[Haskell-cafe] ANN: Elerea, another FRP library

Peter Verswyvelen bugfact at gmail.com
Tue Apr 14 17:04:03 EDT 2009

Ouch, I did not see Wolfgang's email nor your reply, sorry for the noise
(which I'm doing again with this email ;-)
On Tue, Apr 14, 2009 at 11:01 PM, Peter Verswyvelen <bugfact at gmail.com>wrote:

> I will test it on a couple of machines, desktops and laptops. I think the
> problem was my laptop going into power safe mode or something, since
> sometimes it runs smooth, sometimes it doesn't. This could indeed be a
> problem with GLFW's time attribute on windows (which uses the CPU tick
> frequency which gets trottled to safe energy), although I believe the
> Windows API should take care of this. I haven't seen this yet with my own
> frp experiments, which seem to run smooth all the time, but again I will do
> more testing.
> I have been thinking about your approach, using mutable variables to hold a
> signal's sample. This is exactly what I did with on old C# prototype, and it
> worked out nicely. If you take a look what Yampa does: it hides signals and
> only exposes signal functions. But that means that the FRP engine itself
> could indeed use mutable variables for its signals, as long as during the
> evaluation of the circuit at time T no side effects should occur; the side
> effects should take place when the simulation is advanced to T+dT, which is
> done after the circuit is fully evaluated at time T. If you want higher
> order integration, you would need to keep a buffer of more samples, but it
> would still work. So I think you approach is a very good pragmatic one! I'm
> only a bit worried about your automatic insertion of delays; this might
> break referential transparency at time T, since it depends on the order in
> which the nodes in the circuit are evaluated no? The latter could be
> problematic when doing evaluation in parallel on multiple cores I guess.
> 2009/4/14 Patai Gergely <patai_gergely at fastmail.fm>
> > Interesting. I'm testing it on Window though. You're using Linux? Maybe
>> > the scheduling is different.
>> Now I tried it on Windows in VirtualBox, and it still looks quite smooth
>> to me (except that hardware acceleration doesn't seem to work properly
>> through virtualisation, but it's okay as long as I keep the window small
>> enough). However, unlike the Linux version, it does max out the CPU, so
>> the trick with threadDelay 0 doesn't work. Apparently, I'll have to find
>> a real Windows box somewhere, because I couldn't reproduce the jerkiness
>> you're talking about.
>> Gergely
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