[cells-devel] Pentagon of Death [was Re: Vancouver Lisp Users Group meeting for October 2008 - The Nature of Order]
puchacz wrote:
On Oct 4, 11:03 pm, Kenny kentil...@gmail.com wrote:
Patrick May wrote:
Kenny kentil...@gmail.com writes:
Patrick May wrote:
Kenny kentil...@gmail.com writes:
I wonder if Flash can keep up with compiled JS. You don't mind the Flash requirement? I realize it is ubiquitous enough, but still.
It loads relatively slowly, but once it's loaded it's as fast as a desktop app (not surprisingly). I selected it despite the Flash requirement because it provided a nice grid control and the chart displays I needed.
JS frameworks don't have those?
Some have one, some have the others, some have some other bits Iwanted to use. TIBCO's GI was actually my first choice, but there was a bug in Safari that prevented me from using it.
I was just going to say one big win would be insulation from browser variability.
Or was it more like you had zero reason to avoid Flash (and maybe already knew it) so there was no reason to hassle with less polished tools? I suppose you also had the means to acquire the tools.
Actually, I felt rather dirty using Flash. And not in that good,tingly way.
:)
Aside from the chart widgets, the tools are free (as in beer).What's your IDE, Eclipse?
[ . . . ]
No Cells? Are you mad? For a GUI? Celtk and Cells-Gtk (and soon Xello) will show you how to drive an existing framework with Cells.
This application is a trading system. If Cells is fast enough,it might be a good choice for the backend. Can I get a response in 10 milliseconds when an order book changes?
10ms is an eternity! I know, I have a feel for that having done RoboCells in which we handled realtime inputs spaced at 100ms.
Otherwise, not sure what you are asking. Naturally a very interesting question is how long does the functional computation take. But I will presume that is in order and what you are asking is if Cells is a pig. No. (see "RoboCells"). In fact, Cells helps a bit by magically discerning exactly what needs to be updated when X changes. I tried to tell the walking dead at ECLM 2008 that Cells is a library about change. Practically, this means one has complete control over change, including the aforementioned optimization of changing only those things that need to change, but also being able to surgically control "oh, I do not need to update /that/ every 10ms, I can do it every other unless of courese Y changes by 42%". Stuff like that.
Well, if js/html/css get on my nerves I'll take a look at Fex/MXML. Thx for the lead.
kt
Hi,
Is Cells able to handle updates in a "diamond scenario"?
"a": external input "b": driven from "a" "c": driven from "a" "d": driven from "b" and "c"
As "d" is driven indirectly from a single input "a", and processing of "b" and "c" may take different time, it is important to wait with updating of "d" until both "b" and "c" is finished. Otherwise, "d" may publish its value twice, and the first value would be totally incorrect, like a huge spike in the series.
PWUAHAHAHAHAHHAHAA! I thought I invented that. Philip Eby gave it a more dramatic name when I explained it to him while justifying the Cells mechanism -- the Pentagon of Death, I think it was. Why Pentagon aka 5?
I settled on a tougher case in which, eg, d did not depend directly on c, but did so indirectly thru an intermediary depencency c2 which depended on c. Why does this matter? If a changes c needs to be recalculated, period, no question. But C might recompute and come up with the same value, say if A changes from 3 to 6 and C is (mod A 3). In that case we cannot know C2 is obsolete until C runs, and this defeats some algorithms (assuming we have a rule that says "never calculate unecessarily").
I also made it nastier in that...well, it gets complicated, but Cells tracks dynamic dependencies, not lexical, so I cannot just inspect the dependency graph as it stands -- the change to 'a' might make 'd' go after 'c2' for the first time ever in 'd's life.
Philip struggled mightily to find a better way than the Cells algorithm, but in the end the Pentagon of Death beat every alternative.
Thx for the heads up on the prior art.
cheers,ken
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Kenny