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• Clojure: Avoiding stack overflow in Sieve of Erathosthene?

  - by nixx

  Here's my implementation of Sieve of Erathosthene in Clojure (based on SICP lesson on streams): (defn nats-from [n] (iterate inc n)) (defn divide? [p q] (zero? (rem q p))) (defn sieve [stream] (lazy-seq (cons (first stream) (sieve (remove #(divide? (first stream) %) (rest stream)))))) (def primes (sieve (nats-from 2))) Now, it's all OK when i take first 100 primes: (take 100 primes) But, if i try to take first 1000 primes, program breaks because of stack overflow. I'm wondering if is it possible to change somehow function sieve to become tail-recursive and, still, to preserve "streamnes" of algorithm? Any help???

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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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• Are there any widely-agreed upon guidelines for rating your language knowledge on a scale?

  - by DVK

  The question was imagined after a co-worker was complaining for an hour about some guy who could not answer basic Java questions on an interview after self-identifying himself as "8 out of 10" on Java. While that was an obvious fib, I personally always had major trouble defining my specific language skills on a sliding scale unless I'm given specific guidelines (remember 40 standard libraries by heart? Able to solve 10 random Project Euler problems in <30 mins each? Can write implementation of A, B and C data-structures from scratch in 30 mins? Know 30% of standard? Can answer 50% of questions on StackOverflow pertaining to the language?) So, I was wondering - is there some sort of commonly accepted methodology for translating such tangible benchmarks into "rate yourself on a language between 1-10"? "Kernighan gets an A, God gets a B, everyone else gets C and less" type jokes are not helpful :)

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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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• T-SQL: Build Nested Set From Parent-Child Relationship

  - by Peder Rice

  I have a table that stores my Customer hierarchy with a nested set (due to the specific design of the application, I wasn't able to leverage just a Customer/Parent Customer mapping table). To simplify maintenance of this table, I've built a couple of stored procedures to handle moving nodes around and creating new nodes, but it's significantly more work than maintaining a Customer/Parent Customer table. Further, these structures are very fragile. So I'm looking for a way to have a Customer/Parent Customer table and then convert that table to a nested set on demand. Does anyone have a link to such an implementation?

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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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• 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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• How to click through JGlassPane With MouseListener to UI behind it

  - by Epicmaster

  I have a JFrame and a bunch of JComponents on top of the JFrame. I need to make use of the JGlassPane and I used this implementation to set it up. JPanel glass = new JPanel(); frame.setGlassPane(glass); glass.setVisible(true); glass.setOpaque(false); After doing so I can't select any JButtons or other JComponents under the JGlassPane. Is there a way to have only the components on the GlassPane selectable while still having the ability to select components under the GlassPane? Edit I forgot to mention (not knowing this would be relevant) that I did attach both a MouseListener and a MouseMotionListener to the glass pane. Is there a way to pass the Mouse Events to other components and only use them when needed?

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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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• 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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• 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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• 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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• Why do Java/C# edge out C++ as the recommended language to learn OOP on S.O?

  - by viksit

  I noticed after reading the answers/discussion to this question (What is the best language to learn OOP on?) - that more and more people are recommending C# or Java over C++ to learn OOP on. A simple term search on that answer page results in 10 hits for C++, 21 for C# and 27 for Java. Now, I understand that these 2 languages fix a lot of quirks and issues with C++, and looked up these resources that relate mostly to performance, JVM vs native implementation, systems focus vs applications, manual memory management vs automated et al. My question is - are there any fundamental differences in the OO capabilities of Java/C# vs C++? Or are the former recommended purely due to their generic ease of use/improvements over the latter? Thanks. PS, I'm aware of Java interface inheritance vs C++ multiple inheritance as a difference. I would consider that an implementational one rather than functional.

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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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• 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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• Is there any advantages to integrate Smarty with Zend?

  - by keisimone

  Hi, i am quite familiar with Smarty and recently decided to use Zend framework in implementation. because i am aware of the various advantages of Smarty, i insisted my contractor to integrate Smarty in. But now, i am questioning my assumptions. Should I integrate Smarty in with Zend framework? simply because I am familiar with Smarty syntax? I am also involved with the programming. I got the contractor to help in the architecture and with the prototype.

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• How to create a view of table that contains a timestamp column?

  - by Matt Faus

  This question is an extension of a previous one I have asked. I have a table (2014_05_31_transformed.Video) with a schema that looks like this. I have put up the JSON returned by the BigQuery API describing it's schema in this gist. I am trying to create a view against this table with an API call that looks like this: { 'view': { 'query': u 'SELECT deleted_mod_time FROM [2014_05_31_transformed.Video]' }, 'tableReference': { 'datasetId': 'latest_transformed', 'tableId': u 'Video', 'projectId': 'redacted' } } But, the BigQuery API is returning this error: HttpError: https://www.googleapis.com/bigquery/v2/projects/124072386181/datasets/latest_transformed/tables?alt=json returned "Invalid field name "deleted_mod_time.usec". Fields must contain only letters, numbers, and underscores, start with a letter or underscore, and be at most 128 characters long." The schema that the BigQuery API does not make any distinction between a TIMESTAMP data type and a regular nullable INTEGER data type, so I can't think of a way to programmatically correct this problem. Is there anything I can do, or is this a bug with BigQuery's view implementation?

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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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• 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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• 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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• Implementing an interface with interface members

  - by jstark

  What is the proper way to implement an interface that has its own interface members? (am I saying that correctly?) Here's what I mean: public Interface IFoo { string Forty { get; set; } string Two { get; set; } } public Interface IBar { // other stuff... IFoo Answer { get; set; } } public class Foo : IFoo { public string Forty { get; set; } public string Two { get; set; } } public class Bar : IBar { // other stuff public Foo Answer { get; set; } //why doesnt' this work? } I've gotten around my problem using explicit interface implementation, but I'm wondering if there is a better way?

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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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• 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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• Use delegate for Projection in Linq to SQL

  - by Redeemed1

  I have code something like this in an IRepository implementation in Linq to Sql: var newlist = from h in list where h.StringProp1 == "1" select new MyBusinessBO{ firstProp = h.StringProp1, secondProp = h.StringProp2 }; The projection into MyBusinessBO is not difificult but when the Business Object has many properties the projection code becomes very lengthy. Also, as the projection can occur in several places in the Repository we break the DRY principle. Is there any way to abstract out the projection or replace it with a delegate? I.e. replace the code firstProp = h.StringProp1, secondProp = h.StringProp2 with something reusable?

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• Using read() directly into a C++ std:vector

  - by Joe

  I'm wrapping up user space linux socket functionality in some C++ for an embedded system (yes, this is probably reinventing the wheel again). I want to offer a read and write implementation using a vector. Doing the write is pretty easy, I can just pass &myvec[0] and avoid unnecessary copying. I'd like to do the same and read directly into a vector, rather than reading into a char buffer then copying all that into a newly created vector. Now, I know how much data I want to read, and I can allocate appropriately (vec.reserve). I can also read into &myvec[0], though this is probably a VERY BAD IDEA. Obviously doing this doesn't allow myvec.size to return anything sensible. Is there any way of doing this that 1) Doesn't completely feel yucky from a safety/C++ perspective and 2) Doesn't involve two copies of the data block - once from kernel to user space and once from a C char * style buffer into a C++ vector. Any thoughts collective?

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