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• Distributed transactions and queues, ruby, erlang

  - by chrispanda

  I have a problem that involves several machines, message queues, and transactions. So for example a user clicks on a web page, the click sends a message to another machine which adds a payment to the user's account. There may be many thousands of clicks per second. All aspects of the transaction should be fault tolerant. I've never had to deal with anything like this before, but a bit of reading suggests this is a well known problem. So to my questions. Am I correct in assuming that secure way of doing this is with a two phase commit, but the protocol is blocking and so I won't get the required performance? It appears that DBs like redis and message queuing system like Rescue, RabbitMQ etc don't really help me a lot - even if I implement some sort of two phase commit, the data will be lost if redis crashes because it is essentially memory-only. All of this has led me to look at erlang - but before I wade in and start learning a new language, I would really like to understand better if this is worth the effort. Specifically, am I right in thinking that because of its parallel processing capabilities, erlang is a better choice for implementing a blocking protocol like two phase commit, or am I confused?

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• Rule Engine in .net

  - by user641812

  I have to import data from excel to SQL database. Excel data contains various parameters and there value like P1,P1,P4,P5 etc. I have to apply business rules Like if( P1 100 and P1 < 200) then insert the record in database. Similarly in some cases string values are also validated. Can I have any open source rule engine that contains UI to change , add , delete the rules. Am using C# to read the excel and and insert the records One more thing which is best approach: Read excel first and store every record as an object in a collection, then iterate through the collection, apply business rules on every object and then insert record in the database Or Read one record from excel apply business rule and then insert record in the database. Repeat the process for whole excel.

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• unit/integration testing web service proxy client

  - by cori

  I'm rewriting a PHP client/proxy library that provides an interface to a SOAP-based .Net webservice, and in the process I want to add some unit and integration tests so future modifications are less risky. The work the library I'm working on performs is to marshall the calls to the web service and do a little reorganizing of the responses to present a slightly more -object-oriented interface to the underlying service. Since this library is little else than a thin layer on top of web service calls, my basic assumption is that I'll really be writing integration tests more than unit tests - for example, I don't see any reason to mock away the web service - the work that's performed by the code I'm working on is very light; it's almost passing the response from the service right back to its consumer. Most of the calls are basic CRUD operations: CreateRole(), CreateUser(), DeleteUser(), FindUser(), &ct. I'll be starting from a known database state - the system I'm using for these tests is isolated for testing purposes, so the results will be more or less predictable. My question is this: is it natural to use web service calls to confirm the results of operations within the tests and to reset the state of the application within the scope of each test? Here's an example: One test might be createUserReturnsValidUserId() and might go like this: public function createUserReturnsValidUserId() { // we're assuming a global connection to the service $newUserId = $client->CreateUser("user1"); assertNotNull($newUserId); assertNotNull($client->FindUser($newUserId); $client->deleteUser($newUserId); } So I'm creating a user, making sure I get an ID back and that it represents a user in the system, and then cleaning up after myself (so that later tests don't rely on the success or failure of this test w/r/t the number of users in the system, for example). However this still seems pretty fragile - lots of dependencies and opportunities for tests to fail and effect the results of later tests, which I definitely want to avoid. Am I missing some options of ways to decouple these tests from the system under test, or is this really the best I can do? I think this is a fairly general unit/integration testing question, but if it matters I'm using PHPUnit for the testing framework.

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• Is there such a thing as too much experience?

  - by sunpech

  For modern software developers in today's world, is there such a thing as having too much experience with a certain technology or programming language? To a recruiter, interviewer, or company hiring-- could there often be cases where a particular candidate has so much experience in a certain area or technology where it works against the candidate to being hired? I'm not talking about cases where a senior developer is applying for an entry-level developer position, and has a lot of experience in that sense. Nor am I talking about cases where a candidate is outright lying (e.g. 20+ years experience with Ruby on Rails). I've overheard this in conversations between hiring managers/developers during happy hours, yet I'm not quite sure I fully understand what they mean.

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• Are certification courses worth it?

  - by Bill Williams

  I'm planning on getting certification in Database Development for SQL Server (MSTC - 70-433). I'm a junior level report writer at a new job and the company is offering to pay the majority, if not all, of training course fees. The course is five days. I noticed that MS has a self-paced training kit (book) that I could use. I'm wondering if this would be a better option because it will allow me to go as quick as possible. I've also heard about video training sessions (Lynda.com) but they seem to go at slow pace. My questions are: What should I expect at a certification course? Is it hands-on training? Small classes with personal feedback or not? Would I be better off learning at my own pace using the training kit? (I'd rather this not turn into a certifications are pointless discussion..)

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• Changing from Frontend Development to .Net

  - by Ivo

  On of my colleagues is going to change jobs from full time frontend developer(jquery, css,html) to 50% frontend 50% .Net (MVC 3 with razor) What are good techniques to get him up to speed asap. I have the following idea's myself Read Clean Code Read/Pratice with the book Pro ASP.NET MVC 3 Framework Watch Asp.net video's http://www.asp.net/mvc/videos Do the nerd dinner intro http://www.asp.net/mvc/videos Start building the json services from jQuery 0.5/1 day of pair programming with an experienced .Net developer each week Is this a good way to go? Is it totally wrong? Any other tips

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• Explanation of the definition of interface inheritance as described in GoF book

  - by Geek

  I am reading the first chapter of the Gof book. Section 1.6 discusses about class vs interface inheritance: Class versus Interface Inheritance It's important to understand the difference between an object's class and its type. An object's class defines how the object is implemented.The class defines the object's internal state and the implementation of its operations.In contrast,an object's type only refers to its interface--the set of requests on which it can respond. An object can have many types, and objects of different classes can have the same type. Of course, there's a close relationship between class and type. Because a class defines the operations an object can perform, it also defines the object's type . When we say that an object is an instance of a class, we imply that the object supports the interface defined by the class. Languages like c++ and Eiffel use classes to specify both an object's type and its implementation. Smalltalk programs do not declare the types of variables; consequently,the compiler does not check that the types of objects assigned to a variable are subtypes of the variable's type. Sending a message requires checking that the class of the receiver implements the message, but it doesn't require checking that the receiver is an instance of a particular class. It's also important to understand the difference between class inheritance and interface inheritance (or subtyping). Class inheritance defines an object's implementation in terms of another object's implementation. In short, it's a mechanism for code and representation sharing. In contrast,interface inheritance(or subtyping) describes when an object can be used in place of another. I am familiar with the Java and JavaScript programming language and not really familiar with either C++ or Smalltalk or Eiffel as mentioned here. So I am trying to map the concepts discussed here to Java's way of doing classes, inheritance and interfaces. This is how I think of of these concepts in Java: In Java a class is always a blueprint for the objects it produces and what interface(as in "set of all possible requests that the object can respond to") an object of that class possess is defined during compilation stage only because the class of the object would have implemented those interfaces. The requests that an object of that class can respond to is the set of all the methods that are in the class(including those implemented for the interfaces that this class implements). My specific questions are: Am I right in saying that Java's way is more similar to C++ as described in the third paragraph. I do not understand what is meant by interface inheritance in the last paragraph. In Java interface inheritance is one interface extending from another interface. But I think the word interface has some other overloaded meaning here. Can some one provide an example in Java of what is meant by interface inheritance here so that I understand it better?

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• Merge two different API calls into One

  - by dhilipsiva

  I have two different apps in my django project. One is "comment" and an other one is "files". A comment might save some file attached to it. The current way of creating a comment with attachments is by making two API calls. First one creates an actual comment and replies with the comment ID which serves as foreign key for the Files. Then for each file, a new request is made with the comment ID. Please note that file is a generic app, that can be used with other apps too. What is the cleanest way of making this into one API call? I want to have this as a single API call because I am in a situation where I need to send user an email with all the files as attachment when a comment is made. I know Queueing is the ideal way to do it. But I don't have the liberty to add queing to our stack now. So this was the only way I could think of.

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• How can I implement an EPUB reader in JavaScript?

  - by Vlad Nicula

  I'm wondering if I can create an EPUB (free and open e-book standard) reader in JavaScript. The basic requirements would be: Server parts of the EPUB reader from a server API. Read the EPUB data in JavaScript. Render it on page. Provide some extra functionality, like text highlights or page notes. I have no information about how I could do this. I'm willing to try a prototype project. What are the steps that I could take towards implementing such a thing?

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• Perl numerical sorting: how to ignore leading alpha character [migrated]

  - by Luke Sheppard

  I have a 1,660 row array like this: ... H00504 H00085 H00181 H00500 H00103 H00007 H00890 H08793 H94316 H00217 ... And the leading character never changes. It is always "H" then five digits. But when I do what I believe is a numerical sort in Perl, I'm getting strange results. Some segments are sorted in order, but then a different segment starts up. Here is a segment after sorting: ... H01578 H01579 H01580 H01581 H01582 H01583 H01584 H00536 H00537 H00538 H01585 H01586 H01587 H01588 H01589 H01590 ... What I'm trying is this: my @sorted_array = sort {$a <=> $b} @raw_array; But obviously it is not working. Anyone know why?

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• Is Perforce as good as merging as DVCSs?

  - by dukeofgaming

  I've heard that Perforce is very good at merging, I'm guessing this has to do with that it tracks changes in the form of changelists where you can add differences across several files in a single blow. I think this implies Perforce gathers more metadata and therefore has more information to do smarter merging (at least smarter than Subversion, being Perforce centralized). Since this is similar to how Mercurial and Git handle changes (I know DVCSs track content rather than files), I was wondering if somebody knew what were the subtle differences that makes Perforce better or worse than a DVCS like Mercurial or Git.

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• How to depict Import a file action in the Sequence diagram

  - by user970696

  Everyone says sequence diagrams are so easy but I just cannot figure this out. Basically user clicks on an 'Import from temp folder' button, the program opens a window with a list populated with filenames, user clicks on a filename, clicks on OK and the document is imported. I know the order of the actions but how to depict e.g. populating a list, or selecting an item from a list? So I assume the objects would be like: [USER] [ImportDialogWindow] [ListOfFiles:STRING] [?where to go with selected file]

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• I'm a CS student, and honestly I don't understand Knuth's books..

  - by Raymond Ho

  I stumbled this quote from Bill Gates: "You should definitely send me a resume if you can read the whole thing." He was talking about The Art of Programming books.. So I was pretty curious and want to read it all but honestly, I don't understand it at all.. I'm really not that highly intellectual being.. So this should be the reason why I can't understand it, but I am eager to learn.. I'm currently reading volume 1 about fundamental algo.. So is there any books out there that are friendly to novice/slow people like me? So I can build up myself and hopefully in the future I can read Knuth's book at ease..

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• Should I ditch a creative pet project in lieu of one that would demonstrate skills more applicable to an employer?

  - by Hart Simha

  I am currently working on a project on github that I think would be a good demonstration of my initiative, creativity and enthusiasm. It is an educational game I am developing in pygame that enables the user to learn to improve their development productivity by using vim, specifically with python, though learning to code faster with vim should be transferable to any language. I think this is something that might have a mass appeal and benefit to a lot of people in a measurable way. -However- I am graduating from college in a month (my degree is computer science with a minor in english), with no experience that is relevant to helping me get any kind of job in the field, and a gpa that doesn't tout my merits. I could pursue a career in game development, but it's not necessarily what I'm most interested in, and see myself applying to startups around the country. To the places I am looking at applying, showing that I have experience with pygame is going to be largely irrelevant, except in demonstration of my ability to code, period. A lot of skills that ARE more marketable, such a data modeling, GIS, mobile development, javascript, .net framework, and various web development technologies, are not going to be showcased by this project (on the upside, employers do like to see familiarity with git and python). I'm wondering if I should sink all my free time in the next couple of months into this project, since I'm motivated and interested in it, and if the value of being able to demonstrate ambition and 'good ideas' (for lack of a better term, and in my own opinion) will compensate for the absence of demonstrating more sought-after skills. I am probably at a point where I should either commit fully to this project now, or put it on the backburner in favor of something else, and I am leaning towards continuing with what I am already working on, because I think it's a great idea, and something achievable to me with enough dedication over the next couple months. But the most important thing to me is being able to get a job out of college, which I am exceedingly concerned about as the professional landscape which I am navigating for the first time is a lot more intimidating than I could have anticipated, with almost every job (even short-term contract positions) requiring years of experience which I lack. Oh, and in case anyone is interested, my repository is here: www.github.com/hmsimha/vimagine

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• Should generated documentation go in version control history?

  - by dukeofgaming

  I'm against compiled stuff going into version control, specially when it comes to compiled binaries, however, my principles are now in question after adding doxygen support for a project. Should the hundreds of files generated by doxygen go into version control?, what is the recommended practice here?, I think the ideal would be automating the process in a server that publishes that documentation at the same time, however, there is no such server now nor there will be for some time.

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• New code base, what experiences/recommendations do you have?

  - by hlovdal

  I will later this year start on a project (embedded hardware, C, small company) where I believe that most (if not all) code will be new. So what experiences do you have to share as advice to starting a new code base? What have you been missing in projects that you have been working on? What has worked really well? What has not worked? Let's limit this question to be about things that relate directly to the code (e.g "banning the use of gets()": in scope, version control: border line, build system: out of scope).

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• How to design highly scalable web services in Java?

  - by Kshitiz Sharma

  I am creating some Web Services that would have 2000 concurrent users. The services are offered for free and are hence expected to get a large user base. In the future it may be required to scale up to 50,000 users. There are already a few other questions that address the issue like - Building highly scalable web services However my requirements differ from the question above. For example - My application does not have a user interface, so images, CSS, javascript are not an issue. It is in Java so suggestions like using HipHop to translate PHP to native code are useless. Hence I decided to ask my question separately. This is my project setup - Rest based Web services using Apache CXF Hibernate 3.0 (With relevant optimizations like lazy loading and custom HQL for tune up) Tomcat 6.0 MySql 5.5 My questions are - Are there alternatives to Mysql that offer better performance for what I'm trying to do? What are some general things to abide by in order to scale a Java based web application? I am thinking of putting my Application in two tomcat instances with httpd redirecting the request to appropriate tomcat on basis of load. Is this the right approach? Separate tomcat instances can help but then database becomes the bottleneck since both applications access the same database? I am a programmer not a Db Admin, how difficult would it be to cluster a Mysql database (or, to cluster whatever database offered as an alternative to 1)? How effective are caching solutions like EHCache? Any other general best practices? Some clarifications - Could you partition the data? Yes we could but we're trying to avoid it. We need to run a lot of data mining algorithms and the design would evolve over time so we can't be sure what lines of partition should be there.

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• OpenGL CPU vs. GPU

  - by Nitrex88

  So I've always been under the impression that doing work on the GPU is always faster than on the CPU. Because of this, in OpenGL, I usually try to do intensive tasks in shaders so they get the speed boost from the GPU. However, now I'm starting to realize that some things simply work better on the CPU and actually perform worse on the GPU (particularly when a geometry shader is involved). For example, in a recent project I did involving procedurally generated terrain, I tried passing a grid of single triangles into a geometry shader, and tesselated each of these triangles into quads with 400 vertices whose height was determined by a noise function. This worked fine, and looked great, but easily maxed out the GPU with only 25 base triangles and caused a very slow framerate. I then discovered that tesselating on the CPU instead, and setting the height (using noise function) in the vertex shader was actually faster! This prompted me to question the benefits of using the GPU as much as possible... So, I was wondering if someone could describe the general pros and cons of using the GPU vs CPU for intensive graphics tasks. I know this mainly comes down to what your trying to achieve, so if necessary, use the above scenario to discuss why the "CPU + vertex shader" was actually faster than doing everything in the geometry shader on the GPU. It's possible my hardware (newest macbook pro) isn't optomized well for the geometry shader (thus causing the slow framerate). Also, I read that the vertex shader is very good with parallelism, and would love a quick explanation of how this may have played a role in speeding up my procedural terrain. Any info/advice about CPU/GPU/shaders would be awesome!

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• Is there an easy way to type in common math symbols?

  - by srcspider

  Disclaimer: I'm sure someone is going to moan about easy-of-use, for the purpose of this question consider readability to be the only factor that matters So I found this site that converts to easting northing, it's not really important what that even means but here's how the piece of javascript looks. /** * Convert Ordnance Survey grid reference easting/northing coordinate to (OSGB36) latitude/longitude * * @param {OsGridRef} gridref - easting/northing to be converted to latitude/longitude * @returns {LatLonE} latitude/longitude (in OSGB36) of supplied grid reference */ OsGridRef.osGridToLatLong = function(gridref) { var E = gridref.easting; var N = gridref.northing; var a = 6377563.396, b = 6356256.909; // Airy 1830 major & minor semi-axes var F0 = 0.9996012717; // NatGrid scale factor on central meridian var f0 = 49*Math.PI/180, ?0 = -2*Math.PI/180; // NatGrid true origin var N0 = -100000, E0 = 400000; // northing & easting of true origin, metres var e2 = 1 - (b*b)/(a*a); // eccentricity squared var n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n; // n, n², n³ var f=f0, M=0; do { f = (N-N0-M)/(a*F0) + f; var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (f-f0); var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(f-f0) * Math.cos(f+f0); var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(f-f0)) * Math.cos(2*(f+f0)); var Md = (35/24)*n3 * Math.sin(3*(f-f0)) * Math.cos(3*(f+f0)); M = b * F0 * (Ma - Mb + Mc - Md); // meridional arc } while (N-N0-M >= 0.00001); // ie until < 0.01mm var cosf = Math.cos(f), sinf = Math.sin(f); var ? = a*F0/Math.sqrt(1-e2*sinf*sinf); // nu = transverse radius of curvature var ? = a*F0*(1-e2)/Math.pow(1-e2*sinf*sinf, 1.5); // rho = meridional radius of curvature var ?2 = ?/?-1; // eta = ? var tanf = Math.tan(f); var tan2f = tanf*tanf, tan4f = tan2f*tan2f, tan6f = tan4f*tan2f; var secf = 1/cosf; var ?3 = ?*?*?, ?5 = ?3*?*?, ?7 = ?5*?*?; var VII = tanf/(2*?*?); var VIII = tanf/(24*?*?3)*(5+3*tan2f+?2-9*tan2f*?2); var IX = tanf/(720*?*?5)*(61+90*tan2f+45*tan4f); var X = secf/?; var XI = secf/(6*?3)*(?/?+2*tan2f); var XII = secf/(120*?5)*(5+28*tan2f+24*tan4f); var XIIA = secf/(5040*?7)*(61+662*tan2f+1320*tan4f+720*tan6f); var dE = (E-E0), dE2 = dE*dE, dE3 = dE2*dE, dE4 = dE2*dE2, dE5 = dE3*dE2, dE6 = dE4*dE2, dE7 = dE5*dE2; f = f - VII*dE2 + VIII*dE4 - IX*dE6; var ? = ?0 + X*dE - XI*dE3 + XII*dE5 - XIIA*dE7; return new LatLonE(f.toDegrees(), ?.toDegrees(), GeoParams.datum.OSGB36); } I found that to be a really nice way of writing an algorythm, at least as far as redability is concerned. Is there any way to easily write the special symbols. And by easily write I mean NOT copy/paste them.

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• How to convince management to deal with technical debt?

  - by Desolate Planet

  This is a question that I often ask myself when working with developers. I've worked at four companies so far, and I've noticed a lack of attention to keeping code clean and dealing with technical debt that hinders future progress in a software app. For example, the first company I worked for had written a database from scratch rather than take something like MySQL and that created hell for the team when refacoring or extending the app. I've always tried to be honest and clear with my manager when he discusses projections, but management doesn't seem interested in fixing what's already there and it's horrible to see the impact it has on team morale and in their attitude towards others. What are your thoughts on the best way to tackle this problem? What I've seen is people packing up and leaving and the company becomes a revolving door with developers coming and and out and making the code worse. How do you communicate this to management to get them interested in sorting out technical debt?

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• How abstract should you get with BDD

  - by Newton

  I was writing some tests in Gherkin (using Cucumber/Specflow). I was wondering how abstract should I get with my tests. In order to not make this open-ended, which of the following statements is better for BDD: Given I am logged in with email [email protected] and password 12345 When I do something Then something happens as opposed to Given I am logged in as the Administrator When I do something Then something happens The reason I am confused is because 1 is more based on the behaviour (filing in email and password) and 2 is easier to process and write the tests.

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• Why did an interviewer ask me a question about people eating curry?

  - by Barry

  I had an interview question once which went... Interviewer: "Could you tell me how many people will eat curry for their dinner this evening" Me: "Er, sorry?" Interviewer: "Not the actual number just an estimate" I actually started to stumble my way through it, when I stopped and questioned what it had to do with anything about the job. The interviewer mumbled something and moved on. I guess the question is, what is the point in the ridiculous questions? I just don't understand why they started coming up with these things.

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• Composite-like pattern and SRP violation

  - by jimmy_keen

  Recently I've noticed myself implementing pattern similar to the one described below. Starting with interface: public interface IUserProvider { User GetUser(UserData data); } GetUser method's pure job is to somehow return user (that would be an operation speaking in composite terms). There might be many implementations of IUserProvider, which all do the same thing - return user basing on input data. It doesn't really matter, as they are only leaves in composite terms and that's fairly simple. Now, my leaves are used by one own them all composite class, which at the moment follows this implementation: public interface IUserProviderComposite : IUserProvider { void RegisterProvider(Predicate<UserData> predicate, IUserProvider provider); } public class UserProviderComposite : IUserProviderComposite { public User GetUser(SomeUserData data) ... public void RegisterProvider(Predicate<UserData> predicate, IUserProvider provider) ... } Idea behind UserProviderComposite is simple. You register providers, and this class acts as a reusable entry-point. When calling GetUser, it will use whatever registered provider matches predicate for requested user data (if that helps, it stores key-value map of predicates and providers internally). Now, what confuses me is whether RegisterProvider method (brings to mind composite's add operation) should be a part of that class. It kind of expands its responsibilities from providing user to also managing providers collection. As far as my understanding goes, this violates Single Responsibility Principle... or am I wrong here? I thought about extracting register part into separate entity and inject it to the composite. As long as it looks decent on paper (in terms of SRP), it feels bit awkward because: I would be essentially injecting Dictionary (or other key-value map) ...or silly wrapper around it, doing nothing more than adding entires This won't be following composite anymore (as add won't be part of composite) What exactly is the presented pattern called? Composite felt natural to compare it with, but I realize it's not exactly the one however nothing else rings any bells. Which approach would you take - stick with SRP or stick with "composite"/pattern? Or is the design here flawed and given the problem this can be done in a better way?

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• Why doesn't Haskell have type-level lambda abstractions?

  - by Petr Pudlák

  Are there some theoretical reasons for that (like that the type checking or type inference would become undecidable), or practical reasons (too difficult to implement properly)? Currently, we can wrap things into newtype like newtype Pair a = Pair (a, a) and then have Pair :: * -> * but we cannot do something like ?(a:*). (a,a). (There are some languages that have them, for example, Scala does.)

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• Imitating Exchange Server's "RBAC AuthZ" in my own application... (is there something similar?)

  - by makerofthings7

  Exchange 2010 has a delegation model where groups of winrm cmdlets are essentally grouped into roles, and the roles assigned to a user. (Image source) This is a great & flexible model considering how I can leverage all the benefits of PowerShell, while using the right low level technologies (WCF, SOAP etc), and requiring no additional software on the client side. (Image source) Question(s) Is there a way for me to leverage Exchange's delegation model in my .NET application? Has anyone attempted to imitate this model? If I must start from scratch, how would I go about imitating this approach?

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