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• What are practical guidelines for evaluating a language's "Turing Completeness"?

  - by AShelly

  I've read "what-is-turing-complete" and the wikipedia page, but I'm less interested in a formal proof than in the practical implications of being Turing Complete. What I'm actually trying to decide is if the toy language I've just designed could be used as a general-purpose language. I know I can prove it is if I can write a Turing machine with it. But I don't want to go through that exercise until I'm fairly certain of success. Is there a minimum set of features without which Turing Completeness is impossible? Is there a set of features which virtually guarantees completeness? (My guess is that conditional branching and a readable/writeable memory store will get me most of the way there) EDIT: I think I've gone off on a tangent by saying "Turing Complete". I'm trying to guess with reasonable confidence that a newly invented language with a certain feature set (or alternately, a VM with a certain instruction set) would be able to compute anything worth computing. I know proving you can building a Turing machine with it is one way, but not the only way. What I was hoping for was a set of guidelines like: "if it can do X,Y,and Z, it can probably do anything".

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• F#: Define an abstract class that inherits an infterface, but does not implement it

  - by akaphenom

  I owuld like to define an abstract class that inerhits from UserControl and my own Interface IUriProvider, but doesn't implement it. The goal is to be able to define pages (for silverlight) that implement UserControl but also provide their own Uri's (and then stick them in a list / array and deal with them as a set: type IUriProvider = interface abstract member uriString: String ; abstract member Uri : unit -> System.Uri ; end type UriUserControl() as this = inherit IUriProvider with abstract member uriString: String ; inherit UserControl() Also the Uri in the definition - I would like to implement as a property getter - and am having issues with that as well. this does not compile type IUriProvider = interface abstract member uriString: String with get; end Thank you...

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• Database solutions for storing/searching EXIF data

  - by webdestroya

  I have thousands of photos on my site (each with a numeric PhotoID) and I have EXIF data (photos can have different EXIF tags as well). I want to be able to store the data effectively and search it. Some photos have more EXIF data than others, some have the same, so on.. Basically, I want to be able to query say 'Select all photos that have a GPS location' or 'All photos with a specific camera' I can't use MySQL (tried it, it doesn't work). I thought about Cassandra, but I don't think it lets me query on fields. I looked at SimpleDB, but I would rather: not pay for the system, and I want to be able to run more advanced queries on the data. Also, I use PHP and Linux, so it would be awesome if it could interface nicely to PHP. Any ideas?

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• Gmail-like labelling system

  - by Dimitris

  Hi I am looking into a number of ways to implement a labelling system similar to the one in Gmail. Basically I have a Resource at the lowest level and I would like to provide a number of organisational groupings for that resource in the form of labels. If anyone has implemented something like that I would like to hear your views. My idea is to have within the Resource instance a List<Label>. I need to have an efficient mechanism in order to do very fast searches based on the labels or based on the resources. Thanks Dimitris

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• Subversion Repository Layout

  - by Tim Long

  Most subversion tools create a default repository layout with /trunk, /branches and /tags. The documentation also recommends not using separate repositories for each project, so that code can be more easily shared. Following that advice has led to me having a repository with the following layout: /trunk /Project1 /Project2 /branches /Project1 /Project2 /tags /Project1 /Project2 and so on, you get the idea. Over time, I've found this structure a bit clumsy and it occurred to me that there's an alternative interpretation of the recommendations, such as: /Project1 /trunk /branches /tags /Project2 /trunk /branches /tags So, which layout do people use, and why? Or - is there another way to do things that I've completely missed?

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• What is the basic pattern for using (N)Hibernate?

  - by Vilx-

  I'm creating a simple Windows Forms application with NHibernate and I'm a bit confused about how I'm supposed to use it. To quote the manual: ISession (NHibernate.ISession) A single-threaded, short-lived object representing a conversation between the application and the persistent store. Wraps an ADO.NET connection. Factory for ITransaction. Holds a mandatory (first-level) cache of persistent objects, used when navigating the object graph or looking up objects by identifier. Now, suppose I have the following scenario: I have a simple classifier which is a MSSQL table with two columns - ID (auto_increment) and Name (nvarchar). To edit this classifier I create a form which contains a single gridview and two buttons - OK and Cancel. The user can nearly directly edit the table in the gridview, and when he hits OK the changes he made are persisted to the DB (or if he hits cancel, nothing happens). Now, I have several questions about how to organize this: What should the lifetime of my ISession be? Should I create a single ISession for my whole application; an ISession for each of my forms (the application is single-threaded MDI); or an ISession for every DB operation/transaction? Does NHibernate offer some kind of built-in dirty tracking or must I do this myself? The manual mentions something like it here and there but does not go into details. How is this done? Is there not a huge overhead? Is it somehow tied with the cache(s) that NHibernate has? What are these caches for? Are they not specific to a single ISession? That is, if I use a seperate ISession for every transaction, won't it break the dirty tracking? How does the built-in dirty tracking detect deleted objects?

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• Why Use PHP OOP over Basic Functions and When?

  - by Codex73

  There are some posts about this matter, but I didn't clearly get when to use Object Oriented coding and when to use programmatic functions in an include. Somebody also mentioned to me that OOP is very heavy to run, and makes more workload. Is this right? Lets say I have a big file with 50 functions, why will I want to call these in a class? and not by function_name(). Should I switch and create object which holds all of my functions? What will be the advantage or specific difference? What benefits does it bring to code OOP in php ? Modularity?

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• How to do dependency injection python-way?

  - by Konstantin

  I've been reading a lot about python-way lately so my question is How to do dependency injection python-way? I am talking about usual scenarios when, for example, service A needs access to UserService for authorization checks.

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• [NEWVERSION]algorithm || method to write prog[UNSOLVED] [closed]

  - by fatai

  I am one of the computer science student. Everyone solve problem with a different or same method, ( but actually I dont know whether they use method or I dont know whether there are such common method to approach problem.) if there are common method, What is it ? If there are different method, which method are you using ? All teacher give us problem which in simple form sometimes, but they donot introduce any approach or method(s) so that we cannot make a decision to choose the method then apply that one to problem , afterward find solution then write code.No help from teacher , push us to find method to solve homework. Ex: my friend is using no method , he says "I start to construct algorithm while I try to write prog." I have found one method when I failed the course, More accurately, my method: When I counter problem in language , I will get more paper and then ; first, input/ output step ; my prog will take this / these there argument(s) and return namely X , ex : in c, input length is not known and at same type , so I must use pointer desired output is in form of package , so use structure second, execution part ; in that step , I am writing all step which are goes to final output ex : in python ; 1.) [ + , [- , 4 , [ * , 1 , 2 ]], 5] 2.) [ + , [- , 4 , 2 ],5 ] 3.) [ + , 2 , 5] 4.) 7 ==> return 7 third, I will write test code ex : in c++ input : append 3 4 5 6 vector_x remove 0 1 desired output vector_x holds : 5 6 now, my other question is ; What is/are other method(s) which have/has been; used to construct class :::: for c++ , python, java used to communicate classes / computers used for solving embedded system problem ::::: for c by other user? Some programmer uses generalized method without considering prog-language(java , perl .. ), what is this method ? Why I wonder , because I learn if you dont costruct algorithm on paper, you may achieve your goal. Like no money no lunch , I can say no algorithm no prog therefore , feel free when you write your own method , a way which is introduced by someone else but you are using and you find it is so efficient

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• O(log n) algorithm to find the element having rank i in union of pre-sorted lists

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Which Code Should Go Where in MVC Structure

  - by Oguz

  My problem is in somewhere between model and controller.Everything works perfect for me when I use MVC just for crud (create, read, update, delete).I have separate models for each database table .I access these models from controller , to crud them . For example , in contacts application,I have actions (create, read, update, delete) in controller(contact) to use model's (contact) methods (create, read, update, delete). The problem starts when I try to do something more complicated. There are some complex processes which I do not know where should I put them. For example , in registering user process. I can not just finish this process in user model because , I have to use other models too (sending mails , creating other records for user via other models) and do lots of complex validations via other models. For example , in some complex searching processes , I have to access lots of models (articles, videos, images etc.) Or, sometimes , I have to use apis to decide what I will do next or which database model I will use to record data So where is the place to do this complicated processes. I do not want to do them in controllers , Because sometimes I should use these processes in other controllers too. And I do not want to put these process in models because , I use models as database access layers .May be I am wrong,I want to know . Thank you for your answer .

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• DLCALENDAR date picker causing KB927917 error in IE8

  - by Lynn

  I've used this calendar widget for several years and several pages, but IE8 refuses to load my new page when I add the date picker. Has anyone seen/overcome this kind of problem? Thanks!

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• Why are alloc and init called separately in Objective-C?

  - by André Hoffmann

  Note: I'm relatively new to Objective-C and am coming from Java and PHP. Could someone explain to me why I always have to first allocate and then initialize an instance? Couldn't this be done in the init methods like this: + (MyClass*)init { MyClass *instance = [MyClass alloc]; [instance setFoo:@"bla"]; return instance; } + (MyClass*)initWithString:(NSString*)text { MyClass *instance = [MyClass init]; [instance setFoo:text]; return instance; } ... Is this just a relict from the old C days or is there something that I'm not seeing? I know this isn't a problem as I could as well always call alloc and init, but since it's a bit tedious I'd like to at least know why I'm doing it. I'm liking the expressiveness of the language so far, but this is something that I want to fully understand in order to think the Objective-C way. Thank you!

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• Saving complex aggregates using Repository Pattern

  - by Kevin Lawrence

  We have a complex aggregate (sensitive names obfuscated for confidentiality reasons). The root, R, is composed of collections of Ms, As, Cs, Ss. Ms have collections of other low-level details. etc etc R really is an aggregate (no fair suggesting we split it!) We use lazy loading to retrieve the details. No problem there. But we are struggling a little with how to save such a complex aggregate. From the caller's point of view: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r); Our competing solutions are: Dirty flags Each entity in the aggregate in the aggregate has a dirty flag. The save() method in the repository walks the tree looking for dirty objects and saves them. Deletes and adds are a little trickier - especially with lazy-loading - but doable. Event listener accumulates changes. Repository subscribes a listener to changes and accumulates events. When save is called, the repository grabs all the change events and writes them to the DB. Give up on repository pattern. Implement overloaded save methods to save the parts of the aggregate separately. The original example would become: r = repository.find(id); r.Ps.add(factory.createP()); r.Cs[5].updateX(123); r.Ms.removeAt(5); repository.save(r.Ps); repository.save(r.Cs); repository.save(r.Ms); (or worse) Advice please! What should we do?

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• Understanding colors

  - by Ankur Gupta

  Hello everyone, Kindly point towards theory/material to read for understanding colors and what makes a good color combinations. Mind it that I am not interested in say "Color combinations for web application" etc. More of the lines of say "Colors and humans". Material free to read is what i am looking for. Thanks

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• How do I call exec in psake to an executable with a variable path?

  - by Josh Kodroff

  I can't seem to call this executable correctly in my psake deploy script. If I do this: exec { "$ArchiverOutputDir\NServiceBus.Host.exe /install" } It simply outputs this (and is clearly not calling the executable - just outputting the value of that expression): c:\ReloDotNet2_ServiceEndpoints\Archiver\NServiceBus.Host.exe /install But if I do this: exec { c:\ReloDotNet2_ServiceEndpoints\Archiver\NServiceBus.Host.exe /install } I get the expected output from the executable. How do I correctly call an executable with a variable in the path to the executable in psake? If this is actually a PowerShell issue, please feel free to correct the question to reflect that insight. I

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• Resources on wordpress theme-development

  - by Espenhh

  What are the best resources for Wordpress theme-development? I am currently in the phase of starting my own blog, and don't want to use one of the many free themes. I already have a theme for my website, so I want to read about best-practices. Any advice on how to get started would be very welcome :) I have now created my theme (wohoo!), and thought I should summarize the best resources I found. Lets see.. Resources: ThemeTation's three-part guide to create a wordpress-theme from scratch Nettuts.com's guide: How to Create a Wordpress Theme from Scratch (And Part 2) Didn't actually use this, it's a quite new article, but anyway - it's great. It will get a follow-up in the next few days too.. Wordpress.org's own guide on templates Definatly a must-read for everyone new to wordpress-designing.. "The loop" Essential knowledge, also a must-read Directory of all the template tags Used by wordpress to actually output blog-content.. Inspiration: Smashing Magazine's lists: first, one more, yet another one Wordpress.org's theme-directory

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• Conceptual website designer ideas?

  - by Alex Tang

  Hi, I'm just wondering if anyone knows of any tool (apart from Visio) to generate visually nice looking website site maps or diagrams of a conceptual website. We're wanting to present some nice diagrams to our client but we're unsure about where to get started - we're all coders, not designers. Visio shapes or stencils are quite old. Just wondered what others in the industry are using!

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• How to record different authentication types (username / password vs token based) in audit log

  - by RM

  I have two types of users for my system, normal human users with a username / password, and delegation authorized accounts through OAuth (i.e. using a token identifier). The information that is stored for each is quite different, and are managed by different subsytems. They do however interact with the same tables / data within the system, so I need to maintain the audit trail regardless of whether human user, or token-based user modified the data. My solution at the moment is to have a table called something like AuditableIdentity, and then have the two types inheriting off that table (either in the single table, or as two seperate tables with 1 to 1 PK with AuditableIdentity. All operations would use the common AuditableIdentity PK for CreatedBy, ModifiedBy etc columns. There isn't any FK constraint on the audit columns, so any text can go in there, but I want an easy way to easily determine whether it was a human or system that made the change, and joining to the one AuditableIdentity table seems like a clean way to do that? Is there a best practice for this scenario? Is this an appropriate way of approaching the problem - or would you not bother with the common table and just rely on joins (to the two seperate un-related user / token tables) later to determine which user type matches which audit records?

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• FWA for CSS based sites

  - by weotch

  Does anyone have a favorite style site that posts the latest and greatest sites constructed with CSS + HTML + JS? I'm thinking of something like thefwa.com but not for all flash microsites. Trying to find the definitive portal.

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• ER Data Model - confused by diagram.

  - by Khou

  Hi im a little confused by this diagram http://www.b-eye-network.com/images/content/i030ht0104.gif (Last diagram in the article) 1 - In the "ACCOUNTING ENTRY" table it shows "DebitEntry" and "CreditEntry" i) is this two column or ii) is this two rows of data? or iii) is it two separate tables on its own, Acounting_entry_credit and Accounting_entry_debit? Same question with the "ACCOUNT" table, it shows asset account, livabilities account, equaity account? are they 3 columns or are they 3 rows? Source: http://www.tdan.com/view-articles/5227/

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• Conditional Styling In Silverlight?

  - by DeanMc

  Hi, While I'm fine with standard control styling in silverlight I have recently began using more dynamic methods of fetching data to be displayed in items controls. One of the controls I am reworking is a collection of links. The issue I am having is that each link is coloured differently when moused over. One red, one blue, one green, etc. Is there a way to style these items without sacrificing the dynamics of using an items control with a data template?

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• C# Memoization of functions with arbitrary number of arguments

  - by Lirik

  I'm trying to create a memoization interface for functions with arbitrary number of arguments, but I'm failing miserably. The first thing I tried is to define an interface for a function which gets memoized automatically upon execution: class EMAFunction:IFunction { Dictionary<List<object>, List<object>> map; class EMAComparer : IEqualityComparer<List<object>> { private int _multiplier = 97; public bool Equals(List<object> a, List<object> b) { List<object> aVals = (List<object>)a[0]; int aPeriod = (int)a[1]; List<object> bVals = (List<object>)b[0]; int bPeriod = (int)b[1]; return (aVals.Count == bVals.Count) && (aPeriod == bPeriod); } public int GetHashCode(List<object> obj) { // Don't compute hash code on null object. if (obj == null) { return 0; } // Get length. int length = obj.Count; List<object> vals = (List<object>) obj[0]; int period = (int) obj[1]; return (_multiplier * vals.GetHashCode() * period.GetHashCode()) + length;; } } public EMAFunction() { NumParams = 2; Name = "EMA"; map = new Dictionary<List<object>, List<object>>(new EMAComparer()); } #region IFunction Members public int NumParams { get; set; } public string Name { get; set; } public object Execute(List<object> parameters) { if (parameters.Count != NumParams) throw new ArgumentException("The num params doesn't match!"); if (!map.ContainsKey(parameters)) { //map.Add(parameters, List<double> values = new List<double>(); List<object> asObj = (List<object>)parameters[0]; foreach (object val in asObj) { values.Add((double)val); } int period = (int)parameters[1]; asObj.Clear(); List<double> ema = TechFunctions.ExponentialMovingAverage(values, period); foreach (double val in ema) { asObj.Add(val); } map.Add(parameters, asObj); } return map[parameters]; } public void ClearMap() { map.Clear(); } #endregion } Here are my tests of the function: private void MemoizeTest() { DataSet dataSet = DataLoader.LoadData(DataLoader.DataSource.FROM_WEB, 1024); List<String> labels = dataSet.DataLabels; Stopwatch sw = new Stopwatch(); IFunction emaFunc = new EMAFunction(); List<object> parameters = new List<object>(); int numRuns = 1000; long sumTicks = 0; parameters.Add(dataSet.GetValues("open")); parameters.Add(12); // First call for(int i = 0; i < numRuns; ++i) { emaFunc.ClearMap();// remove any memoization mappings sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks not-memoized " + (sumTicks/numRuns)); sumTicks = 0; // Repeat call for (int i = 0; i < numRuns; ++i) { sw.Start(); emaFunc.Execute(parameters); sw.Stop(); sumTicks += sw.ElapsedTicks; } Console.WriteLine("Average ticks memoized " + (sumTicks/numRuns)); } The performance is confusing me... I expected the memoized function to be faster, but it didn't work out that way: Average ticks not-memoized 106,182 Average ticks memoized 198,854 I tried doubling the data instances to 2048, but the results were about the same: Average ticks not-memoized 232,579 Average ticks memoized 446,280 I did notice that it was correctly finding the parameters in the map and it going directly to the map, but the performance was still slow... I'm either open for troubleshooting help with this example, or if you have a better solution to the problem then please let me know what it is.

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• Modelling problem - Networked devices with commands

  - by Schneider

  I encountered a head scratching modelling problem today: We are modelling a physical control system composed of Devices and NetworkDevices. Any example of a Device is a TV. An example of a NetworkDevice is an IR transceiver with Ethernet connection. As you can see, to be able to control the TV over the internet we must connect the Device to the NetworkDevice. There is a one to many relationship between Device and NetworkDevice i.e. TV only has one NetworkDevice (the IR transceiver), but the IR transceiver may control many Devices (e.g. many TVs). So far no problem. The complicated bit is that every Device has a collection of Commands. The type of the Command (e.g IrCommand, SerialCommand - N.B. not currently modelled) depends on the type of NetworkDevice that the Device is connected to. In the current legacy system the Device has a collection of generic Commands (no typing) where fields are "interpreted" depending on the NetworkDevice type. How do I go about modelling this in OOP such that: You can only ever add a Command of the appropriate type, given the NetworkDevice the Device is attached to? If I change the NetworkDevice the Commands collection changes to the appropriate type Make it so the API is simple/elegant/intuitive to use

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• Need some help understanding this problem about maximizing graph connectivity

  - by Legend

  I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. I am not sure if this is a really a problem but I somehow have a feeling that there might exist more than one order in which case, it is required to choose the best order. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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