[reactive] Bounce

[Greg Fitzgerald]

>>> 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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>
>