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  • F# for C#/Haskell programmer

    - by Maciej Piechotka
    What is recommended tutorial of F# for Haskell programmer? F# seems to borrow a lot from Haskell but there are little traps which makes hard to write. Generally I need walkthrough the F# which would not explain what is the difference between mutable data and immutable (Haskell is much more strict in this area) etc. I know C# a little so I know more or less what .Net is about as well.

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  • [Haskell]Curious about the Hash Table problem

    - by astamatto
    I read that hash tables in haskell are crippled ( citation: http://flyingfrogblog.blogspot.com/2009/04/more-on-haskells-hash-table-problems.html ) and since i like haskell it worried me. Since the blog-post one year has passed and im curious, The hash table problem in haskell was "fixed" in the traditional compilers? (like ghc) ps: I love stack overflow, im a long time visitor but only today i decided to try to post a question.

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  • Beginning Haskell: "not in scope" Unprecedented error

    - by user1071838
    So I just started learning Haskell, and this (http://learnyouahaskell.com) nifty book is giving a lot of help. So yesterday I wrote in a text file doubleMe x = x + x and saved it as double.hs. So after saving that I open up my command prompt, CD to the right folder, type in "ghci" to get haskell started, and then type in >doubleMe 5 10 and everything seems to work. Now today, I do the same thing and this happens (actual copy paste from command line) . . . C:\Users\myName\haskell>ghci GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package ffi-1.0 ... linking ... done. Prelude> :l double.hs [1 of 1] Compiling Main ( double.hs, interpreted ) Ok, modules loaded: Main. *Main> doubleMe 5 <interactive>:1:1: Not in scope: `doubleMe' So basically, everything was working fine, but now haskell can't find the function I wrote in double.hs. Can anyone tell what is going on? I'm pretty lost and confused. This is just a guess but does it have to do with *Main at all? Thanks for the help.

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  • How difficult is Haskell multi-threading?

    - by mvid
    I have heard that in Haskell, creating a multi-threaded application is as easy as taking a standard Haskell application and compiling it with the -threaded flag. Other cases, however, have described the use of a par command within the actual source code. What is the state of Haskell multi-threading? How easy is it to introduce into programs? Is there a good multi-threading tutorial that goes over these different commands and their uses?

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  • Implementing simple business model in Haskell

    - by elmes
    Supose we have a very simple model: Station has at least one Train Train has at least two Stations The model has to allow to check what stations any given train visits and to check what trains visit a particular station. How to model it in Haskell? I am a Haskell newbie, so please correct me: once an object is created, you cannot modify it - you can only make a new object based on that one (~immutability). Am I right? If so, I'll have to create a lot of temporary variables with semi-initialized objects (during deserialization or even in unit tests). Basically what I need is an example of modeling domain classes in Haskell - after reading "Learn you a haskell.." I still have no idea how to use this language.

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  • Literate Haskell (.lhs) and Haddock

    - by finnsson
    At the moment I'm only using Haddock but after seeing some really interesting examples (e.g. this gist ) of literate Haskell I'm interested in trying it out in a project. The questions I got are: What do you write as Haddock comments and what do you write in the literate part? How do you scale literate programming to multiple files? Can anyone point me to an example where literate programming is used in a package with multiple modules? What is your experience of using literate programming in larger packages? Which flavour (markdown, latex, ...) of literate Haskell is preferred? Why are you programming in literate Haskell or plain vanilla Haskell? Are you programming in both styles and if so why? Do you prefer block-style (\begin{code}) or Bird-style (>)? Why?

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  • Using perfectly formatted input as list in Haskell

    - by RankWeis
    I'm doing a program in Haskell (on the Haskell platform), and I know I'm getting perfectly formatted inputs, so the input may look like [ ['a'], ['b'], ['c'] ] I want Haskell to be able to take this and use it as a list of it's own. And, I'd like this list to be over multiple lines, i.e., I want this to also work: [ ['a'], ['b'], ['c'] ] I can parse this input, but I've been told there's a way to do this easily - this is supposed to be the 'trivial' part of the assignment, but I don't understand it.

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  • Debugging the NetBeans Platform

    - by Geertjan
    Once you've set up the NetBeans Platform sources as your NetBeans Platform, you're able to debug the NetBeans Platform itself. That's an occasional question (certainly not a frequent question) on the mailing list and in NetBeans Platform courses: "Is it possible to debug the NetBeans Platform?" Well, here's how: Firstly, set up the NetBeans Platform sources as your NetBeans Platform. Now, open into NetBeans IDE the NetBeans module where you'd like to place a breakpoint. That in itself is the hardest part of this task. I.e., you know you want to debug the NetBeans Platform, but have no idea where to place your breakpoint. One way to figure that out, from 7.1 onwards, is to take a visual snapshot of the NetBeans Platform and then analyze that snapshot in NetBeans IDE. To do this, right-click a module that you've set as using the NetBeans Platform sources as your NetBeans Platform and then choose Debug. The application, i.e., the NetBeans Platform, including your custom module, starts up and you'll see this, i.e., NetBeans IDE in debug mode together with your NetBeans Platform application:Notice there's a new toolbar button (new in NetBeans IDE 7.1) that resembles an orange camera. Click that button and the IDE creates a visual snapshot of the running application, which in this case is the NetBeans Platform. When you click components in the visual snapshot, the Navigator and Properties window display information about the related GUI component: By clicking the above components, you can end up identifying the component you'd like to debug and even the module where it is found. Open that module. Set a breakpoint on the line of interest. Right-click the module again and choose Debug. A debug session starts and when the breakpoint is hit, the Debugger in the IDE will open and there you can step through the NetBeans Platform sources.

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  • Best Way To Develop Robust Cross-Platform Application?

    - by Clay
    Windows C programmer here (going back to 1992 and Windows95 back when it was called Windows93). Can function in C++, but mostly still a C programmer. Looking to build a cross-platform casual game. Very numbers heavy with only a few artistic embellishments and animations, so perhaps a development environment for business apps might be the best option. Or an easy-to-use 2D game dev platform. Target platforms: Windows, Mac, MS Tablet, iPhone, iPad, Android. I currently develop on Windows with Visual Studio 2012, but we could spend up to $50K on hardware/software/middleware if necessary. Not very competent getting open-source software working. Would rather pay the money and jump right into app development. Recommendations?

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  • What is the most compatible, widely used production language to export knowledge and skills gained from Haskell?

    - by World Engineer
    I like Haskell, plain and simple. While Haskell is used in production software, it's not especially widely deployed from what I've seen. What is the most similar and still widely used language in regards to production projects so that I might have a snowball's chance of using something similarly awesome in industry? Also is the same language from the first part available on large numbers of platforms? If not, what is the best alternative that has wide platform deployment? I'd like a single language to put on my to-do list rather than a massive swarm or family. Hard evidence would be a plus.

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  • Database platform migration from Windows-32bit to Linux-64bit

    - by [email protected]
    We have a customer which have all they core business database on RAC over Windows OS. Last year they were affected by a virus that destroyed the registry and all their RAC environments were "OUT OF ORDER", the result, thousand people on vacation for a day.They were distrustful about Linux and after came an agreement to migrate their Enterprise Manager from Windows to Linux (OMS and Repository). How we did demonstrate how powerful and easy is RMAN to migrate databases across platforms.Fist of check of target platform is available from sourceSQL> select platform_name from v$db_transportable_platform;PLATFORM_NAME-----------------------------------------------------------Microsoft Windows IA (32-bit)Linux IA (32-bit)HP Tru64 UNIXLinux IA (64-bit)HP Open VMSMicrosoft Windows IA (64-bit)Linux 64-bit for AMDMicrosoft Windows 64-bit for AMDSolaris Operating System (x86)Check database object as directories that can change across platforms, also check external tables.Startup source database in read only modeRun the following RMAN ScriptRMAN> connect target / RMAN> convert database on target platform convert script 'c:/temp/convert_grid.rman'transport script 'c:/TEMP/transporta_grid.sql' new database 'gridbd' format 'c:/temp/gridmydb%U' db_file_name_convert 'C:\oracle\oradata\grid','/oracle/gridbd/data2/data';(Notice tha path change on db_file_name_convert)Move from source to target:PfileNew scriptsexternal table filesbfilesdata filesCheck pfile, and ensure that the paths are OKCreate temporary control file to connect rmanExecute the RMAN scriptRMAN> connect target / RMAN> @/home/oracle/pboixeda/win2lnx.rmanShutdown the instance and remove temporary control filesRecreate controlfile/s, take care about the used paths.Execute the transport script, transporta_grid.sqlDue we were moving from a 32-bit architecture to a 64-bit architecture, there is bug reported in 386990.1 note, we had to recreate OLAP , check the note for more details. Alter or Recreate all necessary objects Launch utlrpAfter this experience with Linux they are on the way to migrate all their RAC from 10gR2 on Windows to 11gR2 Linux 64 bit.Hope it helps

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  • Cross platform development query

    - by Ian
    I'm a Microsoft developer mainly, but there are a couple of small-ish projects I'd like to fiddle with which would benefit from being cross platform. The platforms I want to target are: Windows, Linux, Mac, Android and preferably iPhone, web (running in a browser). I need 3D (Around the level of support seen in something like Minecraft (I'm not writing Minecraft)), some networking. I'm pretty certain Java would work on all except iPhone. Looking at the "related questions" above it's offered up QT (no browser or phone afaik) and also HTML/CSS/Javascript (3D? package for desktop?) The other alternative is to have seperate versions for seperate platforms, developed with some common code where possible. That option isn't something I know anything about. Does anyone have experience of this sort of conundrum? I figured here was better than SO, because I imagine there are compromises which extend beyond technical choice. Finally, this is not a commercial operation, so some of the very expensive cross platform tools are out of the question unless they offer some sort of community edition. Thanks for your time.

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  • Suggestions to start a cross-platform project

    - by Gabriele
    I have a big project in my head, it should be cross-platform (Win, Max and Linux), online (Client - Server) and with 3D graphics. I would like some suggestions to start with the right things. Currently I'm a PHP/MySQL coder, I used to code in C and Pascal on DOS ages (Borland Times ;)), my C knowlegde need a refresh but it's ok. I guess C++ it's the right language. What platform and what i should use to code? I can choose from all three platforms. My idea was to use Visual Studio 2010 C++, but i'm not sure if it support Native code. What kind of libraries should i use? I guessed OpenSSL for the login, OpenGL for graphics part. For the Audio or the GUI? Any other suggestions are well accepted. I know it's a "BIG DEAL" but I have no rush and it'll be a free-time project, only for my pleasure. Thank you in advance.

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  • Which platform to choose from .Net or Java [closed]

    - by SahilMahajanMj
    I know that there is a lot healthy discussion about this topic. but my case is entirely different from these discussions. I have just passed out my graduation. During the graduation period, i had done C#.net and java as well. Now i am working as Android programmer in a company. In the recent times, i have heard a lot about pros and cons of these platforms. What our seniors used to suggest that, ASP.net is a lot better than JSP for website developement. .net provides us lot of in built tools and API's for building powerfull applications. Java's platform independancy has always been issue among them. Security fetures are more in java. .Net has more powerfull IDE's. Now i am a bit confused on which platform to choose from these. I found java better from two, so did i prefer to choose android. Also, the discussion always ends with an issue that java has no scope for job as far has .net does. I would like to hear suggestions on this topic, but it would be better, if you consider indian IT market for this discussion.

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  • finite state machine used in mario like platform game

    - by juakob
    I dont understand how to use a finite state machine with the entity controlled by the player. For example i have a mario(2d platform) i can jump,run,walk,take damage,swim,etc so my first thought was to use this actions as states. But what happen when you are running when you take damage? or jumping taking damage and shooting at the same time? I just want to add functionalities(actions) to the player in a clean way(not using ifs for all the actions in the entity update)

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  • Cross-Platform Google Chrome App Installer

    - by Volomike
    I have fallen in love with the Google Chrome App way of making an "app" (and extensions as well). What kind of installer would you recommend (free and/or cheap is preferred) that is cross-platform (Mac, Windows 2000+, Linux (Ubuntu, Debian, Suse, Redhat, or derivatives)) and lets me deploy Google Chrome Apps on workstations? It would need to let me deploy Google Chrome, or update Google Chrome to a particular version, as necessary, in order for my app to work.

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  • Good starting platform for a teenage games programmer

    - by gkrogers
    My son (15) has decided that he wants to pursue a career as a games programmer. I've said that he should get started now with a simple game. He has no programming experience yet, but I am a programmer (business apps, not games) so I can teach him programming, but what would be a good platform for him to start on? Initially I'm looking for something that can provide quick results, to keep his enthusiasm up. What would you suggest?

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  • Haskell math performance

    - by Travis Brown
    I'm in the middle of porting David Blei's original C implementation of Latent Dirichlet Allocation to Haskell, and I'm trying to decide whether to leave some of the low-level stuff in C. The following function is one example—it's an approximation of the second derivative of lgamma: double trigamma(double x) { double p; int i; x=x+6; p=1/(x*x); p=(((((0.075757575757576*p-0.033333333333333)*p+0.0238095238095238) *p-0.033333333333333)*p+0.166666666666667)*p+1)/x+0.5*p; for (i=0; i<6 ;i++) { x=x-1; p=1/(x*x)+p; } return(p); } I've translated this into more or less idiomatic Haskell as follows: trigamma :: Double -> Double trigamma x = snd $ last $ take 7 $ iterate next (x' - 1, p') where x' = x + 6 p = 1 / x' ^ 2 p' = p / 2 + c / x' c = foldr1 (\a b -> (a + b * p)) [1, 1/6, -1/30, 1/42, -1/30, 5/66] next (x, p) = (x - 1, 1 / x ^ 2 + p) The problem is that when I run both through Criterion, my Haskell version is six or seven times slower (I'm compiling with -O2 on GHC 6.12.1). Some similar functions are even worse. I know practically nothing about Haskell performance, and I'm not terribly interested in digging through Core or anything like that, since I can always just call the handful of math-intensive C functions through FFI. But I'm curious about whether there's low-hanging fruit that I'm missing—some kind of extension or library or annotation that I could use to speed up this numeric stuff without making it too ugly.

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  • Web development: Haskell or Scheme

    - by Robert E. Lester
    I would like to to choose one of these languages for building web applications. I'm not interested in framework per say, but have the following needs: Rapid development. Easy to scale. Strong community for the web. Quick and easy to deploy. I'm very familiar with Haskell, and have some familiarity with scheme (in particular PLT). Scheme appeals to me as good candidate for web development due to it's simple syntax which is homogenous across libraries. I state this despite my subjective opinion that Haskell is a 'cleaner' language. Haskell web apps seem to require learning and building a patchwork of different combinator libraries. On the plus side, I realise this can be quite expressive, although I'd prefer to eliminate impedance mismatches where possible. While scheme-plt looks to be a good fit, I can find but one example of it being used in the "real world". Haskell doesn't seem to fair too much better here, but there seems to be a bigger community behind the web side. Please help me make up my mind. For the most part I'm interested in real-world use cases.

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  • Learning Haskell maps, folds, loops and recursion

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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  • Haskell lazy I/O and closing files

    - by Jesse
    I've written a small Haskell program to print the MD5 checksums of all files in the current directory (searched recursively). Basically a Haskell version of md5deep. All is fine and dandy except if the current directory has a very large number of files, in which case I get an error like: <program>: <currentFile>: openBinaryFile: resource exhausted (Too many open files) It seems Haskell's laziness is causing it not to close files, even after its corresponding line of output has been completed. The relevant code is below. The function of interest is getList. import qualified Data.ByteString.Lazy as BS main :: IO () main = putStr . unlines =<< getList "." getList :: FilePath -> IO [String] getList p = let getFileLine path = liftM (\c -> (hex $ hash $ BS.unpack c) ++ " " ++ path) (BS.readFile path) in mapM getFileLine =<< getRecursiveContents p hex :: [Word8] -> String hex = concatMap (\x -> printf "%0.2x" (toInteger x)) getRecursiveContents :: FilePath -> IO [FilePath] -- ^ Just gets the paths to all the files in the given directory. Are there any ideas on how I could solve this problem? The entire program is available here: http://haskell.pastebin.com/PAZm0Dcb

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  • Help! I'm a Haskell Newbie

    - by Darknight
    I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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