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• what is the purpose of arrows?

  - by Simon

  I am learning functionnal programming with Haskell, and I try to grab concepts by first understanding why do I need them. I would like to know the goal of arrows in functional programming languages. What problem do they solve? I checked http://en.wikibooks.org/wiki/Haskell/Understanding_arrows and http://www.cse.chalmers.se/~rjmh/afp-arrows.pdf. All I understand is that they are used to describe graphs for computations, and that they allow easier point free style coding. The article assume that point free style is generally easier to understand and to write. This seems quite subjective to me. In another article (http://en.wikibooks.org/wiki/Haskell/StephensArrowTutorial#Hangman:_Main_program), a hangman game is implemented, but I cannot see how arrows makes this implementation natural. I could find a lot of papers describing the concept, but nothing about the motivation. What I am missing?

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• What's the difference between the code inside a finally clause and the code located after catch clause?

  - by facebook-100005613813158

  My java code is just like below: public void check()throws MissingParamException{ ...... } public static void main(){ PrintWriter out = response.getWriter(); try { check(); } catch (MissingParamException e) { // TODO Auto-generated catch block out.println("message:"+e.getMessage()); e.printStackTrace(); out.close(); }finally{ out.close(); } //out.close(); } Then, my confusion is: what the difference if I put out.close() in a finally code block or if I just remove finally code block and put out.close() behind catch clause (which has been commented in the code). I know that in both ways, the out.close() will be executed because I know that whether the exception happened, the code behind the catch clause will always be executed.

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• oracle certification

  - by Victor

  I am a j2ee developer with 6+ yrs of experience. I have scjp1.4 and scwcd 1.4. To puruse my dream of becoming an architect, I wish to round out my knowledge and make my knowledge base broader. To that respect, I have decided to take the 1Z0-047 Oracle Database SQL Expert Exam as a first step. My questions are: What is a good book/resource for this? Should I follow this website http://www.sql-ex.ru/certification/certification.php Also after completing this ceritificate, will I get a physical certificate that I will put on my resume?

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• How to visualize code?

  - by gablin

  I've mostly only had to read my own code. As such, I've had no need to visualize the code as I already know how each and every class and module communicate with one another. But the few times I've had to read someone else's code - let us now assume we are talking about at least one larger module which contains several internal classes - I've almost always found myself wishing "This would have been so much easier to understand if I could just visualize it!" So what are the common methods or tools for enabling this? Which do you use, and why do you prefer them over the others? I've heard stuff like UML, module and class diagrams, but I imagine there are more. Furthermore, any of these is most likely better than anything I can devise on my own. EDIT: For those who answer with "Use pen and paper and just draw it": This isn't very helpful unless you explain this further. What exactly am I supposed to draw? A box for each class? Should I include the public methods? What about its fields? How should I draw connections that explain how one class uses another? What about modules? What if the language isn't object-oriented but functional or logical, or even just imperative (C, for instance)? What about global variables and functions? Is there an already-standardized way of drawing this, or do I need to think up of a method of my own? You get the drift.

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• Software Agent construction guidelines

  - by lsoto

  I'm currently studying a Master in Computer Science and I am interested in working with Software Agents and C#. I have found so much information regarding theoretical aspects but just a few articles focused on practical programming aspects such as architecture, design or implementation. Could anybody suggest any good source that I could explore? I wouldn't like to "reinvent the wheel" but to contribute with something better to the current state of the art.

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• Can I use wikipedia/commons images to create a logo for my program?

  - by bitmask

  I'm not perfectly clear on the implications of the GFDL for reusing pictures in this manner. Would adding a reference in the git's root folder's README suffice, or would that clutter every use of the logo, as you would have to attribute all original contributors on every single usage (like, e.g. presentations, flyers, websites, ...)? The software itself qualifies as FOSS, although it doesn't have a GNU* license.

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• Is there a file browser like an ER diagram for viewing website physical path structures?

  - by EASI

  I wish to know if there is a tool like this to replace windows explorer and similar in the work of managing files, specially those web-site structures that sometimes can get very big. I am asking it here because I sincerely do not know what terms to use in Google to find anything like it. It is like a diagram, but showing the tree directory structure and the contents of every folder at the same time, not just the one that is in focus.

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• How to manually detect deadlocks

  - by Dawson

  I understand the concepts of deadlock well enough, but when I'm given a problem like the one below I'm not sure how to go about solving it. I can draw a resource allocation graph, but I'm not sure how to solve it from there. Is there a better more formal way of solving this? Consider a system with five processes, P1 through P5, and five resources, R1 through R5. Resource ownership is as follows. • P1 holds R1 and wants R3 • P2 holds R2 and wants R1 • P3 holds R3 and wants R5 • P4 holds R5 and wants R2 • P5 holds R4 and wants R2 Is this system deadlocked? Justify your answer. If the system is deadlocked, list the involved processes.

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• Generic Adjacency List Graph implementation

  - by DmainEvent

  I am trying to come up with a decent Adjacency List graph implementation so I can start tooling around with all kinds of graph problems and algorithms like traveling salesman and other problems... But I can't seem to come up with a decent implementation. This is probably because I am trying to dust the cobwebs off my data structures class. But what I have so far... and this is implemented in Java... is basically an edgeNode class that has a generic type and a weight-in the event the graph is indeed weighted. public class edgeNode<E> { private E y; private int weight; //... getters and setters as well as constructors... } I have a graph class that has a list of edges a value for the number of Vertices and and an int value for edges as well as a boolean value for whether or not it is directed. The brings up my first question, if the graph is indeed directed, shouldn't I have a value in my edgeNode class? Or would I just need to add another vertices to my LinkedList? That would imply that a directed graph is 2X as big as an undirected graph wouldn't it? public class graph { private List<edgeNode<?>> edges; private int nVertices; private int nEdges; private boolean directed; //... getters and setters as well as constructors... } Finally does anybody have a standard way of initializing there graph? I was thinking of reading in a pipe-delimited file but that is so 1997. public graph GenereateGraph(boolean directed, String file){ List<edgeNode<?>> edges; graph g; try{ int count = 0; String line; FileReader input = new FileReader("C:\\Users\\derekww\\Documents\\JavaEE Projects\\graphFile"); BufferedReader bufRead = new BufferedReader(input); line = bufRead.readLine(); count++; edges = new ArrayList<edgeNode<?>>(); while(line != null){ line = bufRead.readLine(); Object edgeInfo = line.split("|")[0]; int weight = Integer.parseInt(line.split("|")[1]); edgeNode<String> e = new edgeNode<String>((String) edges.add(e); } return g; } catch(Exception e){ return null; } } I guess when I am adding edges if boolean is true I would be adding a second edge. So far, this all depends on the file I write. So if I wrote a file with the following Vertices and weights... Buffalo | 18 br Pittsburgh | 20 br New York | 15 br D.C | 45 br I would obviously load them into my list of edges, but how can I represent one vertices connected to the other... so on... I would need the opposite vertices? Say I was representing Highways connected to each city weighted and un-directed (each edge is bi-directional with weights in some fictional distance unit)... Would my implementation be the best way to do that? I found this tutorial online Graph Tutorial that has a connector object. This appears to me be a collection of vertices pointing to each other. So you would have A and B each with there weights and so on, and you would add this to a list and this list of connectors to your graph... That strikes me as somewhat cumbersome and a little dismissive of the adjacency list concept? Am I wrong and that is a novel solution? This is all inspired by steve skiena's Algorithm Design Manual. Which I have to say is pretty good so far. Thanks for any help you can provide.

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• How would you price a dynamic real estate property management website? [closed]

  - by user1217550

  Imagine, hypothetically of course, that you are being commissioned to develop a full-fledged real estate website that includes: 1) a search engine with ajax/json autofill, 2) google maps and geolocation integration, google streetview, 3) user registration, login and account management 4) administrative panels to control data input 5) search results page 6) user statistics 7) property inquiry to allow internal messaging between users How much would you charge? Suppose you are developing the most advanced and specific system in PhP/MySQL, and your total development time is roughly 1500 hours? Any suggestions?

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• Does data size in TCP/UDP make a difference on transmission time

  - by liortal

  While discussing the development of a network component for our game engine, a member of our team suggested that transmitting either 500 bytes or 1k of data using UDP makes no difference from performance perspective of the system (the time it takes to transmit the data). He actually said that as long as you don't cross the MTU size, the size of the transmitted data doesn't really matter as it's all the same. Is that true for UDP? what about TCP? That sounds just plain wrong to me, but i am not a network expert. *I've been reading about other companies' game networking architectures, and it seems they're all trying to keep transmitted data to a minimum, making my colleague's claims seem even more unreasonable.

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• Mechanics of reasoning during programming interviews

  - by user129506

  This is not the usual "I don't want to write code during an interview", in this question the assumption is that I need to write code during an interview (think about the level of rewriting the quicksort or mergesort from scratch) I know how the algorithm work or I have a basic idea of how I should start working from there, i.e. I don't remember the algorithm by heart I noticed that even on a whiteboard, I always end up writing bugged code or code that doesn't compile. If there's a typo, whatever I usually live with that.. but when there's a crash due to some uncaught particular case I end up losing confidence in my skills. I realize that perhaps interviewers might want to look at how I write code and/or how I solve problems rather than proof-compiling my whiteboard code, but I'd like to ask how should I approach the above problem in mental terms, i.e. what mental steps should I follow when writing code for an interview with the two bullet points above. There must be a unique and agreed series of steps I should follow to avoid getting stuck/caught into particular exception cases (limit cases) that might end up wasting my time and my energies rather than focusing on the overall algorithm for the general case. I hope I made my point clear

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• Is there a word or description for this type of query?

  - by Nick

  We have the requirement to find a result in a collection of records based on a prioritised set of search criteria against a relational db (I'm talking indexed field matching here rather than text search). The way we are thinking about designing the query is to begin with a highly refined and specific set of criteria. If there are no results for this initial query we want to progressively reduce the criteria one by one in order of reducing priority, querying each time such a less specific set of criteria until we find a result we can accept. Alternatively, we have considered starting with a smaller set of criteria and increasing until we have reduced number of results down to the last set. What I would like to know is if an existing term to describe this type of query exists? So that we can look to model our own on existing patterns and use best practice.

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• Tail-recursive implementation of take-while

  - by Giorgio

  I am trying to write a tail-recursive implementation of the function take-while in Scheme (but this exercise can be done in another language as well). My first attempt was (define (take-while p xs) (if (or (null? xs) (not (p (car xs)))) '() (cons (car xs) (take-while p (cdr xs))))) which works correctly but is not tail-recursive. My next attempt was (define (take-while-tr p xs) (let loop ((acc '()) (ys xs)) (if (or (null? ys) (not (p (car ys)))) (reverse acc) (loop (cons (car ys) acc) (cdr ys))))) which is tail recursive but needs a call to reverse as a last step in order to return the result list in the proper order. I cannot come up with a solution that is tail-recursive, does not use reverse, only uses lists as data structure (using a functional data structure like a Haskell's sequence which allows to append elements is not an option), has complexity linear in the size of the prefix, or at least does not have quadratic complexity (thanks to delnan for pointing this out). Is there an alternative solution satisfying all the properties above? My intuition tells me that it is impossible to accumulate the prefix of a list in a tail-recursive fashion while maintaining the original order between the elements (i.e. without the need of using reverse to adjust the result) but I am not able to prove this. Note The solution using reverse satisfies conditions 1, 3, 4.

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• booth multiplication algorithm

  - by grassPro

  Is booth algorithm for multiplication only for multiplying 2 negative numbers (-3 * -4) or one positive and one negative number (-3 * 4) ? Whenever i multiply 2 positive numbers using booth algorithm i get a wrong result. example : 5 * 4 A = 101 000 0 // binary of 5 is 101 S = 011 000 0 // 2's complement of 5 is 011 P = 000 100 0 // binary of 4 is 100 x = 3 y = 3 m = 5 -m = 2's complement of m r = 4 After right shift of P by 1 bit 0 000 100 After right shift of P by 1 bit 0 000 010 P+S = 011 001 0 After right shift by 1 bit 0 011 001 Discarding the LSB 001100 But that comes out to be the binary of 12 . It should have been 20(010100)

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• Terra lang and Lua

  - by msalese

  I was reading on terralang site about terra language as "a new low-level system programming language that is designed to interoperate seamlessly with the Lua programming language..." Zach DeVito (the main author) write about the use of terra : A scripting-language with high-performance extensions..... An embedded JIT-compiler for building languages..... A stand-alone low-level language.... But (may be my fault) I don't understand if terra is: a luaJit competitor a better system to interface with c library something better than luaJit using llvm Can someone help me to better understand what is going on terralang project ? Thanks

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• Does it make sense to write tests for legacy code when there is no time for a complete refactoring?

  - by is4

  I usually try to follow the advice of the book Working Effectively with Legacy Code. I break dependencies, move parts of the code to @VisibleForTesting public static methods and to new classes to make the code (or at least some part of it) testable. And I write tests to make sure that I don't break anything when I'm modifying or adding new functions. A colleague says that I shouldn't do this. His reasoning: The original code might not work properly in the first place. And writing tests for it makes future fixes and modifications harder since devs have to understand and modify the tests too. If it's GUI code with some logic (~12 lines, 2-3 if/else block, for example), a test isn't worth the trouble since the code is too trivial to begin with. Similar bad patterns could exist in other parts of the codebase, too (which I haven't seen yet, I'm rather new); it will be easier to clean them all up in one big refactoring. Extracting out logic could undermine this future possibility. Should I avoid extracting out testable parts and writing tests if we don't have time for complete refactoring? Is there any disadvantage to this that I should consider?

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• Is there any way to optimize my search blob program?

  - by Vicky

  I written this code to search the blob items (text files) on the basis of there content. For ex : if I search for "Good", then the files that contains "Good or good" word the name of that files should appear in search result. My code is working but i want to optimize it. class BlobSearch { public static int num = 1; static void Main(string[] args) { string accountName = "accountName"; string accessKey = "accesskey"; string azureConString = "DefaultEndpointsProtocol=https;AccountName=" + accountName + ";AccountKey=" + accessKey; string blob = "MyBlobContainer"; string searchText = string.Empty; Console.WriteLine("Type and enter to search : "); searchText = Console.ReadLine(); CloudStorageAccount account = CloudStorageAccount.Parse(azureConString); CloudBlobClient blobClient = account.CreateCloudBlobClient(); CloudBlobContainer blobContainer = blobClient.GetContainerReference(blob); blobContainer.FetchAttributes(); var blobItemList = blobContainer.ListBlobs(); GetBlobList(searchText, blobContainer, blobItemList); Console.ReadLine(); } private static async void GetBlobList(string searchText, CloudBlobContainer blobContainer, IEnumerable<IListBlobItem> blobItemList) { foreach (var item in blobItemList) { string line = string.Empty; CloudBlockBlob blockBlob = blobContainer.GetBlockBlobReference(item.Uri.ToString()); if (blockBlob.Name.Contains(".txt")) { await Search(searchText, blockBlob); } } } private async static Task Search(string searchText, CloudBlockBlob blockBlob) { string text = await blockBlob.DownloadTextAsync(); if (text.ToLower().IndexOf(searchText.ToLower()) != -1) { Console.WriteLine("Result : " + num + " => " + blockBlob.Name.Substring(blockBlob.Name.LastIndexOf('/') + 1)); num++; } } } I think blobContainer.ListBlobs(); is blocking code because search will not work until all the blob items loaded. Is there anyway to optimize it or anywhere else in my code. Thanks

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• Code Design question, circular reference across classes?

  - by dsollen

  I have no code here, as this is more of a design question (I assume this is still the best place to ask it). I have a very simple server in java which stores a mapping between certain values and UUID which are to be used by many systems across multiple platforms. It accepts a connection from a client and creates a clientSocket which stores the socket and all the other relevant data unique to that connection. Each clientSocket will run in their own thread and will block on the socket waiting for a read. I expect very little strain on this system, it will rarely get called, but when it does get a call it will need to respond quickly and due to the risk of it having a peak time with multiple calls coming in at once threaded is still better. Each thread has a reference to a Mapper class which stores the mapping of UUID which it's reporting to others (with proper synchronization of course). This all works until I have to add a new UUID to the list. When this happens I want to report to all clients that care about that particular UUID that a new one was added. I can't multicast (limitation of the system I'm running on) so I'm having each socket send the message to the client through the established socket. However, since each thread only knows about the socket it's waiting on I didn't have a clear method of looking up every thread/socket that cares about the data to inform them of the new UUID. Polling is out mostly because it seems a little too convoluted to try to maintain a list of newly added UUID. My solution as of now is to have the 'parent' class which creates the mapper class and spawns all the threads pass itself as an argument to the mapper. Then when the mapper creates a new UUID it can make a call to the parent class telling it to send out updates to all the other sockets that care about the change. I'm concerned that this may be a bad design due to the use of a circular reference; parent has a reference to mapper (to pass it to new ClientSocket threads) and mapper points to parent. It doesn't really feel like a bad design to me but I wanted to check since circular references are suppose to be bad. Note: I realize this means that the thread associated with whatever socket originally received the request that spawned the creation of a UUID is going to pay the 'cost' of outputting to all the other clients that care about the new UUID. I don't care about this; as I said I suspect the client to receive only intermittent messages. It's unlikely for one socket to receive multiple messages at one time, and there won't be that many sockets so it shouldn't take too long to send messages to each of them. Perhaps later I'll fix the fact that I'm saddling higher work load on whatever unfortunate thread gets the first request; but for now I think it's fine.

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• C++ compiler structures such as Virtual method Table etc

  - by Roger

  I am aware of the C++ Virtual Table which allows dynamic dispatch for doing things at runtime (although if I am honest I am not completely sure of the full list of things it achieves). I am wondering what other "low level" aspects of C++ are there, which one doesnt usually come across when learning the C++ language? Things like: -How is multithreading and locking on objects performed? -Overloading/overwriting functions -Generics Are there other "structures", similar to the vtable, which assist with these types of things on a lower level? (and if anyone can help with what the VTable actually does it would be most appreciated!)

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• Writing drivers for a printer?

  - by user828584

  My goal is to be able to fax 20 page pdf documents for free. I've looked online, and there are some free fax services, but all of them have their limits. I do have an old fax machine, but the documents that need to be faxed are on the computer, and to print them would be far from free. Unfortunately, the only way to send a fax with the machine is by scanning it. What's strange is that it can scan to the computer and print from it, but it won't fax from it... :(. Is it possible to write something (preferably C#, but it's going to take some learning anyway) that will allow me to send a fax from the computer? I have very little software experience, and none in anything like this, so I have no idea where to start. If it is possible, where can I find all the information needed to write the program?

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• iOS - Unit tests for KVO/delegate codes

  - by ZhangChn

  I am going to design a MVC pattern. It could be either designed as a delegate pattern, or a Key-Value-Observing(KVO), to notify the controller about changing models. The project requires certain quality control procedures to conform to those verification documents. My questions: Does delegate pattern fit better for unit testing than KVO? If KVO fits better, would you please suggest some sample codes?

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• Best options for freelance or part-time programming? [closed]

  - by Andrew

  I apologize in advance if this is an inappropriate question for this SE. A few years back I was all set to study computer science and get a job programming, but went a totally different route and went into healthcare. I currently work as a paramedic on a rotating 24/48 schedule, so I have two days off for every day I work, and a decent bit of downtime on the days that I do work. I've been looking at ways to earn some extra money with all that spare time, and was wondering if it'd be worth the effort to try and find a part-time/freelance gig. I know HTML/CSS, PHP, and I'm pretty familiar with Python and Ruby (and Rails). Anyways, was hoping that someone could point me in the right direction as what "skill set" would give me the best chance to be able to land a part-time/freelance gig. I realize this is a rather open-ended question but any direction is appreciated.

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• How do I transition from physics and math to programming?

  - by inovaovao

  I'm a physics PhD with little actual programming experience. I've always liked programming and played around with BASIC, Pascal as a teen, but the extent of my experience writing complex programs comes from an introductory course in computer science. Now I've decided that I'm more interested in programming than in physics and started to learn Java. Coming from a physics or math-heavy background, what would be the best strategy to maximize my value in the field?

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• What is a *slightly* less extreme equivalent to being "fluent" in a language?

  - by Mehrdad

  tl;dr: What is a less extreme (but still noticeable) alternative to the word "fluent", when saying e.g. "I am fluent in C++/Python/whatever?" I think I can call myself "fluent" in C#, because I know the language and runtime very well, and I'm very familiar with the .NET framework's APIs and classes, etc. I would like to claim the same thing for Python and C++. But while I can program in Python (I did so for an entire summer, making a website with Django), for example, I would not call myself fluent because my code isn't always "Pythonic" (e.g. using map/filter vs. list comprehensions), and I'm not too intimate with some aspects of the language and standard library yet (e.g. the introspection API, etc.). Is there a word or phrase I can use on e.g. a resume to describe what I know? I can think of "very familiar with", but is there a better word/phrase I can use?

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