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• Implementing `let` without using a macro

  - by Matt Fenwick

  I'm learning Lisp, and I've just gotten to let, which I don't quite understand (the implementation of). A common definition for it is given in terms of lambda as a macro. However, nowhere have I seen that let must be implemented as a macro or in terms of lambda. Is it possible to define let without using a macro or lambda? I know it can be implemented as a primitive, but I want to know whether it can be implemented in Lisp without creating a macro -- by creating a special form or a function.

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• Ctrl-Alt-T doesn't open terminal

  - by user204591

  I'm using Ubuntu 13.10 and I've been using for a while now as ran it from a daily build about a month ago. It's fully updated with updates, upgrades an dist-upgrades and it was working up until very recently. Not sure exactly when I last issued a Ctrl+Alt+T as I quite often just leave it running however it will have been certainly in the last week. Basically when I hit that key combo I do not get a terminal. I know that each of the keys function as I can Atl+Tab through open applications and I can Ctrl+C to copy and past Ctrl+V to paste and I've typed plenty here that has a "T" in it. I have checked Keyboard Layout in Settings and the correct combo is assigned to the terminal. You'll have to take my word for that as I'm not allowed to post my screenshot!!!!!

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• sprite group doesn't support indexing

  - by user3956

  I have a sprite group created with pygame.sprite.Group() (and add sprites to it with the add method) How would I retrieve the nth sprite in this group? Code like this does not work: mygroup = pygame.sprite.Group(mysprite01) print mygroup[n].rect It returns the error: group object does not support indexing. For the moment I'm using the following function: def getSpriteByPosition(position,group): for index,spr in enumerate(group): if (index == position): return spr return False Although working, it just doesn't seem right... Is there a cleaner way to do this? EDIT: I mention a "position" and index but it's not important actually, returning any single sprite from the group is enough

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• Creating several instances of the same object, and selecting only one

  - by hustlerinc

  I'm playing around with making a puzzle game, haven't done that much before I run into my first problem. Basically, I want to create a certain amount of the same object/function. But without hardcoding the different instances. I think maybe an array is a good idea? and then a for loop to push the objects in? And then I need to be able to select one of these objects by clicking on it, how would I do that? How do I know which ball in the array was clicked? A loop again? I made a jsFiddle example (you need to click the orange ball to select, then you can move it around by clicking the canvas). This is what I want to do, but with more balls. How would you solve this? Help appreciated.

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• Upgraded to Ubuntu 12.04--keyboard & mouse no longer work--system down!

  - by Mackey Morgan

  I upgraded from Ubuntu 11 to 12.04, today, and everything seemed to go smoothly up to, and including the reboot. However, I now find that my mouse and keyboard no longer function, so I cannot login or otherwise use my computer. I have read other posts on this topic, but most of the answers seem to require the use of a keyboard to implement the solution--and I can't use my keyboard! I downloaded a 12.04 LiveCD and tried booting from it, but I have the same issue with that--no keyboard! My systems is a Lenovo with an AMD64 dual processor, and my keyboard and mouse are USB attached and shared with two other Windows PCs via a KVM switch (so I no the keyboard and mouse work!). I would appreciate some hints about how to make this PC usable, again. Thanks!

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• Rotate 2d sprite towards pointer

  - by Phil

  I'm using Crafty.js and am trying to point a sprite towards the mouse pointer. I have a function for getting the degree between two points and I'm pretty sure it works mathematically (I have it under unit tests). At least it responds that the degree between { 0,0} and {1,1} is 45, which seems right. However, when I set the sprite rotation to the returned degree, it's just wrong all the time. If I manually set it to 90, 45, etc, it gets the right direction.. I have a jsfiddle that shows what I've done so far. Any ideas?

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• Creating an OpenGL FPS camera: I have the position and orientation vectors, now what?

  - by Synthetix

  I have been struggling to create a first person camera in OpenGL ES 2.0 without using gluLookAt(). I grab the camera's orientation vectors (the way it's looking) from the current modelview matrix, and use that to calculate the new forward/backward (Z) translation value. I then calculate the strafe (X) value from the dot product of Z and Y (which is always 1.0). So, I have all the information I need to create a view matrix, but how do I do that without using gluLookAt? Almost all the examples I've seen use gluLookAt, but no such function exists in OpenGL ES 2.0. Besides, one of the moderators on cprogramming.com mentioned that gluLookAt is not appropriate for FPS cameras: http://cboard.cprogramming.com/game-programming/135390-how-properly-move-strafe-yaw-pitch-camera-opengl-glut-using-glulookat.html I am really confused by all the conflicting information I'm getting. I just want to create a first person camera that goes forward (W,S keys), side-to-side (A,D keys) and rotates around its center (Y axis only), Wolfenstein style. Any help on this would be much appreciated!

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• ubuntu is becoming more unstable

  - by Michael Hennessey

  I find ubuntu extremely unstable with mouse freezes (that can be corrected with control key), constant Compiz crashes ( with ATI non proprietary drivers also), problems installing drivers ( why would I want a video driver that fails to play most games, with loss of function of so many games (BZ flag?? has been around for years with no problems). I get the feeling that there is so one in your dept who is intentionally making poor and unstable choices for less than altruistic reasons. Whatever happened has been worsening ever since Unity became a choice. I have tried Kubuntu, Mint, Lubuntu and several other variants with similar poor results. Be aware I have used Ubuntu for many years.

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• Inventory Item Exist checker

  - by Annalyne

  I have a question regarding declaring my inventory. I made it a string named inventory, with a constant number as its max value. The thing is, I want the user to use an item if he / she gains an item. The problem is, I do not know what syntax should I use to determine if the user has an item and use that item. Here's my code I just started: so declaring the inventory: const int MAX_ITEMS = 15; string game_inventory [MAX_ITEMS]; int itemnum = 0; I have some items like potion, antidote, gems and others. I use the: game_inventory[itemnum++] = "Potion" to place items in my inventory. If I want to use the potion, IF I HAVE one, how can i make a function to check whether I have a potion or anything and use it?

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• Dump an arbitrary object To Html String

  - by Michael Freidgeim

  For debugging purposes me and my collegue wanted to dump details of the arbitrary object, and created function that uses LINQPad Dump functionality (thanks to http://stackoverflow.com/a/6035014/52277 and original http://linqpad.uservoice.com/forums/18302-linqpad-feature-suggestions/suggestions/447166-make-dump-extension-method-available-in-visual-s discussion)    public static string DumpToHtmlString<T>(this T objectToSerialize)        {            string strHTML = "";            try            {                var writer = LINQPad.Util.CreateXhtmlWriter(true);                writer.Write(objectToSerialize);                strHTML = writer.ToString();            }            catch (Exception exc)            {                Debug.Assert(false, "Investigate why ?" + exc);            }            return strHTML;        }You will need to add the linqpad executable as a reference in your project.TO DO similar in plain text ,look at https://github.com/ServiceStack/ServiceStack.Text StringExtensions , e.g. JsonSerializer/CsvSerializer or http://objectdumper.codeplex.com/

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• Several classes need to access the same data, where should the data be declared?

  - by Juicy

  I have a basic 2D tower defense game in C++. Each map is a separate class which inherits from GameState. The map delegates the logic and drawing code to each object in the game and sets data such as the map path. In pseudo-code the logic section might look something like this: update(): for each creep in creeps: creep.update() for each tower in towers: tower.update() for each missile in missiles: missile.update() The objects (creeps, towers and missiles) are stored in vector-of-pointers. The towers must have access to the vector-of-creeps and the vector-of-missiles to create new missiles and identify targets. The question is: where do I declare the vectors? Should they be members of the Map class, and passed as arguments to the tower.update() function? Or declared globally? Or are there other solutions I'm missing entirely?

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• multitenancy with some data sharing

  - by user55108

  I'm in the planning stages of a new webapp, and I am leaning strongly toward a multitenancy model. The app has a file storage function, where the user can upload (and operate on) files. I would like the ability of the user to share these files, however. How is this typically accomplished in a multi-tenant model? The example would be something like google docs. Each user has their own files; they can edit and tag and build collections with these files. Then, they can share a doc or a collection with someone else for collaboration. If every user has their own Database and tables, what strategy would one use to allow this kind of sharing while minimizing duplication of files and associated metadata?

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• How to populate a form list with buttons using javascript

  - by StealingMana

  I made a script that, when you press one button(accessories) the selection(mylist) populates with one array(accessoryData), and when you hit the other button(weapons) the other array(weaponData) populates the selection. However, in the current state of the code the second button press is not re-populating the selection. What is wrong here? Also if there is a more efficient way to do this, that might be helpful. Full code function runList(form, test) { var html = ""; var x; dataType(test); while (x < dataType.length) { html += "<option>" + dataType[x]; x++; } document.getElementById("mylist").innerHTML = html; }

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• OpenGL: Drawing to a texture

  - by Danran

  Well im just a bit stuck wondering how to draw an item to a texture. Specifically, i'm using; glDrawArrays(GL_LINE_STRIP, indices[0], indices.size()); Because what i'm drawing via the above function updates every-frame, i'm just totally not sure how to go about drawing what i have to a texture. Any help is greatly appreciated! Edit: Well unfortunately my graphics card doesn't support FrameBuffer Objects :/. So i've been trying to get the copy contents from backbuffer method working. Here's what i currently have; http://pastebin.com/dJpPt6Pd And sadly all i get is a white square. Its probably something stupid that i'm doing wrong. Just unsure what it could be?

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• Using T[1] instead of T for functions overloaded for T(&)[N]

  - by Abyx

  The asio::buffer function has (void*, size_t) and (PodType(&)[N]) overloads. I didn't want to write ugly C-style (&x, sizeof(x)) code, so I wrote this: SomePacket packet[1]; // SomePacket is POD read(socket, asio::buffer(packet)); foo = packet->foo; But that packet-> looks kinda weird - the packet is an array after all. (And packet[0]. doesn't look better.) Now, I think if it was a good idea to write such code. Maybe I should stick to unsafe C-style code with void* and sizeof? Upd: here is another example, for writing a packet: SomePacket packet[1]; // SomePacket is POD packet->id = SomePacket::ID; packet->foo = foo; write(socket, asio::buffer(packet));

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• is this the correct way to use glTexCoordPointer?

  - by RubyKing

  Hey all Just trying to work out how to use this function glTexCoordPointer. Here is the man pages http://www.opengl.org/sdk/docs/man/xhtml/glTexCoordPointer.xml which states that I must set a pointer to the first element of the array that uses the texture cordinate. Here is my array static const GLfloat GUIVertices[] = { //FIRST QUAD 1.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f, 1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f, 0.94f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.94f, 0.0f, 1.0f, 1.0f, 1.0f, //2ND QUAD // x y z w X Y 1.0f, -1.0f, 0.0f, 1.0f, 1.0f, 0.0f, -1.0f,-1.0f, 0.0f, 1.0f, 0.0f, 0.0f, -1.0f,-0.94f, 0.0f,1.0f, 0.0f, 1.0f, 1.0f, -0.94f, 0.0f,1.0f, 1.0f, 1.0, }; But how do I set the pointer correctly? like this glTexCoordPointer(1, GL_FLOAT, 6, reinterpret_cast(29 * sizeof(float)) ); for the fifth element on the 2nd quad first row. any help is thankful

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• "// ..." comments at end of code block after } - good or bad?

  - by gablin

  I've often seen such comments be used: function foo() { ... } // foo while (...) { ... } // while if (...) { ... } // if and sometimes even as far as if (condition) { ... } // if (condition) I've never understood this practice and thus never applied it. If your code is so long that you need to know what this ending } is then perhaps you should consider splitting it up into separate functions. Also, most developers tools are able to jump to the matching bracket. And finally the last is, for me, a clear violation to the DRY principle; if you change the condition you would have to remember to change the comment as well (or else it could get messy for the maintainer, or even for you). So why do people use this? Should we use it, or is it bad practice?

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• How can you procedurally place objects in a non-gridded game?

  - by nickbadal

  This is a follow-up question to this question. I mistakenly worded the question, but got a good answer before I could correct myself, so I didn't want to delete it. Sorry! Now that I know that it is possible, I'd like to implement procedural world generation, but I don't want it to look gridded or blocky, where everything is obviously placed on an integer grid. I know that you can do this in gridded worlds by inputting a square's x and y into a noise function, or similar, but how can I generate a more natural looking object placement using procedural methods? This is in the context of an adventure game, if it matters.

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• how do i make maximum minimum and average score statistic in this code? [on hold]

  - by goldensun player

  i wanna out put the maximum minimum and average score as a statistic category under the student ids and grades in the output file. how do i do that? here is the code: #include "stdafx.h" #include <iostream> #include <string> #include <fstream> #include <assert.h> using namespace std; int openfiles(ifstream& infile, ofstream& outfile); void Size(ofstream&, int, string); int main() { int num_student = 4, count, length, score2, w[6]; ifstream infile, curvingfile; char x; ofstream outfile; float score; string key, answer, id; do { openfiles(infile, outfile); // function calling infile >> key; // answer key for (int i = 0; i < num_student; i++) // loop over each student { infile >> id; infile >> answer; count = 0; length = key.size(); // length represents number of questions in exam from exam1.dat // size is a string function.... Size (outfile, length, answer); for (int j = 0; j < length; j++) // loop over each question { if (key[j] == answer[j]) count++; } score = (float) count / length; score2 = (int)(score * 100); outfile << id << " " << score2 << "%"; if (score2 >= 90)//<-----w[0] outfile << "A" << endl; else if (score2 >= 80)//<-----w[1] outfile << "B" << endl; else if (score2 >= 70)//<-----w[2] outfile << "C" << endl; else if (score2 >= 60)//<-----w[3] outfile << "D" << endl; else if (score2 >= 50)//<-----w[4] outfile << "E" << endl; else if (score2 < 50)//<-----w[5] outfile << "F" << endl; } cout << "Would you like to attempt a new trial? (y/n): "; cin >> x; } while (x == 'y' || x == 'Y'); return 0; } int openfiles(ifstream& infile, ofstream& outfile) { string name1, name2, name3, answerstring, curvedata; cin >> name1; name2; name3; if (name1 == "exit" || name2 == "exit" || name3 == "exit" ) return false; cout << "Input the name for the exam file: "; cin >> name1; infile.open(name1.c_str()); infile >> answerstring; cout << "Input the name for the curving file: "; cin >> name2; infile.open(name2.c_str()); infile >> curvedata; cout << "Input the name for the output: "; cin >> name3; outfile.open(name3.c_str()); return true; } void Size(ofstream& outfile, int length, string answer) { bool check;// extra answers, lesser answers... if (answer.size() > length) { outfile << "Unnecessary extra answers"; } else if (answer.size() < length) { outfile << "The remaining answers are incorrect"; } else { check = false; }; } and how do i use assert for preconditions and post conditional functions? i dont understand this that well...

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• Triangles in a C++ STL Vector as an Objective-C member sometimes draws incorrectly in OpenGL ES

  - by Rahil627

  The polygons draw correctly 80% of the time. When it fails, a vertex is dislocated. The polygon is consistently drawn with the wrong vertex. I checked that the vector is correct during initialization, even when it's wrongly drawn. I'm using Cocos2d. The class member: @interface Polygon : CCSprite { std::vector<float> triangleVertices; } The draw function called in [Polygon draw]: + (void)drawTrianglesWithVertices:(const std::vector<float> &)v { //glEnableClientState(GL_VERTEX_ARRAY); glDisable(GL_TEXTURE_2D); glDisableClientState(GL_TEXTURE_COORD_ARRAY); glDisableClientState(GL_COLOR_ARRAY); glVertexPointer(2, GL_FLOAT, 0, &v[0]); glDrawArrays(GL_TRIANGLES, 0, v.size()); //glDisableClientState(GL_VERTEX_ARRAY); glEnableClientState(GL_COLOR_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); glEnable(GL_TEXTURE_2D); } Any ideas?

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• "more than 3 levels of indentation, you're screwed" How should I understand this quote ?

  - by jokoon

  The answer to that is that if you need more than 3 levels of indentation, you're screwed anyway, and should fix your program. What can I deduct from this quote ? On top of the fact that too long methods are hard to maintain, are they hard or impossible to optimize for the compiler ? I don't really understand if this quote encourages better coding practice or is really a mathematical/algorithmic sort of truth... I also read in some C++ optimizing guide that dividing up a program into more function improves its design is a common thing taught at school, but it should be not done too much, since it can turn into a lot of JMP calls (even if the compiler can inline some methods by itself).

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• Automatic Statistics Update Slows Down SQL Server 2005

  I have a database which has several tables that have very heavy write operations. These table are very large and some are over a hundred gigabytes. I noticed performance of this database is getting slower and after some investigation we suspect that the Auto Update Statistics function is causing a performance degradation. Join SQL Backup’s 35,000+ customers to compress and strengthen your backups "SQL Backup will be a REAL boost to any DBA lucky enough to use it." Jonathan Allen. Download a free trial now.

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• Event Aggregator.. not getting a response, how to determine completion?

  - by Duncan_m

  I'm rewriting a vehicle tracking application, a google maps based thing.. The users are able to search for a vehicle by typing a few characters of the vehicles "callsign". My application is based around a sort of "event bus" within Backbone.. when a search occurs I send a message on the bus saying something like "does anyone match this?".. If a marker matches the search term it responds with a sort of "yes, I match!".. My challenge arises when no-one matches, I get no response.. it feels a little hacky to "wait a little while" and check if a response has been recieved.. The application is based around Backbone.js and using the Event Aggregator pattern described in the answer to this question on Stack Overflow: http://stackoverflow.com/questions/7708195/access-function-in-one-view-from-another-in-backbone-js Is there a well defined design pattern that might assist me here? Sending a request for a response and not getting any responses?

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• I cannot change the screen brightness

  - by user1793249

  here's my problem: Ever since I installed Ubuntu 12.10 on my computer I haven't been able to change the screen brightness, it was always set to the maximum. I did take a look at this post: Decrease Backlight Below Minimum And it helped me resolved the issue with the unbearable brightness, however one problem persists: I cannot change it through "Brightness & Lock" or the function buttons (F2 and F3), when I press the buttons, the animation shows up but nothing happens. I tried the following: http://www.refreshit.info/2012/08/solved-brightness-increase-and-decrease.html It did nothing... If it helps: I have an HP-dv6 6185la, it has an ATI Radeon 6770M HD card and an Intel HD Integrated Graphics Card It only detects the "Intel® Sandybridge Mobile" Thanks in advance.

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• MVC Design Pattern to Combine Multiple Models for use

  - by roverred

  In my design, I have multiple models and each model has a controller. I need to use all the models to process some operation. Most examples I see are pretty simple with 1 view, 1 controller, and 1 model. How would you get all these models together? Only ways I can think of are 1) Have a top-level controller which has a reference to every controller. Those controllers will have a getter/setter function for their model. Does this violate MVC because every controller should have a model? 2) Have an Intermediate class to combine every model into a one model. Then you create a controller for that new super model. Do you know of any better ideas? Thanks.

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