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• Functional languages & support for memoization

  - by Joel

  Do any of the current crop of popular functional languages have good support for memoization & if I was to pick one on the strength of its memoisation which would you recommend & why? Update: I'm looking to optimise a directed graph (where nodes could be functions or data). When a node in the graph is updated I would like the values of other nodes to be recalculated only if they depend the node that changed. Update2: require free or open-source language/runtime.

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• Algorithms for modern hardware?

  - by Jurily

  Once again, I find myself with a set of broken assumptions. The article itself is about a 10x performance gain by modifying a proven-optimal algorithm to account for virtual memory: What good is an O(log2(n)) algorithm if those operations cause page faults and slow disk operations? For most relevant datasets an O(n) or even an O(n^2) algorithm, which avoids page faults, will run circles around it. Are there more such algorithms around? Should we re-examine all those fundamental building blocks of our education? What else do I need to watch out for when writing my own?

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• A good approach to db planing for reporting service

  - by Itay Moav

  The scenario: Big system (~200 tables). 60,000 users. Complex reports that will require me to do multiple queries for each report and even those will be complex queries with inner queries all over the place + some processing in PHP. I have seen an approach, which I am not sure about: Having one centralized, de-normalized, table that registers any activity in the system which is reportable. This table will hold mostly foreign keys, so she should be fairly compact and fast. So, for example (My system is a virtual learning management system), A user enrolls to course, the table stores the user id, date, course id, organization id, activity type (enrollment). Of course I also store this data in a normalized DB, which the actual application uses. Pros I see: easy, maintainable queries and code to process data and fast retrieval. Cons: there is a danger of the de-normalized table to be out of sync with the real DB. Is this approach worth considering, or (preferably from experience) is total $#%#%t?

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• How can I utilize or mimic Application OnStart in an HttpModule?

  - by Sailing Judo

  We are trying to remove the global.asax from our many web applications in favor of HttpModules that are in a common code base. This works really well for many application events such as BeginRequest and PostAuthentication, but there is no Application Start event exposed in the HttpModule. I can think of a couple of smelly ways to overcome this deficit. For example, I can probably do this: protected virtual void BeginRequest(object sender, EventArgs e) { Log.Debug("Entered BeginRequest..."); var app = HttpContext.Current.Application; var hasBeenSet app["HasBeenExecuted"] == null ? false : true; if(!hasBeenSet) { app.Lock(); // ... do app level code app.Add("HasBeenSet", true); app.Unlock(); } // do regular begin request stuff ... } But this just doesn't smell well to me. What is the best way to invoke some application begin logic without having a global.asax?

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• Must a Language that Implements Monads be Statically Typed?

  - by Morgan Cheng

  I am learning functional programming style. From this link http://channel9.msdn.com/shows/Going+Deep/Brian-Beckman-Dont-fear-the-Monads/, Brian Beckman gave a brilliant introduction about Monad. He mentioned that Monad is about composition of functions so as to address complexity. A Monad includes a unit function that transfers type T to an amplified type M(T); and a Bind function that, given function from T to M(U), transforms type M(T) to another type M(U). (U can be T, but is not necessarily). In my understanding, the language implementing monad should be type-checked statically. Otherwise, type errors cannot be found during compilation and "Complexity" is not controlled. Is my understanding correct?

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• How to create a string array in matlab?

  - by aduric

  I would like to pass a vector of strings from C++ to matlab. I have tried using the functions available such as mxCreateCharMatrixFromStrings but it doesn't give me the correct behavior. So, I have something like this: void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) { vector<string> stringVector; stringVector.push_back("string 1"); stringVector.push_back("string 2"); //etc... The problem is how do I get this vector to the matlab environment? plhs[0] = ??? My goal is to be able to run: >> [strings] = MyFunc(...) >> strings(1) = 'string 1'

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• Using Visual Studio 2005 (32bit) on a Windows 7 64bit machine.

  - by Krakkos

  I need to use Visual Studio 2005 (C++) on my new laptop - a Sony Vaio with Windows 7 64bit.. I don't need to develop for a 64bit environment, my work is all 32bit, so how can I be sure that I can still develop/debug/test for a 32bit target environment using VS2005 on a 64bit machine....? What's the best option: 1) Just install VS2005 on Windows 7 64bit and carry on.. (suspect problems with 64bit runtime libs..?) 2) Dual boot the laptop with Windows XP 32bit. 3) Run some kind of Virtual Machine with Windows XP in it... (I don't have a VM yet, but would look into it) Thanks

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• correct way to store an exception in a variable

  - by Evan Teran

  I have an API which internally has some exceptions for error reporting. The basic structure is that it has a root exception object which inherits from std::exception, then it will throw some subclass of that. Since catching an exception thrown in one library and catching it in another can lead to undefined behavior (at least Qt complains about it and disallows it in many contexts). I would like to wrap the library calls in functions which will return a status code, and if an exception occurred, a copy of the exception object. What is the best way to store an exception (with it's polymorphic behavior) for later use? I believe that the c++0x futures API makes use of something like this. So what is the best approach? The best I can think of is to have a clone() method in each exception class which will return a pointer to an exception of the same type. But that's not very generic and doesn't deal with standard exceptions at all. Any thoughts?

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• regex pattern to match only strings that don't contain spaces PHP

  - by Jamex

  Hi, I want to match the word/pattern that is contained in the variable, but only match against the words that don't have white spaces. Please give suggestions. $var = 'look'; $array = ('look', 'greatlook', 'lookgreat', 'look great', 'badlook', 'look bad', 'look ', ' look'); matches words: look, greatlook, lookgreat, badlook non matches: look great, bad look, look (trailing space(s)), (space(s)) look. The syntax of the below functions are OK, but it matches everything $match = preg_grep ("/$var/", $array); $match = preg_grep ("/^$var/", $array); (match words with 'look' at the start) but when I include the [^\s], it gives an error $match = preg_grep ("/$var[^\s]/", $array); Parse error: syntax error, unexpected '^', expecting T_STRING or T_VARIABLE TIA

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• "import as" leads to unresolved import error, "from .. import" does not

  - by Markus R.

  I'm trying to write some plugins for the irc bot supybot with eclipse/pydev. Pydev gives me errors about unresolved imports on supybot-modules/packages (e. g. import supybot.utils as utils), but works ok on e. g. "from supybot.commands import *". So I guess I set up dydev correctly, as it finds the wanted modules. The problem must be in pydev/eclipse, as the bot works correct and in eric5 I get also no errors about that. Removing the interpreter and setting it up didn't help. Any other ideas on how to fix this? System: Arch Linux, Eclipse Juno, PyDev 2.7.1, wanted (and set up) python interpreter is 2.7, supybot is installed in site-packages for Python 2.7. Edit: Just noticed: PyDev doesn't mark the "from ... import *" as error, but if I use functions imported from there I get an error on that function.

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• Running matlab in the background

  - by msandbot

  Hi, I am running matlab on 48 virtual machines and would like to automate it. I ssh into the machines then use matlab -r matlab_command > outfile.txt & to get the process to run in the background and run fine when I logout. The only problem is that when i jobs my process is stopped and won't start until I fg ^z bg. Is there a matlab flag so that I can run it in the background without having it stop? Thanks, Mike

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• Caching result of setUp() using Python unittest

  - by dbr

  I currently have a unittest.TestCase that looks like.. class test_appletrailer(unittest.TestCase): def setup(self): self.all_trailers = Trailers(res = "720", verbose = True) def test_has_trailers(self): self.failUnless(len(self.all_trailers) > 1) # ..more tests.. This works fine, but the Trailers() call takes about 2 seconds to run.. Given that setUp() is called before each test is run, the tests now take almost 10 seconds to run (with only 3 test functions) What is the correct way of caching the self.all_trailers variable between tests? Removing the setUp function, and doing.. class test_appletrailer(unittest.TestCase): all_trailers = Trailers(res = "720", verbose = True) ..works, but then it claims "Ran 3 tests in 0.000s" which is incorrect.. The only other way I could think of is to have a cache_trailers global variable (which works correctly, but is rather horrible): cache_trailers = None class test_appletrailer(unittest.TestCase): def setUp(self): global cache_trailers if cache_trailers is None: cache_trailers = self.all_trailers = all_trailers = Trailers(res = "720", verbose = True) else: self.all_trailers = cache_trailers

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• What would you do if you coded a C++/OO cross-platform framework and realize its laying on your disk

  - by Manuel

  This project started as a development platform because i wanted to be able to write games for mobile devices, but also being able to run and debug the code on my desktop machine too (ie, the EPOC device emulator was so bad): the platforms it currently supports are: Window-desktop WinCE Symbian iPhone The architecture it's quite complete with 16bit 565 video framebuffer, blitters, basic raster ops, software pixel shaders, audio mixer with shaders (dsp fx), basic input, a simple virtual file system... although this thing is at it's first write and so there are places where some refactoring would be needed. Everything has been abstracted away and the guiding principle are: mostly clean code, as if it was a book to just be read object-orientation, without sacrifying performances mobile centric The idea was to open source it, but without being able to manage it, i doubt the software itself would benefit from this move.. Nevertheless, i myself have learned a lot from unmaintained projects. So, thanking you in advance for reading all this... really, what would you do?

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• use callback function to report stack backtrace

  - by user353394

  Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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• How to join table to itself and select max values in SQL

  - by Jakub Konop

  I have a contracts table: contractId date price partId 1 20120121 10 1 2 20110130 9 1 3 20130101 15 2 4 20110101 20 2 The contract with greatest date being the active contract (don't blame me, I blame infor for creating xpps) I need to create query to see only active contracts (one contract per part, the contract with highest date). So the result of the query should be like this: contractId date price partId 1 20120121 10 1 3 20130101 15 2 I am out of ideas here, I tried self joining the table, I tried aggregation functions, but I can't figure it out. If anyone would have any idea, please share them with me..

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• Why can't I *override* and *new* a Property (C#) at the same time?

  - by Tim Lovell-Smith

  According to this question it seems like you can do this for Methods. What I want to know is why it doesn't work when I try it with properties. public class Foo { public virtual object Value { get; set; } } public class Foo<T> : Foo { public override object Value { get { return base.Value; } set { base.Value = (T)value; //inject type-checking on sets } } public new T Value { get { return (T)base.Value; } set { base.Value = value; } } } Error message from C# 4.0 RC1 Error 1 The type 'ClassLibrary1.Foo' already contains a definition for 'Value' ClassLibrary1\Class1.cs 31 22 ClassLibrary1

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• Type patterns in Haskell

  - by finnsson

  I'm trying to compile a simple example of generic classes / type patterns (see http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html) in Haskell but it won't compile. Any ideas about what's wrong with the code would be helpful. According to the documentation there should be a module Generics with the data types Unit, :*:, and :+: but ghc (6.12.1) complaints about Not in scope: data constructor 'Unit' etc. It seems like there's a package instant-generics with the data types :*:, :+: and U but when I import that module (instead of Generics) I get the error Illegal type pattern in the generic bindings {myPrint _ = ""} The complete source code is import Generics.Instant class MyPrint a where myPrint :: a -> String myPrint {| U |} _ = "" myPrint {| a :*: b |} (x :*: y) = "" (show x) ++ ":*:" ++ (show y) myPrint {| a :+: b |} _ = "" data Foo = Foo String instance MyPrint a => MyPrint a main = myPrint $ Foo "hi" and I compile it using ghc --make Foo.hs -fglasgow-exts -XGenerics -XUndecidableInstances P.S. The module Generics export no data types, only the functions: canDoGenerics mkGenericRhs mkTyConGenericBinds validGenericInstanceType validGenericMethodType

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• Maintaining the query string in ASP.Net MVC

  - by Mantorok

  Hi all Just beginning my journey in ASP.Net MVC and I have a query about something before I dig myself in too deep. I have a table, which is paged, and I have 2 controls above the table: Dropdown that defines order of the results and apply button next to it Textbox that defines a filter and apply button next to it What I need to achieve is that if the user changes the order or adds a filter I fire of an AJAX call to my action like such: /Membership/Users?sort=value&filter=value&page=pagenumber. So my controller action is: // GET Membership/Users?sort=&filter=&page= public ActionResult Users(string sort, string filter, string page) So I have 3 questions: Is this the correct approach? What would be the best way to ensure that the query string is maintained, bearing in mind that the action will nearly always be called by Jquery/Ajax functions? If I wanted to link directly to this action passing the arguments would I need to hard-code the querystring? Thanks

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• Issues rendering image in flash via Context.Response.Write C# asp.

  - by Justin

  I am having an issue rendering images in flash via a character array. I am sending it from a webhandler via Context.Response.Write as a Base64CharacterArray. It functions 100% properly in a windows environment, however when using a Mac the image data is not retrieved correctly causing the image to appear incorrectly. It does not affect the data,however as it is rendered properly in a player which accesses the data via a webservice. I am at the end of my rope on this one. Anything will help. You can find an example at the following url http://www.discoverirelandtoday.com/photoalbum/Public/Main.aspx Thanks

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• C++ visitor pattern handling templated string types?

  - by Steve the Plant

  I'm trying to use the visitor pattern to serialize the contents of objects. However one snag I'm hitting is when I'm visiting strings. My strings are of a templated type, similar to STL's basic_string. So something like: basic_string<char_type, memory_allocator, other_possible_stuff> \\ many variations possible! Since I can have very many different templated string types, I can't go and add them to my visitor interface. It would be ridiculous. But I can't add templates to my VisitString method because C++ prevents using templates parameters in virtual methods. So what are my options to work around this?

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• Full-Text Search in SQL Server Express Won't Recognize Latest IFilters

  - by Brandon King

  I'm having difficulty getting full-text search working in SQL Server 2008 Express with Advanced Services. I have a table loaded with .DOCX files as varbinary(MAX) data that I want to use for a full-text catalog, but it doesn't seem to recognize the .DOCX format. Here are the steps that I've taken... Installed the latest Filter Pack 2.0 Exec sp_fulltext_service 'load_os_resources', 1 Exec sys.sp_help_fulltext_system_components 'all' (NOTE: .DOCX is not shown as a filter) Building the full-text catalog fails to identify any key words I initially thought there might be a conflict between x86 SQL Express and x64 Filter Pack on my Windows 7 machine, but I just tried it with everything x86 in a Windows XP virtual machine and got the same result.

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• Setting the Cursor Position in a Win32 Console Application

  - by Jim Fell

  How can I set the cursor position in a Win32 Console application? Preferably, I would like to avoid making a handle and using the Windows Console Functions. (I spent all morning running down that dark alley; it creates more problems than it solves.) I seem to recall doing this relatively simply when I was in college using stdio, but I can't find any examples of how to do it now. Any thoughts or suggestions would be greatly appreciated. Thanks.

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• Tab widget example not running

  - by michbeck

  I'm trying to reproduce the tabwidget example (http://developer.android.com/resources/tutorials/views/hello-tabwidget.html). I'm not really sure what's the problem, I got no errors while compiling, but i cannot see the application on the emulators screen. It would be excellent if maybe anyone could have a look at my classes and tell me what's my mistake? I've packed my project here: http://etanto.com/TabTest.zip here's the console dump while the run: [2010-06-10 09:18:34 - TabTest] Launching a new emulator with Virtual Device 'Virtual1' [2010-06-10 09:18:35 - TabTest] New emulator found: emulator-5554 [2010-06-10 09:18:35 - TabTest] Waiting for HOME ('android.process.acore') to be launched... [2010-06-10 09:19:05 - TabTest] WARNING: Application does not specify an API level requirement! [2010-06-10 09:19:05 - TabTest] Device API version is 8 (Android 2.2) [2010-06-10 09:19:05 - TabTest] HOME is up on device 'emulator-5554' [2010-06-10 09:19:05 - TabTest] Uploading TabTest.apk onto device 'emulator-5554' [2010-06-10 09:19:05 - TabTest] Installing TabTest.apk... [2010-06-10 09:19:22 - TabTest] Success! [2010-06-10 09:19:22 - TabTest] \TabTest\bin\TabTest.apk installed on device [2010-06-10 09:19:22 - TabTest] Done!

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• Why my print current date time (C language) gives different answer

  - by vodkhang

  I want to get the current date (day, mon and year). I found out there are some functions in C to do that like ctime (get the string of time), localtime and gmtime. I tried with following code but the output are different. I get this output: The date and time is Tue Apr 20 2010 (which is correct) The year is : 110 The year is : 110. Does anybody know why? int main(int argc, char** argv) { time_t now; if((now = time(NULL)) == (time_t)-1) { puts("Failure in getting time"); } else { printf("The date and time is: %s\n", ctime(&now)); printf("The year is: %ld\n", localtime(&now)->tm_year); printf("The year is: %ld\n", gmtime(&now)->tm_year); } getchar(); }

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• Is it bad practice to use python's getattr extensively?

  - by Wilduck

  I'm creating a shell-like environment. My original method of handleing user input was to use a dictionary mapping commands (strings) to methods of various classes, making use of the fact that functions are first class objects in python. For flexibility's sake (mostly for parsing commands), I'm thinking of changing my setup such that I'm using getattr(command), to grab the method I need and then passing arguments to it at the end of my parser. Another advantage of this approach is not having to update my (currently statically implemented) command dictionary every time I add a new method/command. My question is, will I be taking a hit to the efficiency of my shell? Does it matter how many methods/commands I have? I'm currently looking at 30 some commands, which could eventually double.

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