- Reactive - Haskell.org

Simple Example ..
by Tom Poliquin 24 Mar '09

24 Mar '09

I've been struggling trying to get a simple Reactive example running .. I'm a newbie to FRP and few months of Haskell (Scheme before that). David Sankel previously posted a simple example which I loaded up with great joy .. but I get the error .. ConsoleAdapter.hs:24:50: Couldn't match expected type `Event Char' against inferred type `FRP.Reactive.Internal.Misc.Sink a' In the first argument of `f', namely `stdinEvent' In the second argument of `fmap', namely `(f stdinEvent)' In the second argument of `forkE', namely `(fmap putChar (f stdinEvent))' Failed, modules loaded: none. I posted the full details up at, http://www.hpaste.org/fastcgi/hpaste.fcgi/view?id=2810#a2810 I also tried the Example.hs (that comes with the 0.10.5 package) but it fails with many errors even after I replaced the import to what I believed was appropriate. ..... --import Reactive.Reactive import FRP.Reactive ........ Examples.hs:72:19: Not in scope: type constructor or class `Reactive' Examples.hs:76:17: Not in scope: `mkEvent' Examples.hs:81:20: Not in scope: `replace' Examples.hs:85:17: Not in scope: `mkEvent' Examples.hs:94:16: Not in scope: type constructor or class `Sink' I know Reactive is in the state of flux so I don't expect things to work without a bit of hacking but a little help would be greatly (!!!) appreciated just to get me started. I've tried wandering the web without success. Thanks, Tom

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Ordering of events in Reactive / Phooey
by Mads Lindstrøm 23 Mar '09

23 Mar '09

Hi If an end-user of a Reactive-based GUI (e.g. Phooey) triggers two events, am I sure that event one will be processed before event two ? (I am assuming that event one occurs before event two) The reason behind this question is: 1) that Reactive uses threads when two event sources are merged - the unambiguous choice function (Unamb.unamb). 2) the scheduler decides when a thread becomes active. So even if an end-user has triggered some event, the scheduler may decide to wait running a thread and thus the processing of the event. >From "Simply efﬁcient functional reactivity" paper I can see that the unamb function should only be called when both arguments will give the same result (not necessarily at the same time). So there should be no problems. And as I understand it, unamb is used to compare min-bound-times with respect to events. Thus the two events will be processed in the right order - I guess. However, this must also mean that events-sources are tagged with min-bound-times - e.g. all event-sources in a GUI, could get the min-bound-time of the latest occurring event. However, looking at the sources for Phooey I cannot see this tagging happening. What am I missing ? When looking at the Phooey and the Reactive code, I could not find the mkEvent function in newer Reactive releases. I therefore also looked at version 0.5, which did not seem to have these bounded time values. This may be the cause of some of my confusion. Greetings, Mads Lindstrøm

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FRP + physics / status of hpysics
by Peter Verswyvelen 11 Mar '09

11 Mar '09

Regarding hpysics, did anybody did some experiments with this? The blog seems to be inactive since december 2008; has development ceased? Do alternatives exist? Maybe good wrappers (hopefully pure...) around existing engines? Integrating hpysics with Grapefruit might be a good topic for the Hackaton, trying to make a simple game (e.g. Pong or Breakout) without using recursive signal functions, but with correct collision response and better-than-Euler integration, all handled by the physics engine. Other FRP engines could be tried, but Grapefruit hacking is already a topic on the Hackaton, so it would combine efforts. It feels as if none of the current FRP engines can handle physics correctly, since a typical physics implementations requires "time backtracking", in the sense that when you want to advance the current simulation time by a timestep, collision events can happen during that time interval, and hence the FRP engine can only advance time until the earliest collision event. So to do physics *with* an FRP engine, the implementation and maybe even semantics of the FRP system might need to be changed. *Using* a physics engine as a blackbox inside an FRP system might make more sense. Thanks to Wolfgang Jeltsch and Christopher Lane Hinson for having a discussion with me that lead to this. Interestingly a similar discussion was help by other people in the Reactive mailing list at the same time :-) Cheers, Peter Verswyvelen

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mappend laziness issue
by Sasha Rush 02 Mar '09

02 Mar '09

I started playing with reactive again and got stuck on a laziness issue with mappend. My codes pretty simple, two events controlled by legacy adapters, one and two. I'm combining them with mappend. both = one `mappend` two For some reason the events get clogged up. So for the first "one" event to fire, a "two" needs to come through, and sometimes vice-versa. It's possible I'm misunderstanding how mappend works, but the docs make it seem that both should fire whenever either fires. Thanks in advance.

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memory leak with justE?
by Sakari Jokinen 28 Feb '09

28 Feb '09

Hi, I have a somewhat larger program using reactive which seems to leak memory. I have narrowed at least one possible cause to justE. If I run main_justE in ghci it eats all the memory while main_filterE seems to run fine in constant. What am I missing here? I'm using ghc 6.10 and reactive 0.10.5. > module Main where > import Control.Monad.Trans(MonadIO, liftIO) > import Control.Concurrent > import Control.Monad > import FRP.Reactive > import FRP.Reactive.LegacyAdapters > import Data.Monoid(mappend) > import Data.Maybe > main_justE = do > clock <- makeClock > (sink, taskevents) <- makeEvent clock > let go _ = Just $ sink $ Nothing > adaptE $ justE $ fmap go (atTimes [0, 0.1 .. ]) `mappend` taskevents > instance Show (IO a) where > show _ = "IO" > main_filterE = do > clock <- makeClock > (sink, taskevents) <- makeEvent clock > let go _ = Just $ sink $ Nothing > justE' = fmap fromJust . filterE (maybe False (const True)) > adaptE $ justE' $ fmap go (atTimes [0, 0.1 ..]) `mappend` taskevents Br, Sakari

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reactive 0.10.5 Install problem
by Tom Poliquin 18 Feb '09

18 Feb '09

I hope this is the correct place to ask this. I've been playing with Haskell for a few months (I'm a long time imperative programmer with a couple years of Scheme) and *still* feel like a complete newbie. It seems like there's always something new to wrap my head around (one could argue this makes it fun .. ?). Java never twisted my brain :-) I eventually want to write a simulator for an alternate computer architecture in Haskell. . I played around with arrows and managed to understand the Arrow SF versions fibonacci and factorial and get them running. It appears reactive may be more appropriate. I was running ghc 6.8.3 and upgraded to 6.10.1 as it seemed that it would be more 'reactive' friendly. Platform is x86_64 GNU/Linux. All seemed to go smoothly but I can't install reactive 0.10.5. Details of the problem are given below. Any help greatly appreciated, Tom Error message ............ [poliquin@curunir reactive-0.10.5]$ runghc Setup configure --user Configuring reactive-0.10.5... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package reactive-0.10.5 requires QuickCheck-1.2.0.0 package checkers-0.1.3 requires QuickCheck-1.2.0.0 package Stream-0.3.1 requires QuickCheck-2.1.0.1 Misc Info ........... [poliquin@curunir ~]$ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.10.1 [poliquin@curunir ~]$ ghc-pkg list /usr/local/lib/ghc-6.10.1/./package.conf: Cabal-1.6.0.1, HUnit-1.2.0.3, QuickCheck-1.2.0.0, array-0.2.0.0, base-3.0.3.0, base-4.0.0.0, bytestring-0.9.1.4, containers-0.2.0.0, directory-1.0.0.2, (dph-base-0.3), (dph-par-0.3), (dph-prim-interface-0.3), (dph-prim-par-0.3), (dph-prim-seq-0.3), (dph-seq-0.3), editline-0.2.1.0, filepath-1.1.0.1, (ghc-6.10.1), ghc-prim-0.1.0.0, haddock-2.3.0, haskell-src-1.0.1.3, haskell98-1.0.1.0, hpc-0.5.0.2, html-1.0.1.2, integer-0.1.0.0, mtl-1.1.0.2, network-2.2.0.1, old-locale-1.0.0.1, old-time-1.0.0.1, packedstring-0.1.0.1, parallel-1.1.0.0, parsec-2.1.0.1, pretty-1.0.1.0, process-1.0.1.0, random-1.0.0.1, regex-base-0.72.0.2, regex-compat-0.71.0.1, regex-posix-0.72.0.3, rts-1.0, stm-2.1.1.2, syb-0.1.0.0, template-haskell-2.3.0.0, time-1.1.2.2, unix-2.3.1.0, xhtml-3000.2.0.1 /home/poliquin/.ghc/x86_64-linux-6.10.1/package.conf: FTGL-1.1, GLUT-2.1.1.2, HGL-3.2.0.0, MemoTrie-0.4.3, OpenGL-2.2.1.1, QuickCheck-2.1.0.1, Stream-0.3.1, TypeCompose-0.6.4, X11-1.4.5, arrows-0.4.1, category-extras-0.53.5, checkers-0.1.3, lazysmallcheck-0.3, unamb-0.1.9, vector-space-0.5.3

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reactive-glut keyAction problem
by stefan kersten 12 Feb '09

12 Feb '09

hi all, i'm having a problem with key events in reactive-glut: import FRP.Reactive import FRP.Reactive.LegacyAdapters import FRP.Reactive.GLUT.Adapter keyDown :: Event (KeyState, Key) -> Event Key keyDown = fmap snd . filterE ((==Down) . fst) keyUp :: Event (KeyState, Key) -> Event Key keyUp = fmap snd . filterE ((==Up) . fst) partitionE :: (Show a) => (a -> Bool) -> Event a -> (Event a, Event a) partitionE p e = (filterE p e, filterE (not . p) e) key :: Key -> Event (KeyState, Key) -> (Event (KeyState, Key), Event (KeyState, Key)) key k = partitionE ((==k) . snd) keyB :: Event (KeyState, Key) -> Behavior Bool keyB k = flipFlop (keyDown k) (keyUp k) mainB :: UI -> Behavior Action mainB ui = return () `stepper` (print `fmap` e) where (k1, k) = key (Char '1') (keyAction ui) e = snapshot (keyB k1) k main :: IO () main = adaptSimple "Testfest" mainB on my system (osx 10.5, reactive-0.10.5, reactive-glut-0.1.6) nothing is printed until i press '1' a few times, then it gets stuck again. what i'd expect to happen is ((KeyState, Key), Bool) to be printed everytime i press a key different from '1', where the second tuple element is True as long as '1' is being held. what am i missing? is this related to the laziness bug mentioned earlier? many thanks, <sk>

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Request/invitation for input on licensing
by Conal Elliott 04 Feb '09

04 Feb '09

In case you haven't seen it, I'm welcoming input about license choice for Reactive & FieldTrip in a blog post, http://conal.net/blog/posts/seeking-advice-on-software-licensing/ . I am especially interested in hearing from the folks on the Reactive & FieldTrip mailing lists. I'd appreciate comments directed to the blog post itself, to keep the discussion from fragmenting. Thanks! - Conal

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Fun with existentials
by Achim Schneider 30 Jan '09

30 Jan '09

XHB uses existentials to enable X extensions to define their own events and still have them delivered to the user by the main library, so I had the chance to mess around with them and reactive. If you comment out the keyPressH, things are perfectly fine, but there's no dispatch on event types. With the forkIO, the program stumbles over an indefinite block on the next event. The adaptE without fromEventE is the only thing keeping the program alive: It seems that if there is only a single event that is possibly not handled, things go haywire... even if every event is guaranteed to be handled (in some other adaptE). Without any adaptE things work fine, too. I don't know if multiple adaptE's are supposed to work, but it'd be certainly nice if they would. I'm going to try to join the Nothings sorted out by joinMaybes back into the stream, hopefully that'll convince the RTS. {-# LANGUAGE ExistentialQuantification #-} module Main where -- current darcs XHB -- hack it to export Graphics.XHB.Connection.Types -- port of http://en.wikibooks.org/wiki/X_Window_Programming/XCB -- run your X server on :0 or change getScreen import Graphics.XHB as X import FRP.Reactive as R import FRP.Reactive.LegacyAdapters import Control.Concurrent import Control.Monad import System.Exit import Control.Applicative printErrors c = (forkIO . forever) $ waitForError c >>= print getScreen = head . roots_Setup . conf_setup . conn_conf castXid = fromXid . toXid main = do (Just c) <- connect printErrors c print $ displayInfo c let s = getScreen c black = black_pixel_SCREEN s white = white_pixel_SCREEN s root = root_SCREEN s depth = root_depth_SCREEN s visual = root_visual_SCREEN s g <- newResource c createGC c (MkCreateGC g (castXid root) (toValueParam [(GCForeground,white) ,(GCGraphicsExposures,0) ] )) w <- newResource c createWindow c (MkCreateWindow depth w root 0 0 640 480 0 0 visual (toValueParam [(CWBackPixel,black) ,(CWEventMask,toMask [ EventMaskExposure , EventMaskKeyPress ] ) ] )) lock <- newEmptyMVar sync <- makeSync evs <- eventsE sync c mapWindow c w forkIO $ adaptE $ keyPressH lock c $ fromEventE evs -- forkIO $ adaptE $ exposeH c $ fromEventE evs adaptE $ (fmap.const) (putStrLn "some event" ) evs --readMVar lock keyPressH :: MVar () -> Connection -> R.Event KeyPress -> R.Event Action keyPressH lock _ = (fmap.const) $ putStrLn "key" >> putMVar lock () exposeH :: Connection -> R.Event KeyPress -> R.Event Action exposeH _ = fmap print fromEventE :: X.Event a => R.Event SomeEvent -> R.Event a fromEventE = joinMaybes <$> fmap fromEvent type Sync = Clock TimeT makeSync = makeClock eventsE :: Sync -> Connection -> IO (R.Event SomeEvent) eventsE cl c = do (sink, res) <- makeEvent cl (forkIO . forever) $ putStrLn "tick " >> waitForEvent c >>= sink return res -- (c) this sig last receiving data processing entity. Inspect headers for copyright history. All rights reserved. Copying, hiring, renting, performance and/or quoting of this signature prohibited.

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Is Reactive.integral broken?
by Eyal Lotem 14 Jan '09

14 Jan '09

The problematic expression is: let ticks = R.atTimes [0,0.1..] :: R.Event () integration = ticks `R.integral` R.time in integration The value inside integration is always 0. But here is a full sample program to demonstrate the problem: {-# OPTIONS -fglasgow-exts -O2 -Wall #-} import Control.Applicative import qualified FRP.Reactive as R import qualified Graphics.FieldTrip as FT import Graphics.FieldTrip((*%)) import qualified FRP.Reactive.FieldTrip.Adapter as FieldTripA resize :: (FT.Transform (FT.Transform3 s) a) => s -> a -> a resize size = (FT.uscale3 size *%) utext :: String -> FT.Geometry3 utext = FT.flatG . FT.utext main :: IO () main = do let ticks = R.atTimes [0,0.1..] :: R.Event () integration = ticks `R.integral` R.time FieldTripA.anim3 . pure $ resize (0.3::Double) . utext . show <$> integration

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