From: Rick DeNatale <rick.denatale@...>
Date: 2007-06-07T05:39:09+09:00
Subject: Re: code problems

On 6/6/07, Robert Dober <robert.dober@gmail.com> wrote:

> >
> >
> Hi Rick I am still struggeling with continuations :(, as a matter of
> fact I hoped that they would behave as described above, but they do
> not, it seems.
>
> When I execute the code from your blog
>  def continuation
>    i = 0
>    lola = nil
>    callcc {|cc| puts "In callcc";lola = cc}
>    puts "i is now #{i}"
>    i += 1
>    lola
>    end
>  cont = continuation
>  # point of looping
>  cont.call
>
> I just get an endless loop, do you have an explanation for it?
>

Robert, you are right, it loops in ruby, but not in irb.

I was trying to cook up a simple example and got hoist by irb's petard.

What happens in ruby is that calling the continuation goes back to the
method, which returns to the point before the cont.call and away we go
again.

Continuations normally aren't reused in the way I did in the example.
I'm actually not sure why it works the way it does in irb.

Here's a simpler example which shows the flow of control concept.

rick@frodo:/public/rubyscripts$ cat testcontin.rb
def continuation
  puts "Before callcc"
  callcc {|cc| puts "In callcc";return cc}
  puts "After callcc"
end

puts "Begin"
cont = continuation
puts "Got cont #{cont.inspect}"
if cont
  cont.call
  puts "After call"
end
puts "All done"
rick@frodo:/public/rubyscripts$ ruby testcontin.rb
Begin
Before callcc
In callcc
Got cont #<Continuation:0xb7de3840>
After callcc
Got cont nil
All done





-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/