ago, and I considered
> that was the only way to handle continuations.
> Than I found "new Continuation" in javascript, and I wondered if we
> could have (on side with callcc ) something like what exist in
> Rhino[1].

But your example would not work with the Rhino version.
Continuation.new creates a continuation that returns from the
enclosing block. Since the enclosing block is the top level, when you
do $cc.call, it would exit the program.

I find the ruby version clearer. When you do callcc{|c| ... }, it
means: when you'll do c.call, it will return exactly to this point.

In the Rhino version, when you do c = Continuation.new, it means: when
you'll do c.call, it will return from the enclosing
block/function/etc...

Your modified example from Pickaxe then would become something like:

 arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ]
 dummy = begin
#      ^-- cc.call will return here
   cc = Continuation.new
 end
 puts(message = arr.shift)
 cc.call unless message =~ /Max/

And what happens with Continuation.new inside iterators? cc.call
should return like next or like break?

def loop
  while true
   dummy = yield
#        ^-(1)
  end
end

dummy = loop do
#     ^-(2)
  cc = Continuation.new
  break
end
puts(message = arr.shift)
cc.call unless message =~ /Max/ # <- returns to (1) (next) or (2) (break)?

Bah.. it's all more complicated... better stay with the ruby version
:)