Re: [Haskell-cafe] Can this be done?

On Wed, Feb 11, 2009 at 4:08 PM, Manlio Perillo wrote:

Cristiano Paris ha scritto:

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On Wed, Feb 11, 2009 at 2:30 PM, Peter Verswyvelen wrote:

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I haven't looked at the details, but I think this is what a library like Reactive from Conal Elliott could do, but as far as I understand it, it is still work in progress.

I'm interested in the possibility of stopping/pickling/unpickling/resuming a computation.

Not sure this is a good thing in a web application.

I'm thinking of complex workflows and inversion of control. A computation may stop, return a response, wait for a new request to be passed by the HTTP server and return back a new response, stopping again. This goes on forever. All this can be achieved in Haskell but the serialization path, which is crucial for swapping out idle sessions (containing the stopped computation) or to get back to life after server stopped (for maintenance for instance). I guess this should be doable in Clean, which has mechanisms to do dynamic binding and serialization of closures. I once did something close to this using Stackless Python, which sports serializable iterators. I did funny things like moving all the sessions to a different server transparently. Nevertheless, the use of yield, specially in sub-computation, is tricky to handle. Notice that this is not a main concern in my daily work but the possibility fascinates me and it turns out to be not a simple problem to solve. During my explorations, I considered continuations, delimited continuations and zippers, and I learned a lot even if I can't still catch delimited continuations. Recently, I stumbled upon Factor and realized that most of the complications are simply cut out in that language as it is purely concatenative (no symbol bindings to mess around). Cristiano