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• Postfix and right-associative operators in LR(0) parsers

  - by Ian

  Is it possible to construct an LR(0) parser that could parse a language with both prefix and postfix operators? For example, if I had a grammar with the + (addition) and ! (factorial) operators with the usual precedence then 1+3! should be 1 + 3! = 1 + 6 = 7, but surely if the parser were LR(0) then when it had 1+3 on the stack it would reduce rather than shift? Also, do right associative operators pose a problem? For example, 2^3^4 should be 2^(3^4) but again, when the parser have 2^3 on the stack how would it know to reduce or shift? If this isn't possible is there still a way to use an LR(0) parser, possibly by converting the input into Polish or Reverse Polish notation or adding brackets in the appropriate places? Would this be done before, during or after the lexing stage?

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• Should every class have its own namespace?

  - by thehouse

  Something that has been troubling me for a while: The current wisdom is that types should be kept in a namespace that only contains functions which are part of the type's non-member interface (see C++ Coding Standards Sutter and Alexandrescu or here) to prevent ADL pulling in unrelated definitions. Does this imply that all classes must have a namespace of their own? If we assume that a class may be augmented in the future by the addition of non-member functions, then it can never be safe to put two types in the same namespace as either one of them may introduce non-member functions that could interfere with the other. The reason I ask is that namespaces are becoming cumbersome for me. I'm writing a header-only library and I find myself using classes names such as project::component::class_name::class_name. Their implementations call helper functions but as these can't be in the same namespace they also have to be fully qualified!

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• Split string into sentences based on periods

  - by rookie

  Hi all, I have written this piece of code that splits a string and stores it in a string array:- String[] sSentence = sResult.split("[a-z]\.\s+"); However, I've added the [a-z] because I wanted to deal with some of the abbreviation problem. But then my result shows up as so:- Furthermore when Everett tried to instruct them in basic mathematics they proved unresponsiv I see that I loose the pattern specified in the split function. Its okay for me to loose the period, but loosing the last letter of the word disturbs its meaning. Could some one help me with this and in addition also could someone help me with dealing with abbreviations? Like because I split the string based on periods, I do not want to loose the abbreviations. Thanks in advance

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• Eclipse compiler with APT

  - by westcam

  What is the correct way to call the Eclipse compiler with an APT processor from Java? I am using the following Maven dependency for the compiler <dependency> <groupId>org.eclipse.jdt.core.compiler</groupId> <artifactId>ecj</artifactId> <version>3.5.1</version> </dependency> I want to test an APT processor with the Eclipse compiler in addition to Javac.

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• hibernate distributed 2nd level cache options

  - by ishmeister

  Not really a question but I'm looking for comments/suggestions from anyone who has experiences using one or more of the following: EhCache with RMI EhCache with JGroups EhCache with Terracotta Gigaspaces Data Grid A bit of background: our applications is read only for the most part but there is some user data that is read-write and some that is only written (and can also be reasonably inaccurate). In addition, it would be nice to have tools that enable us to flush and fill the cache at intervals or by admin intervention. Regarding the first option - are there any concerns about the overhead of RMI and performance of Java serialization?

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• What time function do I need to use with pthread_cond_timedwait?

  - by Vincent

  The pthread_cond_timedwait function needs an absolute time in a time timespec structure. What time function I'm suppose to use to obtain the absolute time. I saw a lot of example on the web and I found almost all time function used. (ftime, clock, gettimeofday, clock_gettime (with all possible CLOCK_...). The pthread_cond_timedwait uses an absolute time. Will this waiting time affected by changing the time of the machine? Also if I get the absolute time with one of the time function, if the time of the machine change between the get and the addition of the delta time this will affect the affect the wait time? Is there a possibility to wait for an event with a relative time instead?

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• lwjgl isKeyDown canceling out other keys

  - by AKrush95

  While trying to create a simple game where a square is manipulated via the keyboard keys, I have come across a small, rather irritating problem. I would like it to work so that when the opposite directional key is pressed, the character will stop; the character may move the other two directions while stopped in this situation. This works perfectly with LEFT and RIGHT held down; the player may move UP or DOWN. If UP and DOWN are held down, however, the player will not move, nor will Java recognize that the LEFT or RIGHT keys were pressed. import java.util.ArrayList; import java.util.Random; import org.lwjgl.*; import org.lwjgl.input.Keyboard; import org.lwjgl.opengl.*; import static org.lwjgl.opengl.GL11.*; public class Main { private Man p; private ArrayList<Integer> keysDown, keysUp; public Main() { try { Display.setDisplayMode(new DisplayMode(640, 480)); Display.setTitle("LWJGLHelloWorld"); Display.create(); } catch (LWJGLException e) { e.printStackTrace(); } p = new Man(0, 0); keysDown = new ArrayList<>(); keysUp = new ArrayList<>(); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0, 640, 480, 0, 1, -1); glMatrixMode(GL_MODELVIEW); while (!Display.isCloseRequested()) { glClear(GL_COLOR_BUFFER_BIT); checkKeys(); p.draw(); Display.update(); Display.sync(60); } Display.destroy(); } public void checkKeys() { ArrayList<Integer> keys = new ArrayList<>(); keys.add(Keyboard.KEY_A); keys.add(Keyboard.KEY_D); keys.add(Keyboard.KEY_W); keys.add(Keyboard.KEY_S); for (int key : keys) { if (Keyboard.isKeyDown(key)) keysDown.add(key); else keysUp.add(key); } keysDown.removeAll(keysUp); keysUp = new ArrayList<>(); int speed = 4; int dx = 0; int dy = 0; if (keysDown.contains(keys.get(2))) { System.out.println("keyUP"); dy -= speed; } if (keysDown.contains(keys.get(3))) { System.out.println("keyDOWN"); dy += speed; } if (keysDown.contains(keys.get(0))) { System.out.println("keyLEFT"); dx -= speed; } if (keysDown.contains(keys.get(1))) { System.out.println("keyRIGHT"); dx += speed; } //if (keysDown.contains(keys.get(0)) && keysDown.contains(keys.get(1))) dx = 0; //if (keysDown.contains(keys.get(2)) && keysDown.contains(keys.get(3))) dy = 0; p.update(dx, dy); } public static void main(String[] args) { new Main(); } class Man { public int x, y, w, h; public float cR, cG, cB; public Man(int x, int y) { this.x = x; this.y = y; w = 50; h = 50; Random rand = new Random(); cR = rand.nextFloat(); cG = rand.nextFloat(); cB = rand.nextFloat(); } public void draw() { glColor3f(cR, cG, cB); glRecti(x, y, x+w, y+h); } public void update(int dx, int dy) { x += dx; y += dy; } } } That is the code that I am working with. In addition, I am unsure how to compile an executable jar that is using the lwjgl library in addition to slick-util.

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• R.matlab/readMat : Error in readTag(this)

  - by Megan

  I am trying to read a matlab file into R using R.matlab but am encountering this error: require(R.matlab) r <- readMat("file.mat", verbose=T) Trying to read MAT v5 file stream... Error in readTag(this) : Unknown data type. Not in range [1,19]: 18569 In addition: Warning message: In readMat5Header(this, firstFourBytes = firstFourBytes) : Unknown MAT version tag: 512. Will assume version 5. How can this issue be solved or is there an alternative way to load matlab files? I can use hdf5load but have heard this can mess with the data. Thanks!

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• using helper methods in a view in rails 3

  - by Frida777

  Hello everyone, there is something that is disturbing me a bit about rails 3. i am trying to upgrade my application from rails 2 to rails 3. i followed all the steps necessary to do and things were working well for me till now except one thing: i have a helper method that is defined differently in different helpers, for example it is defined in the application_helper in one way and the same method defined in a different way in the homepage_helper, and defined differently in another helper, let's say video_helper, in addition to that, it is used in a shared view that is used throughout the application, now if i am in the homepage, i want this function to get called from the homepage_helper and if i am in the video page, the function must be called from the video_helper, based on the concept of convention in rails, this worked perfectly in rails 2 but in rails 3, the function is always called from the last helper, alphabetically ordered, that is in the example, video_helper. How can i fix this? Kindly advice. Appreciate all the help.

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• How do I create "undo" in c++?

  - by b3y4z1d

  I've got a couple of codes to do some things but I need to create a function that undoes the previous task/addition/change.How do I do this in Borland C++? (the program stores strings of text in a text file using "list",it is stored and then erased unless I use the save-function I've created) right,so I don't know if I've forgotten to mention anything of importance for you to be able to help me better,but if there's something you're wondering about the functions just ask. I meant creating an undo function in a simple consol application by the way.

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• Starting an ASP.NET MVC 4 project. Is it necessary to use RequireJS if I'm using bundling?

  - by SCS

  If RequireJS makes it so that multiple js files are combined into a single main.js file, is it essentially the same as ASP.NET's script bundling functionality? Would the only bonus of using RequireJS in addition to bundling be the ability to have certain scripts be loaded according to RequireJS configuration? I'm very new to both bundling and RequireJS, but after doing some reading, it seems like bundling takes care of multiple requests to load several js files. Are there any other things I might be missing out on with regards to using RequireJS with bundling?

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• Why Use java.lang.reflect.Array For Anything Other Than Array Creation?

  - by dimo414

  Java Class java.lang.reflect.Array provides a set of tools for creating an array dynamically. However in addition to that it has a whole set of methods for accessing (get, set, and length) an array. I don't understand the point of this, since you can (and presumably would) cast your dynamically generated array as an array upon creation, which means you can use the normal array access (bracket notation) functionality. In fact, looking at the source code you can see that is all the class does, cast the array, and throw an exception if the cast fails. So what's the point / usefulness of all of these extra methods?

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• Cannot see index view of my controller - routing related

  - by olst

  Hi. I have a controller named Content, which has an Index action, which is associated with a view. I would like the simple route "content" to show me the index view of the content controller, so I use the following code (with the addition of the default site home route): routes.MapRoute( "ContentIndex", "content", new { controller = "Content", action = "Index"} ); routes.MapRoute( "Default", "{controller}/{action}", new { controller = "Home", action = "Index" } ); when I type the url : "http://localhost/content/", I get an error 404 saying the resource cannot be found, but when I type "http://localhost/content/index", it shows the content index view. How can I get rid of the index in the url ? Thanks !

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• Django: Why Doesn't the Current URL Match any Patterns in urls.py

  - by austin_sherron

  I've found a few questions here related to my issue, but I haven't found anything that has helped me resolve my issue. I'm using Python 2.7.5 and Django 1.8.dev20140627143448. I have a view that's interacting with my database to delete objects, and it takes two arguments in addition to a request: def delete_data_item(request, dataclass_id, dataitem_id): form = AddDataItemForm(request.POST) data_set = get_object_or_404(DataClass, pk=dataclass_id) context = {'data_set': data_set, 'form': form} data_item = get_object_or_404(DataItem, pk=dataitem_id) data_item.delete() data_set.save() return HttpResponseRedirect(reverse('detail', args=(dataclass_id,))) The URL in myapp.urls.py looks something like this: url(r'^(?P<dataclass_id>[0-9]+)/(?P<dataitem_id>[0-9]+)/delete_data_item/$', views.delete_data_item, name='delete_data_item') and the portion of my template relevant to the view is: <a href="{% url 'delete_data_item' data_set.id data_item.id %}">DELETE</a> Whenever I click on the DELETE link, django tells me that the request URL: http://127.0.0.1:8000/myapp/5/%7B%%20url%20'delete_data_item'%20data_set.id%20data_item.id%20%%7D doesn't match any of my URL patterns. What am I missing? The URL on which the DELETE links exist is myapp/(<dataclass_id>[0-9]+)/

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• Recommendations for Slideshow Publishing Tool

  - by Chris_K

  A client has asked me to research production tools for publishing slideshows on their Web site. The tool must be very easy to use and it has to generate a mobile version as well as a desktop version of the slideshow. (I'll spare you the rest of the specs.) Tools under consideration include SlideShowPro and Soundslides. Do you have a favorite tool, intended for publishers? In addition to generating code for pasting into a Web page, it would be great if the tool had a hosting component as well, so that a future iPhone app could consume an XML feed of the slideshows, similar to what SlideShowPro offers.

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• How can I use an array within a SQL query

  - by ThinkingInBits

  So I'm trying to take a search string (could be any number of words) and turn each value into a list to use in the following IN statement) in addition, I need a count of all these values to use with my having count filter $search_array = explode(" ",$this->search_string); $tag_count = count($search_array); $db = Connect::connect(); $query = "select p.id from photographs p left join photograph_tags c on p.id = c.photograph_id and c.value IN ($search_array) group by p.id having count(c.value) >= $tag_count"; This currently returns no results, any ideas?

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• What is the best software to write and organize written copy / content for a website?

  - by johnqtaxpayer

  I'm a newbie product manager, looking for tips on how to write and organize text copy for my company's website. I need to be able to prepare the content for our public site and turn it over to the web designer who publishes it to our live site. I want our UI team to be able to quickly glance at the copy I write and immediately know where on the page I intend for it to go. Currently, I'm using microsoft word to write and color code different text to signify where I want specific text to go. It is difficult for the UI guy to immediately know if something goes into the nav bar or into a header or a description below a header. In addition to that, it would be helpful for me to be able to write the copy in such a way that the web designer could copy and paste it into the XHTML without having to go back and manually replace special punctuation characters with the XHTML entities. What software is out there that will allow a comprehensive solution to these web copywriting issues?

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• Process AJAX response with long runing tasks

  - by mpz

  I have long time task in controller action. I use delayed job for it. (Also in heroku it is good practice for perfomance - dyno must work for small time in each request) But my client need result of it work and users can wait on that task. It is more clear: no any addition models or records in it, simple view and js... I think about such way: On client run AJAX with very long timeout (5 min for example) Client make request to server as usual On controller in action1 def start_work (with delay work setup) i need NO any response to client After work performs (delay job finished) i need run new action2 with response to client Client recieve response after about 1-5 min It is possible?

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• Recover a deleted webpage

  - by rc

  Suppose, a blog or a nice article was hosted on a website and it got deleted or worse the website was brought down. How do you view that web page? I tried searching for the cached version in Google. But, looks like the content was deleted long ago and is not listed in the search results directly. There are annotations to the link from many other sites, but still the actual content is not fully available. Now, can anybody help me see this page... I am actually looking for http://effectize.com/become-coolest-programmer :) And, moreover, in addition to bookmarking a favorite link, is it possible to cache the content of the link as well for later reference in case it gets deleted? EDIT: Looks like a URL can be cached for future reference. Try: http://backupurl.com/

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• Should I still use querystrings for page number, etc, when using ASP.NET 4 URL Routing?

  - by Scott

  I am switching from Intelligencia's UrlRewriter to the new web forms routing in ASP.NET 4.0. I have it working great for basic pages, however, in my e-commerce site, when browsing category pages, I previously used querystrings that were built into my pager control to control paging. An old url (with UrlRewriting) would be: http://www.mysite.com/Category/Arts-and-Crafts_17 I now have a MapPageRoute defined in global.asax as: routes.MapPageRoute("category-browse", "Category/{name}_{id}", ~/CategoryPage.aspx"); This works great. Now, somebody clicks to go to page 2. Previously I would have just tacked on ?page=2 as the querystring. Now, How do I handle this using web forms routing? I know I can do something like: http://www.mysite.com/Category/Arts-and-Crafts_17/page/2 But in addition to page, I can have filters, age ranges, gender, etc. Should I just keep defining routes that handle these variables, or should I continue using querystrings and can I define a route that allows me to use my querstrings like before?

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• Confused by "let" in Clojure

  - by Tom Dalling

  I just started playing with Clojure, and I wrote a small script to help me understand some of the functions. It begins like this: (def *exprs-to-test* [ "(filter #(< % 3) '(1 2 3 4 3 2 1))" "(remove #(< % 3) '(1 2 3 4 3 2 1))" "(distinct '(1 2 3 4 3 2 1))" ]) Then it goes through *exprs-to-test*, evaluates them all, and prints the output like this: (doseq [exstr *exprs-to-test*] (do (println "===" (first (read-string exstr)) "=========================") (println "Code: " exstr) (println "Eval: " (eval (read-string exstr))) ) ) The above code is all working fine. However, (read-string exstr) is repeated so I tried to use let to eliminate the repetition like so: (doseq [exstr *exprs-to-test*] (let [ex (read-string exstr)] ( (do (println "===" (first ex) "=========================") (println "Code: " exstr) (println "Eval: " (eval ex)) ) )) ) But this works once for the first item in *exprs-to-test*, then crashes with a NullPointerException. Why is the addition of let causing the crash?

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• How to implement nested SQL transactions with ADO.NET?

  - by manza_jurjur

  I need to implement nested transactions in .NET using ADO.NET. The situation is as follows: --> Start Process (Begin Transaction) --> Begin Transaction for step 1 --> Step 1 --> Commit transaction for step 1 --> Begin transaction for step 2 --> Step 2 --> Rollback transaction for step 2 --> etc ... --> End Process (Commit or Rollback ALL commited steps) Can that be done with transaction scopes? Could anyone post an example? In addition I'd need the prcoess to work for SQL Server 2005 AND Oracle 10g databases... will transaction scopes work with both database engines?

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• [php + mysql] Save IP in database

  - by Knarf

  When a user logs inn I want to save their IP in the database. How would I do that? What type is best to use for the MySQL field? How would the PHP code to get IP look like? I'm thinking of using it as an extra security feature for the login/session stuff. I'm thinking of checking the IP the user logged in with from the DB with the IP the user have now as addition to checking the session. So that it first check the session, and then check if you have a valid IP. Is that an allright extra feature? And what other things can I do to make it more secure?

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• When designing an event, is it a good idea to prevent listeners from being added twice?

  - by Matt

  I am creating an event-based API where a user can subscribe to an event by adding listener objects (as is common in Java or C#). When the event is raised, all subscribed listeners are invoked with the event information. I initially decided to prevent adding an event listener more than once. If a listener is added that already exists in the listener collection, it is not added again. However, after thinking about it some more, it doesn't seem that most event-based structures actually prevent this. Was my initial instinct wrong? I'm not sure which way to go here. I guess I thought that preventing addition of an existing listener would help to avoid a common programming error. Then again, it could also hide a bug that would lead to code being run multiple times when it shouldn't.

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• Reset JPA generated value between tests

  - by Rythmic

  I'm running spring + hibernate + JUnit with springJunit4runner and transactional set to default rollback I'm using in-memory derbydb as Database. Hibernate is used as a JPA Provider and I am successfully testing CRUD kinds of stuff. However, I have a problem with JPA and the behaviour of @GeneratedValue If I run one of my tests in isolation, two entitys are persisted with id 1 and 2. If i run the whole test suite the ids are instead 6 and 7. Spring does rollbacks just fine so there are only these two entitys in the database after addition and of course zero before. But behaviour of @GeneratedValue doesn't allow me to reliable findById unless I would return the Id from the dao.add(Entity e) //method I don't feel like doing that for the sake of testing, or is it a good practise to return the entity that was persisted so I should be doing it anyway?

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