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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • Linux Scheduling Mechanism in 2.6.22?

    - by Mazen
    Hello, I'm doing some kind of performance evaluation using two different vanilla Linux kernels, 2.6.22 and 2.6.31, since I assume each of them uses a different scheduling mechanism: 2.6.22 uses the old O(1) scheduler, whilst 2.6.31 adopts the CFS. Could anybody confirm the correction of this assumption?

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  • jquerry in rails

    - by Matthias Günther
    I'm iteration over records and want to create the toggle-options for records but I can't replace the div-id with the records: <% for bill in @bills % <% tmp = "test"% <%= link_to '&raquo now','#', :onclick = '$("#{tmp}").toggle();' % Instead of getting: &raquo now I'm getting: &raquo now So he isn't evaluation the ruby variable in the string. How can I do this? Thanks for your help and I'm new in jquerry.

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  • cpu floating operations cost

    - by wiso
    I'm interesting in the time cost on a modern desktop cpu of some floating point operations in order to optimize a mathematical evaluation. In particular I'm interested on the comparison between complex operations like exp, log and simple operation like +, *, /. I tried to search for these information, but I can't find a source.

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  • Does Ruby have a special stack for returning a value?

    - by prosseek
    The following Ruby code def a(b,c) b+c end is the same as follows with Python def a(b,c): return b+c It looks like that ruby has the special stack that stores the final evaluation result and returns the value when a function is called. If so, what's the name of the stack, and how can I get that stack? If not, how does the Ruby code work without returning something?

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  • Minimize the sequence by putting appropriate operations ' DP'

    - by Vikas
    Given a sequence,say, 222 We have to put a '+' or '* ' between each adjacent pair. '* ' has higher precedence over '+' We have to o/p the string whose evaluation leads to minimum value. O/p must be lexicographically smallest if there are more than one. inp:222 o/p: 2*2+2 Explaination: 2+2+2=6 2+2*2=6 2*2+2=6 of this 3rd is lexicographically smallest. I was wondering how to construct a DP solution for this.

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  • Best Embedded SQL DB for write performance?

    - by max.minimus
    Has anybody done any benchmarking/evaluation of the popular open-source embedded SQL DBs for performance, particularly write performance? I've some 1:1 comparisons for sqlite, Firebird Embedded, Derby and HSQLDB (others I am missing?) but no across the board comparisons... Also, I'd be interested in the overall developer experience for any of these (for a Java app).

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  • How does the CLR (.NET) internally allocate and pass around custom value types (structs)?

    - by stakx
    Question: Do all CLR value types, including user-defined structs, live on the evaluation stack exclusively, meaning that they will never need to be reclaimed by the garbage-collector, or are there cases where they are garbage-collected? Background: I have previously asked a question on SO about the impact that a fluent interface has on the runtime performance of a .NET application. I was particuarly worried that creating a large number of very short-lived temporary objects would negatively affect runtime performance through more frequent garbage-collection. Now it has occured to me that if I declared those temporary objects' types as struct (ie. as user-defined value types) instead of class, the garbage collector might not be involved at all if it turns out that all value types live exclusively on the evaluation stack. What I've found out so far: I did a brief experiment to see what the differences are in the CIL generated for user-defined value types and reference types. This is my C# code: struct SomeValueType { public int X; } class SomeReferenceType { public int X; } . . static void TryValueType(SomeValueType vt) { ... } static void TryReferenceType(SomeReferenceType rt) { ... } . . var vt = new SomeValueType { X = 1 }; var rt = new SomeReferenceType { X = 2 }; TryValueType(vt); TryReferenceType(rt); And this is the CIL generated for the last four lines of code: .locals init ( [0] valuetype SomeValueType vt, [1] class SomeReferenceType rt, [2] valuetype SomeValueType <>g__initLocal0, // [3] class SomeReferenceType <>g__initLocal1, // why are these generated? [4] valuetype SomeValueType CS$0$0000 // ) L_0000: ldloca.s CS$0$0000 L_0002: initobj SomeValueType // no newobj required, instance already allocated L_0008: ldloc.s CS$0$0000 L_000a: stloc.2 L_000b: ldloca.s <>g__initLocal0 L_000d: ldc.i4.1 L_000e: stfld int32 SomeValueType::X L_0013: ldloc.2 L_0014: stloc.0 L_0015: newobj instance void SomeReferenceType::.ctor() L_001a: stloc.3 L_001b: ldloc.3 L_001c: ldc.i4.2 L_001d: stfld int32 SomeReferenceType::X L_0022: ldloc.3 L_0023: stloc.1 L_0024: ldloc.0 L_0025: call void Program::TryValueType(valuetype SomeValueType) L_002a: ldloc.1 L_002b: call void Program::TryReferenceType(class SomeReferenceType) What I cannot figure out from this code is this: Where are all those local variables mentioned in the .locals block allocated? How are they allocated? How are they freed? Why are so many anonymous local variables needed and copied to-and-fro only to initialize my two local variables rt and vt?

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  • Accessing Arbitrary Columns from an R Data Frame using with()

    - by johnmyleswhite
    Suppose that I have a data frame with a column whose name is stored in a variable. Accessing this column using the variable is easy using bracket notation: df <- data.frame(A = rep(1, 10), B = rep(2, 10)) column.name <- 'B' df[,column.name] But it is not obvious how to access an arbitrary column using a call to with(). The naive approach with(df, column.name) effectively evaluates column.name in the caller's environment. How can I delay evaluation sufficiently that with() will provide the same results that brackets give?

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  • Does Ruby have a special stack for return value?

    - by prosseek
    The following Ruby code def a(b,c) b+c end is the same as follows with Python def a(b,c): return b+c It looks like that ruby has the special stack that stores the final evaluation result and returns the value when a function is called. If so, what's the name of the stack, and how can I get that stack? If not, how does the Ruby code work without returning something?

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  • How to apply %% to a variable in a script with input parameter?

    - by murxx
    Hi, I asked a question yesterday about how to manage to get %% around a variable without getting the evaluation. Well, the thing is, it does not work that way in my case... I have a .bat file which gets an input parameter. Later on I want to use the value of this input parameter and put %...% around, like: call script.bat testValue script.bat: set inputPar=%1 set newValue=%%inputPar%% Now I get: echo %inputPar% testValue echo %newValue% %inputPar% But I would like to get: echo %newValue% %testValue% Is that somehow possible?

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  • Confused about ASP.NET AJAX, AJAX, jQUERY and javascript

    - by Mr.Y
    Yesterday, I read couple of chapters on ASP.NET Ajax,and jQuery from my ASP.NET 4.0 book and I found those frameworks pretty interesting and decide to learn more about it. Today, I borrow some books from library on AJAX and Javascript. It seems ASP.NET ajax is different from Ajax and jQuery seems like the "new" javascript. Is that means I can skip javascript and learn jQUERY directly? On the other hand, the Ajax(non asp.net) book I borrow from library seems apply to the client side web programming only and looks quite difference from what I learned from ASP.NET AJAX. If I'm a ASP.NET developer I guess I should stick with ASP.NET AJAX instead of client side AJAX right? What about PHP? Is there a "PHP AJAX" similar to ASP.NET AJAX? It's not that I'm "lazy" to learn other tools, but I just want to focus on the right ones. Thx. The more I going deep

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  • Automatically Create Your Project&rsquo;s NuGet Package Every Time It Builds Via NuGet

    - by deadlydog
    Originally posted on: http://geekswithblogs.net/deadlydog/archive/2013/06/22/automatically-create-your-projectrsquos-nuget-package-every-time-it-builds.aspxSo you’ve got a super awesome library/assembly that you want to share with others, but you’re too lazy to actually use NuGet to package it up and upload it to the gallery; or maybe you don’t know how to create a NuGet package and don’t have the time or desire to learn.  Well, my friends, now this can all be handled for you automatically. Read more at http://blog.danskingdom.com/automatically-create-your-projects-nuget-package-every-time-it-builds-via-nuget/

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  • Popup Details for a Table Record

    - by shay.shmeltzer
    This one started as an OTN how-to question that seemed like something that should work automatically - turns out you need a couple of small tweaks to get it working. The idea is to have a table on a page showing multiple records, you can click any row in the table - and get a pop-up window that shows more data about that row. At first I thought I'll just need to drag the same view twice to the page - once as a table and then as a form in a pop-up. But then the Form didn't reflect the new row that got selected in the table - you'll always see the first row you selected. Adding a Partial Page Rendering between the table and the pop-up didn't do the trick either. Then I realized that the content delivery attribute of the pop-up was set to lazy, when I switched it to immediate - everything worked. Here is a little demo showing the whole development process: Note that the content delivery method attribute is also something you might want to check if you see your tables being refreshed too often when you scroll through records for example.

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  • Using the af:poll to refresh parts of the page periodically

    - by shay.shmeltzer
    Just a quick sample of using the af:poll components. A component that enables you to do things in a periodic fashion. For example check if something has changed on the server and update the UI. A more "modern" approach is to actually use push instead of pull, and ADF Faces will allow you to do that with ADS (here, and here). But the poll still has its place. It's quite useful for dashboard type of applications where you want periodic updates of the graphs shown on the page. As you can see it's quite simple to use the tag. I also show my lazy approach to invoking declarative operations on a data control from a backing bean without manually writing code.

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  • Simplifying the process of compiling and running objective-c apps in GNUstep

    - by Matthew
    I just installed GNUstep (following this post: http://www.jaysonjc.com/programming/objective-c-programming-in-windows-gnustep-projectcenter.html) It says to run this code: gcc -o helloworld helloworld.m -I /GNUstep/System/Library/Headers -L /GNUstep/System/Library/Libraries -lobjc -lgnustep-base -fconstant-string-class=NSConstantString every time I want to compile. It works just fine for me. However as I'm learning and will be compiling/running apps way often (making little changes and trying again), I'd like a simpler way to do this. Is there an easier way to compile and then run the app? Or am I just being lazy?

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  • PowerShell Try Catch Finally

    - by PointsToShare
    PowerShell Try Catch Finally I am a relative novice to PowerShell and tried (pun intended) to use the “Try Catch Finally” in my scripts. Alas the structure that we love and use in C# (or even – shudder of shudders - in VB) does not always work in PowerShell. It turns out that it works only when the error is a terminating error (whatever that means). Well, you can turn all your errors to the terminating kind by simply setting - $ErrorActionPreference = "Stop", And later resetting it back to “Continue”, which is its normal setting. Now, the lazy approach is to start all your scripts with: $ErrorActionPreference = "Stop" And ending all of them with: $ErrorActionPreference = "Continue" But this opens you to trouble because should your script have an error that you neglected to catch (it even happens to me!), your session will now have all its errors as “terminating”. Obviously this is not a good thing, so instead let’s put these two setups in the beginning of each Try block and in the Finally block as seen below: That’s All Folks!!

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  • jQuery AJAX Validation Using The Validity Plugin

    - by schnieds
    Input validation is one of those areas that most developers view as a necessary evil. We know that it is necessary and we really do want to ensure that we get good input from our users. But most of us are lazy (me included) and input validation is one of those things that gets done but usually is a quick and dirty implementation. This is partly due to laziness and partly do to input validation being painful. Thanks to the amazing jQuery Validity plug in, input validation can be really slick, easy and robust enough to work any any scenario. I specifically like the Validity plugin because it supports jQuery AJAX input validation. Other input validation implementations that I have worked with require a form post to take place. However, if you are using jQuery.ajax methods then there isn’t a form and you need to validate the formless input. [Read More] Aaron Schniederhttp://www.churchofficeonline.com

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  • Implementing an Interceptor Using NHibernate’s Built In Dynamic Proxy Generator

    - by Ricardo Peres
    NHibernate 3.2 came with an included proxy generator, which means there is no longer the need – or the possibility, for that matter – to choose Castle DynamicProxy, LinFu or Spring. This is actually a good thing, because it means one less assembly to deploy. Apparently, this generator was based, at least partially, on LinFu. As there are not many tutorials out there demonstrating it’s usage, here’s one, for demonstrating one of the most requested features: implementing INotifyPropertyChanged. This interceptor, of course, will still feature all of NHibernate’s functionalities that you are used to, such as lazy loading, and such. We will start by implementing an NHibernate interceptor, by inheriting from the base class NHibernate.EmptyInterceptor. This class does not do anything by itself, but it allows us to plug in behavior by overriding some of its methods, in this case, Instantiate: 1: public class NotifyPropertyChangedInterceptor : EmptyInterceptor 2: { 3: private ISession session = null; 4:  5: private static readonly ProxyFactory factory = new ProxyFactory(); 6:  7: public override void SetSession(ISession session) 8: { 9: this.session = session; 10: base.SetSession(session); 11: } 12:  13: public override Object Instantiate(String clazz, EntityMode entityMode, Object id) 14: { 15: Type entityType = Type.GetType(clazz); 16: IProxy proxy = factory.CreateProxy(entityType, new _NotifyPropertyChangedInterceptor(), typeof(INotifyPropertyChanged)) as IProxy; 17: 18: _NotifyPropertyChangedInterceptor interceptor = proxy.Interceptor as _NotifyPropertyChangedInterceptor; 19: interceptor.Proxy = this.session.SessionFactory.GetClassMetadata(entityType).Instantiate(id, entityMode); 20:  21: this.session.SessionFactory.GetClassMetadata(entityType).SetIdentifier(proxy, id, entityMode); 22:  23: return (proxy); 24: } 25: } Then we need a class that implements the NHibernate dynamic proxy behavior, let’s place it inside our interceptor, because it will only need to be used there: 1: class _NotifyPropertyChangedInterceptor : NHibernate.Proxy.DynamicProxy.IInterceptor 2: { 3: private PropertyChangedEventHandler changed = delegate { }; 4:  5: public Object Proxy 6: { 7: get; 8: set;} 9:  10: #region IInterceptor Members 11:  12: public Object Intercept(InvocationInfo info) 13: { 14: Boolean isSetter = info.TargetMethod.Name.StartsWith("set_") == true; 15: Object result = null; 16:  17: if (info.TargetMethod.Name == "add_PropertyChanged") 18: { 19: PropertyChangedEventHandler propertyChangedEventHandler = info.Arguments[0] as PropertyChangedEventHandler; 20: this.changed += propertyChangedEventHandler; 21: } 22: else if (info.TargetMethod.Name == "remove_PropertyChanged") 23: { 24: PropertyChangedEventHandler propertyChangedEventHandler = info.Arguments[0] as PropertyChangedEventHandler; 25: this.changed -= propertyChangedEventHandler; 26: } 27: else 28: { 29: result = info.TargetMethod.Invoke(this.Proxy, info.Arguments); 30: } 31:  32: if (isSetter == true) 33: { 34: String propertyName = info.TargetMethod.Name.Substring("set_".Length); 35: this.changed(this.Proxy, new PropertyChangedEventArgs(propertyName)); 36: } 37:  38: return (result); 39: } 40:  41: #endregion 42: } What this does for every interceptable method (those who are either virtual or from the INotifyPropertyChanged) is: For methods that came from the INotifyPropertyChanged interface, add_PropertyChanged and remove_PropertyChanged (yes, events are methods ), we add an implementation that adds or removes the event handlers to the delegate which we declared as changed; For all the others, we direct them to the place where they are actually implemented, which is the Proxy field; If the call is setting a property, it fires afterwards the PropertyChanged event. In order to use this, we need to add the interceptor to the Configuration before building the ISessionFactory: 1: using (ISessionFactory factory = cfg.SetInterceptor(new NotifyPropertyChangedInterceptor()).BuildSessionFactory()) 2: { 3: using (ISession session = factory.OpenSession()) 4: using (ITransaction tx = session.BeginTransaction()) 5: { 6: Customer customer = session.Get<Customer>(100); //some id 7: INotifyPropertyChanged inpc = customer as INotifyPropertyChanged; 8: inpc.PropertyChanged += delegate(Object sender, PropertyChangedEventArgs e) 9: { 10: //fired when a property changes 11: }; 12: customer.Address = "some other address"; //will raise PropertyChanged 13: customer.RecentOrders.ToList(); //will trigger the lazy loading 14: } 15: } Any problems, questions, do drop me a line!

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  • Turbo C++ to Visual Studio 2010 migration [closed]

    - by BigGenius
    OK, based on my previous questions and your help., I have gone to install Visual Studio Express. But now problem is, the programs which I successfully code at home on Visual Studio don't run on Turbo C++ compiler at school (assuming I type the program instead of exporting code). Is there anything I can do? Also I am just learning basic syntax and data handling, loops, structures, arrays and all. But Visual Studio has auto completion and pretty typing (which may be advantageous) but crap for a beginner getting hold on to language. Sorry, if I have been unclear. But what should I do? This will make me lazy programmer and will reflect in my grades. Is there any other IDE, which I can use, very similar to Turbo C++ and able to run in Windows 7 in fullsreen mode.

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  • Tab Sweep - More OSGi, Coherence, Oracle Java moves, JMS 2.0 and more

    - by alexismp
    Recent Tips and News on Java, Java EE 6, GlassFish & more : • Why I will use Java EE (JEE, and not J2EE) instead of Spring in new Enterprise Java Projects (Kai) • What is Happening vs. What is Interesting (Geertjan) • Oracle Coherence & Oracle Service Bus: REST API Integration (Nino) • Oracle's Top 10 Java Moves of 2011 (eWeek) • JEP 122: Remove the Permanent Generation (OpenJDK.org) • JEE6 – Glassfish 3.1, Clustering & Failover (Xebia.fr) • Testing LAZY mechanism in EJB 3 (e-blog-java) • Discoing with Vorpal (Chuk) • Devoxx : les évolutions de JMS 2.0 (Ippon.fr) • More OSGi... (Jarda) • Practical Migration to Java 7 - Small Codeexamples (FOSSLC) • Coherence Part III : Filtres (Zenika.com)

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  • Web standards or risk avoidance?

    - by Junior Dev
    My company is building an App Engine application. The app encounters a bug (possibly due to an issue with App Engine itself, as per our research) on IE9, but it cannot be reliably reproduced and is experienced by a small percentage of users. The workaround is to force IE9 to use IE8 mode. As a lazy front end developer (who doesn't like CSS hacks, shims and polyfills) I think it's OK to at least try going back to IE9 mode and see what happens, while we're still in private beta. The senior engineer (being more pragmatic) would rather that we continue forcing IE9 users to use the older IE8 mode. Who is right?

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  • Installed Ruby 1.9.2 but new gems won't create scripts into /usr/bin

    - by karatedog
    I had previously ruby 1.8 on my Ubuntu 10.10, which I removed through Synaptics. Then I have installed ruby 1.9.1 also via Synaptics (which is then saying that itself is version 1.9.2). Then I installed ruby-debug19 and rspec gems with sudo gem install ruby-debug19 rspec However I can't start rdebug or rspec, but I can invoke the debugger from inside my ruby script, so the debugger is working. I inspected the starting scipts rdebug and rspec and then I realized that they are still old scripts back from ruby1.8 time. In other worlds, the current 1.9 install of these gems haven't created the starting scripts anywhere. What is the easiest solution for a lazy soul like me? It looks like removing-reinstalling ruby 1.9.2 won't help, and installing these gems over and over againg won't create the starting scripts.

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