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  • list permutations in haskell

    - by turingcomplete
    So I'm new to haskell and I've been playing with it for a while now. I want to get my function that outputs all list permutations to work. I have written 2 implementations, one works well, the other is giving me an error. Any help would be awesome. This is the first (working) implementation: permute [] = [[]] permute xs = [y| x <- xs, y <- map (x:) $ permute $ delete x xs] This one is giving me an error: permute [] = [[]] permute xs = map (\x -> map (x:) $ permute $ delete x xs) xs and here's the error message: Occurs check: cannot construct the infinite type: t0 = [t0] Expected type: [t0] Actual type: [[t0]] In the expression: map (x :) $ permute $ delete x xs In the first argument of `map', namely `(\ x -> map (x :) $ permute $ delete x xs)' I'd appreciate if someone could explain why I'm getting this error. Thanks

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  • Should a protected property in a C# child class hide access to a public property on the parent?

    - by Tim
    I have the following code: public class Parent { public string MyField { get; set; } } public class Child : Parent { protected new int MyField { get; set; } } I try and access this with: static void Main(string[] args) { Child child = new Child(); child.MyField = "something"; } Visual studio 2008 compiles this without comment, but under Mono (2.4.2, Ubuntu) I get the error message 'HideTest.Child.MyField' is inaccessible due to its protection level (CS0122) Is one implementation or the other more compliant with the standard here?

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  • C# 2D Vector Graphics Game using DirectX or OpenGL?

    - by Brian
    Hey Guys, So it has been a while since I have done any game programming in C#, but I have had a recent bug to get back into it, and I wanted some opinions on what configuration I should use. I wanted to use C# as that is what I use for work, and have become vary familiar with. I have worked with both DirectX and OpenGL in the past, but mostly in 3D, but now I am interested in writing a 2D game with all vector graphics, something that resembles the look of Geometry Wars or the old Star Wars arcade game. Key points I am interested in: • Ease of use/implementation. • Easy on memory. (I plan on having a lot going on at once) • Looks good, I don't want curve to look pixelated. • Maybe some nice effects like glow or particle. I am open to any and all suggestions, maybe even something I have not thought of... Thanks in advance!

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  • Added a tableview in a viewcontroller. How do I load tableview cells

    - by user1509593
    I have a view controller In storyboard, added tableview to view controller. Created an IBOutlet for tableview to View controller's header file. The view controller's header file includes an resultsarray Changed the @interface to include delegates <\UITableViewDelegate, UITableViewDataSource View controller implementation file has mandatory tableview protocols (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath The view controller has search button in storyboard and IBAction in view controller header file. On click of search button, results are obtained. How do I load the array and redisplay tableview with results in search method. After I loaded the results in array, I tried [self viewdidload];, hoping the cells will be loaded. But didn't. I thought of calling [self.detailView cellForRowAtIndexPath:?indexpath], but dontknow what the value of index path is. Appreciate help from guru's to load the UItableviewcell Thanks

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  • Examining a lambda expression at runtime in C#

    - by Ben Aston
    I have a method Get on a type MyType1 accepting a Func<MyType2, bool> as a parameter. An example of its use: mytype1Instance.Get(x => x.Guid == guid)); I would like create a stub implementation of the method Get that examines the incoming lambda expression and determines what the value of guid is. Clearly the lambda could be "anything", but I'm happy for the stub to make an assumption about the lambda, that it is trying to match on the Guid property. How can I do this? I suspect it involves the use of the built-in Expression type?

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  • Unit Testing: hard dependency MessageBox.Show()

    - by Sean B
    What ways can the SampleConfirmationDialog be unit tested? The SampleConfirmationDialog would be exercised via acceptance tests, however how could we unit test it, seeing as MessageBox is not abstract and no matching interface? public interface IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> bool? Confirm(); } /// <summary> /// Implementation of a confirmation dialog /// </summary> public class SampleConfirmationDialog : IConfirmationDialog { /// <summary> /// Confirms the dialog with the user /// </summary> /// <returns>True if confirmed, false if not, null if cancelled</returns> public bool? Confirm() { return MessageBox.Show("do operation x?", "title", MessageBoxButton.YesNo, MessageBoxImage.Question) == MessageBoxResult.Yes; } }

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  • Does "Value Restriction" practically mean that there is no higher order functional programming?

    - by Sadache
    Does "Value Restriction" practically mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" and I would like to know whether it is a problem of a prticular implementation of VR or it is a general problem that has no solution in a mutable type-infered language that doesn't include mutation in the type system.

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  • Interview Programming Questions - In house Exam

    - by David McGraw
    I have a company that would like to bring me in to serve me an hour long exam. No resources other than a pencil and paper. I really couldn't get any sort of feedback on the type of exam (implementation or generic) beside that it would test a few specific areas. Have you done anything like this? What sort of questions did they ask? What's a good way to prepare? I'll probably go in a couple weeks before school starts back up. A time sensitive exam structure is a weak point for me, so what should I absolutely focus down on? If they like the exam, that's when I'll get a face-to-face meeting. An advance thanks goes to everybody who provide their time.

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  • Partial coverage of a return statement in C++/CLI

    - by brickner
    I have C++/CLI code and I'm using Visual Studio 2008 Team Suite Code Coverage. The code header: // Library.h #pragma once #include <string> using namespace System; namespace Library { public ref class MyClass { public: static void MyFoo(); static std::string Foo(); }; } The code implementation: #include "Library.h" using namespace Library; using namespace System; void MyClass::MyFoo() { Foo(); } std::string MyClass::Foo() { return std::string(); } I have a C# unit test, that calls MyClass.MyFoo(): [TestMethod] public void TestMethod1() { Library.MyClass.MyFoo(); } For some reason, I don't get a full code coverage for MyClass. The Foo() method has 3 uncovered blocks and 5 covered blocks. The closing curly brackets (}) are marked in orange - partially covered. I have no idea why is it partially covered instead of fully covered, and this is my question.

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  • How to save state of the app when app terminates?

    - by user164589
    Hi guys. I am trying to save the app state by encoding when the app terminates. I've found the solution related this issue. But I don't know how to use. I am really trying to make encoding and decoding like this: http://cocoaheads.byu.edu/wiki/nscoding in CustomObject.h @interface CustomObject : NSObject <NSCoding> { NSArray *someArray; } in CustomObject.m @implementation CustomObject // Other method implementations here - (void) encodeWithCoder:(NSCoder*)encoder { [encoder encodeObject:someArray forKey:@"someArray"]; } - (id) initWithCoder:(NSCoder*)decoder { if (self = [super init]) { someArray = [[decoder decodeObjectForKey:@"someArray"] retain]; } return self; } @end My object to save is another NSArray. Not "someArray" in CustomObject. We call it that "MySaveObject". I want to pass "MySaveObject" to "someArray" in CustomObject. Actually I don't know how to encode "MySaveObject" and to pass to "someArray" in CustomObject. Thanks in advance.

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  • Looking for suggestions about an architecture of a MultiThreaded app.

    - by Dimitri
    Hello everyone. I am looking to develop a multithreaded application that will be running in unconditional loop and processing high volume of data. High volume is 2000+ records per minute. Processing will involve data retrieval, calculations and data updates. I need the application to perform so that there is virtually no back log, meaning i need to be able to finish up all of the 2000 points in one minute or even faster. Our current implementation features a multithreaded application that is spawn multiple times (from 10 to 20) and we are noticing that it's not handling data as expected and i even feel that instances of the application compete with each other for processor time and eventually if not slowing, not benefiting each other for sure. I would like to know what would be the best approach: have a single instance running but maximize threads that can run simultaneously? or is there other ways i don't know? I'm open to suggestions. Thank you in advance

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  • Implement VOIP in iphone and ipad.

    - by user339994
    Hi, Does anybody is aware of implementing VOIP feature in iphone and ipad. The Things for which i need clarity is, By using which third party library/protocol can i implement this feature? or is der any in built classed available in objective c which i can make use of?? Is there any Apple store accepted iphone application which uses VOIP iplementation?? If so where can i get implementation details of it. This is a generic question. Can we use any third party's in our iphone application or do we need to get any special permission from Apple reg the usage of third party's used. Please let me know if needed more details reg this. Thanks , Santhana

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  • What do the external JSF libraries/frameworks add?

    - by kgrad
    I have seen mention of a bunch of external JSF Libraries such as ICEfaces, Richfaces, etc. However, I am unsure as to what these libraries actually add over just using JSF 2.0. Are they just additional components that are pre-built? I know that PrettyFaces adds URL rewriting, and I Believe that ICEFaces/Richfaces add Ajax enabled components? What are some other major component libraries, what are their benefits / why should people use them? Additionally, what does a framework like SEAM add over using straight JSF2 with EJB? Is MYFaces simply a different implementation of JSF?

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  • android dev: how to implement for add method in menu interface?

    - by wsgjj
    who knows about the method "add" in menu interface? how to implement exactly? which is it's imlementation class? i couldn't find detail implementation in source code of sdk. i want to check how to implement in android source code for "add" method. e.g. public boolean onCreateOptionsMenu(Menu menu) { menu.***add***(0, MENU_NEW_GAME, 0, "New Game"); menu.add(0, MENU_QUIT, 0, "Quit"); return true; } thanks in advance!

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  • Given a short (2-week) sprint, is it ever acceptable to forgo TDD to "get things done"?

    - by Ben Aston
    Given a short sprint, is it ever acceptable to forgo TDD to "get things done" within the sprint. For example a given piece of work might need say 1/3 of the sprint to design the object model around an existing implementation. Under this scenario you might well end up with implemented code, say half way through the sprint, without any tests (implementing unit tests during this "design" stage would add significant effort and the tests would likely be thrown away a few times until the final "design" is settled upon). You might then spend a day or two in the second week adding in unit / integration tests after the fact. Is this acceptable?

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  • Does std::multiset guarantee insertion order?

    - by Naveen
    I have a std::multiset which stores elements of class A. I have provided my own implementation of operator< for this class. My question is if I insert two equivalent objects into this multiset is their order guaranteed? For example, first I insert a object a1 into the set and then I insert an equivalent object a2 into this set. Can I expect the a1 to come before a2 when I iterate through the set? If no, is there any way to achieve this using multiset?

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  • Use multiple inheritance to discriminate useage roles?

    - by Arne
    Hi fellows, it's my flight simulation application again. I am leaving the mere prototyping phase now and start fleshing out the software design now. At least I try.. Each of the aircraft in the simulation have got a flight plan associated to them, the exact nature of which is of no interest for this question. Sufficient to say that the operator way edit the flight plan while the simulation is running. The aircraft model most of the time only needs to read-acess the flight plan object which at first thought calls for simply passing a const reference. But ocassionally the aircraft will need to call AdvanceActiveWayPoint() to indicate a way point has been reached. This will affect the Iterator returned by function ActiveWayPoint(). This implies that the aircraft model indeed needs a non-const reference which in turn would also expose functions like AppendWayPoint() to the aircraft model. I would like to avoid this because I would like to enforce the useage rule described above at compile time. Note that class WayPointIter is equivalent to a STL const iterator, that is the way point can not be mutated by the iterator. class FlightPlan { public: void AppendWayPoint(const WayPointIter& at, WayPoint new_wp); void ReplaceWayPoint(const WayPointIter& ar, WayPoint new_wp); void RemoveWayPoint(WayPointIter at); (...) WayPointIter First() const; WayPointIter Last() const; WayPointIter Active() const; void AdvanceActiveWayPoint() const; (...) }; My idea to overcome the issue is this: define an abstract interface class for each usage role and inherit FlightPlan from both. Each user then only gets passed a reference of the appropriate useage role. class IFlightPlanActiveWayPoint { public: WayPointIter Active() const =0; void AdvanceActiveWayPoint() const =0; }; class IFlightPlanEditable { public: void AppendWayPoint(const WayPointIter& at, WayPoint new_wp); void ReplaceWayPoint(const WayPointIter& ar, WayPoint new_wp); void RemoveWayPoint(WayPointIter at); (...) }; Thus the declaration of FlightPlan would only need to be changed to: class FlightPlan : public IFlightPlanActiveWayPoint, IFlightPlanEditable { (...) }; What do you think? Are there any cavecats I might be missing? Is this design clear or should I come up with somethink different for the sake of clarity? Alternatively I could also define a special ActiveWayPoint class which would contain the function AdvanceActiveWayPoint() but feel that this might be unnecessary. Thanks in advance!

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  • Qt and finding partial matches in a QList

    - by ExpatEgghead
    I have a struct viz: struct NameKey { std::string fullName; std::string probeName; std::string format; std::string source; } which are held in a QList: QList<NameKey> keyList; what I need to do is find an occurence in keyList of a partial match where the search is for a NameKey that only has two members filled. All the keyList entries are full NameKey's. My current implementation is , well, boring in the extreme with too many if's and conditions. So, If I have a DataKey with a fullName and a format I need to find all the occurences in keyList which match. Any useful Qt/boost things available?

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  • Windows Phone 7 Application + WCF + SSL + Username Authentication

    - by s7orm
    Hello, I have developed a test service with WCF, which I try to consume from a Windows Phone 7 Application, however when calling a method from the service I get a weird exception: There was no endpoint listening at https://server/Service.svc that could accept the message. This is often caused by an incorrect address or SOAP action. The WCF service uses a custom binding with UserNameOverTransport authentication and SSL. For the authorization I am using an implementation of the UserNamePasswordValidator. If I try to consume the service from a console or silverlight application (cross domain policy is enabled) - it works fine (authorization as well). And the most weird thing is that the ServiceReferences.ClientConfig file generated for the WP7 App is exactly the same as the config file generated for the silverlight application. I have no idea what is wrong with my service...

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  • How do I get the current Application Name (in terms of IIS) in a classic asp Web application

    - by Mr AH
    I have a classic asp application which retrieves the current application name and sets an Application variable containing that name. This name is important (I wont go into why) and is essentially the friendly name in IIS. The problem is, the implementation used to get this name is flawed, it a) assumes the home directory contains the string wwwroot, and b) assumes the folder name is the same as the application name. I can no longer guarantee these conditions. I would have thought the application name is know at run-time but I can't seem to find it in either Session or Application variables (at application start up entry point in global.asa). Any ideas?

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  • Java Enum Newbie Question

    - by ikurtz
    i have a situation where i need the Checker enum below used in multiple classes: package Sartre.Connect4; public enum Checker { EMPTY, RED, YELLOW } so i put the Checker in a Checker.java file and then from the classes that need it i simply do the following: example: public Cell(){ currentCell = Checker.EMPTY; } example: public Cell(Checker checker){ currentCell = checker; } and the code compiles fine and runs fine also. so what is my question? well being new to Java i am just wondering if the way i use Checker without encapsulating it in a class is a sound implementation? it may be because of The enum declaration defines a class (called an enum type). as noted in Java docs enum tutorial page. thank you for your insight into this matter.

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  • PyPy: What is all the buzz about?

    - by sub
    Note: The title is provocating (to make you click on it and want to close-vote the question) and I don't want to look preoccupated. Since some time now I read and heard more and more about PyPy. It's like a linear graph. Why is PyPy so special? As far as I know implementations of dynamic languages written in the languages itself aren't such a rare thing, or am I not getting something? Some even people call PyPy "the future" [of python], or see some sort of deep potential in this implementation. What exactly is the meaning of this?

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  • Recommend a local LDAP store for development

    - by Paul Stovell
    Our project uses an LDAP repository for storing users. In production this will be Active Directory. For development, we seem to have a couple of options: Install an AD LDS instance that everyone uses Install an AD LDS instance on every developer machine We're trying to keep the 'F5' experience as lightweight as possible, so installing things or relying on a central AD store aren't my favorite ideas. There are other LDAP servers, like Open LDAP. I was hoping there might be an LDAP server that simply talks to an XML file. This would allow us to store the XML file in source control and have something that is fast and works. Our nightly builds would still use AD to pick up any differences, but the hope is since we're using LDAP it should Just Work. Can you recommend an LDAP implementation that works well for zero-config shared-nothing development?

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  • Trouble shooting openGL text textures not showing up correctly cross platform

    - by Michael Minerva
    I have been tasked with solving a problem that is outside of my domain of knowledge and I was hoping I could get some troubleshooting advice from someone more experienced with openGL (I have very little experience with openGL). We are working on a cross platform application that is implemented in a common lisp implementation called ccl. In this application we have a need to display some 3D objects that display text. On the mac, all of the text displays fine but on the PC instead of displaying the text it displays some other texture. At first I thought that maybe the wrong texture was just being referenced so I tried changing the texture number but none of the textures in the list appeared to be the text (or if it was the texture was distorted and did not look like text). I know this problem is very vague and I am not looking for someone to post a solution, but I was wondering if people could suggest places I might look to try and get a handle on this issue.

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  • Grouped UITableView's cell separator missing when setting backgroundView with an image

    - by Howard Spear
    I have a grouped UITableView with a custom UITableViewCell class and I am adding a custom background image to each cell. However, when I do this, the cell's separator is not visible. If simply switch the table style to Plain instead of Grouped, the separator is showing up. I need the grouped table - how do I make the separator show up? Here's my code: @interface MyCustomTableViewCell : UITableViewCell @end @implementation MyCustomTableViewCell // because I'm loading the cell from a xib file - (id)initWithCoder:(NSCoder *)coder { self = [super initWithCoder:coder]; if (self) { // Create a background image view. self.backgroundView = [[UIImageView alloc] init]; } return self; } // MyViewController - (UITableViewCell *)tableView:(UITableView *)aTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { // // standard cell dequeue + create cell code here // // // Configure the cell background now // UIImage *backgroundImage = [UIImage imageNamed:@"odd_row.png"]; if (indexPath.row % 2 == 0) { backgroundImage = [UIImage imageNamed:@"even_row.png"]; } UIImageView *backgroundView = (UIImageView *)cell.backgroundView; backgroundView.image = backgroundImage; }

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