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• How to use the `itemDoubleClicked(QTreeWidgetItem*,int)` signal in qtHaskell

  - by nano

  I want to use the itemDoubleClicked(QTreeWidgetItem*,int) signal in a Haskell program I'm writing where I am using qtHaskell for the GUI. To connect a function I have at other places done the following: dummyWidget <- myQWidget connectSlot object signal dummyWidget "customSlot()" $ f Where object is some QWidget and signal is a string giving the signal, e.g. "triggered()", and f is the function I want to be called when the signaled is send. The definition of connectSlot in the API is: class Qcs x where connectSlot :: QObject a -> String -> QObject b -> String -> x -> IO () where the instances ofQcs are: Qcs () Qcs (QObject c -> String -> IO ()) Qcs (QObject c -> Object d -> IO ()) Qcs (QObject c -> Bool -> IO ()) Qcs (QObject c -> Int -> IO ()) Qcs (QObject c -> IO ()) Qcs (QObject c -> OpenGLVersionFlag -> IO ()) The first Arguments passed is supposed to be the QObject of which I'm using a signal. As you can see, there is no instance where f, the function to connect to the signal, can have two further arguments to recieve the QWidget and the integer send by the signal. Is there a way to nevertheless connect that signal to a custom function?

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• Appropriate uses of Monad `fail` vs. MonadPlus `mzero`

  - by jberryman

  This is a question that has come up several times for me in the design code, especially libraries. There seems to be some interest in it so I thought it might make a good community wiki. The fail method in Monad is considered by some to be a wart; a somewhat arbitrary addition to the class that does not come from the original category theory. But of course in the current state of things, many Monad types have logical and useful fail instances. The MonadPlus class is a sub-class of Monad that provides an mzero method which logically encapsulates the idea of failure in a monad. So a library designer who wants to write some monadic code that does some sort of failure handling can choose to make his code use the fail method in Monad or restrict his code to the MonadPlus class, just so that he can feel good about using mzero, even though he doesn't care about the monoidal combining mplus operation at all. Some discussions on this subject are in this wiki page about proposals to reform the MonadPlus class. So I guess I have one specific question: What monad instances, if any, have a natural fail method, but cannot be instances of MonadPlus because they have no logical implementation for mplus? But I'm mostly interested in a discussion about this subject. Thanks! EDIT: One final thought occured to me. I recently learned (even though it's right there in the docs for fail) that monadic "do" notation is desugared in such a way that pattern match failures, as in (x:xs) <- return [] call the monad's fail. It seems like the language designers must have been strongly influenced by the prospect of some automatic failure handling built in to haskell's syntax in their inclusion of fail in Monad.

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• Haskel dot (.) and dollar ($) composition: correct use.

  - by Robert Massaioli

  I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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• Problem with incomplete input when using Attoparsec

  - by Dan Dyer

  I am converting some functioning Haskell code that uses Parsec to instead use Attoparsec in the hope of getting better performance. I have made the changes and everything compiles but my parser does not work correctly. I am parsing a file that consists of various record types, one per line. Each of my individual functions for parsing a record or comment works correctly but when I try to write a function to compile a sequence of records the parser always returns a partial result because it is expecting more input. These are the two main variations that I've tried. Both have the same problem. items :: Parser [Item] items = sepBy (comment <|> recordType1 <|> recordType2) endOfLine For this second one I changed the record/comment parsers to consume the end-of-line characters. items :: Parser [Item] items = manyTill (comment <|> recordType1 <|> recordType2) endOfInput Is there anything wrong with my approach? Is there some other way to achieve what I am attempting?

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• Using items in a list as arguments

  - by Travis Brown

  Suppose I have a function with the following type signature: g :: a -> a -> a -> b I also have a list of as—let's call it xs—that I know will contain at least three items. I'd like to apply g to the first three items of xs. I know I could define a combinator like the following: ($$$) :: (a -> a -> a -> b) -> [a] -> b f $$$ (x:y:z:_) = f x y z Then I could just use g $$$ xs. This makes $$$ a bit like uncurry, but for a function with three arguments of the same type and a list instead of a tuple. Is there a way to do this idiomatically using standard combinators? Or rather, what's the most idiomatic way to do this in Haskell? I thought trying pointfree on a non-infix version of $$$ might give me some idea of where to start, but the output was an abomination with 10 flips, a handful of heads and tails and aps, and 28 parentheses. (NB: I know this isn't a terribly Haskelly thing to do in the first place, but I've come across a couple of situations where it seems like a reasonable solution, especially when using Parsec. I'll certainly accept "don't ever do this in real code" if that's the best answer, but I'd prefer to see some clever trick involving the ((->) r) monad or whatever.)

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• Could someone explain gtk2hs drag and drop to me, the listDND.hs demo just isn't doing it for me?

  - by Tom Carstens

  As the title says, I just don't get DND (or rather I understand the concept and I understand the order of callbacks, I just don't understand how to setup DND for actual usage.) I'd like to say that I've done DND stuff before in C, but considering I never really got that working... So I'm trying (and mostly succeeding, save DND) to write a text editor (using gtksourceview, because it has built in code highlighting.) Reasons are below if you want them. Anyways, there's not really a good DND demo or tutorial available for gtk2hs (listDND.hs just doesn't translate well in my head.) So what I'm asking is for code that demonstrates simple DND on a window widget (for example.) Ideally, it should accept drops from other windows (such as Thunar) and print out the information in string form. I think I can take it from there... Reasons: I'm running a fairly light weight setup, dwm and a few gtk+2 programs. I really don't want to have to pull in gtk+3 to get the current gedit from the repos (Arch Linux.) Currently, I'm using geany for all of my text editing needs, however, geany is a bit heavy for editing config files. Further, geany doesn't care for my terminal of choice (st;) so I don't even get the benefit of using it as an IDE. Meaning I'd like a lightweight text editor with syntax highlighting. I could configure emacs or vim or something, but that seems to me to be more of a hack then a proper solution. Thus my project was born. It's mostly working (aside from DND, all that's left is proper multi-tab support.) Admittedly, I could probably work this out if I wrote it in C, but there isn't that much state in a text editor so Haskell's been working fine with almost no need for mutable variables.

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• Flowcharting functional programming languages

  - by Sadface

  Flowcharting. This ancient old practice that's been in use for over 1000 years now, being forced upon us poor students, without any usefulness (or so do I think). It might work well with imperative, sequentially running languages, but what about my beloved functional programming? Sadly, I'm forced to create a flow chart for my programm (that is written in Haskell). I imagine it being easy for something like this: main :: IO () main = do someInput <- getLine let upped = map toUpper someInput putStrLn upped Which is just 3 sequenced steps, fetching data, uppercasing it, outputting it. Things look worse this time: main :: IO () main = do someInput <- fmap toUpper getLine putStrLn someInput Or like this: main :: IO () main = interact (map toUpper) Okay, that was IO, you can handle that like an imperative language. What about pure functions? An actual example: onlyMatching :: String -> [FilePath] -> [FilePath] onlyMatching ext = filter f where f name = lower ('.' : ext) == (lower . takeExtension $ name) lower = map toLower How would you flowchart that last one?

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• trouble with state monad composition

  - by user1308560

  I was trying out the example given at http://www.haskell.org/haskellwiki/State_Monad#Complete_and_Concrete_Example_1 How this makes the solution composible is beyond my understanding. Here is what I tried but I get compile errors as follows: Couldn't match expected type `GameValue -> StateT GameState Data.Functor.Identity.Identity b0' with actual type `State GameState GameValue' In the second argument of `(>>=)', namely `g2' In the expression: g1 >>= g2 In an equation for `g3': g3 = g1 >>= g2 Failed, modules loaded: none. Here is the code: See the end lines module StateGame where import Control.Monad.State type GameValue = Int type GameState = (Bool, Int) -- suppose I want to play one game after the other g1 = playGame "abcaaacbbcabbab" g2 = playGame "abcaaacbbcabb" g3 = g1 >>= g2 m2 = print $ evalState g3 startState playGame :: String -> State GameState GameValue playGame [] = do (_, score) <- get return score playGame (x:xs) = do (on, score) <- get case x of 'a' | on -> put (on, score + 1) 'b' | on -> put (on, score - 1) 'c' -> put (not on, score) _ -> put (on, score) playGame xs startState = (False, 0) main str = print $ evalState (playGame str) startState

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• Monads with Join() instead of Bind()

  - by MathematicalOrchid

  Monads are usually explained in turns of return and bind. However, I gather you can also implement bind in terms of join (and fmap?) In programming languages lacking first-class functions, bind is excruciatingly awkward to use. join, on the other hand, looks quite easy. I'm not completely sure I understand how join works, however. Obviously, it has the [Haskell] type join :: Monad m = m (m x) - m x For the list monad, this is trivially and obviously concat. But for a general monad, what, operationally, does this method actually do? I see what it does to the type signatures, but I'm trying to figure out how I'd write something like this in, say, Java or similar. (Actually, that's easy: I wouldn't. Because generics is broken. ;-) But in principle the question still stands...) Oops. It looks like this has been asked before: Monad join function Could somebody sketch out some implementations of common monads using return, fmap and join? (I.e., not mentioning >>= at all.) I think perhaps that might help it to sink in to my dumb brain...

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• Heap Algorithmic Issue

  - by OberynMarDELL

  I am having this algorithmic problem that I want to discuss about. Its not about find a solution but about optimization in terms of runtime. So here it is: Suppose we have a race court of Length L and a total of N cars that participate on the race. The race rules are simple. Once a car overtakes an other car the second car is eliminated from the race. The race ends when no more overtakes are possible to happen. The tricky part is that the k'th car has a starting point x[k] and a velocity v[k]. The points are given in an ascending order, but the velocities may differ. What I've done so far: Given that a car can get overtaken only by its previous, I calculated the time that it takes for each car to reach its next one t = (x[i] - x[i+1])/(v[i] - v[i+1]) and I insert these times onto a min heap in O(n log n). So in theory I have to pop the first element in O(logn), find its previous, pop it as well , update its time and insert it in the heap once more, much like a priority queue. My main problem is how I can access specific points of a heap in O(log n) or faster in order to keep the complexity in O(n log n) levels. This program should be written on Haskell so I would like to keep things simple as far as possible EDIT: I Forgot to write the actual point of the race. The goal is to find the order in which cars exit the game

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• How can I bind the second argument in a function but not the first (in an elegant way)?

  - by Frank Osterfeld

  Is there a way in Haskell to bind the second argument but not the first of a function without using lambda functions or defining another "local" function? Example. I have a binary function like: sub :: Int -> Int -> Int sub x y = x - y Now if I want to bind the first argument, I can do so easily using (sub someExpression): mapSubFrom5 x = map (sub 5) x *Main> mapSubFrom5 [1,2,3,4,5] [4,3,2,1,0] That works fine if I want to bind the first n arguments without "gap". If I want to bind the second argument but not the first, the two options I am aware of are more verbose: Either via another, local, function: mapSub5 x = map sub5 x where sub5 x = sub x 5 *Main> mapSub5 [1,2,3,4,5] [-4,-3,-2,-1,0] Or using lambda: mapSub5 x = map (\x -> sub x 5) x While both are working fine, I like the elegance of "sub 5" and wonder if there is a similarly elegant way to bind the n-th (n 1) argument of a function?

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• The Business case for Big Data

  - by jasonw

  The Business Case for Big Data Part 1 What's the Big Deal Okay, so a new buzz word is emerging. It's gone beyond just a buzzword now, and I think it is going to change the landscape of retail, financial services, healthcare....everything. Let me spend a moment to talk about what i'm going to talk about. Massive amounts of data are being collected every second, more than ever imaginable, and the size of this data is more than can be practically managed by today’s current strategies and technologies. There is a revolution at hand centering on this groundswell of data and it will change how we execute our businesses through greater efficiencies, new revenue discovery and even enable innovation. It is the revolution of Big Data. This is more than just a new buzzword is being tossed around technology circles.This blog series for Big Data will explain this new wave of technology and provide a roadmap for businesses to take advantage of this growing trend. Cases for Big Data There is a growing list of use cases for big data. We naturally think of Marketing as the low hanging fruit. Many projects look to analyze twitter feeds to find new ways to do marketing. I think of a great example from a TED speech that I recently saw on data visualization from Facebook from my masters studies at University of Virginia. We can see when the most likely time for breaks-ups occurs by looking at status changes and updates on users Walls. This is the intersection of Big Data, Analytics and traditional structured data. Ted Video Marketers can use this to sell more stuff. I really like the following piece on looking at twitter feeds to measure mood. The following company was bought by a hedge fund. They could predict how the S&P was going to do within three days at an 85% accuracy. Link to the article Here we see a convergence of predictive analytics and Big Data. So, we'll look at a lot of these business cases and start talking about what this means for the business. It's more than just finding ways to use Hadoop + NoSql and we'll talk about that too. How do I start in Big Data? That's what is coming next post.

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• My Speaking Engagements in the Last Two Months

  - by gsusx

  I’ve been so busy lately with the activities around Moesion that I haven’t had time to blog about a couple of great conferences I had the opportunity to speak at in the last two months. Software Architect Conference, UK ( http://www.software-architect.co.uk/ ) This conference is becoming one of my favorite events of the year. As always Nick Payne and his team did a remarkable job lining up an all-star group of speakers that covered some of the hottest topics in today’s software industry. The first...(read more)

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• Using AdMob with Games that use Open GLES

  - by Vishal Kumar

  Can anyone help me integrating Admob to my game. I've used the badlogic framework by MarioZencher ... and My game is like the SuperJumper. I am unable to use AdMob after a lot of my attempts. I am new to android dev...please help me..I went thru a number of tutorials but not getting adds displayed ... I did the following... get the libraries and placed them properly My main.xml looks like this android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/hello" / My Activity class onCreate method: public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); RelativeLayout layout = new RelativeLayout(this); adView = new AdView(this, AdSize.BANNER, "a1518637fe542a2"); AdRequest request = new AdRequest(); request.addTestDevice(AdRequest.TEST_EMULATOR); request.addTestDevice("D77E32324019F80A2CECEAAAAAAAAA"); adView.loadAd(request); layout.addView(glView); RelativeLayout.LayoutParams adParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT); adParams.addRule(RelativeLayout.ALIGN_PARENT_BOTTOM); adParams.addRule(RelativeLayout.CENTER_IN_PARENT); layout.addView(adView, adParams); setContentView(layout); requestWindowFeature(Window.FEATURE_NO_TITLE); getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); glView = new GLSurfaceView(this); glView.setRenderer(this); //setContentView(glView); glGraphics = new GLGraphics(glView); fileIO = new AndroidFileIO(getAssets()); audio = new AndroidAudio(this); input = new AndroidInput(this, glView, 1, 1); PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE); wakeLock = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK, "GLGame"); } My Manifest file looks like this .... <activity android:name="com.google.ads.AdActivity" android:configChanges="keyboard|keyboardHidden|orientation|smallestScreenSize"/> </application> <uses-permission android:name="android.permission.WAKE_LOCK" /> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <uses-sdk android:minSdkVersion="7" /> When I first decided to use the XML for admob purpose ..it showed no changes..it even didn't log the device id in Logcat... Later when I wrote code in the Main Activity class.. and run ... Application crashed ... with 7 errors evry time ... The android:configChanges value of the com.google.ads.AdActivity must include screenLayout. The android:configChanges value of the com.google.ads.AdActivity must include uiMode. The android:configChanges value of the com.google.ads.AdActivity must include screenSize. The android:configChanges value of the com.google.ads.AdActivity must include smallestScreenSize. You must have AdActivity declared in AndroidManifest.xml with configChanges. You must have INTERNET and ACCESS_NETWORK_STATE permissions in AndroidManifest.xml. Please help me by telling what wrong is there with the code? Can I write code only in xml files without changing the Activity class ... I will be very grateful to anyone providing support.

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• Flash Actionscript 3.0 Game Projectile Creation

  - by Christian Basar

  I have been creating a side-scrolling Actionscript 3.0 game. In this game I want the Player to be able to shoot blow darts as weapons. I had some trouble getting the darts to be created in the right place (in front of the player), but eventually got it working with some help from this page (please look at it for background information on this problem): http://stackoverflow.com/questions/8031553/flash-actionscript-3-0-game-projectile-creation I got the darts to be created in the right place (near the player) and a 'movePlayerDarts()' function moves them. But I actually have a new problem. When the player moves after firing a dart, the dart tries to follow him! If the player jumps, the dart rises up. If the player moves to the left, the dart moves slightly to the left. Obviously, there is some code somewhere which is telling the darts to follow the player. I do not see how, unless the 'playerDartContainer' has something to do with that. But the container is always at position (0,0) and it does not move. Also, as a test I traced a dart's 'y' coordinate within the constantly-running 'movePlayerDarts()' function. As you can see, that function constantly moves the dart down the y axis by increasing its y-coordinate value. But when I jump, the 'y' coordinate being traced is never reduced, even though the dart clearly looks like it's rising! If anybody has any suggestions, I'd appreciate them! Here is the code I use to create the darts: // This function creates a dart public function createDart():void { if (playerDartContainer.numChildren <= 4) { // Play dart shooting sound sndDartShootIns.play(); // Create a new 'PlayerDart' object playerDart = new PlayerDart(); // Set the new dart's initial position and direction depending on the player's direction // Player's facing right if (player.scaleX == 1) { // Create dart in front of player's dart gun playerDart.x = player.x + 12; playerDart.y = player.y - 85; // Dart faces right, too playerDart.scaleX = 1; } // Player's facing left else if (player.scaleX == -1) { // Create dart in front of player's dart gun playerDart.x = player.x - 12; playerDart.y = player.y - 85; // Dart faces left, too playerDart.scaleX = -1; } playerDartContainer.addChild(playerDart); } } // End of 'createDart()' function This code is the EnterFrameHandler for the player darts: // In every frame, call 'movePlayerDarts()' to move the darts within the 'playerDartContainer' public function playerDartEnterFrameHandler(event:Event):void { // Only move the Player's darts if their container has at least one dart within if (playerDartContainer.numChildren > 0) { movePlayerDarts(); } } And finally, this is the code that actually moves all of the player's darts: // Move all of the Player's darts public function movePlayerDarts():void { for (var pdIns:int = 0; pdIns < playerDartContainer.numChildren; pdIns++) { // Set the Player Dart 'instance' variable to equal the current PlayerDart playerDartIns = PlayerDart(playerDartContainer.getChildAt(pdIns)); // Move the current dart in the direction it was shot. The dart's 'x-scale' // factor is multiplied by its speed (5) to move the dart in its correct // direction. If the 'x-scale' factor is -1, the dart is pointing left (as // seen in the 'createDart()' function. (-1 * 5 = -5), so the dart will go // to left at a rate of 5. The opposite is true for the right-ward facing // darts playerDartIns.x += playerDartIns.scaleX * 1; // Make gravity work on the dart playerDartIns.y += 0.7; //playerDartIns.y += 1; // What if the dart hits the ground? if (HitTest.intersects(playerDartIns, floor, this)) { playerDartContainer.removeChild(playerDartIns); } //trace("Dart x: " + playerDartIns.x); trace("Dart y: " + playerDartIns.y); } }

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• HTML5 mobile game development vs. native game apps

  - by Vic Szpilman

  What is the current state of game engines, frameworks, libraries and conversions related to the HTML5 set of technologies (including CSS3 and JavaScript libraries such as RaphaelJS, Impact, gameQuery); and how does the best of that compare with developing a native app (especially for iOS and Android)? Especially in terms of performance, visuals and getting that "native feel". Thoughts on solutions such as Appcelerator and Corona SDK are also appreciated. In regards to Unity3D, is it possible to develop in it and still have the game be playable on a browser (such as current releases of Chrome or Firefox, at least) without any dependencies or having the user install anything (no unity web player). What I'm looking for is how to develop in web standards as to reach the maximum number of platforms (including outside mobile) while still retaining a native experience for mobile without having to implement the game anew for iOS and Android.

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• Is Ubuntu workable as a laptop for an IT consultant?

  - by Eric Wilson

  I work as a consultant programmer, typically in large businesses. I use a Windows Laptop, and many of my colleagues use a Mac. My personal preference would be to run Ubuntu if I could have complete control over my development environment. But I will have occasional need for Microsoft specific products, especially IE. My colleagues that use a Mac often run Windows on a virtual machine for these situations. My question is: Is Ubuntu a workable solution for the laptop of an enterprise programmer? For example, is it as easy to run Windows on a VM on Ubuntu as it is on a Mac? Has anyone out there tried this? Is there any particular reason why Ubuntu would not serve as well as a Mac for development in this environment? Note that I am not doing .NET development, so I am typically dealing with Java that is going to be run on an Apache server and used by clients running Windows.

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• Platform for Efficiency: Boeing Defense, Space & Security integrates supply chain processes using Oracle Business Process Management solutions. by Fred Sandsmark

  - by JuergenKress

  Like most companies, aerospace giant Boeing has its jargon - words and phrases that uniquely define its products and processes. Take the word platform. It is used at Boeing to mean a family of aircraft - the F/A-18 fighter, for example, or the 777 jetliner. Boeing Defense, Space & Security since August 2009, employees in the Global Services & Support (GS&S) division of Boeing Defense, Space & Security have been talking about a different sort of platform: a supply chain technology platform, based on Oracle Business Process Management (Oracle BPM) solutions and Oracle SOA Suite. That platform, built with the assistance of Oracle Diamond Partner Capgemini, is serving as a jumping-off point for Boeing's GS&S staff to deploy radically improved business processes supported by Oracle Fusion Applications to build a high-visibility, end-to-end supply chain. This business process-driven technology platform has ambitious goals: to help GS&S respond more quickly and accurately to its customers' needs, to make business processes at all GS&S sites more consistent and less expensive, and to create a foundation for further improvement and efficiency. Read the full article here. Want to publish your BPM11g success story - request for a partner/customer reference? BPM Center of Excellent & First 100 Days of BPM documents to our SOA Community Workspace MWD_bpm_si_Centre_of_Excellence_0811.pdf First 100 Days of BPM whitepaper.pdf Please visit our SOA Community Workspace (SOA Community membership required). SOA & BPM Partner Community For regular information on Oracle SOA Suite become a member in the SOA & BPM Partner Community for registration please visit  www.oracle.com/goto/emea/soa (OPN account required) If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Technorati Tags: BPM,BPM reference,BPM Capgemini,BPM first 100 days,BPM center of Excellence,SOA Community,Oracle SOA,Oracle BPM,Community,OPN,Jürgen Kress

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• Oracle Hyperion Customer Briefing 2011

  - by antonella.buonagurio(at)oracle.com

  Lo scorso 24 febbraio a Milano e il 9 marzo a Roma si è tenuto l'Oracle Hyperion Customer Briefing 2011 un workshop riservato ai clienti Oracle su tutte le novità Oracle Hyperion EPM SYstem 11.1.2. La giornata si è sviluppata attraverso un percorso guidato di quattro sessioni tematiche su  come poter migliorare ulteriormente processi di management nelle  aziende in tutti gli ambiti di interesse.  

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• How to do reflective collisions with particles hitting background tiles?

  - by Shawn LeBlanc

  In my 2d pixel old-school platformer, I'm looking for methods for bouncing particles off of background tiles. Particles aren't affected by gravity and collisions are "reflective". By that I mean a particle hitting the side of a square tile at 45 degrees should bounce off at 45 degrees as well. We can assume that tiles will always be perfectly square. No slopes or anything. What are efficient methods and algorithms to do this? I'd be implementing this on a Sega Genesis.

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• Correct DB details produce “Database server was not found” (Prestashop Installation)

  - by Steve

  At stage 3 of the Prestashop Installation, I enter the DB details which I know to be correct, and I receive the error: Database server was not found. Please verify the login, password, and database server name fields. The server is localhost, and I have verified the database name and username. Why can Prestashop not find the server? This occurs when choosing InnoDB and MyIsam. If I change the server from localhost to the public hostname I receive the same error.

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• Can Flash games packed for iOS and other mobile devices achieve reasonable performance?

  - by puppybeard

  I was thinking of developing a game in Flash, as a hobby/educational project. However, I was hoping I could make it run on a smartphone, but a friend who develops in Flash says that in their experience things will move really slow on the likes of an iPad when the Flash packager is used. So slowly that you can't use it commercially for fast-moving games. Has anyone else experienced this slowness? Is there a way around it or is the technology just not there yet?

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• Cross-platform distributed fault-tolerant (disconnected operation/local cache) filesystem

  - by Adrian Frühwirth

  We are facing a design "challenge" where we are required to set up a storage solution with the following properties: What we need HA a scalable storage backend offline/disconnected operation on the client to account for network outages cross-platform access client-side access from certainly Windows (probably XP upwards), possibly Linux backend integrates with AD/LDAP (permission management (user/group management, ...)) should work reasonably well over slow WAN-links Another problem is that we don't really know all possible use cases here, if people need to be able to have concurrent access to shared files or if they will only be accessing their own files, so a possible solution needs to account for concurrent access and how conflict management would look in this case from a user's point of view. This two years old blog posts sums up the impression that I have been getting during the last couple of days of research, that there are lots of current übercool projects implementing (non-Windows) clustered petabyte-capable blob-storage solutions but that there is none that supports disconnected operation nicely and natively, but I am hoping that we have missed an obvious solution. What we have tried OpenAFS We figured that we want a distributed network filesystem with a local cache and tested OpenAFS (which, as the only currently "stable" DFS supporting disconnected operation, seemed the way to go) for a week but there are several problems with it: it's a real pain to set up there are no official RHEL/CentOS packages the package of the current stable version 1.6.5.1 from elrepo randomly kernel panics on fresh installs, this is an absolute no-go Windows support (including the required Kerberos packages) is mystical. The current client for the 1.6 branch does not run on Windows 8, the current client for the 1.7 does but it just randomly crashes. After that experience we didn't even bother testing on XP and Windows 7. Suffice to say, we couldn't get it working and the whole setup has been so unstable and complicated to setup that it's just not an option for production. Samba + Unison Since OpenAFS was a complete disaster and no other DFS seems to support disconnected operation we went for a simpler idea that would sync files against a Samba server using Unison. This has the following advantages: Samba integrates with ADs; it's a pain but can be done. Samba solves the problem of remotely accessing the storage from Windows but introduces another SPOF and does not address the actual storage problem. We could probably stick any clustered FS underneath Samba, but that means we need a HA Samba setup on top of that to maintain HA which probably adds a lot of additional complexity. I vaguely remember trying to implement redundancy with Samba before and I could not silently failover between servers. Even when online, you are working with local files which will result in more conflicts than would be necessary if a local cache were only touched when disconnected It's not automatic. We cannot expect users to manually sync their files using the (functional, but not-so-pretty) GTK GUI on a regular basis. I attempted to semi-automate the process using the Windows task scheduler, but you cannot really do it in a satisfactory way. On top of that, the way Unison works makes syncing against Samba a costly operation, so I am afraid that it just doesn't scale very well or even at all. Samba + "Offline Files" After that we became a little desparate and gave Windows "offline files" a chance. We figured that having something that is inbuilt into the OS would reduce administrative efforts, helps blaming someone else when it's not working properly and should just work since people have been using this for years. Right? Wrong. We really wanted it to work, but it just doesn't. 30 minutes of copying files around and unplugging network cables/disabling network interfaces left us with (silent! there is only a tiny notification in Windows explorer in the statusbar, which doesn't even open Sync Center if you click on it!) undeletable files on the server (!) and conflicts that should not even be conflicts. In the end, we had one successful sync of a tiny text file, everything else just exploded horribly. Beyond that, there are other problems: Microsoft admits that "offline files" in Windows XP cannot cope with "large files" and therefore does not cache/sync them at all which would mean those files become unavailable if the connection drop In Windows 7 the feature is only available in the Professional/Ultimate/Enterprise editions. Summary Unless there is another fault-tolerant DFS that supports Windows natively I assume that stacking a HA Samba cluster on top of something like GlusterFS/Lustre/whatnot is the only option, but I hope that I am wrong here. How do other companies allow fault-tolerant network access to redundant storage in a heterogeneous environment with Windows?

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• Two BULK INSERT issues I worked around recently

  - by AaronBertrand

  Since I am still afraid of SSIS, and because I am dealing mostly with CSV files and table structures that are relatively simple and require only one of the three letters in the acronym "ETL," I find myself using BULK INSERT a lot. I have been meaning to switch to using CLR, since I am doing a lot of file system querying using xp_cmdshell, but I haven't had the chance to really explore it yet. I know, a lot of you are probably thinking, wow, look at all those bad habits. But for every person thinking...(read more)

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• Two BULK INSERT issues I worked around recently

  - by AaronBertrand

  Since I am still afraid of SSIS, and because I am dealing mostly with CSV files and table structures that are relatively simple and require only one of the three letters in the acronym "ETL," I find myself using BULK INSERT a lot. I have been meaning to switch to using CLR, since I am doing a lot of file system querying using xp_cmdshell, but I haven't had the chance to really explore it yet. I know, a lot of you are probably thinking, wow, look at all those bad habits. But for every person thinking...(read more)

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