Yariv,
I suggest you have a look at seaside. Continuations not only make the
code development easy, but you can suddenly start to develop "true"
components and they are straightforwardly embeddable - the complexity
of mixing and matching components becomes additive rather the
geometric if that makes sense.
I can't explain the gist of my argument - its one of those matrix
things - when it sinks in you go "Wow!".
Why am I still programming in erlang? I really like the scalability
and a lot of my applications need lots of concurrent processes.
I have been told any system that supports first class function objects
with lexical closure is able to support continuation passing style - I
think it would even be easier with erlang considering you don't have
to worry about variable mutations and the like.
hafeez
On Feb 13, 8:32 pm, "Yariv Sadan" <[EMAIL PROTECTED]> wrote:
> Dang, I actually realized I just overlooked something big: my examples
> didn't use real closures -- just anonymous functions. With framework
> support, those functions could be used as closures and their
> environment data could be accessible in subsequent actions without the
> controller's using the session store explicitly. I should have thought
> a bit harder before voicing my skepticism :) (However, I believe some
> of the disadvantages I listed still hold true.)
>
> Yariv
>
> On Feb 12, 2008 10:35 PM, Yariv Sadan <[EMAIL PROTECTED]> wrote:
>
> > My impression (and I could be very wrong because I haven't used a
> > continuations-based framework) is that continuations can be useful to
> > streamline the code for some multi-page interactions, but for general
> > web development purposes they cause too many problems: non meaningful
> > URLs, sticky load balancing, no back button support, no crash
> > recovery, and apparently also high memory requirements (I'm not sure
> > why, but I'll take your word for it.)
>
> > Also, I'm not sure that continuations create such a dramatic decrease
> > in code size. Consider these two similar examples, one that uses
> > continuations and one that doesn't (I'm using the terms continuation
> > and closure interchangeably here):
>
> > index(A) ->
> > form([input("name"), input("age"), submit()],
> > fun(A1) ->
> > [Name, Age] = [get_param(A1, "name"), get_param(A1, "age")],
> > save(Name, Age)
> > end).
>
> > index(A) ->
> > case method(A) of
> > 'GET' ->
> > form([input("name"), input("age"), submit()]);
> > 'POST' ->
> > [Name, Age] = [get_param(A, "name"), get_param(A, "age")],
> > save(Name, Age)
> > end.
>
> > Is the first version really that much better?
>
> > By the way, you can write code that looks like it uses continuations
> > but without any framework support:
>
> > index(A) ->
> > get_inputs(A, ["name", "age"],
> > fun([Name, Age]) -> save(Name, Age) end).
>
> > with this utility function:
>
> > get_inputs(A, Inputs, Fun) ->
> > case method(A) of
> > 'GET' ->
> > form([input(Input) || Input <- Inputs] ++ submit());
> > 'POST' ->
> > Fun([get_param(A, Input) || Input <- Inputs])
> > end.
>
> > I'll appreciate any enlightenment in case I'm missing something big here.
>
> > Yariv
>
> > > I was think of "unrolling continuations". Unrolling similarly to loop
> > > unrolling in language compilers. One of the problems with continuations
> > > is the amount of memory consumed. I watched a talk off google video by
> > > one of the developers of seaside, sorry can't remember which talk, where
> > > he was asked how much memory was consumed by the use of continuations.
> > > He stated about 2MB per session. He was likely making a "guessimate"
> > > based on he's experience and not base on actual measurements but even so
> > > that's alot. When you consider that for most sites most of the time the
> > > use of continuations is to allow the extra functionality it provides is
> > > unwarranted. Being mostly queries of static data versus editing,
> > > multipart forms and the dreaded shopping cart example. In fact the use
> > > of continuations and the associated session can be annoying. Consider
> > > the seaside tutorial located at
> > >http://www.swa.hpi.uni-potsdam.de/seaside/tutorial. I aim to read about
> > > a page a day, but the session information times out and I have to go
> > > back to the first page before finding my place. Very frustrating. It
> > > would be much better to have this functionality turned off by default
> > > and only turn it on as needed.
>
> > > Anyway, what I was thinking it might be possible to "unrolling
> > > continuations" in loose terms. Would it be possible to do this is such a
> > > way as to,
>
> > > 1) reduce memory usage
> > > 2) be able to turn it on only for a section of code
> > > 3) serial to a database such as mnesia, so that,
> > > 4) unlike continuations be distributed for the purposes of redundancy
> > > and load balancing.
>
> > > Can anyone point be to some good references on continuation so that I
> > > can actually get a deep understanding of continuations, etc?
>
> > > trying to run out the door,
>
> > > Jeff.
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