[plt-scheme] web programming, continuation, CPS transform, etc.

Why don't you turn this message into the core of a Tutorial that  
others can supplement later? -- Matthias





On May 3, 2007, at 10:42 AM, Jay McCarthy wrote:

> On 5/3/07, YC <yinso.chen at gmail.com> wrote:
>> > > Understood.  I would say that the ilities are probably neither  
>> better
>> > > nor worse than you would expect, but just different.  We have, in
>> > > effect, run a many-year experiment using Continue, a semi- 
>> commercial
>> > > Web application for conference paper management written  
>> entirely in
>> > > PLT Scheme (continue.cs.brown.edu ).  Over the years we have  
>> gradually
>> > > refined our understanding of its performance, and some of  
>> Jay's work
>> > > on continuation replacement strategies (not written up  
>> anywhere, but
>> > > I'm sure he can say more here if he feels inclined) stems from  
>> our
>> > > observations of this system (and of its sibling, Resume, which  
>> handles
>> > > the faculty job ads for Brown CS and was also used at  
>> Northeastern CCS
>> > > this past year).
>>
>> Thanks - hopefully Jay would be feeling inclined to share ;)
>
> The vanilla server originally used simple timeouts to reap the memory
> of old continuations. I found that using a LRU replacement policy
> works wonders. This is available in the SVN server as `continuation
> managers', the two most useful being: timeouts.ss and lru.ss. Noel
> recently sent mail to the list with a simple servlet using it.
>
> Secondly, I found it fairly simple to contain coarse information about
> the continuation in the URLs generated by the server. These
> information can be used if the continuation id refers to a dead
> continuation. If that is the case, such information can reconstruct
> the continuation coarsely.
>
> For example, suppose you have the k-url:
>
> http://localhost:8888/servlets;1*2*3/servlet.ss
>
> which is instance 1, continuation 2, which refers to the list of
> papers, you could instead give the URL:
>
> http://localhost:8888/servlets;1*2*3/servlet.ss;place=list
>
> If continuation 2 is alive, the extra URL content is ignored.
> Otherwise, the servlet can, say, redisplay the login and then go
> directly to the list.
>
> The PLaneT module url-param.plt helps with this process.
>
> I've found this very simple to do in Continue (a very large
> application), only about 50 lines of code to get a fair coverage of
> the possible coarse continuation locations.
>
> Jay
>
> -- 
> Jay McCarthy <jay.mccarthy at gmail.com>
> http://jay.teammccarthy.org
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