[Haskell-cafe] Instances for continuation-based FRP
Alberto G. Corona
agocorona at gmail.com
Wed Apr 24 21:09:43 CEST 2013
If you are not looking for the full reactive formalism but to treat event
driven applications in a procedural ,sequential, imperative way (whatever
you may call it) by means o continuations, then this is a good paper in
the context of web applications:
inverting back the inversion of control
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.29.3112
2013/4/24 Conal Elliott <conal at conal.net>
> Hi Hans.
>
> I'm delighted to hear that you have a precise denotation to define
> correctness of your implementation. So much of what gets called "FRP" these
> days abandons any denotational foundation, as well as continuous time,
> which have always been the two key properties of FRP<http://stackoverflow.com/a/5878525/127335>for me.
>
> I like your goal of finding a provably correct (perhaps correct by
> construction/derivation) implementation of the simple denotational
> semantics. I'm happy to give feedback and pointers if you continue with
> this goal.
>
>
> While I like the idea of TCMs very much, they do not seem to be applicable
>> for things that lack a denotation, such as IO
>>
>
> I suppose so, although I'd say it the other way around: things that lack
> denotation are not applicable for fulfilling denotational principles. Which
> suggests to me that IO will not get you to your goal. Instead, I recommend
> instead looking for a subset of imperative computation that suffices to
> implement the denotation you want, but is well-defined denotationally and
> tractable for reasoning. IO (general imperative computation) is neither,
> which is why we have denotative/functional programming in the first place.
>
> Regards, - Conal
>
>
> On Wed, Apr 24, 2013 at 8:31 AM, Hans Höglund <hans at hanshoglund.se> wrote:
>
>> Hi Conal,
>>
>> Thank you for replying.
>>
>> My aim is to find the simplest possible implementation of the semantics
>> you describe in Push-pull FRP <http://conal.net/papers/push-pull-frp/>,
>> so the denotational semantics are already in place. I guess what I am
>> looking for is a simple translation of a denotational program into an
>> imperative one. My intuition tells me that such a translation is possible,
>> maybe even trivial, but I am not sure how to reason about correctness.
>>
>> While I like the idea of TCMs very much, they do not seem to be
>> applicable for things that lack a denotation, such as IO. Maybe it is a
>> question of how to relate denotational semantics to operational ones?
>>
>> Hans
>>
>>
>> On 24 apr 2013, at 02:18, Conal Elliott wrote:
>>
>> Hi Hans,
>>
>> Do you have a denotation for your representation (a specification for
>> your implementation)? If so, it will likely guide you to exactly the right
>> type class instances, via the principle of type class morphisms<http://conal.net/papers/type-class-morphisms/>(TCMs). If you don't have a denotation, I wonder how you could decide what
>> correctness means for any aspect of your implementation.
>>
>> Good luck, and let me know if you want some help exploring the TCM
>> process,
>>
>> -- Conal
>>
>>
>> On Tue, Apr 23, 2013 at 6:22 AM, Hans Höglund <hans at hanshoglund.se>wrote:
>>
>>> Hi everyone,
>>>
>>> I am experimenting with various implementation styles for classical FRP.
>>> My current thoughts are on a continuation-style push implementation, which
>>> can be summarized as follows.
>>>
>>> > newtype EventT m r a = E { runE :: (a -> m r) -> m r -> m r }
>>> > newtype ReactiveT m r a = R { runR :: (m a -> m r) -> m r }
>>> > type Event = EventT IO ()
>>> > type Reactive = ReactiveT IO ()
>>>
>>> The idea is that events allow subscription of handlers, which are
>>> automatically unsubscribed after the continuation has finished, while
>>> reactives allow observation of a shared state until the continuation has
>>> finished.
>>>
>>> I managed to write the following Applicative instance
>>>
>>> > instance Applicative (ReactiveT m r) where
>>> > pure a = R $ \k -> k (pure a)
>>> > R f <*> R a = R $ \k -> f (\f' -> a (\a' -> k $ f' <*> a'))
>>>
>>> But I am stuck on finding a suitable Monad instance. I notice the
>>> similarity between my types and the ContT monad and have a feeling this
>>> similarity could be used to clean up my instance code, but am not sure how
>>> to proceed. Does anyone have an idea, or a pointer to suitable literature.
>>>
>>> Best regards,
>>> Hans
>>>
>>> _______________________________________________
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe at haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>
>>>
>>
>>
>
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--
Alberto.
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