[Haskell-cafe] [reactive] A pong and integrate

[Limestraël]

> But you have to be aware that Elerea, Yampa, Lucid Synchrone and Lustre
> are all very similar in their foundations.

Okay. I just thought that reactive programming was a quite new field of
research, but I saw that Lustre and Esterel date back to 1980...
I assumed also that it was a field which was still under research, however,
Lustre, again, is used "for critical control software in aircraft,
helicopters, and nuclear power plants", according to wikipedia.

2010/5/24 Patai Gergely <patai_gergely at fastmail.fm>

> > One problem with Elerea experimental branch besides the update time
> > control:
> > the memo function. I can't understand when I have to call it and when I
> > don't.
> Technically, you never have to. However, if you have a signal derived
> from others by pure application (i.e. fmap or <*>), keep in mind that
> its output will be recalculated as many times as you request it. The
> memo element can be used as a proxy to prevent that. E.g. if you have z
> = liftA2 f x y, and you request z n times, f will also be called n
> times. But if you have z <- memo (liftA2 f x y) instead, then the
> calculation will only happen once. If Elerea wasn't an EDSL, these memo
> elements could be inserted automatically, but now I have no means to
> tell how many times a certain signal is referred to, so the burden is on
> the programmer.
>
> The old version doesn't have this inconvenience, because it memoises all
> the applicative nodes too. Since most of them are only referred to once,
> this is adds a lot of unnecessary overhead.
>
> > Just to know, have you been told of a language dedicated to reactive
> > programming (even experimental)? I mean, not an embedded language just
> > like Yampa is.
> Those that Peter mentioned are good examples, and there is also Lustre.
> But you have to be aware that Elerea, Yampa, Lucid Synchrone and Lustre
> are all very similar in their foundations.
>
> Gergely
>
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