From: james_b <james_b@...>
Date: 2003-08-06T22:38:09+09:00
Subject: Re: Why does Ruby have callcc?

Brian Candler wrote:
> On Wed, Aug 06, 2003 at 08:38:25PM +0900, Harry Ohlsen wrote:
> 
>>I'd be interested to read about some real-world examples where people have
>>used callcc, not just to try it out, but because it was the "right" way to
>>do something (for efficiency, or code brevity or whatever reason).
> 
> 
> I think Seaside/Borges falls into this category.
> 
> I haven't had a chance to use it in anger, but I think the idea is that
> continuations can represent CGI session state; you code can be written in a
> linear fashion (e.g. display page, fetch response, display next page, fetch
> next response etc) without any explicit session maintenance. Furthermore, by
> retaining continuation objects which represent earlier pages, it will work
> even if the user clicks 'back' in their browser and re-enters data in a
> previous form.
> 
> I'd have a number of concerns in a practical application - I'd want old
> continuations to expire and be garbage-collected so that they don't cause
> infinite memory growth - but otherwise it sounds like a great way to write
> web applications.

As I recall from RubyConf 2002, the use of continuations in Borges was 
elegant but did not scale.  Tracking all that previous state gets 
expensive.

Perhaps see Avi Bryant's presentation slides:
http://www.zenspider.com/Languages/Ruby/RubyConf2002/index.html

James

> 
> Regards,
> 
> Brian.
> 
>