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• Haskell: Pattern Matching with Lists

  - by user1670032

  I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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• java methods and race condition in a jsp/servlets application.

  - by A.S al-shammari

  Hi. Suppose that I have a method called doSomething() and I want to use this method in a multithreaded application (each servlet inherits from HttpServlet).I'm wondering if it is possible that a race condition will occur in the following cases: doSomething() is not staic method and it writes values to a database. doSomething() is static method but it does not write values to a database. what I have noticed that many methods in my application may lead to a race condition or dirty read/write. for example , I have a Poll System , and for each voting operation, a certain method will change a single cell value for that poll as the following: [poll_id | poll_data ] [1 | {choice_1 : 10, choice_2 : 20}] will the JSP/Servlets app solve these issues by itself, or I have to solve all that by myself? Thanks..

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• Using Apache Velocity with StringBuilders/CharSequences

  - by mindas

  We are using Apache Velocity for dynamic templates. At the moment Velocity has following methods for evaluation/replacing: public static boolean evaluate(Context context, Writer writer, String logTag, Reader reader) public static boolean evaluate(Context context, Writer out, String logTag, String instring) We use these methods by providing StringWriter to write evaluation results. Our incoming data is coming in StringBuilder format so we use StringBuilder.toString and feed it as instring. The problem is that our templates are fairly large (can be megabytes, tens of Ms on rare cases), replacements occur very frequently and each replacement operation triples the amount of required memory (incoming data + StringBuilder.toString() which creates a new copy + outgoing data). I was wondering if there is a way to improve this. E.g. if I could find a way to provide a Reader and Writer on top of same StringBuilder instance that only uses extra memory for in/out differences, would that be a good approach? Has anybody done anything similar and could share any source for such a class? Or maybe there any better solutions to given problem?

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• What are the advantages of learning Go?

  - by Pangea

  What is so unique about Go? Over the 11 years of my career I've learnt Pascal, C, C++, COBOL and then Java. I always felt that going from C to C++ to Java was a incremental and value added progression. Now I see a proliferation of functional programming languages and I understand the benefit of learning few of them (like actors in scala etc). Now I was going through the Go programming language and was wondering why would I want to learn this? Is this going to simplify how I have been writing the code? What are its use cases? How can I make a case to promote it in my team? What is the next programming language that a Java team that builds business applications like us can benefit from? Appreciate your comments on this.

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• Using Property Builtin with GAE Datastore's Model

  - by ejel

  I want to make attributes of GAE Model properties. The reason is for cases like to turn the value into uppercase before storing it. For a plain Python class, I would do something like: Foo(db.Model): def get_attr(self): return self.something def set_attr(self, value): self.something = value.upper() if value != None else None attr = property(get_attr, set_attr) However, GAE Datastore have their own concept of Property class, I looked into the documentation and it seems that I could override get_value_for_datastore(model_instance) to achieve my goal. Nevertheless, I don't know what model_instance is and how to extract the corresponding field from it. Is overriding GAE Property classes the right way to provides getter/setter-like functionality? If so, how to do it? Added: One potential issue of overriding get_value_for_datastore that I think of is it might not get called before the object was put into datastore. Hence getting the attribute before storing the object would yield an incorrect value.

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• How To Discover RSS Feeds for a given site.

  - by ktolis

  The quest is, given a site url (say http://stackoverflow.com/ ) to return the list of all the feeds available on the site. Methods acceptable: a) use a 3rd party service (google?, yahoo?, ...) programmatically b) using a crawler/spider (and some tips on how to configure the spider to return the rss/xml feeds only) c) programmatically using c/c++/php (any language/library) The task here is not to get the feeds contained on the page returned by the url but ALL the feeds that are available on the server at any depth... in any cases please provide a simple usage example.

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• Splitting a double vector into equal parts

  - by Cosmin

  Greetings, Any input on a way to divide a std::vector into two equal parts ? I need to find the smallest possible difference between |part1 - part2|. This is how I'm doing it now, but from what you can probably tell it will yield a non-optimal split in some cases. auto mid = std::find_if(prim, ultim, [&](double temp) -> bool { if(tempsum >= sum) return true; tempsum += temp; sum -= temp; return false; }); The vector is sorted, highest to lowest, values can indeed appear twice. I'm not expecting part1 and part2 to have the same numbers of elements, but sum(part1) should be as close as possible to sum(part2) For example if we would have { 2.4, 0.12, 1.26, 0.51, 0.70 }, the best split would be { 2.4, 0.12 } and { 1.26, 0.51, 0.70 }. If it helps, I'm trying to achieve the splitting algorithm for the Shannon Fano encoding. Any input is appreciated, thanks!

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• Javascript function as a parameter to another function?

  - by Alex

  Hello there, I'm learning lots of javascript these days, and one of the things I'm not quite understanding is passing functions as parameters to other functions. I get the concept of doing such things, but I myself can't come up with any situations where this would be ideal? My question is: When do you want to have your javascript functions take another function as a parameter? Why not just assign a variable to that functions return value and pass that variable to the function like so: // Why not do this var foo = doStuff(params); callerFunction(foo); //instead of this callerFunction(doStuff); I'm confused as to why I would ever choose to do things as in my second example. Why would you do this? What are the use cases? Thanks!!

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• Efficient synchronization of querying an array of resources

  - by Erel Segal Halevi

  There is a list of N resources, each of them can be queried by at most a single thread at a time. There are serveral threads that need to do the same thing at approximately the same time: query each of the resources (each thread has a different query), in arbitrary order, and collect the responses. If each thread loops over the resources in the same order, from 0 to N-1, then they will probably have to wait for each other, which is not efficient. I thought of letting the threads loop over the resources in a random permutation, but this seems too complex and also not so efficient, for example, for 2 resources and 2 threads, in half the cases they will choose the same order and wait for each other. Is there a simple and more efficient way to solve this?

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• FieldError when annotating over foreign keys

  - by X_9

  I have a models file that looks similar to the following: class WithDate(models.Model): adddedDate = models.DateTimeField(auto_now_add=True) modifiedDate = models.DateTimeField(auto_now=True) class Meta: abstract = True class Match(WithDate): ... class Notify(WithDate): matchId = models.ForeignKey(Match) headline = models.CharField(null=True, blank=True, max_length=10) For each Match I'm trying to get a count of notify records that have a headline. So my call looks like matchObjs = Match.objects.annotate(notifies_made=Count('notify__headline__isnull')) This keeps throwing a FieldError. I've simplified the query down to matchObjs = Match.objects.annotate(notifies_made=Count('notify')) And I still get the same FieldError... I've seen this work in other cases (other documentation, other SO questions like this one) but I can't figure out why I'm getting an error. The specific error that is returned is as follows: Cannot resolve keyword 'notify' into field. Choices are: (all fields from Match model) Does anyone have a clue as to why I can't get this annotation to work across tables? I'm baffled after looking at the other SO question and various Django docs where I've seen this done. Edit: I am using Django 1.1.1

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• VendInvoiceJour.InvoiceAccount <- VendTable.AccountNum relation

  - by vukis

  Hi. I have following situation: I need to join VendInvoiceJour.InvoiceAccount <- VendTable.AccountNum and take VendTable.Vendgroup. In all cases (queries,or even views) Dynamics ax joins tables VendInvoiceJour.OrderAccount<- VendTable.AccountNum not VendInvoiceJour.InvoiceAccount <- VendTable.AccountNum. I`m trying to use this kind of query: qBdSVendJour = element.query().dataSourceTable(tablenum(VendInvoiceJour)); qBdSVendTbl = qBdSVendJour.addDataSource(tablenum(VendTable)); qBdSVendTbl.relations(true); qBdSVendTbl.joinMode(JoinMOde::InnerJoin); qBdSVendTbl.fetchMode(QueryFetchMode::One2One); qBdSVendTbl.addLink(FieldNum(VendInvoiceJour,InvoiceAccount),FieldNum(VendTable,AccountNum));//(Dynamics ax automaticaly corrects InvoiceAccount to orderaccount in reports if trying this link in morphx)

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• Flex: How can I use the @ContextRoot in a Button or LinkButton

  - by Dave Meurer

  I'm trying to create a button that will simply link back to the context root. I noticed flex has a @ContextRoot attribute that appears to work only in certain cases. For example, if I try to use it in the following mxml: <mx:Button label="Back to Root" click="navigateToURL(new URLRequest(@ContextRoot()), '_parent')"/> I get the following error: Error: Attributes are not callable. I can't seem to find this technique explained anywhere, is there another way? Thanks for the help! Dave

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• Running GUI application in the Windows service mode

  - by Leonid

  I'm writing a server running as a Windows service that by request invokes Firefox to generate a pdf snapshot of a webpage. I know it is a bad idea to run a GUI program in service mode, but the server nature of my program restricts from running it in the user mode. Running a user-level 'proxy' also is not an option, since there might be no interactive user logged-in on the machine with the server running. In my experiments Firefox successfully produced pdf when the service was running under a user account that was already logged-in. Obviously it didn't work in other cases: for Local System and user accounts that weren't logged-in. Under LocalSystem with 'Allow service to interact with desktop' option enabled I could see the Firefox started that reports that it's unable to find a printer. Since it wouldn't be practical to require an opened user session for the pdf server to run, is there any workaround for this except running the whole thing from a virtual machine?

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• JUnit4 + Eclipse "An internal error occured during Launching"

  - by Mike

  Hello I'm trying to run JUnit4 test cases on Eclipse 3.4.2 but it's not even starting for me. I am sure that I properly have junit-4.7.jar in my build path and the test application. Here is a simple example that illustrates my problem package test; import org.junit.Before; import org.junit.Test; public class UTest { @Test public void test() { } @Before public void setUp() throws Exception { } } This compiles fine Then I do "Run JUnit Test case" from Eclipse and I get an error dialog with this message "Launching UTest' has encountered a problem An internal error occurred during: "Launching UTest". java.lang.NullPointerException I'm not sure how to figure out what exactly generating this NullPointerException. Some pointers would be appreciated

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• Source control Branching needs

  - by Mükremin

  Hello, we are creating hospital information system software. The project will be different hospital to hospital and contain different use cases. But lots of parts will be the same. So we will use branching mechanism of the source control. If we find a bug in one hospital, how can we know the other branches have the same bug or not. Resim The numbers in the picture which we attached show the each hospital software. Do you have a solution about this problem ? Which source control(SVN,Git,Hg) we will be suitable about this problem ? Thank you.!

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• No-overflow cast on x64

  - by Cheeso

  I have an existing C codebase that works on x86. I'm now compiling it for x64. What I'd like to do is cast a size_t to a DWORD, and throw an exception if there's a loss of data. Q: Is there an idiom for this? Here's why I'm doing this: A bunch of Windows APIs accept DWORDs as arguments, and the code currently assumes sizeof(DWORD)==sizeof(size_t). That assumption holds for x86, but not for x64. So when compiling for x64, passing size_t in place of a DWORD argument, generates a compile-time warning. In virtually all of these cases the actual size is not going to exceed 2^32. But I want to code it defensively and explicitly. This is my first x64 project, so... be gentle.

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• Can't declare unused exception variable when using catch-all pattern

  - by b0x0rz

  what is a best practice in cases such as this one: try { // do something } catch (SpecificException ex) { Response.Redirect("~/InformUserAboutAn/InternalException/"); } the warning i get is that ex is never used. however all i need here is to inform the user, so i don't have a need for it. do i just do: try { // do something } catch { Response.Redirect("~/InformUserAboutAn/InternalException/"); } somehow i don't like that, seems strange!!? any tips? best practices? what would be the way to handle this. thnx

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• just-in-time list

  - by intuited

  I'd like to know if there is a class available, either in the standard library or in pypi, that fits this description. The constructor would take an iterator. It would implement the container protocol (ie _getitem_, _len_, etc), so that slices, length, etc., would work. In doing so, it would iterate and retain just enough values from its constructor argument to provide whatever information was requested. So if jitlist[6] was requested, it would call self.source.next() 7 times, save those elements in its list, and return the last one. This would allow downstream code to use it as a list, but avoid unnecessarily instantiating a list for cases where list functionality was not needed, and avoid allocating memory for the entire list if only a few members ended up being requested. It seems like a pretty easy one to write, but it also seems useful enough that it's likely that someone would have already made it available in a module.

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• Unicode data from NSData to NSString

  - by Jeff

  So if I have NSData from an HTTP request, then I do something like this: NSString *test = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; This will result in null if the data contains weird unicode data (title is from reddit): {"title":"click..¦¦me..and..then¦¦________ ¦¦check¦¦_.your...¦¦.__...¦¦____ ¦¦....¦¦¦¦¦¦¦¦¦¦¦¦¦¦....¦¦____ ¦¦¦¦¦¦....¦¦¦¦¦¦....¦¦¦¦¦¦____ ¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦____ ....¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦¦______ ........¦¦..._recently....¦¦________ ....¦¦....viewed....links....¦¦_____"}, How would I convert the data to a string? Ideally, it would best if the string wasn't null so I could parse it as JSON, but even a lossy conversion is fine with me in these cases. I'm not familiar with unicode (naive American I am), so any enlightenment about that would be a nice bonus :)

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• Django finding which field matched in a multiple OR query

  - by Greg Hinch

  I've got a couple models which are set up something like this: class Bar(models.Model): baz = models.CharField() class Foo(models.Model): bar1 = models.ForeignKey(Bar) bar2 = models.ForeignKey(Bar) bar3 = models.ForeignKey(Bar) And elsewhere in the code, I end up with an instance of Bar, and need to find the Foo it is attached to in some capacity. Right now I came up with doing a multiple OR query using Q, something like this: foo_inst = Foo.objects.get(Q(bar1=bar_inst) | Q(bar2=bar_inst) | Q(bar3=bar_inst)) What I need to figure out is, which of the 3 cases actually hit, at least the name of the member (bar1, bar2, or bar3). Is there a good way to do this? Is there a better way to structure the query to glean that information?

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• WPF - How do I style a row based on a binding property value?

  - by Nick

  Hey! So I am trying to bind a collection of objects (IList<) to a WPF datagrid. I would like to make the row background a different color if the 'artist' property is null or empty. I am checking the value stored at the property on the LoadingRow datagrid event. Currently my implementation seems to style all of the rows with an empty or null 'artist' property correctly. The problem is that is also styles the rows where the property is not null or empty in some cases. So some rows are given the red background even though the rows 'artist' property is not null. Can anyone tell me why this could be?? Here is the LoadingRow event: private void trackGrid_LoadingRow(object sender, DataGridRowEventArgs e) { Track t = e.Row.DataContext as Track; if (String.IsNullOrEmpty(t.Artist)) { e.Row.Background = new System.Windows.Media.SolidColorBrush(System.Windows.Media.Color.FromArgb(255, 255, 125, 125)); } }

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• problem when opening new window in asp.net application, new window didnt show anything

  - by Ashian

  Hello I have an asp.net application which I used some Ajax method. in some cases I open an new window ( Full Screen ) and users must work on it. the problem is , some users report me that some times new window was blank and didnt show any content , in status bar just write connecting .... and nothing else. Just when customers closed all opening browser and open again , they can view pages. this happend when users work for a while and click open new window links before the page loaded compeletly. how can I fix this problem? regards

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• Where would async calls make sense in an ASP.net (MVC) Web Application?

  - by Michael Stum

  I'm just wondering, if I have an ASP.net Web Application, either WebForms or MVC, is there any situation where doing stuff asynchronously would make sense? The Web Server already handles threading for me in that it spins up multiple threads to handle requests, and most request processing is rather simple and straight forward. I see some use for when stuff truly is a) expensive and b) can be parallelized. but these are the minority cases (at least from what I've encountered). Is there any gain from async in the simple "Read some input, do some CRUD, display some output" scenario?

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• Pass errors in Django using HttpResponseRedirect

  - by JPC

  I know that HttpResponseRedirect only takes one parameter, a URL. But there are cases when I want to redirect with an error message to display. I was reading this post: How to pass information using an http redirect (in Django) and there were a lot of good suggestions. I don't really want to use a library that I don't know how works. I don't want to rely on messages which, according to the Django docs, is going to be removed. I thought about using sessions. I also like the idea of passing it in a URL, something like: return HttpResponseRedirect('/someurl/?error=1') and then having some map from error code to message. Is it good practice to have a global map-like structure which hard codes in these error messages or is there a better way? Or should I just use a session EDIT: I got it working using a session. Is that a good practice to put things like this in the session?

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• Parsing and validating arbitrary date formats in ruby (on rails)

  - by Matt Briggs

  I have a requirement to handle custom date formats in an existing app. The idea is that the users have to do with multiple formats from outside sources they have very little control over. We will need to be able to take the format and both validate Dates against it, as well as parse strings specifically in that format. The other thing is that these can be completely arbitrary, like JA == January, FE == February, etc... to my understanding, chronic only handles parsing (and does it in a more magical way then I can use), and enter code here DateTime#strptime comes close, but doesn't really handle the whole two character month scenario, even with custom formatters. The 'nuclear' option is to write in custom support for edge cases like this, but I would prefer to use a library if something like this exists.

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