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  • (type theoretical) How is ([] ==) [] typed in haskell?

    - by Ingo
    It sounds silly, but I can't get it. Why can the expression [] == [] be typed at all? More specifically, which type (in class Eq) is inferred to the type of list elements? In a ghci session, I see the following: Prelude> :t (==[]) (==[]) :: (Eq [a]) => [a] -> Bool But the constraint Eq [a] implies Eq a also, as is shown here: Prelude> (==[]) ([]::[IO ()]) <interactive>:1:1: No instance for (Eq (IO ())) arising from use of `==' at <interactive>:1:1-2 Probable fix: add an instance declaration for (Eq (IO ())) In the definition of `it': it = (== []) ([] :: [IO ()]) Thus, in []==[], the type checker must assume that the list element is some type a that is in class Eq. But which one? The type of [] is just [a], and this is certainly more general than Eq a = [a].

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  • Render graphics using Doubles in Graphics2D

    - by thedeadlybutter
    Currently, I have a JFrame for my game to render in, and I'm using Graphics2D for drawing (The games graphics are fairly simple 2D sprites). However, my delta variable is a double, and all of the Graphics 2D methods (And Grpahics) use int. I tried to type cast the delta to an int, but it just rounds down to 0. So my question is, how can I render graphics using Graphics2D in Java with coordinates that are doubles. Can I convert it to work with Graphics2D if there is no built in way? Or, is there a graphics library that can support doubles for coordinates?

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  • Guidelines of when to use locking

    - by miguel
    I would like to know if there are any guidelineswhich a developer should follow as to when (and where) to place locks. For instance: I understand that code such as this should be locked, to avoid the possibility of another thread changing the value of SomeHeapValue unexpectedly. class Foo { public SomeHeapObject myObject; public void DoSummat(object inputValue_) { myObject.SomeHeapValue = inputValue_; } } My question is, however, how deep does one go with the locking? For instance, if we have this code: class Foo { public SomeHeapObject myObject; public void DoSummat(object inputValue_) { myObject.SomeHeapValue = GetSomeHeapValue(); } } Should we lock in the DoSummat(...) method, or should we lock in the GetSomeHeapValue() method? Are there any guidelines that you all keep in mind when strcturing multi-threaded code?

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  • How do you avoid working on the wrong branch?

    - by henginy
    Being careful is usually enough to prevent problems, but sometimes I need to double check the branch I'm working on (e.g. "hmm... I'm in the dev branch, right?") by checking the source control path of a random file. In looking for an easier way, I thought of naming the solution files accordingly (e.g. MySolution_Dev.sln) but with different file names in each branch, I can't merge the solution files. It's not that big of a deal but are there any methods or "small tricks" you use to quickly ensure you're in the correct branch? I'm using Visual Studio 2010 with TFS 2008.

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  • ATI graphics card, with gnome shell on Ubuntu 11.10, screen flickers

    - by bioShark
    After installing gnome shell, without any problem, after log in the fonts are missing and it looks like crap...nothing is readable. Don't want to make it a double post, because my issue is similar to the one from this question but for me the problems have not been solved properly. After running the commands from that post, and installing the latest AMD 11.10 driver, the Gnome shell display issues have been solved. But each time I move the mouse in the upper left corner, to bring up the applications...my entire screen flickers. Without the applications been displayed, everything looks fine. Hardware: ATI HD4870, Intel Q6600.

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  • Adding dynamic controls to Silverlight application after WCF Service Asynchronous Callback

    - by Birk
    I'm trying to add some dynamic controls to my Silverlight page after a WCF call. When I try to add a control to I get an error: Object reference not set to an instance of an object. Here is a simplified version of my code: using edm = SilverlightBusinessApplication.ServiceRefrence; public partial class ListWCF : Page { edm.ServiceClient EdmClient = new ServiceClient(); public ListWCF() { EdmClient.GetTestCompleted += EdmGetTestCompleted; EdmClient.GetTestAsync(); } private void EdmGetTestCompleted(object sender, edm.GetTestCompletedEventArgs e) { //This is where I want to add my controls Button b = new Button(); LayoutRoot.Children.Add(b); //Error: Object reference not set to an instance of an object } } Is it not possible to modify the page after it has been loaded? What am I missing? Thanks

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  • Cocos2d: is it good practice to use a shared GameScene when having various levels?

    - by mm24
    In my code (based on the ShootEmUp example in this book, which I highly reccomend, source code in chapter 8 available here) I often use the trick of accessing the GameScene via: +(GameScene*) sharedGameScene; which returns a reference to the static instance of GameScene. Is a static instance of GameScene as in the book still a valid pattern in case I want a MainMenu calling GameScene initialized with different level data each time (e.g. different enemies)? (I have created a sceneWithId:(int) method where I load different level data each time. Or should I pheraps create a GameScene class and then sublcass it? E.g. FirstGameScene : GameScene

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  • Programming mid-terms

    - by Dervin Thunk
    Hello. Unfortunately, (written) midterms are necessary in most university CS programs in the world. They tell us how well our students (and ourselves as teachers) are doing. Needless to say, designing midterms for a C Programming Language course is not easy. For instance, when we do program for real, we have a myriad of information at our disposal: websites, books, cheat sheets to "remember" the syntax and so on. My question is this: did you find any way, during your years at school or training, where you said: ok, this midterm evaluation of my programming skills is tough, but fair. For instance: I found "find 5 problems with this code"-type questions hard but interesting and telling. Are there any others? Thanks.

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  • Thread Proc for an instancable class?

    - by user146780
    Basically I have a class and it is instincable (not static). Basically I want the class to be able to generate its own threads and manage its own stuff. I don't want to make a global callback for each instance I make, this doesnt seem clean and proper to me. What is the proper way of doing what I want. If I try to pass the threadproc to CreateThread and it is the proc from a class instance the compiler says I cannot do this. What is the best way of achieving what I want? Thanks

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  • Libre Office Impress opens in 11.10, but not in the launcher

    - by Ruben
    I double click my presentation to open it w/Impress and it opens, but there is no icon in the launcher (or alt-tab switcher) to indicate that its open. I tried keeping the Impress icon in the launcher, then opening my presentation, but the same thing happened. Then I tried opening Impress from the launcher and opening my file from inside impress...no luck either. What's up with that? btw, im using 11.10 and the file was made with office 2010 and saved as a .ppt if that has anything to do with it. Any help is appreciated

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  • method __getattr__ is not inherited from parent class

    - by ??????
    Trying to subclass mechanize.Browser class: from mechanize import Browser class LLManager(Browser, object): IS_AUTHORIZED = False def __init__(self, login = "", passw = "", *args, **kwargs): super(LLManager, self).__init__(*args, **kwargs) self.set_handle_robots(False) But when I make something like this: lm["Widget[LinksList]_link_1_title"] = anc then I get an error: Traceback (most recent call last): File "<pyshell#8>", line 1, in <module> lm["Widget[LinksList]_link_1_title"] = anc TypeError: 'LLManager' object does not support item assignment Browser class have overridden method __getattr__ as shown: def __getattr__(self, name): # pass through _form.HTMLForm methods and attributes form = self.__dict__.get("form") if form is None: raise AttributeError( "%s instance has no attribute %s (perhaps you forgot to " ".select_form()?)" % (self.__class__, name)) return getattr(form, name) Why my class or instance don't get this method as in parent class?

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  • increasing amazon root volume size

    - by OCD
    I have a default amazon ec2 instance with 8GB root volume size. I am running out of space. I have: Detach the current EBS volume in AWS Management Console (Web). Create snapshot of this volume. Created a new Volume with 50G space with my snapshot. Attach the new volume back to the instance to /dev/sda1 However, when I reconnect to the account with: > df -h I can see from the management console that my new Filesystem 1K-blocks Used Available Use% Mounted on /dev/xvda1 8256952 8173624 0 100% / tmpfs 308508 40 308468 1% /dev/shm It's still not using my new volume's size, how to make this work?

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  • What is design principle behind Servlets being Singleton

    - by Sandeep Jindal
    A servlet container "generally" create one instance of a servlet and different threads of the same instance to serve multiple requests. (I know this can be changed using deprecated SingleThreadModel and other features, but this is the usual way). I thought, the simple reason behind this is performance gain, as creating threads is better than creating instances. But it seems this is not the reason. On the other hand, creating instances have little advantage that developers never have to worry about thread safety. I am trying to understand the reason for this decision over the trade-off of thread-safety.

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  • WCF 4: Fileless Activation Fails On XP (IIS 5) that has SSL port enabled.

    - by Richard Collette
    I have a service being hosted in IIS on XP via fileless activation. The service starts fine when there is no SSL port enabled for IIS but when the SSL port is enabled, I get the error message: System.ServiceModel.ServiceActivationException: The service '/SkillsPrototype.Web/services/Linkage.svc' cannot be activated due to an exception during compilation. The exception message is: A binding instance has already been associated to listen URI 'http://rcollet.hsb-corp.hsb.com/SkillsPrototype.Web/Services/Linkage.svc'. If two endpoints want to share the same ListenUri, they must also share the same binding object instance. The two conflicting endpoints were either specified in AddServiceEndpoint() calls, in a config file, or a combination of AddServiceEndpoint() and config. . ---> System.InvalidOperationException: A binding instance has already been associated to listen URI 'http://rcollet.hsb-corp.hsb.com/SkillsPrototype.Web/Services/Linkage.svc'. If two endpoints want to share the same ListenUri, they must also share the same binding object instance. The two conflicting endpoints were either specified in AddServiceEndpoint() calls, in a config file, or a combination of AddServiceEndpoint() and config. My service model configuration is <system.serviceModel> <diagnostics wmiProviderEnabled="true"> <messageLogging logEntireMessage="true" logMalformedMessages="true" logMessagesAtServiceLevel="true" logMessagesAtTransportLevel="true" maxMessagesToLog="3000"/> </diagnostics> <standardEndpoints> <webHttpEndpoint> <standardEndpoint name="" helpEnabled="true" automaticFormatSelectionEnabled="true" /> </webHttpEndpoint> </standardEndpoints> <behaviors> <serviceBehaviors> <behavior> <serviceMetadata httpGetEnabled="true"/> <serviceDebug includeExceptionDetailInFaults="true" /> </behavior> </serviceBehaviors> </behaviors> <bindings> <webHttpBinding> <binding> <security mode="None"> <transport clientCredentialType="None"/> </security> </binding> </webHttpBinding> </bindings> <protocolMapping> </protocolMapping> <services> </services> <serviceHostingEnvironment multipleSiteBindingsEnabled="false"> <serviceActivations> <clear/> <add factory="System.ServiceModel.Activation.WebScriptServiceHostFactory" service="SkillsPrototype.ServiceModel.Linkage" relativeAddress="~/Services/Linkage.svc"/> </serviceActivations> </serviceHostingEnvironment> </system.serviceModel> When you look in the svclog file, there two base addresses that are returned when SSL is enabled, one for http and one for https. I suspect that this is part of the issue but I am not sure how to resolve it. <E2ETraceEvent xmlns="http://schemas.microsoft.com/2004/06/E2ETraceEvent"> <System xmlns="http://schemas.microsoft.com/2004/06/windows/eventlog/system"> <EventID>524333</EventID> <Type>3</Type> <SubType Name="Information">0</SubType> <Level>8</Level> <TimeCreated SystemTime="2010-06-16T17:40:55.8168605Z" /> <Source Name="System.ServiceModel" /> <Correlation ActivityID="{95927f9a-fa90-46f4-af8b-721322a87aaa}" /> <Execution ProcessName="aspnet_wp" ProcessID="1888" ThreadID="5" /> <Channel/> <Computer>RCOLLET</Computer> </System> <ApplicationData> <TraceData> <DataItem> <TraceRecord xmlns="http://schemas.microsoft.com/2004/10/E2ETraceEvent/TraceRecord" Severity="Information"> <TraceIdentifier>http://msdn.microsoft.com/en-US/library/System.ServiceModel.ServiceHostBaseAddresses.aspx</TraceIdentifier> <Description>ServiceHost base addresses.</Description> <AppDomain>/LM/w3svc/1/ROOT/SkillsPrototype.Web-1-129211836532542949</AppDomain> <Source>System.ServiceModel.WebScriptServiceHost/49153359</Source> <ExtendedData xmlns="http://schemas.microsoft.com/2006/08/ServiceModel/CollectionTraceRecord"> <BaseAddresses> <Address>http://rcollet.hsb-corp.hsb.com/SkillsPrototype.Web/Services/Linkage.svc</Address> <Address>https://rcollet.hsb-corp.hsb.com/SkillsPrototype.Web/Services/Linkage.svc</Address> </BaseAddresses> </ExtendedData> </TraceRecord> </DataItem> </TraceData> </ApplicationData> </E2ETraceEvent> I can't post the full service log due to character limits on the post.

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  • Sql Server copying table information between databases

    - by Andrew
    Hi, I have a script that I am using to copy data from a table in one database to a table in another database on the same Sql Server instance. The script works great when I am connected to the Sql Server instance as myself as I have dbo access to both databases. The problem is that this won't be the case on the client's Sql Server. They have seperate logins for each database (Sql Authentication Logins). Does anyone know if there is a way to run a script under these circumstances. The script would be doing something like. use sourceDB Insert targetDB.dbo.tblTest (id, test_name) Select id, test_name from dbo.tblTest Thanks

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  • Subversion for version control

    - by Gabriel Parenza
    Hi, I am working on an application whose primary purpose would be to provide source control management. My idea is to use to SVNKit for file check-out and check-in. However, while working with SVNKit, I realised it does not have the speed I was looking for. For instance, whenever developers create a ChangeRequest, which can encompass change in 3-40 files, I have to create a directory structure distributed across 32 folders. Doing so takes around 50 seconds, Another instance is that after creating change request developers can add files to the request. Copying even a single file from Trunk to branch takes around 6-7 secs. My question is has anyone had experience like this and what did you do to improve the performance? Moreover, is my approach correct? NOTE: I am using "http" protocol and can't use "svn" protocol.

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  • what's wrong with this Lua code (creating text inside listener in Corona)

    - by Greg
    If you double/triple click on the myObject here the text does NOT disappear. Why is this not working when there are multiple events being fired? That is, are there actually multiple "text" objects, with some existing but no longer having a reference to them held by the local "myText" variable? Do I have to manually removeSelf() on the local "myText" field before assigning it another "display.newText(...)"? display.setStatusBar( display.HiddenStatusBar ) local myText local function hideMyText(event) print ("hideMyText") myText.isVisible = false end local function showTextListener(event) if event.phase == "began" then print("showTextListener") myText = display.newText("Hello World!", 0, 0, native.systemFont, 30) timer.performWithDelay(1000, hideMyText, 1 ) end end -- Display object to press to show text local myObject = display.newImage( "inventory_button.png", display.contentWidth/2, display.contentHeight/2) myObject:addEventListener("touch", showTextListener) Question 2 - Also why is it the case that if I add a line BEFORE "myText = ..." of: a) "if myText then myText:removeSelf() end" = THIS FIXES THINGS, whereas b) "if myText then myText=nil end" = DOES NOT FIX THINGS Interested in hearing how Lua works here re the answer...

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  • Retrieving/Updating Entity Framework POCO objects that already exist in the ObjectContext

    - by jslatts
    I have a project using Entity Framework 4.0 with POCOs (data is stored in SQL DB, lazyloading is enabled) as follows: public class ParentObject { public int ID {get; set;} public virtual List<ChildObject> children {get; set;} } public class ChildObject { public int ID {get; set;} public int ChildRoleID {get; set;} public int ParentID {get; set;} public virtual ParentObject Parent {get; set;} public virtual ChildRoleObject ChildRole {get; set;} } public class ChildRoleObject { public int ID {get; set;} public string Name {get; set;} public virtual List<ChildObject> children {get; set;} } I want to create a new ChildObject, assign it a role, then add it to an existing ParentObject. Afterwards, I want to send the new ChildObject to the caller. The code below works fine until it tries to get the object back from the database. The newChildObjectInstance only has the ChildRoleID set and does not contain a reference to the actual ChildRole object. I try and pull the new instance back out of the database in order to populate the ChildRole property. Unfortunately, in this case, instead of creating a new instance of ChildObject and assigning it to retreivedChildObject, EF finds the existing ChildObject in the context and returns the in-memory instance, with a null ChildRole property. public ChildObject CreateNewChild(int id, int roleID) { SomeObjectContext myRepository = new SomeObjectContext(); ParentObject parentObjectInstance = myRepository.GetParentObject(id); ChildObject newChildObjectInstance = new ChildObject() { ParentObject = parentObjectInstance, ParentID = parentObjectInstance.ID, ChildRoleID = roleID }; parentObjectInstance.children.Add(newChildObjectInstance); myRepository.Save(); ChildObject retreivedChildObject = myRepository.GetChildObject(newChildObjectInstance.ID); string assignedRoleName = retreivedChildObject.ChildRole.Name; //Throws exception, ChildRole is null return retreivedChildObject; } I have tried setting MergeOptions to Overwrite, calling ObjectContext.Refresh() and ObjectContext.DetectChanges() to no avail... I suspect this is related to the proxy objects that EF injects when working with POCOs. Has anyone run into this issue before? If so, what was the solution?

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  • How to scale MongoDB

    - by terence410
    I know that MongoDB can scale vertically. What about if I running out of disk? I am currently using EC2 with EBS. As you know, I have to assign EBS for a fixed size. What if the mongodb growth bigger than the EBS size? Do I have to create a larger EBS and Copy & Paste the files? Or shall we start more MongoDB instance and each connect to different EBS disk? In such case, I could connect to a different instance for different databases.

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  • Wubi downloaded and installed 64bit 12.10 on my 32bit netbook

    - by Troy
    I downloaded the Wubi installer on my atom N450 netbook. When I started up Ubuntu I got an error that read failed to change the mode of /ect/passwd- to 0600. Then while it booted it froze and several strange characters filled the screen. Finally it loaded it ran pretty slow, and I could connect to my router, but not to the internet. Ping 8.8.8.8 showed no server found. So I checked the about computer and it said I was running the 64 bit installation. Now I know that my computer has a low power 32 bit chip and even the Ubuntu iso download suggested a 32 bit installation. So I went to double check and see if I just missed the option for a 32 bit Wubi install and I did not. There was no option. Is there any way to download a 32 bit version of 12.10 through the Wubi?

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  • How to query a date in HQL (Hibernate) with Joda Time?

    - by fabien7474
    I am sure that someone familiar with HQL (I am myself a newbie) can easily answer this question. In my Grails application, I have the following domain class. class Book { org.joda.time.DateTime releaseDate //I use the PersistentDateTime for persisting via Hibernate (that use a DATETIME type for MySQL DB) } In my HQL query, I want to retrieve books whose release date is included in range date1..date2 For instance I tried: DateTime date1, date2 ... def queryStr = "select * from Book as b where b.releaseDate > $date1 and b.releaseDate < $date2" def res = Book.executeQuery(queryStr) But I got the exception ...caused by: org.springframework.orm.hibernate3.HibernateQueryException: unexpected token: The error token points to date format (for instance 2009-11-27T21:57:18.010+01:00 or Fri Nov 27 22:01:20 CET 2009) I have also tried to convert date1 into a Date class without success So what is the correct HQL code ? Should I convert to a specific format (which one?) using the patternForStyle method or is there another -cleaner- way to do it? Thanks, Fabien.

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  • Lua : Dynamicly calling a function with arguments.

    - by Tipx
    Using Lua, I'm trying to dynamicly call a function with parameters. What I want to have it done is I send a string to be parsed in a way that : 1st argument is a class instance "Handle" 2nd is the function to be called All that is left are arguments "modules" is a a table like { string= } split() is a simple parser that returns a table with indexed strings function Dynamic(msg) local args = split(msg, " ") module = args[1] table.remove(args, 1) if module then module = modules[module] command = args[1] table.remove(args, 1) if command then if not args then module[command]() else module[command](unpack(args)) -- Reference 1 end else -- Function doesnt exist end else -- Module doesnt exist end end When I try this with "ignore remove bob", by "Reference 1", it tries to call "remove" on the instance associated with "ignore" in modules, and gives the argument "bob", contained in a table (with a single value). However, on the other side of the call, the remove function does not receive the argument. I even tried to replace the "Reference 1" line with module[command]("bob") but I get the same result.

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  • Multiple Controls on a Page with Multiple Instances of Javascript

    - by mattdell
    I have created a Web Control in ASP for use in integrating with Telligent CommunityServer. The control is written in ASP with some 10 lines of C# backend for controlling visibility of the UI elements based on permissions, but I'd say 90% of the functionality is straight-up Javascript. The control works beautifully, until you drop two instances of the Control on the same page--since they reference the exact same Javascript functions, only one control works. How can I take this functionality that I have, this 1200 lines of Javascript, and make it so that each instance of the control can reference its each unique instance of Javascript?

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  • "Reverse" encryption? - EncFS the other way around?

    - by stwissel
    Currently I'm using EncFS to encrypt my directory "confidential" to ".encconfidential" and sync that encrypted directory using an online service (e.g. Dropbox, UbuntuOne etc). However my entire disk is already LUKS encrypted, so the double encryption takes a toll on performance. I wonder is there an "inverted" EncFS option? An unencrypted directory gets mounted and in the mounted directory you only see encrypted files. So I could work with the unencrypted documents while the sync tool sees and read/writes the encrypted files only.

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  • Create an object in C# from an F# object with optional arguments

    - by Mark Pearl
    I have a object in F# as follows... type Person(?name : string) = let name = defaultArg name "" member x.Name = name I want to be able to create an instance of this object in a C# project. I have added as a reference the correct libraries to the project and can see the object via intellisense however I am not sure on the correct syntaxt to create an instance of the object. Currently I have the following in my C# project - which the compiler doesn't like... var myObj1 = new Person("mark");

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