[Haskell-cafe] Unambiguous choice implementation

[Bartosz Milewski]

I'm trying to understand Reactive Banana, but there isn't much 
documentation to go about. How is RB positioned vis a vis Elliott (and then 
there is the earlier Elliot and Hudak, and the later Elliot with the push 
implementation and type classes). Do you have a toy applet that 
demonstrates the use of Reactive Banana, something like Elliotts Bezier 
editor,  http://research.microsoft.com/pubs/69665/deop-tr.pdf  ? 
--Bartosz

On Sunday, June 24, 2012 7:21:07 AM UTC-7, Heinrich Apfelmus wrote:
>
> Bartosz Milewski wrote: 
> > I'm reading Conal Elliot's paper, Push-Pull FRP. At some point he needs 
> an 
> > unambiguous choice operator, essentially to implement select: a future 
> that 
> > waits for one of its future arguments to fire. His implementation of 
> unamb 
> > creates two threads racing on a shared MVar. By his own admission, this 
> is 
> > very inefficient. My question is, is there a better implementation? 
>
> The thing about unambiguous choice is that it goes beyond the dynamic 
> semantics of the Haskell language. To implement it, you either need a 
> new evaluation model built into the compiler, or you have to fake it 
> somehow and that is likely to be inefficient. 
>
>
> Also note that Conal's paper describes just one possible implementation 
> of FRP. My reactive-banana library uses an implementation that doesn't 
> require unambiguous choice at all. For a basic model, see 
>
>
> http://hackage.haskell.org/packages/archive/reactive-banana/latest/doc/html/Reactive-Banana-Model.html 
>
> The key idea is to keep all events synchronous and to reify some cases 
> of "this event does not occur right now". 
>
>
> Best regards, 
> Heinrich Apfelmus 
>
> -- 
> http://apfelmus.nfshost.com 
>
>
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