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• A scripting engine for Ruby?

  - by Earlz

  Hello, I am creating a Ruby On Rails website, and for one part it needs to be dynamic so that (sorta) trusted users can make parts of the website work differently. For this, I need a scripting language. In a sort of similar project in ASP.Net, I wrote my own scripting language/DSL. I can not use that source code(written at work) though, and I don't want to make another scripting language if I don't have to. So, what choices do I have? The scripting must be locked down and not be able to crash my server or anything. I'd really like if I could use Ruby as the scripting language, but it's not strictly necessary. Also, this scripting part will be called on almost every request for the website, sometimes more than once. So, speed is a factor. I looked at the RubyLuaBridge but it is Alpha status and seems dead. What choices for a scripting language do I have in a Ruby project? Also, I will have full control over where this project is deployed(root access), so there are no real limits..

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• Scheme: Mysterious void in pattern match.

  - by Schemer

  Hi. I am writing a function called annotate that uses match-lambda -- often with recursive calls to annotate. Here is one of the pattern matches: (`(lambda (,<param1> . ,<params>) ,<stmts>) `(CLOSURE ENV (,<param1> . ,<params>) (lambda (ENV) ,(map annotate (map (lambda (x) (append `(,<param1> . ,<params>) (list x))) `(,<stmts>)))))) However, when this pattern is matched this is what returns: '(CLOSURE ENV (x) (lambda (ENV) ((CLOSURE ENV (x y) (lambda (ENV) ((+ x y)))))) #<void>) Specifically I can't figure out where "void" is coming from. In fact, if I include the line: ,(displayln (map annotate (map (lambda (x) (append `(,<param1> . ,<params>) (list x))) `(,<stmts>)))) it prints: ((CLOSURE ENV (x y) (lambda (ENV) ((+ x y))))) notably without "void". If someone could tell me what the problem is it would be greatly appreciated. Thanks.

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• Best implementation of Java Queue?

  - by Georges Oates Larsen

  I am working (In java) on a recursive image processing algorithm that recursively traverses the pixels of the image, outward from a center point. Unfortunately... That causes stack overflows, so I have decided to switch to a Queue-based algorithm. Now, this is all fine and dandy -- But considering the fact that its queue will be analyzing THOUSANDS of pixels in a very short amount of time, while constantly popping and pushing, WITHOUT maintaining a predictable state (It could be anywhere between length 100, and 20000); The queue implementation needs to have significantly fast popping and pushing abilities. A linked list seems attractive due to its ability to push elements unto its self without rearranging anything else in the list, but in order for it to be fast enough, it would need easy access to both its head, AND its tail (or second-to-last node if it were not doubly-linked). Sadly, though I cannot find any information related to the underlying implementation of linked lists in Java, so it's hard to say if a linked list is really the way to go... This brings me to my question... What would be the best implementation of the Queue interface in Java for what I intend to do? (I do not wish to edit or even access anything other than the head and tail of the queue -- I do not wish to do any sort of rearranging, or anything. On the flip side, I DO intend to do a lot of pushing and popping, and the queue will be changing size quite a bit, so preallocating would be inefficient)

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• Best Functional Approach

  - by dbyrne

  I have some mutable scala code that I am trying to rewrite in a more functional style. It is a fairly intricate piece of code, so I am trying to refactor it in pieces. My first thought was this: def iterate(count:Int,d:MyComplexType) = { //Generate next value n //Process n causing some side effects return iterate(count - 1, n) } This didn't seem functional at all to me, since I still have side effects mixed throughout my code. My second thought was this: def generateStream(d:MyComplexType):Stream[MyComplexType] = { //Generate next value n return Stream.cons(n, generateStream(n)) } for (n <- generateStream(initialValue).take(2000000)) { //process n causing some side effects } This seemed like a better solution to me, because at least I've isolated my functional value-generation code from the mutable value-processing code. However, this is much less memory efficient because I am generating a large list that I don't really need to store. This leaves me with 3 choices: Write a tail-recursive function, bite the bullet and refactor the value-processing code Use a lazy list. This is not a memory sensitive app (although it is performance sensitive) Come up with a new approach. I guess what I really want is a lazily evaluated sequence where I can discard the values after I've processed them. Any suggestions?

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• Entity Framework LINQ Query using Custom C# Class Method - Once yes, once no - because executing on the client or in SQL?

  - by BrooklynDev

  I have two Entity Framework 4 Linq queries I wrote that make use of a custom class method, one works and one does not: The custom method is: public static DateTime GetLastReadToDate(string fbaUsername, Discussion discussion) { return (discussion.DiscussionUserReads.Where(dur => dur.User.aspnet_User.UserName == fbaUsername).FirstOrDefault() ?? new DiscussionUserRead { ReadToDate = DateTime.Now.AddYears(-99) }).ReadToDate; } The linq query that works calls a from after a from, the equivalent of SelectMany(): from g in oc.Users.Where(u => u.aspnet_User.UserName == fbaUsername).First().Groups from d in g.Discussions select new { UnReadPostCount = d.Posts.Where(p => p.CreatedDate > DiscussionRepository.GetLastReadToDate(fbaUsername, p.Discussion)).Count() }; The query that does not work is more like a regular select: from d in oc.Discussions where d.Group.Name == "Student" select new { UnReadPostCount = d.Posts.Where(p => p.CreatedDate > DiscussionRepository.GetLastReadToDate(fbaUsername, p.Discussion)).Count(), }; The error I get is: LINQ to Entities does not recognize the method 'System.DateTime GetLastReadToDate(System.String, Discussion)' method, and this method cannot be translated into a store expression. My question is, why am I able to use my custom GetLastReadToDate() method in the first query and not the second? I suppose this has something to do with what gets executed on the db server and what gets executed on the client? These queries seem to use the GetLastReadToDate() method so similarly though, I'm wondering why would work for the first and not the second, and most importantly if there's a way to factor common query syntax like what's in the GetLastReadToDate() method into a separate location to be reused in several different places LINQ queries. Please note all these queries are sharing the same object context.

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• Why can't you return a List from a Compiled Query?

  - by Andrew

  I was speeding up my app by using compiled queries for queries which were getting hit over and over. I tried to implement it like this: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id) End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, List(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ (From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u).ToList()) This did not work and I got this error message: Type : System.ArgumentNullException, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 Message : Value cannot be null. Parameter name: value However, when I changed my compiled query to return IQueryable instead of List like so: Function Select(ByVal fk_id As Integer) As List(SomeEntity) Using db As New DataContext() db.ObjectTrackingEnabled = False Return CompiledSelect(db, fk_id).ToList() End Using End Function Shared CompiledSelect As Func(Of DataContext, Integer, IQueryable(Of SomeEntity)) = _ CompiledQuery.Compile(Function(db As DataContext, fk_id As Integer) _ From u In db.SomeEntities _ Where u.SomeLinkedEntity.ID = fk_id _ Select u) It worked fine. Can anyone shed any light as to why this is? BTW, compiled queries rock! They sped up my app by a factor of 2.

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• How to write a simple Lexer/Parser with antlr 2.7?

  - by Burkhard

  Hello, I have a complex grammar (in antlr 2.7) which I need to extend. Having never used antlr before, I wanted to write a very simple Lexer and Parser first. I found a very good explanation for antlr3 and tried to adapt it: header{ #include <iostream> using namespace std; } options { language="Cpp"; } class P2 extends Parser; /* This will be the entry point of our parser. */ eval : additionExp ; /* Addition and subtraction have the lowest precedence. */ additionExp : multiplyExp ( "+" multiplyExp | "-" multiplyExp )* ; /* Multiplication and addition have a higher precedence. */ multiplyExp : atomExp ( "*" atomExp | "/" atomExp )* ; /* An expression atom is the smallest part of an expression: a number. Or when we encounter parenthesis, we're making a recursive call back to the rule 'additionExp'. As you can see, an 'atomExp' has the highest precedence. */ atomExp : Number | "(" additionExp ")" ; /* A number: can be an integer value, or a decimal value */ number : ("0".."9")+ ("." ("0".."9")+)? ; /* We're going to ignore all white space characters */ protected ws : (" " | "\t" | "\r" | "\n") { newline(); } ; It does generate four files without errors: P2.cpp, P2.hpp, P2TokenTypes.hpp and P2TokenTypes.txt. But now what? How do I create a working programm with that? I tried to add these files to a VS2005-WinConsole-Project but it does not compile: p2.cpp(277) : fatal error C1010: unexpected end of file while looking for precompiled header. Did you forget to add '#include "stdafx.h"' to your source?

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• Communication between lexer and parser

  - by FredOverflow

  Every time I write a simple lexer and parser, I stumble upon the same question: how should the lexer and the parser communicate? I see four different approaches: The lexer eagerly converts the entire input string into a vector of tokens. Once this is done, the vector is fed to the parser which converts it into a tree. This is by far the simplest solution to implement, but since all tokens are stored in memory, it wastes a lot of space. Each time the lexer finds a token, it invokes a function on the parser, passing the current token. In my experience, this only works if the parser can naturally be implemented as a state machine like LALR parsers. By contrast, I don't think it would work at all for recursive descent parsers. Each time the parser needs a token, it asks the lexer for the next one. This is very easy to implement in C# due to the yield keyword, but quite hard in C++ which doesn't have it. The lexer and parser communicate through an asynchronous queue. This is commonly known under the title "producer/consumer", and it should simplify the communication between the lexer and the parser a lot. Does it also outperform the other solutions on multicores? Or is lexing too trivial? Is my analysis sound? Are there other approaches I haven't thought of? What is used in real-world compilers? It would be really cool if compiler writers like Eric Lippert could shed some light on this issue.

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• TortoiseSVN Error: "OPTIONS of 'https://...' could not connect to server (...)"

  - by Zack Peterson

  I'm trying to setup a new computer to synchronize with my SVN repository that's hosted with cvsdude.com. I get this error: Here's what I did (these have worked in the past): Downloaded and installed TortoiseSVN Created a new folder C:\aspwebsite Right-clicked, chose SVN Checkout... Entered the following information, clicked OK: URL of repository: https://<reponame>-svn.cvsdude.com/aspwebsite Checkout directory: C:\aspwebsite Checkout depth: Fully recursive Omit externals: Unchecked Revision: HEAD revision Got TortoiseSVN error: OPTIONS of 'https://<reponame>-svn.cvsdude.com/aspwebsite': could not connect to server (https://<reponame>-svn.cvsdude.com) Rather than getting the error, TortoiseSVN should have asked for my username and password and then downloaded about 90MB. Why can't I checkout from my Subversion repository? Kent Fredric wrote: Either their security certificate has expired, or their hosting is broken/down. Contact CVSDude and ask them whats up. It could also be a timeout, because for me their site is exhaustively slow.. It errors after only a couple seconds. I don't think it's a timeout. Matt wrote: Try visiting https://[redacted]-svn.cvsdude.com/aspwebsite and see what happens. If you can visit it in your browser, you ought to be able to get the files in your SVN client and we can work from there. If it fails, then there's your answer. I can access the site in a web browser.

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• parse.json of authenticated play request

  - by niklassaers

  I've set up authentication in my application like this, always allow when a username is supplied and the API-key is 123: object Auth { def IsAuthenticated(block: => String => Request[AnyContent] => Result) = { Security.Authenticated(RetrieveUser, HandleUnauthorized) { user => Action { request => block(user)(request) } } } def RetrieveUser(request: RequestHeader) = { val auth = new String(base64Decode(request.headers.get("AUTHORIZATION").get.replaceFirst("Basic", ""))) val split = auth.split(":") val user = split(0) val pass = split(1) Option(user) } def HandleUnauthorized(request: RequestHeader) = { Results.Forbidden } def APIKey(apiKey: String)(f: => String => Request[AnyContent] => Result) = IsAuthenticated { user => request => if(apiKey == "123") f(user)(request) else Results.Forbidden } } I want then to define a method in my controller (testOut in this case) that uses the request as application/json only. Now, before I added authentication, I'd say "def testOut = Action(parse.json) {...}", but now that I'm using authentication, how can I add parse.json in to the mix and make this work? def testOut = Auth.APIKey("123") { username => implicit request => var props:Map[String, JsValue] = Map[String, JsValue]() request.body match { case JsObject(fields) => { props = fields.toMap } case _ => {} // Ok("received something else: " + request.body + '\n') } if(!props.contains("UUID")) props.+("UUID" -> UniqueIdGenerator.uuid) if (!props.contains("entity")) props.+("entity" -> "unset") props.+("username" -> username) Ok(props.toString) } As a bonus question, why is only UUID added to the props map, not entity and username? Sorry about the noob factor, I'm trying to learn Scala and Play at the same time. :-) Cheers Nik

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• Out-of-memory algorithms for addressing large arrays

  - by reve_etrange

  I am trying to deal with a very large dataset. I have k = ~4200 matrices (varying sizes) which must be compared combinatorially, skipping non-unique and self comparisons. Each of k(k-1)/2 comparisons produces a matrix, which must be indexed against its parents (i.e. can find out where it came from). The convenient way to do this is to (triangularly) fill a k-by-k cell array with the result of each comparison. These are ~100 X ~100 matrices, on average. Using single precision floats, it works out to 400 GB overall. I need to 1) generate the cell array or pieces of it without trying to place the whole thing in memory and 2) access its elements (and their elements) in like fashion. My attempts have been inefficient due to reliance on MATLAB's eval() as well as save and clear occurring in loops. for i=1:k [~,m] = size(data{i}); cur_var = ['H' int2str(i)]; %# if i == 1; save('FileName'); end; %# If using a single MAT file and need to create it. eval([cur_var ' = cell(1,k-i);']); for j=i+1:k [~,n] = size(data{j}); eval([cur_var '{i,j} = zeros(m,n,''single'');']); eval([cur_var '{i,j} = compare(data{i},data{j});']); end save(cur_var,cur_var); %# Add '-append' when using a single MAT file. clear(cur_var); end The other thing I have done is to perform the split when mod((i+j-1)/2,max(factor(k(k-1)/2))) == 0. This divides the result into the largest number of same-size pieces, which seems logical. The indexing is a little more complicated, but not too bad because a linear index could be used. Does anyone know/see a better way?

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• Programming texts and reference material for my Kindle DX, creating the ultimate reference device?

  - by mwilliams

  (Revisiting this topic with the release of the Kindle DX) Having owned both generation Kindle readers and now getting a Kindle DX; I'm very excited for true PDF handling on an e-ink device! An image of _Why's book on my Kindle (from my iPhone). This gives me a device capable of storing hundreds of thousands of pages that are full text search capable in the form factor of a magazine. What references (preferably PDF to preserve things such as code samples) would you recommend? Ultimately I would like reference material for every modern and applicable programming language (C, C++, Objective-C, Python, Ruby, Java, .NET (C#, Visual Basic, ASP.NET), Erlang, SQL references) as well as general programming texts and frameworks (algorithms, design patterns, theory, Rails, Django, Cocoa, ORMs, etc) and anything else that could be thought of. With so many developers here using such a wide array of languages, as a professional in your particular field, what books or references would you recommend to me for my Kindle? Creative Commons material a plus (translate that to free) as well as the material being in the PDF file format. File size is not an issue. If this turns out to be a success, I will update with a follow-up with a compiled list generated from all of the answers. Thanks for the assistance and contributing! UPDATE I have been using the Kindle DX a lot now for technical books. Check out this blog post I did for high resolution photos of different material: http://www.matthewdavidwilliams.com/2009/06/12/technical-document-pdfs-on-the-kindle-dx/

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• How to handle build rule with unknown targets in OMake when target list generator is built

  - by Michael E

  I have a project which uses OMake for its build system, and I am trying to handle a rather tough corner case. I have some definition files and a tool which can take these definition files and create GraphViz files. There are two problems, though: Each definition file can produce multiple graphs, and the list of graphs it can produce is encoded in the file. My dump tool does have a -list option which lists all the graphs a definition file will produce. This dump tool is built in the source tree. I want this list available in the OMakefile so I can use other rules to convert the DOT files to SVG, and have a phony target depend on all the SVGs (goal: a single build command which builds SVG descriptions of all my graphs). If I only had the first problem, it would be easy - I would run the tool to build a list, and then use that list to build a target which invokes the dumper to output the GraphViz files. However, I am rather stuck on forcing the dump tool to be built before it is needed. If this were make, I would just run make recursively to build the dump tool. OMake does not allow recursive invocation, however, and the build function is only usable from osh. Any suggestions for a good solution to this problem?

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• Information about PTE's (Page Table Entries) in Windows

  - by Patrick

  In order to find more easily buffer overflows I am changing our custom memory allocator so that it allocates a full 4KB page instead of only the wanted number of bytes. Then I change the page protection and size so that if the caller writes before or after its allocated piece of memory, the application immediately crashes. Problem is that although I have enough memory, the application never starts up completely because it runs out of memory. This has two causes: since every allocation needs 4 KB, we probably reach the 2 GB limit very soon. This problem could be solved if I would make a 64-bit executable (didn't try it yet). even when I only need a few hundreds of megabytes, the allocations fail at a certain moment. The second problem is the biggest one, and I think it's related to the maximum number of PTE's (page table entries, which store information on how Virtual Memory is mapped to physical memory, and whether pages should be read-only or not) you can have in a process. My questions (or a cry-for-tips): Where can I find information about the maximum number of PTE's in a process? Is this different (higher) for 64-bit systems/applications or not? Can the number of PTE's be configured in the application or in Windows? Thanks, Patrick PS. note for those who will try to argument that you shouldn't write your own memory manager: My application is rather specific so I really want full control over memory management (can't give any more details) Last week we had a memory overwrite which we couldn't find using the standard C++ allocator and the debugging functionality of the C/C++ run time (it only said "block corrupt" minutes after the actual corruption") We also tried standard Windows utilities (like GFLAGS, ...) but they slowed down the application by a factor of 100, and couldn't find the exact position of the overwrite either We also tried the "Full Page Heap" functionality of Application Verifier, but then the application doesn't start up either (probably also running out of PTE's)

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• Matlab fft function

  - by CTZStef

  The code below is from the Matlab 2011a help about fft function. I think there is a problem here : why do they multiply t(1:50) by Fs, and then say it's time in millisecond ? Certainly, it happens to be true in this very particular case, but change the value of Fs to, say, 2000, and it won't work anymore, obviously because of this factor of 2. Right ? Quite misleading, isn't it ? What do I miss ? Fs = 1000; % Sampling frequency T = 1/Fs; % Sample time L = 1000; % Length of signal t = (0:L-1)*T; % Time vector % Sum of a 50 Hz sinusoid and a 120 Hz sinusoid x = 0.7*sin(2*pi*50*t) + sin(2*pi*120*t); y = x + 2*randn(size(t)); % Sinusoids plus noise plot(Fs*t(1:50),y(1:50)) title('Signal Corrupted with Zero-Mean Random Noise') xlabel('time (milliseconds)') Clearer with this : fs = 2000; % Sampling frequency T = 1 / fs; % Sample time L = 1000; % Length of signal t2 = (0:L-1)*T; % Time vector f = 50; % signal frequency s2 = sin(2*pi*f*t2); figure, plot(fs*t2(1:50),s2(1:50)); % NOT good figure, plot(t2(1:50),s2(1:50)); % good

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• Implement a threading to prevent UI block on a bug in an async function

  - by Marcx

  I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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• Multiple Solution Layout for ASP.NET Web Portal?

  - by Jared S

  At work, we've developed a custom ASP.NET Web Portal (That's very similar to iGoogle). We have "Apps" (self-contained, large web forms) and "Modules" (similar to Google Gadgets). Currently, we use a single-solution model. Right now, we have: 3 core projects 60 application projects 80 module projects To reduce copy and pasting between projects, we're going to factor out common functionality (Data Access, Business Logic) into separate projects. I'd also like to introduce Unit Tests, which is going to increase the number of projects even more. We've already reached the point where Visual Studio is choking on the number of projects. We generally only load the 3 core projects and then whatever app's/module's project we're working on. Would a different solution structure help us out? Our number of projects is only going to increase. In general, an app or module only references the 3 core projects. Soon, apps/modules may start referencing the Data Access/Business Logic projects. But in general, apps and modules do not make references between themselves. So to recap, what is the best practice for solution structure when there are MANY projects that use a small number of core projects?

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• Stuck in a loop

  - by Luke

  while (true) { //read in the file StreamReader convert = new StreamReader("../../convert.txt"); //define variables string line = convert.ReadLine(); double conversion; int numberIn; double conversionFactor; //ask for the conversion information Console.WriteLine("Enter the conversion in the form (Amount, Convert from, Convert to)"); String inputMeasurement = Console.ReadLine(); string[] inputMeasurementArray = inputMeasurement.Split(','); //loop through the lines looking for a match while (line != null) { string[] fileMeasurementArray = line.Split(','); if (fileMeasurementArray[0] == inputMeasurementArray[1]) { if (fileMeasurementArray[1] == inputMeasurementArray[2]) { Console.WriteLine("The conversion factor for {0} to {1} is {2}", inputMeasurementArray[1], inputMeasurementArray[2], fileMeasurementArray[2]); //convert to int numberIn = Convert.ToInt32(inputMeasurementArray[0]); conversionFactor = Convert.ToDouble(fileMeasurementArray[2]); conversion = (numberIn * conversionFactor); Console.WriteLine("{0} {1} is {2} {3} \n", inputMeasurementArray[0], inputMeasurementArray[1], conversion, inputMeasurementArray[2]); break; } } else { Console.WriteLine("Please enter two valid conversion types \n"); break; } line = convert.ReadLine(); } } The file consists of the following: ounce,gram,28.0 pound,ounce,16.0 pound,kilogram,0.454 pint,litre,0.568 inch,centimetre,2.5 mile,inch,63360.0 The user will input something like 6,ounce,gram The idea is that it finds the correct line by checking if the first and second words in the file are the same as the second and third the user enters. The problem is that if it checks the first line and it fails the if statement, if goes through to the else statement and stops. I am trying to find a way where it will stop after the it finds the correct line but not until. If someone types in a value that isn't in the file, then it should show an error.

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• How lucene indexing ?

  - by user312140

  Hello I read some document about lucene ; also i read the document in this link ( http://lucene.sourceforge.net/talks/pisa ) . I don't really understand how lucene index documents and don't understand lucene work with which algorithm for indexing ? On above link , said lucene use this algorithm for indexing : * incremental algorithm: o maintain a stack of segment indices o create index for each incoming document o push new indexes onto the stack o let b=10 be the merge factor; M=8 for (size = 1; size < M; size *= b) { if (there are b indexes with size docs on top of the stack) { pop them off the stack; merge them into a single index; push the merged index onto the stack; } else { break; } } How this algorithm help us to have an optimize indexing ? Does lucene use B-tree algorithm or any other algorithm like that for indexing or have a paticular algorithm ? Thank you for reading my post .

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• Avoiding resource (localizable string) duplication with String.Format

  - by Hrvoje Prgeša

  I'm working on a application (.NET, but not relevant) where there is large potential for resource/string duplication - most of these strings are simple like: Volume: 33 Volume: 33 (dB) Volume 33 dB Volume (dB) Command - Volume: 33 (dB) where X, Y and unit are the same. Should I define a new resource for each of the string or is it preferable to use String.Format to simplify some of these, eg.: String.Format("{0}: {1}", Resource.Volume, 33) String.Format("{0}: {1} {2}", Resource.Volume, 33, Resource.dB) Resource.Volume String.Format("{0} ({1})", 33, Resource.dB) String.Format("{0} ({1})", Resource.Volume, Resource.dB) String.Format("Command - {0}: {1} {2}", Resource.Volume, 33, Resource.dB) I would also define string formats like "{0}: {1}" in the resources so there would be a possibility of reordering words... I would not use this approach selectivly and not throughout the whole application.. And how about: String.Format("{0}: {1}", Volume, Resource.Muted_Volume) // = Volume: Muted Resource.Muted_Volume String.Format("{0}: {1} (by user {2})", Volume, Resource.Muted_Volume, "xy") // = Volume: Muted (by user xy) The advantage is cutting the number of resource by the factor of 4-5. Are there any hidden dangers of using this approach? Could someone give me an example (language) where this would not work correctly?

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• Subversion update misses new directories

  - by Mike Q

  Hi all, Periodically we have trouble with SVN when doing updates. Very occasionally when someone adds a new directory doing an update through Tortoise doesn't work. If we do a "Fully Recursive" update using "Update from revision..." option then it picks it up fine. I'm poked around and seen this question which is virtually identical but with no answer. I've found the item on the SVN website, referenced by that post, that talks about an issue in 1.6.0 which is now fixed. However my SVN version is 1.6.9 and Tortoise is 1.6.7 so I wouldn't expect to have this problem any more. This only seems to occur with new directories, never seen it for individual files. We may have had older versions of Tortoise at one point (can't remember which tho) so maybe some issue has been introduced into our repo that an upgrade doesn't solve. We have the workaround but it wastes a few minutes of head-scratching after failed builds to figure it out and people who haven't come across this problem before really struggle until they ask someone else. Anyone know if this is a known bug and any permanent solutions? Thanks.

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• breadth-first traversal of directory tree is not lazy

  - by user855443

  I try to traverse the diretory tree. A naive depth-first traversal seems not to produce the data in a lazy fashion and runs out of memory. I next tried a breadth first approach, which shows the same problem - it uses all the memory available and then crashes. the code i have is: getFilePathBreadtFirst :: FilePath -> IO [FilePath] getFilePathBreadtFirst fp = do fileinfo <- getInfo fp res :: [FilePath] <- if isReadableDirectory fileinfo then do children <- getChildren fp lower <- mapM getFilePathBreadtFirst children return (children ++ concat lower) return (children ++ concat () else return [fp] -- should only return the files? return res getChildren :: FilePath -> IO [FilePath] getChildren path = do names <- getUsefulContents path let namesfull = map (path </>) names return namesfull testBF fn = do -- crashes for /home/frank, does not go to swap fps <- getFilePathBreadtFirst fn putStrLn $ unlines fps I think all the code is either linear or tail recursive, and I would expect that the listing of filenames starts immediately, but in fact it does not. Where is the error in my code and my thinking? where have I lost lazy evaluation?

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• Pascals Triangle by recursion

  - by Olpers

  Note : My Class Teacher gave me this question as an assignment... I am not asked to do it but please tell me how to do it with recursion Binomial coefficients can be calculated using Pascal's triangle: 1 n = 0 1 1 1 2 1 1 3 3 1 1 4 6 4 1 n = 4 Each new level of the triangle has 1's on the ends; the interior numbers are the sums of the two numbers above them. Task: Write a program that includes a recursive function to produce a list of binomial coefficients for the power n using the Pascal's triangle technique. For example, Input = 2 Output = 1 2 1 Input = 4 Output = 1 4 6 4 1 done this So Far but tell me how to do this with recursion... #include<stdio.h> int main() { int length,i,j,k; //Accepting length from user printf("Enter the length of pascal's triangle : "); scanf("%d",&length); //Printing the pascal's triangle for(i=1;i<=length;i++) { for(j=1;j<=length-i;j++) printf(" "); for(k=1;k<i;k++) printf("%d",k); for(k=i;k>=1;k--) printf("%d",k); printf("\n"); } return 0; }

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• Tree iterator, can you optimize this any further?

  - by Ron

  As a follow up to my original question about a small piece of this code I decided to ask a follow up to see if you can do better then what we came up with so far. The code below iterates over a binary tree (left/right = child/next ). I do believe there is room for one less conditional in here (the down boolean). The fastest answer wins! The cnt statement can be multiple statements so lets make sure this appears only once The child() and next() member functions are about 30x as slow as the hasChild() and hasNext() operations. Keep it iterative <-- dropped this requirement as the recursive solution presented was faster. This is C++ code visit order of the nodes must stay as they are in the example below. ( hit parents first then the children then the 'next' nodes). BaseNodePtr is a boost::shared_ptr as thus assignments are slow, avoid any temporary BaseNodePtr variables. Currently this code takes 5897ms to visit 62200000 nodes in a test tree, calling this function 200,000 times. void processTree (BaseNodePtr current, unsigned int & cnt ) { bool down = true; while ( true ) { if ( down ) { while (true) { cnt++; // this can/will be multiple statesments if (!current->hasChild()) break; current = current->child(); } } if ( current->hasNext() ) { down = true; current = current->next(); } else { down = false; current = current->parent(); if (!current) return; // done. } } }

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• PHP: Formatting multi-dimensional array as HTML?

  - by Industrial

  Hi everybody, I have tried to get my head around building a recursive function to handle formatting of a unknown depth multi-dimensional array to HTML and nested Divs. I thought that it should be a piece of cake, but no. Here's what I have come up with this far: function formatHtml($array) { $var = '<div>'; foreach ($array as $k => $v) { if (is_array($v['children']) && !empty($v['children'])) { formatHtml($v['children']); } else { $var .= $v['cid']; } } $var.= '</div>'; return $var; } And here's my array: Array ( [1] => Array ( [cid] => 1 [_parent] => [id] => 1 [name] => 'Root category' [children] => Array ( [2] => Array ( [cid] => 2 [_parent] => 1 [id] => 3 [name] => 'Child category' [children] => Array () ) ) ) ) Thanks a lot!

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