[reactive] Bounce

[Conal Elliott]

Good point.  There is already a VectorSpace instance for behaviors, and
using it in the positionB definition makes for a much more general type.
See FRP.Reactive.VectorSpace.

I wouldn't use v ^* t (or t *^ v), however, because v is dynamic.
Integrating v ought to do the trick.

And I expect that any simple & direct formulation will run into the current
implementation bug with recursive behaviors, since the position depends on
the velocity, the velocity depends on acceleration and accumulated impulse,
and the accumulated impulse depends on position.

  - Conal

On Fri, Nov 21, 2008 at 11:33 AM, Peter Verswyvelen <bugfact at gmail.com>wrote:

> Shouldn't Reactive also have VectorSpace instances for Behaviors of
> VectorSpace elements? So that the code becomes
> > positionB x0 v t = pure x0  ^+^  v  ^*  t
>
> Maybe it already has, in that case, sorry for the spam ;)
>
> On Fri, Nov 21, 2008 at 7:00 PM, Greg Fitzgerald <garious at gmail.com>wrote:
>
>> >>> positionB :: Double -> Behavior Double -> Behavior Double -> Behavior
>> Double
>> >>> positionB x0 v t = (x0 +) <$> liftA2 (*) v t
>> > positionB x0 v t = pure x0 + v * t
>>
>> That's very convenient.  I'm showing this stuff off to visual
>> designers, so tricks like this have great Sales appeal. :)
>>
>> If others are trying this out, the Num instance is implemented in
>> FRP.Reactive.Num.
>>
>> -Greg
>>
>>
>> On Fri, Nov 21, 2008 at 6:48 AM, Conal Elliott <conal at conal.net> wrote:
>> > For that matter, you can also say, thanks to Num overloading:
>> >
>> > positionB :: Double -> Behavior Double -> Behavior Double -> Behavior
>> Double
>> > positionB x0 v t = pure x0 + v * t
>> >
>> > Sadly, similar convenience does not come for free with non-methods, such
>> as
>> > most of the FieldTrip API.  For non-methods, in the past (with Fran),
>> I've
>> > written parallel sets of modules with behavior-lifted functionality.
>>  It's
>> > tedious to set up but convenient to use.  Perhaps a tool could automate
>> the
>> > job.
>> >
>> > By the way, a nice feature of Yampa is that it avoids this lifting
>> business
>> > altogether, via desugaring for the arrow notation.
>> >
>> >    - Conal
>> >
>> > On Fri, Nov 21, 2008 at 12:14 AM, Thomas Davie <tom.davie at gmail.com>
>> wrote:
>> >>>
>> >>> positionB :: Double -> Behavior Double -> Behavior Double -> Behavior
>> >>> Double
>> >>> positionB x0 v t = (x0 +) <$> liftA2 (*) v t
>> >>
>> >> On an unrelated note, I created a package called InfixApplicative,
>> because
>> >> I found that exactly this kind of expression looked ugly in my code.
>>  If you
>> >> import it, you can define this instead:
>> >>
>> >> positionB x0 v t = (x0 +) <$> (v <^(*)^> t)
>> >>
>> >> Hope that helps
>> >>
>> >> Bob
>> >> _______________________________________________
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>> >> Reactive at haskell.org
>> >> http://www.haskell.org/mailman/listinfo/reactive
>> >
>> >
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>
>
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