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  • How do laziness and I/O work together in Haskell?

    - by Bill
    I'm trying to get a deeper understanding of laziness in Haskell. I was imagining the following snippet today: data Image = Image { name :: String, pixels :: String } image :: String -> IO Image image path = Image path <$> readFile path The appeal here is that I could simply create an Image instance and pass it around; if I need the image data it would be read lazily - if not, the time and memory cost of reading the file would be avoided: main = do image <- image "file" putStrLn $ length $ pixels image But is that how it actually works? How is laziness compatible with IO? Will readFile be called regardless of whether I access pixels image or will the runtime leave that thunk unevaluated if I never refer to it? If the image is indeed read lazily, then isn't it possible I/O actions could occur out of order? For example, what if immediately after calling image I delete the file? Now the putStrLn call will find nothing when it tries to read.

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  • What is the best way to manage one's session variables?

    - by donde
    In my .NET web app, I keep basic user info in a user session object. I also usually keep a director class in the session; which is basically just has info about whatever thing it being worked on on that screen (like a customer id). I am trying to keep from adding a ton of sessions. I also want to make sure at any given time ONLY the sessions that are necessary are in memory. This means I need an effective way of managing my session variables. Any suggestions?

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  • How to create a custom ADO Multi Dimensional Catalog with no database

    - by Alan Clark
    Does anyone know of an example of how to dynamically define and build ADO MD (ActiveX Data Objects Multidimensional) catalogs and cube definitions with a set of data other than a database? Background: we have a huge amount of data in our application that we export to a database and then query using the usual SQL joins, groups, sums etc to produce reports. The data in the application is originally in objects and arrays. The problem is the amount of data is so large the export can take 2 hours. So I am trying to figure out a good way of querying the objects in memory, either by a custom OLAP algorithm or library, or ADO MD. But I haven't been able to find an example of using ADO MD without a database behind it. We are using Delphi 2010 so would use ADO ActiveX but I imagine the ADO.NET MD is similar. I realize that if the application data was already stored in a database the problem would solve itself. Also if Delphi had LINQ capability I could query the objects and arrays that way.

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  • A cross between std::multimap and std::vector?

    - by Milan Babuškov
    I'm looking for a STL container that works like std::multimap, but has constant access time to random n-th element. I need this because I have such structure in memory that is std::multimap for many reasons, but items stored in it have to be presented to the user in a listbox. Since amount of data is huge, I'm using list box with virtual items (i.e. list control polls for value at line X). As a workaround I'm currently using additional std::vector to store "indexes" into std::map, and I fill it like this: std::vector<MMap::data_type&> vec; for (MMap::iterator it = mmap.begin(); it != mmap.end(); ++it) vec.push_back((*it).second); But this is not very elegant solution. Is there some such containter?

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  • How to serialize a collection of base type and see the concrete types in easy to read XML

    - by Jason Coyne
    I have a List which is populated with objects of various concrete types which subclass BaseType I am using the WCF DataContractSerializer <Children> <BaseType xmlns:d3p1="http://schemas.datacontract.org/2004/07/Tasks" i:type="d3p1:ConcreteTypeA"></BaseType> <BaseType xmlns:d3p1="http://schemas.datacontract.org/2004/07/Tasks" i:type="d3p1:ConcreteTypeB"></BaseType> </Children> Is there any way to get this to generate <Children> <ConcreteTypeA/> <ConcreteTypeB/> </Children> ? The real goal is to let users generate some XML to load into memory, and the users are of a skill level that asking them for the original XML is not going to be successful.

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  • How can I get this code involving unique_ptr to compile?!

    - by Neil G
    #include <vector> #include <memory> using namespace std; class A { public: A(): i(new int) {} A(A const& a) = delete; A(A &&a): i(move(a.i)) {} unique_ptr<int> i; }; class AGroup { public: void AddA(A &&a) { a_.emplace_back(move(a)); } vector<A> a_; }; int main() { AGroup ag; ag.AddA(A()); return 0; } does not compile... (says that unique_ptr's copy constructor is deleted) I tried replacing move with forward. Not sure if I did it right, but it didn't work for me.

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  • Java OutOfMemoryError strange behaviour

    - by Evgeniy Dorofeev
    Assuming we have a max memory of 256M, why does this code work: public static void main(String... args) { for (int i = 0; i < 2; i++) { byte[] a1 = new byte[150000000]; } byte[] a2 = new byte[150000000]; } but this one throw an OOME? public static void main(String... args) { //for (int i = 0; i < 2; i++) { byte[] a1 = new byte[150000000]; } byte[] a2 = new byte[150000000]; }

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  • C++ Static array vs. Dynamic array?

    - by user69514
    What is the difference between a static array and a dynamic array in C++? I have to do an assignment for my class and it says not to use static arrays, only dynamic arrays. I've looked in the book and online, but I don't seem to understand. I thought static was created at compile time and dynamic at runtime, but I might be mistaken this with memory allocation. Can you explain to me the difference between static array and dynamic array in C++? Thnaks.

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  • SQL CE not loading from network share

    - by David Veeneman
    I installed VS 2010 RC yesterday, and suddenly, SQL Server CE isn't loading files from a network share. In projects compiled with VS 2008, if I try to open a SQL CE file located on a network share, I get an error that reads like this: Internal error: Cannot open the shared memory region. If I try to create a data connection in VS 2010 to a SQL CE file on a network share, I get this error: SQL Server Compact does not support opening database files on a network share. Can anyone shed any light on what's going on? Thanks.

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  • How does a virtual machine work?

    - by Martin
    I've been looking into how programming languages work, and some of them have a so-called virtual machines. I understand that this is some form of emulation of the programming language within another programming language, and that it works like how a compiled language would be executed, with a stack. Did I get that right? With the proviso that I did, what bamboozles me is that many non-compiled languages allow variables with "liberal" type systems. In Python for example, I can write this: x = "Hello world!" x = 2**1000 Strings and big integers are completely unrelated and occupy different amounts of space in memory, so how can this code even be represented in a stack-based environment? What exactly happens here? Is x pointed to a new place on the stack and the old string data left unreferenced? Do these languages not use a stack? If not, how do they represent variables internally?

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  • BigDecimal precision not persisted with javax.persistence annotations

    - by dkaczynski
    I am using the javax.persistence API and Hibernate to create annotations and persist entities and their attributes in an Oracle 11g Express database. I have the following attribute in an entity: @Column(precision = 12, scale = 9) private BigDecimal weightedScore; The goal is to persist a decimal value with a maximum of 12 digits and a maximum of 9 of those digits to the right of the decimal place. After calculating the weightedScore, the result is 0.1234, but once I commit the entity with the Oracle database, the value displays as 0.12. I can see this by either by using an EntityManager object to query the entry or by viewing it directly in the Oracle Application Express (Apex) interface in a web browser. How should I annotate my BigDecimal attribute so that the precision is persisted correctly? Note: We use an in-memory HSQL database to run our unit tests, and it does not experience the issue with the lack of precision, with or without the @Column annotation.

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  • ASP.Net Web Site Project vs. Web Application Project

    - by user144612
    I'm trying to convince my co-workers to switch from a web site project to a web application project, because I want the use of the project file. However I can't diffuse this argument against: The web site project allows each page to be compiled into a single dll. Their argument is this enables easy fixing of errors found after publishing. This is contrast to how the web application project compiles all code behind into a single dll. Is updating a single page's dll essentially different to updating the entire site's dll? Is there some way to compile each page's code behind into a seperate dll in the web application project? Are there some prohibitive (performance,memory?) costs to compiling each page's code behind into seperate dll's that we are unaware of? Why is the feature(?) to compile each page to separate dlls in web site projects and not web app projects?

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  • VC7.1 C1204 internal compiler error

    - by Nathan Ernst
    I'm working on modifying Firaxis' Civilization 4 core game DLL. The host application is built using VC7, hence the constraint (source not provided for the host EXE). I've been working on rewriting a large chunk of the code (focusing on low-hanging performance issues & memory leaks). I recently ran into an internal compiler error when trying to mod the code to use an array class instead of dynamically allocated 2-d arrays, I was going to use matrices from the boost lib (Civ4 is already using boost, so why not?). Basically, the issue comes down to: if I include "boost/numeric/ublas/matrix.hpp", I run into an internal compiler error C1204. MSDN has this to say: MSDN C1204 KB has this to say: KB 883655 So, I'm curious, is it possible to solve this error without a KB/SP being applied and dramatically reducing the complexity of the code? Additionally, as VC7 is no longer "supported", does anyone have a valid (supported) link for a VC7 service pack?

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  • Inserting Large volume of data in SQL Server 2005

    - by Manjoor
    We have a application (written in c#) to store live stock market price in the database (SQL Server 2005). It insert about 1 Million record in a single day. Now we are adding some more segment of market into it and the no of records would be double (2 Millions/day). Currently the average record insertion per second is about 50, maximum is 450 and minimum is 0. To check certain conditions i have used service broker (asynchronous trigger) on my price table. It is running fine at this time(about 35% CPU utilization). Now i am planning to create a in memory dataset of current stock price. we would like to do some simple calculations. I want to know different views of members on this. Please provide your way of dealing with such situation.

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  • Scala Programming for Android

    - by Lemmy
    I have followed the tutorial at Scala and Android with Scala 2.7.3 final. The resulting Android App works but even the most basic application takes several minutes (!) to compile and needs 900 kb compressed, which is a show stopper for mobile applications. Additionally, the IDE runs out of memory every now and then. I assume dex is not made for big libraries like the scala-library. So my question is: Has anyone actually done this and is there any cure for this?

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  • Vertical Scroll not working, are the guides but the screen does not scroll.

    - by Leandro
    package com.lcardenas.infoberry; import net.rim.device.api.system.DeviceInfo; import net.rim.device.api.system.GPRSInfo; import net.rim.device.api.system.Memory; import net.rim.device.api.ui.MenuItem; import net.rim.device.api.ui.component.Dialog; import net.rim.device.api.ui.component.LabelField; import net.rim.device.api.ui.component.Menu; import net.rim.device.api.ui.component.SeparatorField; import net.rim.device.api.ui.container.MainScreen; import net.rim.device.api.ui.container.VerticalFieldManager; import net.rim.device.api.ui.decor.Background; import net.rim.device.api.ui.decor.BackgroundFactory; public class vtnprincipal extends MainScreen { //llamamos a la clase principal private InfoBerry padre; //variables para el menu private MenuItem mnubateria; private MenuItem mnuestado; private MenuItem mnuacerca; public vtnprincipal(InfoBerry padre) { super(); this.padre = padre; } public void incventana(){ VerticalFieldManager _ventana = new VerticalFieldManager(VerticalFieldManager.VERTICAL_SCROLL | VerticalFieldManager.VERTICAL_SCROLLBAR); double tmemoria =((DeviceInfo.getTotalFlashSize()/1024)/1024.00); double fmemoria = ((Memory.getFlashFree()/1024)/1024.00); Background cyan = BackgroundFactory.createSolidBackground(0x00E0FFFF); Background gris = BackgroundFactory.createSolidBackground(0x00DCDCDC ); //Borramos todos de la pantalla this.deleteAll(); //llamamos al menu incMenu(); //DIBUJAMOS LA VENTANA try{ LabelField title = new LabelField("Info Berry", LabelField.FIELD_HCENTER | LabelField.USE_ALL_HEIGHT ); setTitle(title); _ventana.add(new LabelField("Información del Dispositivo", LabelField.FIELD_HCENTER |LabelField.RIGHT | LabelField.USE_ALL_HEIGHT | LabelField.NON_FOCUSABLE )); _ventana.add(new SeparatorField()); _ventana.add(new SeparatorField()); txthorizontal modelo = new txthorizontal("Modelo:", DeviceInfo.getDeviceName()); modelo.setBackground(gris); _ventana.add(modelo); txthorizontal pin = new txthorizontal("PIN:" , Integer.toHexString(DeviceInfo.getDeviceId()).toUpperCase()); pin.setBackground(cyan); _ventana.add(pin); txthorizontal imeid = new txthorizontal("IMEID:" , GPRSInfo.imeiToString(GPRSInfo.getIMEI())); imeid.setBackground(gris); _ventana.add(imeid); txthorizontal version= new txthorizontal("SO Versión:" , DeviceInfo.getSoftwareVersion()); version.setBackground(cyan); _ventana.add(version); txthorizontal plataforma= new txthorizontal("SO Plataforma:" , DeviceInfo.getPlatformVersion()); plataforma.setBackground(gris); _ventana.add(plataforma); txthorizontal numero= new txthorizontal("Numero Telefonico: " , "Hay que firmar"); numero.setBackground(cyan); _ventana.add(numero); _ventana.add(new SeparatorField()); _ventana.add(new SeparatorField()); _ventana.add(new LabelField("Memoria", LabelField.FIELD_HCENTER | LabelField.USE_ALL_HEIGHT | LabelField.NON_FOCUSABLE)); _ventana.add(new SeparatorField()); txthorizontal totalm= new txthorizontal("Memoria app Total:" , mmemoria(tmemoria) + " Mb"); totalm.setBackground(gris); _ventana.add(totalm); txthorizontal disponiblem= new txthorizontal("Memoria app Disponible:" , mmemoria(fmemoria) + " Mb"); disponiblem.setBackground(cyan); _ventana.add(disponiblem); ///txthorizontal estadoram = new txthorizontal("Memoria RAM:" , mmemoria(prueba) + " Mb"); //estadoram.setBackground(gris); //add(estadoram); _ventana.add(new SeparatorField()); _ventana.add(new SeparatorField()); this.add(_ventana); }catch(Exception e){ Dialog.alert("Excepción en clase vtnprincipal: " + e.toString()); } } //DIBUJAMOS EL MENU private void incMenu() { MenuItem.separator(30); mnubateria = new MenuItem("Bateria",40, 10) { public void run() { bateria(); } }; mnuestado = new MenuItem("Estado de Red", 50, 10) { public void run() { estado(); } }; mnuacerca = new MenuItem("Acerca de..", 60, 10) { public void run() { acerca(); } }; MenuItem.separator(70); }; // public void makeMenu(Menu menu, int instance) { if (!menu.isDisplayed()) { menu.deleteAll(); menu.add(MenuItem.separator(30)); menu.add(mnubateria); menu.add(mnuestado); menu.add(mnuacerca); menu.add(MenuItem.separator(60)); } } public void bateria(){ padre.vtnbateria.incventana(); padre.pushScreen(padre.vtnbateria); } public void estado(){ padre.vtnestado.incventana(); padre.pushScreen(padre.vtnestado); } public void acerca(){ padre.vtnacerca.incventana(); padre.pushScreen(padre.vtnacerca); } public boolean onClose(){ Dialog.alert("Hasta Luego"); System.exit(0); return true; } public double mmemoria(double x) { if ( x > 0 ) return Math.floor(x * 100) / 100; else return Math.ceil(x * 100) / 100; } }

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  • HTTP status code for "success with errors"?

    - by Richard Levasseur
    I've poked around a bit, but I don't see an HTTP status code for when a request's succeeds, but there is an error after the "point of no return". e.g., Say you process a request, its committed to the database, but while returning the result you run of memory, or encounter a NPE, or what have you. It would have been a 200 response, but now, internally, you aren't able to return the proper, well-formed response. 202 Accepted doesn't seem to fit since we've already processed the request. What status code means "Success, but errors"? Does one even exist?

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  • DDMS Not Showing Threads From Device

    - by polyclef
    I'd like to check for memory leaks in my Android app using the DDMS feature in Eclipse. When I launch an emulated device, the threads display properly for the emulated device, starting with 8600 and up. However, when I connect my Droid to the PC, the device shows up just fine in DDMS. The logcat is generated correctly, and I can view the file structure. However, threads do not display. I get "no client selected" in the Threads pane, and there is no drop-down icon next to the device listing. Do I need to change some particular setting in Eclipse? Is this maybe a driver issue?

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  • How to find all Classes implemeting IDisposable?

    - by apoorv020
    I am working on a large project, and one of my tasks is to remove possible memory leaks. In my code, I have noticed several IDisposable items not being disposed of, and have fixed that. However, that leads me to a more basic question, how do I find all classes used in my project that implement IDisposable? (Not custom created classes by normal Library classes). I have already found one less-than-obvious class that implements IDisposable ( DataTable implements MarshalByValueComponent, which inherits IDisposable). Right now, I am manually checking any suspected classes by using MSDN, but isn't there some way through which I can automate this process?

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  • Infix to Postfix and unary/binary operators

    - by Jaapjan
    I have a piece of code that converts an infix expression to an expression tree in memory. This works just fine. There's just one small trouble. I just connect work out how to involve the unary operators correctly (the right associative ones). With the following infix expression : +1 + +2 - -3 - -4 I would expect an RPN of: 1+2++3-4-- Yet, none of the online infix-post converters I can find handle this example in the way I would expect. Does anyone have a clear explanation of handling right associative operators, specifically the binary ones that can be mistaken for the unary ones?

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  • C++ Win32 Unhandled Exception Handler

    - by uray
    currently I used SetUnhandledExceptionFilter() to provide callback to get information when an unhandled exception was occurred, that callback will provides me with EXCEPTION_RECORD which provides ExceptionAddress. [1]what is actually ExceptionAddress is? does it the address of function / code that gives exception, or the memory address that some function tried to access? [2]is there any better mechanism that could give me better information when unhandled exception occured? (I can't use debug mode or add any code that affect runtime performance, since crash is rare and only on release build when code run as fast as possible) [3]is there any way for me to get several callstack address when unhandled exception occured. [4]suppose ExceptionAddress has address A, and I have DLL X loaded and executed at base address A-x, and some other DLL Y at A+y, is it good to assume that crash was PROBABLY caused by code on DLL X?

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  • What are the pros and cons of using an in memeory DB rather than a ThreadLocal

    - by Pangea
    we have been using ThreadLocal so far to carry some data so as to not clutter the API. However below are some of issues of using thread local that which I dont like 1) over the years the data items being carried in thread local has increased 2) Since we started using threads (for some light weight processing), we have also migrating these data to the threads in the pool and copying them back again I am thinking of using an in memory DB for these (we doesnt want to add this to the API). I wondering if this approach is good. What r the pros and cons. thx in advance.

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  • Help with parsing lxml

    - by Casey
    Hi To implement a college project, I need to handle XML files. For this I choose lxml after doing some research. However I can't seem to find some nice tutorial to help me get started. I can't choose most specifically which type of parsing I need to use. My XML files don't have that much data but speed is main concern, not memory. Can anyone point me to some tutorial that would help me or some book that I can lookup? I have already tried the tutorial on lxml site but that didn't help me much. Is there some small application I can look up to get a hang of parsing XML with lxml

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  • Compiling my own PHP extension on Windows with Visual Studio 2008

    - by Mickey Shine
    I wrote a PHP extension and it could be compiled and run under linux successfully. But on windows, I met some problems. I did the compiling on windows according to http://blog.slickedit.com/?p=128 with PHP source version 5.2.10, and after the compiling it generated the dll file. But when I tried to use the dll file, it reported me the memory problems when starting Apache(Wamp server). And then I started the debugging process, it seemed that REGISTER_INI_ENTRIES() had problems. Here is the PHP extension source code, http://www.bluefly.cn/xsplit.tar.gz , and it works fine on Linux. But I also want to make it work on Windows. Sorry I am not a pro so that I hope someone can help me. Any help is appreciated and thanks in advance~

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  • Are these tables too big for SQL Server or Oracle

    - by Jeffrey Cameron
    Hey all, I'm not much of a database guru so I would like some advice. Background We have 4 tables that are currently stored in Sybase IQ. We don't currently have any choice over this, we're basically stuck with what someone else decided for us. Sybase IQ is a column-oriented database that is perfect for a data warehouse. Unfortunately, my project needs to do a lot of transactional updating (we're more of an operational database) so I'm looking for more mainstream alternatives. Question Given these tables' dimensions, would anyone consider SQL Server or Oracle to be a viable alternative? Table 1 : 172 columns * 32 million rows Table 2 : 453 columns * 7 million rows Table 3 : 112 columns * 13 million rows Table 4 : 147 columns * 2.5 million rows Given the size of data what are the things I should be concerned about in terms of database choice, server configuration, memory, platform, etc.?

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