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  • cons operator (::) in F#

    - by Max
    The :: operator in F# always prepends elements to the list. Is there an operator that appends to the list? I'm guessing that using @ operator [1; 2; 3] @ [4] would be less efficient, than appending one element.

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  • Haskell - Parsec Parsing <p> element

    - by Martin
    I'm using Text.ParserCombinators.Parsec and Text.XHtml to parse an input like this: This is the first paragraph example\n with two lines\n \n And this is the second paragraph\n And my output should be: <p>This is the first paragraph example\n with two lines\n</p> <p>And this is the second paragraph\n</p> I defined: line= do{ ;t<-manyTill (anyChar) newline ;return t } paragraph = do{ t<-many1 (line) ;return ( p << t ) } But it returns: <p>This is the first paragraph example\n with two lines\n\n And this is the second paragraph\n</p> What is wrong? Any ideas? Thanks!

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  • Other ternary operators besides ternary conditional (?:)

    - by Malcolm
    The "ternary operator" expression is now almost equivalent to the ternary conditional operator: condition ? trueExpression : falseExpression; However, "ternary operator" only means that it takes three arguments. I'm just curious, are there any languages with any other built-in ternary operators besides conditional operator and which ones?

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  • Support Open Source Projects via T-Shirts

    - by The MYYN
    Can we get a list of free and open source projects, which can be supported through purchasing branded garment? Free Software Foundation http://shop.fsf.org/ OpenBSD https://https.openbsd.org/cgi-bin/order Mozilla http://store.mozilla.org/ ps. I know this is extremly off-topic. But I'd like to buy clothing and support open source at the same time. And I'd like to know, where this is possible.

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  • How to access File over the Network

    - by Polo
    Hi! I am having a hard time on this one, I have a folder over the network with public access (no credential restriction). I am trying to do a File.Exist or Directory.Exist and I keep on having a exception. Can someone tell me the good way to do IO over the network. EDIT 1 FOR DETAILS: if i do execture = \agoodip\Public\test.txt I get the file etc etc In my code it look like a basic Directory.Exist(@"\\agoodip\Public") or File.exist(@"\\agoodip\Public\test.txt") The exception I get is Path not found. EDIT 2 : I am using Silverlight 3, Is there any security pattern to be aware of to lookup file on the network? Thanks!

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  • Using pointers, references, handles to generic datatypes, as generic and flexible as possible

    - by Patrick
    In my application I have lots of different data types, e.g. Car, Bicycle, Person, ... (they're actually other data types, but this is just for the example). Since I also have quite some 'generic' code in my application, and the application was originally written in C, pointers to Car, Bicycle, Person, ... are often passed as void-pointers to these generic modules, together with an identification of the type, like this: Car myCar; ShowNiceDialog ((void *)&myCar, DATATYPE_CAR); The 'ShowNiceDialog' method now uses meta-information (functions that map DATATYPE_CAR to interfaces to get the actual data out of Car) to get information of the car, based on the given data type. That way, the generic logic only has to be written once, and not every time again for every new data type. Of course, in C++ you could make this much easier by using a common root class, like this class RootClass { public: string getName() const = 0; }; class Car : public RootClass { ... }; void ShowNiceDialog (RootClass *root); The problem is that in some cases, we don't want to store the data type in a class, but in a totally different format to save memory. In some cases we have hundreds of millions of instances that we need to manage in the application, and we don't want to make a full class for every instance. Suppose we have a data type with 2 characteristics: A quantity (double, 8 bytes) A boolean (1 byte) Although we only need 9 bytes to store this information, putting it in a class means that we need at least 16 bytes (because of the padding), and with the v-pointer we possibly even need 24 bytes. For hundreds of millions of instances, every byte counts (I have a 64-bit variant of the application and in some cases it needs 6 GB of memory). The void-pointer approach has the advantage that we can almost encode anything in a void-pointer and decide how to use it if we want information from it (use it as a real pointer, as an index, ...), but at the cost of type-safety. Templated solutions don't help since the generic logic forms quite a big part of the application, and we don't want to templatize all this. Additionally, the data model can be extended at run time, which also means that templates won't help. Are there better (and type-safer) ways to handle this than a void-pointer? Any references to frameworks, whitepapers, research material regarding this?

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  • Recommended way to support backward/forward compatibility in iPhone app?

    - by MrAleGuy
    I'm in the early stages of an iPhone app and I have a question. I did some searching but did not find what I was looking for. There are features in iPhone OS4 that I would like to take advantage of, but I would like for my app to also run on 3.X. It looks like I want to develop against the 4.0 SDK and do the following: Create a "weak link" to any new (4.0) frameworks Call respondsToSelector: for any new method in an existing framework or any method in a new framework before making that call Am I close? What's recommended? Pointers to similar questions welcome.

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  • shared hacker houses in europe

    - by Mantas
    Hey, I'm a freelance web developer. I'm borred of my hometown, so I want to hit the road. Do you know any shared hacker houses in Europe? Do you have any ideas what is the best way to look for a shared flat? France, Spain, Holland, Italy... I'm interested in virtually any country :) P.S. I speak English and Lithuanian only, so it's hard to look up shared flat in local languages...

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  • Persistent (purely functional) Red-Black trees on disk performance

    - by Waneck
    I'm studying the best data structures to implement a simple open-source object temporal database, and currently I'm very fond of using Persistent Red-Black trees to do it. My main reasons for using persistent data structures is first of all to minimize the use of locks, so the database can be as parallel as possible. Also it will be easier to implement ACID transactions and even being able to abstract the database to work in parallel on a cluster of some kind. The great thing of this approach is that it makes possible implementing temporal databases almost for free. And this is something quite nice to have, specially for web and for data analysis (e.g. trends). All of this is very cool, but I'm a little suspicious about the overall performance of using a persistent data structure on disk. Even though there are some very fast disks available today, and all writes can be done asynchronously, so a response is always immediate, I don't want to build all application under a false premise, only to realize it isn't really a good way to do it. Here's my line of thought: - Since all writes are done asynchronously, and using a persistent data structure will enable not to invalidate the previous - and currently valid - structure, the write time isn't really a bottleneck. - There are some literature on structures like this that are exactly for disk usage. But it seems to me that these techniques will add more read overhead to achieve faster writes. But I think that exactly the opposite is preferable. Also many of these techniques really do end up with a multi-versioned trees, but they aren't strictly immutable, which is something very crucial to justify the persistent overhead. - I know there still will have to be some kind of locking when appending values to the database, and I also know there should be a good garbage collecting logic if not all versions are to be maintained (otherwise the file size will surely rise dramatically). Also a delta compression system could be thought about. - Of all search trees structures, I really think Red-Blacks are the most close to what I need, since they offer the least number of rotations. But there are some possible pitfalls along the way: - Asynchronous writes -could- affect applications that need the data in real time. But I don't think that is the case with web applications, most of the time. Also when real-time data is needed, another solutions could be devised, like a check-in/check-out system of specific data that will need to be worked on a more real-time manner. - Also they could lead to some commit conflicts, though I fail to think of a good example of when it could happen. Also commit conflicts can occur in normal RDBMS, if two threads are working with the same data, right? - The overhead of having an immutable interface like this will grow exponentially and everything is doomed to fail soon, so this all is a bad idea. Any thoughts? Thanks! edit: There seems to be a misunderstanding of what a persistent data structure is: http://en.wikipedia.org/wiki/Persistent_data_structure

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  • what do you do while code is compiling

    - by Jacob
    I'm looking for the best idea for what to do while code is compiling or tests are running. Typically around 5 minutes of thumb twiddling. Only so many cups of coffee can be made and drunk in a day, and I don't want to be seen always in the kitchen or bothering other people.

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  • [C#] How to consume web service adheres to the Event-based Asynchronous Pattern?

    - by codemonkie
    I am following the example from http://msdn.microsoft.com/en-us/library/8wy069k1.aspx to consume a web service implemented (by 3rd party) using the Event-based Asynchronous Pattern. However, my program needs to do multiple calls to the DoStuffAsync() hence will get back as many DoStuffCompleted. I chose the overload which takes an extra parameter - Object userState to distinguish them. My first question is: Is it valid to cast a GUID to Object as below, where GUID is used to generate unique taskID? Object userState = Guid.NewGuid(); Secondly, do I need to spawn off a new thread for each DoStuffAsync() call, since I am calling it multiple times? Also, would be nice to have some online examples or tutorials on this subject. (I've been googling for it the whole day and didn't get much back) Many thanks

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  • Parallel processing via multithreading in Java

    - by Robz
    There are certain algorithms whose running time can decrease significantly when one divides up a task and gets each part done in parallel. One of these algorithms is merge sort, where a list is divided into infinitesimally smaller parts and then recombined in a sorted order. I decided to do an experiment to test whether or not I could I increase the speed of this sort by using multiple threads. I am running the following functions in Java on a Quad-Core Dell with Windows Vista. One function (the control case) is simply recursive: // x is an array of N elements in random order public int[] mergeSort(int[] x) { if (x.length == 1) return x; // Dividing the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Sending them off to continue being divided mergeSort(a); mergeSort(b); // Recombining the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } return x; } The other is in the 'run' function of a class that extends thread, and recursively creates two new threads each time it is called: public class Merger extends Thread { int[] x; boolean finished; public Merger(int[] x) { this.x = x; } public void run() { if (x.length == 1) { finished = true; return; } // Divide the array in half int[] a = new int[x.length/2]; int[] b = new int[x.length/2+((x.length%2 == 1)?1:0)]; for(int i = 0; i < x.length/2; i++) a[i] = x[i]; for(int i = 0; i < x.length/2+((x.length%2 == 1)?1:0); i++) b[i] = x[i+x.length/2]; // Begin two threads to continue to divide the array Merger ma = new Merger(a); ma.run(); Merger mb = new Merger(b); mb.run(); // Wait for the two other threads to finish while(!ma.finished || !mb.finished) ; // Recombine the two arrays int ia = 0, ib = 0, i = 0; while(ia != a.length || ib != b.length) { if (ia == a.length) { x[i] = b[ib]; ib++; } else if (ib == b.length) { x[i] = a[ia]; ia++; } else if (a[ia] < b[ib]) { x[i] = a[ia]; ia++; } else { x[i] = b[ib]; ib++; } i++; } finished = true; } } It turns out that function that does not use multithreading actually runs faster. Why? Does the operating system and the java virtual machine not "communicate" effectively enough to place the different threads on different cores? Or am I missing something obvious?

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  • Enumerating computers in NT4 domain using WNetEnumResourceW (C++) or DirectoryEntry (C#)

    - by Kevin Davis
    I'm trying to enumerate computers in NT4 domains (not Active Directory) and support Unicode NetBIOS names. According to MSDN, WNetEnumResourceW is the Unicode counterpart of WNetEnumResource which to me would imply that using this would do the trick. However, I have not been able to get Unicode NetBIOS names properly using WNetEnumResourceW. I've also tried the C# rough equivalent DirectoryEntry using the WinNT: provider with no luck on Unicode names either. If I use DirectoryEntry on Active Directory (using the LDAP: provider) I do get Unicode names back. I noticed that during some debugging my code using DirectoryEntry and the WinNT: provider, the exceptions I saw were of type System.Runtime.InteropServices.COMException which tends to make me believe that this is just calling WNetEnumResourceW via COM. This web page implies that for some Net APIs the MS documentation is incomplete and possibly inaccurate which further confuses things. Additionally I've found that using the C# method which certainly results in cleaner, more understandable code also yields incomplete results in enumerating computers in domains\workgroups. Does anyone have any insight on this? Is it possible that computer acting as the WINS server is mangling the name? How would I determine this? Thanks

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  • Where is the Open Source alternative to WPF?

    - by Evan Plaice
    If we've learned anything from HTML/CSS it's that, declarative languages (like XML) work best to describe User Interfaces because: It's easy to build code preprocessors that can template the code effectively. The code is in a well defined well structured (ideally) format so it's easy to parse. The technology to effectively parse or crawl an XML based source file already exists. The UIs scripted code becomes much simpler and easier to understand. It simple enough that designers are able to design the interface themselves. Programmers suck at creating UIs so it should be made easy enough for designers. I recently took a look at the meat of a WPF application (ie. the XAML) and it looks surprisingly familiar to the declarative language style used in HTML. It's blindingly apparent to me that the current state of desktop UI development is largely fractionalized, otherwise there wouldn't be so much duplicated effort in the domain of user interfaces (IE. GTK, XUL, Qt, Winforms, WPF, etc). There are 45 GUI platforms for Python alone It's painfully obvious to me that there should be a general purpose, open source, standardized, platform independent, markup language for designing desktop GUIs. Much like what the W3C made HTML/CSS into. WPF, or more specifically XAML seems like a pretty likely step in the right direction. Why hasn't anyone in the Open Source community (AFAIK) even scratched the surface of this issue. Now that the 'browser wars' are over should we look forward to a future of 'desktop gui wars?' Note: This topic is relatively subjective in the attempt to be 'future-thinking.' I think that desktop GUI development in its current state sucks ((really)hard) and, even though WPF is still in it's infancy, it presents a likely solution to the problem. Has no one in the OS community looked into developing something similar because they don't see the value, or because it's not worth the effort?

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  • Why is Visual Basic bad?

    - by Mike
    Why do programmers consider Visual Basic a bad language? Putting aside any gripes with Microsoft or with proprietary/non-free software in general, and looking the language itself. Syntax, style, etc. I have just started using it, and find the syntax rather terrible. But I'm wondering what are the most common specific problems.

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  • Agile language for 2d game prototypes?

    - by instanceofTom
    Occasionally ( read: when my fiancé allows ) I like to prototype different game or game-like ideas I have. Usually I use Java or C# (not xna yet) because they are the languages I have the most practice with. However I would like to learn something more suited to agile development; a language in which it would be easier to knock out quick prototypes. At my job I have recently been working with looser (weak/dynamically typed) languages, specifically python and groovy, and I think something similar would fit what I am looking for. So, my question is: What languages (and framework/engine) would be good for rapidly developing prototypes of 2d game concepts? A few notes: I don't need blazing fast bitcrunching performance. In this case I would strongly prefer ease of development over performance. I'd like to use a language with a healthy community, which to me means a fair amount of maintained 3rd party, libraries. I'd like the language to be cross-platform friendly, I work on a variety of different operating systems and would like something that is portable with minimum effort. I can't imagine myself using a language with out decent options for debugging and editor syntax highlighting support. Note: If you are aware of a Java or C# library/framework that you think streamlines producing game prototypes I open to learning something new for those languages too

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  • Longest Common Subsequence

    - by tsudot
    Consider 2 sequences X[1..m] and Y[1..n]. The memoization algorithm would compute the LCS in time O(m*n). Is there any better algorithm to find out LCS wrt time? I guess memoization done diagonally can give us O(min(m,n)) time complexity.

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  • Language to learn metaprogramming

    - by Erup
    What's the best language (in terms of simplicity, readability and code elegancy) in your opinion, to learn and work with metaprogramming? I think metaprogramming is the "future of coding". Not saying that code will extinct, but we can see this scenario coming on new technologies.

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  • The behavior of send() and recv() in socket communication

    - by gc
    The following is the setup: Server Client | | accept connect | | v | send msg1- | | | v v recv <- send | | v v send msg2- recv | | v v close Here is my question: 1. Client actually receives msg1 before it closes, why is it like this? 2. send msg2 returns normally. Since client closes after receiving msg1, why is send msg2 successful?

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  • Making the sound for a Flash game.

    - by Artemix
    Hu guys, I'm developing a Flash game, and I'm interested in knowing what would be the process of making sound. I want to make my own sounds, if possible, and not to download some premade standard (and possibly lawsuitable if they are not "totally free") sounds from the web. So.. I've read that a synthesizer could be useful.. but, I really dont know. Thx!

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  • What "exotic" language feature do you use every day?

    - by fmark
    For most programmers using procedural or object-oriented languages there is a language-feature lowest common denominator: variables, procedures, standard control structures, and classes. However, almost all languages add features on top of this. Recent C# versions have LINQ and delegates. C++ has template metaprogramming. Java has annotations. What features such as these do you use every day?

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  • Creating a project, from Makefile to static/dynamic libraries in UNIX

    - by Sasha
    Guys, would you describe a few things about c++ building blocks, on unix. I want to create an application that links against static libs and dynamic libs (.so). Question 1: How do I create static library using gcc/g++ ?How do I make my app link against it. Question 2: How to specify it in the makefile, linking against static and dynamic libs, assuming that both libraries have header files Summary: I have been using makefiles and libraries for years, written by someone else. Thus every time I modified it, I simply cut-and-pasted things around, without really understanding it. Now I want to get down to the ground and understand the building/linking/Creating Makfile process in-depth. What is a good book describing these concepts in intimate details? Thanks

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  • Controlling shell command line wildcard expansion in C or C++

    - by Adrian McCarthy
    I'm writing a program, foo, in C++. It's typically invoked on the command line like this: foo *.txt My main() receives the arguments in the normal way. On many systems, argv[1] is literally *.txt, and I have to call system routines to do the wildcard expansion. On Unix systems, however, the shell expands the wildcard before invoking my program, and all of the matching filenames will be in argv. Suppose I wanted to add a switch to foo that causes it to recurse into subdirectories. foo -a *.txt would process all text files in the current directory and all of its subdirectories. I don't see how this is done, since, by the time my program gets a chance to see the -a, then shell has already done the expansion and the user's *.txt input is lost. Yet there are common Unix programs that work this way. How do they do it? In Unix land, how can I control the wildcard expansion? (Recursing through subdirectories is just one example. Ideally, I'm trying to understand the general solution to controlling the wildcard expansion.)

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