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• What is more interesting or powerful: Curry/Mercury/Lambda-Prolog/your suggestion.

  - by Bubba88

  Hi! I would like to ask you about what formal system could be more interesting to implement from scratch/reverse engineer. I've looked through some existing and rather open (open in the sense of free/open-source) projects of logical/declarative programming systems. I've decided to make up something similar in my free time, or at least to catch the general idea of implementation. It would be great if some of these systems would provide most of the expressive power and conciseness of modern academic investigations in logic and it's relation with computational models. What would you recommend to study at least at the conceptual level? For example, Lambda-Prolog is interesting particularly because it allows for higher order relations, but AFAIK (I might really be mistaken :)) is based on intuitionist logic and therefore lack the excluded-middle principle; that's generally a disatvantage for me.. I would also welcome any suggestions about modern logical programming systems which are less popular but more expressive/powerful. I guess, this question will need refactoring, but thank you in advance! :)

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• C# myths about best practices?

  - by TheMachineCharmer

  My colleague keeps telling me of the things listed in comments. I am confused. Can somebody please demystify these things for me? class Bar { private int _a; public int A { get { return _a; } set { _a = value; } } private Foo _objfoo; public Foo OFoo { get { return _objfoo; } set { _objfoo = value; } } public Bar(int a, Foo foo) { // this is a bad idea A = a; OFoo = foo; } // MYTHS private void Method() { this.A //1 - this._a //2 - use this when inside the class e.g. if(this._a == 2) A //3 - use this outside the class e.g. barObj.A _a //4 - // Not using this.xxx creates threading issues. } } class Foo { // implementation }

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• Java: Set<E> collection, where items are identified by its class

  - by mschayna

  I need Set collection, where its items will be identified by items class. Something like ReferenceIdentityMap from Appache Collections, but on class scope i.e. two different instances of same class must be identified as same in this collection. You know, it is a violation of equals()/hashCode() identity principle but in occasional use it makes sense. I have done this in simple class backing with Map<Class<? extends E>, E>, but due to simplicity it doesn't implement Set<E>. There may be a more elegant solution, decorator of any Set<E> would be great. Is there any implementation of such collection there (Apache/Google/something/... Collections)?

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• object representation and value representation

  - by FredOverflow

  3.9 §4 says: The object representation of an object of type T is the sequence of N unsigned char objects taken up by the object of type T, where N equals sizeof(T). The value representation of an object is the set of bits that hold the value of type T. For trivially copyable types, the value representation is a set of bits in the object representation that determines a value, which is one discrete element of an implementation-defined set of values. Does "The value representation of an object" imply that values are always stored in objects? What is the value representation of non-trivially copyable types?

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• Why is the CoreData stack in XCode's CoreData enabled template treated as private?

  - by rob5408

  In regards to XCode templates with CoreData enabled, I've read http://stackoverflow.com/questions/2729055/unclear-use-of-property-in-window-app-using-core-data which goes over the 'what' in the templates. But I am having an issue with the 'why'. By declaring the category in the implementation file, the CoreData accessors act like private methods. The problem with that is whenever you want to use CoreData elsewhere in your app, you need some extra code. I've figured you need to either supply your own method that exposes the managed object context, such as... - (NSManagedObjectContext *)getManagedObjectContext { return self.managedObjectContext; } ...which will allow other parts of your app to use it. Or you would need to jam pack your app delegate with specific methods to return managed objects, ie getProducts or setUser. Can anyone shed light on the reasoning here?

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• What web UI framework is most suitable for building dynamic pages / forms?

  - by waxwing

  Hello, We are at a stage where we are considering different Web UI frameworks (most likely component based ones such as GWT, JSF, Wicket, Vaadin, etc). One of the main use cases / constraints is that it must support generating dynamic pages. I.e., the page/form layout and components is stored in a database and is changeable at runtime, and from this pages are generated. We are also going to write static layouts, but that is not the main focus of this question. I thought maybe the user community here can share experiences of different frameworks in this context. Are there differences in ease of implementation and what is suitable?

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• Delphi> Please explain this: type... procedure of object

  - by Richard Woolf

  I've encountered some code that's new to me... I've never really seen a type declaration of a procedure of object, and I just don't see the point. Why couldn't the developer simply keep a field of type Boolean? interface type TFinishedCaptureEvent = procedure(AFinished: Boolean) of object; TFrameCard = class(TFrame) ... private FOnFinishedCapture: TFinishedCaptureEvent; public property OnFinishedCapture: TFinishedCaptureEvent read FOnFinishedCapture write FOnFinishedCapture; end; implementation ... if Assigned(FOnFinishedCapture) then FOnFinishedCapture(False);

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• I need help translating this portion of the ECMAScript grammar?

  - by ChaosPandion

  I've been working on my own implementation of ECMAScript for quite some time now. I have basically done everything by hand to help gain a deep understanding of the process. Repeated attempts to analyze and understand this portion of the grammar have failed so I've been working on the run time instead. Now I am at a point were I will be working on object literals so I really need to polish my syntactic analyzer. Can anyone put this in terms a language parser novice could understand? My biggest source of confusion is the following: new MemberExpression Arguments This is supposed to be a member expression, but this seemingly conflicts with the following: NewExpression : MemberExpression new NewExpression Is a new expression a member expression or a left hand side expression? To be honest I am having trouble laying out the proper C# classes for the concrete grammar. MemberExpression : PrimaryExpression FunctionExpression MemberExpression [ Expression ] MemberExpression . IdentifierName new MemberExpression Arguments NewExpression : MemberExpression new NewExpression CallExpression : MemberExpression Arguments CallExpression Arguments CallExpression [ Expression ] CallExpression . IdentifierName LeftHandSideExpression : NewExpression CallExpression

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• Are any of these quad-tree libraries any good?

  - by Noctis Skytower

  It appears that a certain project of mine will require the use of quad-trees, something that I have never worked with before. From what I have read they should allow substantial performance enhancements than a brute-force attempt at the problem would yield. Are any of these python modules any good? Quadtree 0.1.2 <= No: unable to execute in Python 3.1 QuadTree <= Yes: simple while working with rectangles quadtree.py <= No: no support for needed operations EDIT: Does anyone know of a better implementation that the one presented on the pygame wiki article?

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• How can I simply "run" lisp files

  - by Annan

  Python When I learned Python I installed it on windows with a nice gui installer and all .py files would automatically run in python, from the command line or explorer. I found this very intuitive and easy, because I could instantly make plain text files and run them. Lisp I'm starting to learn lisp and have decided (from reviews) that SBCL is not a bad lisp implementation. Is there a way to setup SBCL to run .lisp files as easily as with Python? Are there other lisp implementations that have this?

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• Mapping java.util.Date to xs:date instead of xs:dateTime in JAX-WS

  - by Larsing

  Hi all, We hav an EJB, jws-anotated as a web service. It has a pretty complex pojo-model that generates an equally complex xsd. The pojos contain numerous java.util.Date. These all map to xs:dateTime. This service is used as "business service" in Oracle(BEA) OSB(AquaLogic). We also have a "proxy service" which we map to the BS with XQuery (the OSB/AquaLogic way). The proxy service's xsd has xs:date for the corresponding fields. For some reason, Oracle's implementation of XQuery does not support casting from xs:date to xs:dateTime(!). I could solve this by casting to xs:string and concat:ing with "T00:00:00", however, i would rather try to get JAX-WS to generate an xsd with xs:date instead. Only, I can't find any info on how to do this (anotations?). Can anyone give me a hint? Kind regards, Lars

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• Does std::multiset guarntee 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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• Mixing table per subclass and per hierarchy in hibernate

  - by Xelluloid

  In my database there are two three tables. The first one, table ABSTRACT, holds three columns id, type, someText This table contains all abstract information for the abstract class abstract. Now the two tables CONCRETEONE and CONCRETETWO contain all information for the concrete classes concreteOne and concreteTwo. Now I know I could use the table per subclass strategy from hibernate to create a mapping with inheritance. But as I have a column that marks the type of the concrete implementation could it be possible to create some mixed behaviour like a table per subclass strategy with an discriminator?

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• How to handle JPA annotations for a pointer to a generic interface

  - by HDave

  I have a generic class that is also a mapped super class that has a private field that holds a pointer to another object of the same type: @MappedSuperclass public abstract class MyClass<T extends MyIfc<T>> implements MyIfc<T> { @OneToOne() @JoinColumn(name = "previous", nullable = true) private T previous; ... } My problem is that Eclipse is showing an error in the file at the OneToOne "Target Entity "T" for previous is not an Entity." All of the implementations of MyIfc are, in fact, Entities. I should also add that each concrete implementation that inherit from MyClass uses a different value for T (because T is itself) so I can't use the "targetEntity" attribute. I guess if there is no answer then I'll have to move this JPA annotation to all the concrete subclasses of MyClass. It just seems like JPA/Hibernate should be smart enough to know it'll all work out at run-time. Makes me wonder if I should just ignore this error somehow.

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

  - by Sadache

  Does "Value Restriction" 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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• How to implement a lazy loaded Silverlight data grid without using paging

  - by Marc Wittke

  Using the Business Application template from the brand new released RIA Services, you can see lots of examples using the data grid on top of a DomainDataSource in combination with a DataPager. The properties PageSize and LoadSize can be used to adjust the amount of data to be displayed in one page and the data that is prefetched in the background. Now I'd like to have a data grid with a scrollbar and no pager. The underlying DomainDataSource should load only the data that is diplayed in the grid. It should trigger another load, when the user scrolls down to items that are not yet in the data context. Is there any sample implementation how to do this?

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• Nested class with hidden constructor impossible in c#?

  - by luckyluke

  I' ve been doing some programming lately and faced an issue which i found weird in c#. (at least for me) public class Foo { //whatever public class FooSpecificCollection : List<Bar> { //implementation details } public FooSpecificCollection GetFoosStuff() { //return the collection } } I want the consumer of Foo to be able to obtain a reference to FooSpecificCollection, even perform some operations on it. Maybe even set it to some other property of Foo or smth like that, but not To be able to CREATE an instance of this class. (the only class that should be able to instatiate this collection should be Foo. Is my request really that far-fetched? I know that people way smarter defined c# but shouldn't there be such an option that a parent class can create a nested class instance but nobody else can't. So far I created a solution to make an abstract class, or interface available through the property and implement a concrete private class that is not available anywhere else. Is this a correct way to handle such a situation.?

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• Java generics: Illegal forward reference

  - by Arian

  Given a generic interface interface Foo<A, B> { } I want to write an implementation that requires A to be a subclass of B. So I want to do class Bar<A, B super A> implements Foo<A, B> { } // --> Syntax error or class Bar<A extends B, B> implements Foo<A, B> { } // --> illegal forward reference But the only solution that seems to work is this: class Bar<B, A extends B> implements Foo<A, B> { } which is kind of ugly, because it reverses the order of the generic parameters. Are there any solutions or workarounds to this problem?

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• JavaScript inheritance

  - by Tower

  Hi, Douglas Crockford seems to like the following inheritance approach: if (typeof Object.create !== 'function') { Object.create = function (o) { function F() {} F.prototype = o; return new F(); }; } newObject = Object.create(oldObject); It looks OK to me, but how does it differ from John Resig's simple inheritance approach? Basically it goes down to newObject = Object.create(oldObject); versus newObject = Object.extend(); And I am interested in theories. Implementation wise there does not seem to be much difference.

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• What's a good unit test framework for Common Lisp projects?

  - by Lorenzo V.

  I need to write a unit test suite for a project I am developing in my spare time. Being a CL newbie I was overwhelmed by the amount of choices for a CL implementation, I spent quite some time to choose one. Now I am facing exactly the same thing with unit test frameworks. A quick glance at http://www.cliki.net/test%20framework shows 20 unit test frameworks! Choice is good but for a novice like me this can be a bit confusing and given the number of frameworks it would be painful to try them all. I would like to use a framework which: Is reasonably well maintained Easy to use but with some degree of flexibility Offers some sort of integration with Emacs (or it is possible to easily integrate it with Emacs) Integration with git post-commit hooks Integration with a continous integration system (such as buildbot) What are your experiences in this field?

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• Events raised by BackgroundWorker not executed on expected thread

  - by Topdown

  A winforms dialog is using BackgroundWorker to perform some asynchronous operations with significant success. On occasion, the async process being run by the background worker will need to raise events to the winforms app for user response (a message that asks the user if they wish to cancel), the response of which captured in an CancelEventArgs type of the event. Being an implementation of threading, I would have expected the RaiseEvent of the worker to fire, and then the worker would continue, hence requiring me to pause the worker until the response is received. Instead however, the worker is held to wait for the code executed by the raise event to complete. It seems like method I am calling via the event call is actually on the worker thread used by the background worker, and I am surprised, since I expected to see it on the Main Thread which is where the mainform is running. Also surprisingly, there are no cross thread exceptions thrown. Can somebody please explain why this is not as I expect?

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• Determine if a day of week and time fall in a custom weekend period

  - by Y Low

  I've been trying to come up with a method, that given a day of week and time of day, it will return if it falls under a custom weekend period. The weekend period is saved in 4 variables as follows: The day of week when it starts (0-6) The time of day when it starts (0-23) The day of week when it ends (0-6) The time of day when it ends (0-23) Based on these fields, the weekend period can be anything the user selected (even if it is well beyond a regular weekend) I've been banging this one for awhile but to no avail. I'm trying this in delphi but any language will do, as I'm looking for the algorithm and not the implementation.

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• How to instantly termainate an un-supervised script on demand?

  - by errr

  I have a GUI which resembles an interpreter. It allows the user to write a script in Jython (implementation of Python in Java) and run it whenever he wants. Apart from that, I also wish to allow the user to instantly terminate the run whenever he wants. Thing is, I don't really know how to do it. The script is being run on a different Thread, but I don't know of any secure way to stop/interrupt/terminate a thread in the middle of its run, let alone not knowing what is being run by the thread/script (it could be a simple task or maybe some sort of a heavy SQL query against a DB, and a DB is something which requires careful resource handling). How can I instantly terminate such run on demand?

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• EXC_BAD_ACCESS when trying to release an ABRecordRef

  - by synic

  I've got the following class that is a wrapper around an ABPerson (ABRecordRef): @interface Recipient : NSObject { ABRecordRef person; } - (id)initWithPerson:(ABRecordRef)person; @end @implementation - (id)initWithPerson:(ABRecordRef)_person { if(self = [super init]) person = CFRetain(_person); return self; } - (void)dealloc { if(person) CFRelease(person); [super dealloc]; } @end I've left some of the methods out, but they aren't relevant to this question. Everything works fine, except I get an EXC_BAD_ACCESS on the if(person) CFRelease(person); line. Why does this happen? I'm not calling CFRelease or CFRetain at all anywhere else in my app.

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• Java's ThreadPoolExecutor equivalent for C#?

  - by chillitom

  Hi Guys, I used to make good use of Java's ThreadPoolExecutor class and have yet to find a good equivalent in C#. I know of ThreadPool.QueueUserWorkItem which is useful in many cases but no good if you want to control the number of threads assigned to a task or have multiple individual queues for different task types. For example I liked to use a ThreadPoolExecutor with a single thread to guarantee sequential execution of asynchronous calls.. Is there an easy way to do this in C#? Is there a non-static thread pool implementation? Thanks, T.

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