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• Haskell Cons Operator (:)

  - by Carson Myers

  I am really new to Haskell (Actually I saw "Real World Haskell" from O'Reilly and thought "hmm, I think I'll learn functional programming" yesterday) and I am wondering: I can use the construct operator to add an item to the beginning of a list: 1 : [2,3] [1,2,3] I tried making an example data type I found in the book and then playing with it: --in a file data BillingInfo = CreditCard Int String String | CashOnDelivery | Invoice Int deriving (Show) --in ghci $ let order_list = [Invoice 2345] $ order_list [Invoice 2345] $ let order_list = CashOnDelivery : order_list $ order_list [CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, ...- etc... it just repeats forever, is this because it uses lazy evaluation? -- EDIT -- okay, so it is being pounded into my head that let order_list = CashOnDelivery:order_list doesn't add CashOnDelivery to the original order_list and then set the result to order_list, but instead is recursive and creates an infinite list, forever adding CashOnDelivery to the beginning of itself. Of course now I remember that Haskell is a functional language and I can't change the value of the original order_list, so what should I do for a simple "tack this on to the end (or beginning, whatever) of this list?" Make a function which takes a list and BillingInfo as arguments, and then return a list? -- EDIT 2 -- well, based on all the answers I'm getting and the lack of being able to pass an object by reference and mutate variables (such as I'm used to)... I think that I have just asked this question prematurely and that I really need to delve further into the functional paradigm before I can expect to really understand the answers to my questions... I guess what i was looking for was how to write a function or something, taking a list and an item, and returning a list under the same name so the function could be called more than once, without changing the name every time (as if it was actually a program which would add actual orders to an order list, and the user wouldn't have to think of a new name for the list each time, but rather append an item to the same list).

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• C++: Reference and Pointer question (example regarding OpenGL)

  - by Jay

  I would like to load textures, and then have them be used by multiple objects. Would this work? class Sprite { GLuint* mTextures; // do I need this to also be a reference? Sprite( GLuint* textures ) // do I need this to also be a reference? { mTextures = textures; } void Draw( textureNumber ) { glBindTexture( GL_TEXTURE_2D, mTextures[ textureNumber ] ); // drawing code } }; // normally these variables would be inputed, but I did this for simplicity. const int NUMBER_OF_TEXTURES = 40; const int WHICH_TEXTURE = 10; void main() { std::vector<GLuint> the_textures; the_textures.resize( NUMBER_OF_TEXTURES ); glGenTextures( NUMBER_OF_TEXTURES, &the_textures[0] ); // texture loading code Sprite the_sprite( &the_textures[0] ); the_sprite.Draw( WHICH_TEXTURE ); } And is there a different way I should do this, even if it would work? Thanks.

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• Wrapper class that creates objects at runtime and stores data in an array.

  - by scriptingalias

  I tried making a wrapper class that encapsulates an object, a string (for naming and differentiating the object instance), and an array to store data. The problem I'm having now is accessing this class using methods that determine the "name" of the object and also reading the array containing some random variables. import java.util.Arrays; import java.util.Random; public class WrapperClass { String varName; Object varData; int[] array = new int[10]; public WrapperClass(String name, Object data, int[] ARRAY) { varName = name; varData = data; array = ARRAY; } public static void getvalues() { } public static void main(String[] args) { int[] array = new int[10]; Random random = new Random(3134234); for(int i = 0; i < 10; i++) { for (int c = 0; c < 10; c++) { array[c] = random.nextInt();//randomly creates data } WrapperClass w = new WrapperClass("c" + i, new Object(),array); } } }

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• How can I send GET data to multiple URLs at the same time using cURL?

  - by Rob

  My apologies, I've actually asked this question multiple times, but never quite understood the answers. Here is my current code: while($resultSet = mysql_fetch_array($SQL)){ $ch = curl_init($resultSet['url'] . $fullcurl); //load the urls and send GET data curl_setopt($ch, CURLOPT_TIMEOUT, 2); //Only load it for two seconds (Long enough to send the data) curl_exec($ch); //Execute the cURL curl_close($ch); //Close it off } //end while loop What I'm doing here, is taking URLs from a MySQL Database ($resultSet['url']), appending some extra variables to it, just some GET data ($fullcurl), and simply requesting the pages. This starts the script running on those pages, and that's all that this script needs to do, is start those scripts. It doesn't need to return any output. Just the load the page long enough for the script to start. However, currently it's loading each URL (currently 11) one at a time. I need to load all of them simultaneously. I understand I need to use curl_multi_*, but I haven't the slightest idea on how cURL functions work, so I don't know how to change my code to use curl_multi_* in a while loop. So my questions are: How can I change this code to load all of the URLs simultaneously? Please explain it and not just give me code. I want to know what each individual function does exactly. Will curl_multi_exec even work in a while loop, since the while loop is just sending each row one at a time? And of course, any references, guides, tutorials about cURL functions would be nice, as well. Preferably not so much from php.net, as while it does a good job of giving me the syntax, its just a little dry and not so good with the explanations.

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• Android - Parsing XML with XPath

  - by Ruben Deig Ramos

  First of all, thanks to all the people who's going to spend a little time on this question. Second, sorry for my english (not my first language! :D). Well, here is my problem. I'm learning Android and I'm making an app which uses a XML file to store some info. I have no problem creating the file, but trying to read de XML tags with XPath (DOM, XMLPullParser, etc. only gave me problems) I've been able to read, at least, the first one. Let's see the code. Here is the XML file the app generates: <dispositivo> <id>111</id> <nombre>Name</nombre> <intervalo>300</intervalo> </dispositivo> And here is the function which reads the XML file: private void leerXML() { try { XPathFactory factory=XPathFactory.newInstance(); XPath xPath=factory.newXPath(); // Introducimos XML en memoria File xmlDocument = new File("/data/data/com.example.gps/files/devloc_cfg.xml"); InputSource inputSource = new InputSource(new FileInputStream(xmlDocument)); // Definimos expresiones para encontrar valor. XPathExpression tag_id = xPath.compile("/dispositivo/id"); String valor_id = tag_id.evaluate(inputSource); id=valor_id; XPathExpression tag_nombre = xPath.compile("/dispositivo/nombre"); String valor_nombre = tag_nombre.evaluate(inputSource); nombre=valor_nombre; } catch (Exception e) { e.printStackTrace(); } } The app gets correctly the id value and shows it on the screen ("id" and "nombre" variables are assigned to a TextView each one), but the "nombre" is not working. What should I change? :) Thanks for all your time and help. This site is quite helpful! PD: I've been searching for a response on the whole site but didn't found any.

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• Extremely CPU Intensive Alarm Clock

  - by SoulBeaver

  For some reason my program, a console alarm clock I made for laughs and practice, is extremely CPU intensive. It consumes about 2mB RAM, which is already quite a bit for such a small program, but it devastates my CPU with over 50% resources at times. Most of the time my program is doing nothing except counting down the seconds, so I guess this part of my program is the one that's causing so much strain on my CPU, though I don't know why. If it is so, could you please recommend a way of making it less, or perhaps a library to use instead if the problem can't be easily solved? /* The wait function waits exactly one second before returning to the * * called function. */ void wait( const int &seconds ) { clock_t endwait; // Type needed to compare with clock() endwait = clock() + ( seconds * CLOCKS_PER_SEC ); while( clock() < endwait ) {} // Nothing need be done here. } In case anybody browses CPlusPlus.com, this is a genuine copy/paste of the clock() function they have written as an example for clock(). Much why the comment //Nothing need be done here is so lackluster. I'm not entirely sure what exactly clock() does yet. The rest of the program calls two other functions that only activate every sixty seconds, otherwise returning to the caller and counting down another second, so I don't think that's too CPU intensive- though I wouldn't know, this is my first attempt at optimizing code. The first function is a console clear using system("cls") which, I know, is really, really slow and not a good idea. I will be changing that post-haste, but, since it only activates every 60 seconds and there is a noticeable lag-spike, I know this isn't the problem most of the time. The second function re-writes the content of the screen with the updated remaining time also only every sixty seconds. I will edit in the function that calls wait, clearScreen and display if it's clear that this function is not the problem. I already tried to reference most variables so they are not copied, as well as avoid endl as I heard that it's a little slow compared to \n.

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• Obtaining FontMetrics before getting a Graphics instance

  - by Tom Castle

  Typically, I'd obtain a graphics instance something like this: BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB); Graphics2D g = img.createGraphics(); However, in the current project I'm working on, the width and height variables above are dependent upon the size of a number of text fragments that will later be drawn onto the graphics instance. But, to obtain the dimensions of the font being used I would usually use the FontMetrics that I get from the graphics object. FontMetrics metrics = g.getFontMetrics(); So, I have a nasty little dependency cycle. I cannot create the graphics object until I know the size of the text, and I cannot know the size of the text until I have a graphics object. One solution is just to create another BufferedImage/Graphics pair first in order to get the FontMetrics instance I need, but this seems unnecessary. So, is there a nicer way? Or is it the case that the width, height etc. properties for a Font are somehow dependent upon what (graphics, component...) the text is to be drawn on?

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• Creating and appending a big DOM with javascript - most optimized way?

  - by fenderplayer

  I use the following code to append a big dom on a mobile browser (webkit): 1. while(someIndex--) // someIndex ranges from 10 to possibly 1000 2. { 3. var html01 = ['<div class="test">', someVal,'</div>', 4. '<div><p>', someTxt.txt1, someTxt.txt2, '</p></div>', 5. // lots of html snippets interspersed with variables 6. // on average ~40 to 50 elements in this array 7. ].join(''); 8. var fragment = document.createDocumentFragment(), 9. div = fragment.appendChild(document.createElement('div')); 10. div.appendChild(jQuery(html01)[0]); 11. jQuery('#screen1').append(fragment); 12. } //end while loop 13. // similarly i create 'html02' till 'html15' to append in other screen divs Is there a better or faster way to do the above? Do you see any problems with the code? I am a little worried about line 10 where i wrap in jquery and then take it out.

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• C++ Constructor initialization list strangeness

  - by Andy

  I have always been a good boy when writing my classes, prefixing all member variables with m_: class Test { int m_int1; int m_int2; public: Test(int int1, int int2) : m_int1(int int1), m_int2(int int2) {} }; void main() { Test t(10, 20); // Just an example } However, recently I forgot to do that and ended up writing: class Test { int int1; int int2; public: // Very questionable, but of course I meant to assign ::int1 to this->int1! Test(int int1, int int2) : int1(int1), int2(int2) {} }; Believe it or not, the code compiled with no errors/warnings and the assignments took place correctly! It was only when doing the final check before checking in my code when I realised what I had done. My question is: why did my code compile? Is something like that allowed in the C++ standard, or is it simply a case of the compiler being clever? In case you were wondering, I was using Visual Studio 2008 Thank you.

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• return ArrayList from spring controller for ajax call and render in second dropdown

  - by user1708125

  I've a spring bean with 3 Maps all of which are to be populated incrementally. First map is an item category list, second map is a product list and third map is a hobby for item type list All the maps are mapped to and on the JSP. When the page is loaded only the first map is populated on the onchange event of first map, I need to populate the second map in the bean and similarly on the onchange event of second map, I need to populate the third map in the bean. Is there a way to do this using Ajax?? I need some code samples to how to render JSON response in second and third dropdown. Clarification: @Donal: I have a simple JSP page with 3 dropdowns corresponding to 3 maps stored in my commandBean. So when the page loads for the first time only the first map and hence the first dropdown is populated. Now whenever the user selects anything out of the first dropdown, I need to send the same commandbean back with the values of the first dropdown and get the values for the second map and hence the second dropdown and so forth for the 3rd dropdown as well. For each dropdown I 've got 3 maps and 3 variables for storing the selected values. Now I want to understand if this is possible using Ajax. I hope this clarifies whatever you need to know. Thanx

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• Trouble with pointers and references in C++

  - by KingNestor

  I have a PolygonList and a Polygon type, which are std::lists of Points or lists of lists of points. class Point { public: int x, y; Point(int x1, int y1) { x = x1; y = y1; } }; typedef std::list<Point> Polygon; typedef std::list<Polygon> PolygonList; // List of all our polygons PolygonList polygonList; However, I'm confused on reference variables and pointers. For example, I would like to be able to reference the first Polygon in my polygonList, and push a new Point to it. So I attempted to set the front of the polygonList to a Polygon called currentPolygon like so: Polygon currentPolygon = polygonList.front(); currentPolygon.push_front(somePoint); and now, I can add points to currentPolygon, but these changes end up not being reflected in that same polygon in the polygonList. Is currentPolygon simply a copy of the Polygon in the front of polygonList? When I later iterate over polygonList all the points I've added to currentPolygon aren't shown. It works if I do this: polygonList.front().push_front(somePoint); Why aren't these the same and how can I create a reference to the physical front polygon rather than a copy of it?

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• Safari and Chrome back button changes hidden and submit values in forms

  - by OverClocked

  The following problem happens on both Safari and Chrome, so probably a WebKit issue. Page A: a page that requires you to login to see, contains a form that has a type=submit button, with name=submit, and value=a Page B: some other page Page C: ask user to login page, contains a form with a type=submit button, with name=submit and value=c User visits page A, then page B. Then idles and the user's login session times out. User hits back button to go back to page A. Browser redirects user to page C. On Safari and Chrome, when C is rendered, the form on page C has the type=submit button, name=submit, but value shows up as "a". If you reload while on page C, "c" appears as the value of the name=submit button. The same problem appears with type=hidden input fields; when user hits back button, their values are also changed to some other value from some other form. Also, this problem also shows up w/o the redirect, with just submit then back. In this case the previous page renders with incorrect values for hidden and submit CGI variables. So far the only fix I can come up with is use Javascript to reset the type=hidden and type=submit variable values, after page C loads, to make sure the values are correct. But that's not clean and universally applicable. Short of WebKit fixing this error, has anyone ran into a better workaround? Thanks.

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• Form validation

  - by kielie

  Hi guys, I need to create a form that has many of the same fields, that have to be inserted into a database, but the problem I have is that if a user only fills in one or two of the rows, the form will still submit the blank data of the empty fields along with the one or two fields the user has filled in. How can I check for the rows that have not been filled in and leave them out of the query? or check for those that have been filled in and add them to the query. . . The thank_you.php file will capture the $_POST variables and add them to the database. <form method="post" action="thank_you.php"> Name: <input type="text" size="28" name="name1" /> E-mail: <input type="text" size="28" name="email1" /> <br /> Name: <input type="text" size="28" name="name2" /> E-mail: <input type="text" size="28" name="email2" /> <br /> Name: <input type="text" size="28" name="name3" /> E-mail: <input type="text" size="28" name="email3" /> <br /> Name: <input type="text" size="28" name="name4" /> E-mail: <input type="text" size="28" name="email4" /> <input type="image" src="images/btn_s.jpg" /> </form> I am assuming that I could use javascript or jQuery to accomplish this, how would I go about doing this? Thanx in advance for the help.

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• NullPointerException on Activity Testing Tutorial

  - by Bendik

  Hello, I am currently trying the activity testing tutorial (Found here), and have a problem. It seems that whenever I try to call something inside the UIThread, I get a java.lang.NullPointerException. public void testSpinnerUI() { mActivity.runOnUiThread( new Runnable() { public void run() { mSpinner.requestFocus(); } }); } This gives me: Incomplete: java.lang.NullPointerException and nothing else. I have tried this on two different samples now, with the same result. I tried with a try/catch clause around the mSpinner.requestFocus() call, and it seems that mSpinner is null inside the thread. I have set it properly up with the setUp() function found in the same sample, and a quick assertNotNull( mSpinner ) shows me that mSpinner is in fact not null after the setUp() function. What can be the cause of this? EDIT; ok, some more testing has been done. It seems that the application that is being tested resets between each test. This essentially makes me have to reinstantiate all variables between each test. Is this normal?

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• Sending information between JavaScript and Web Services using AJAX

  - by COB-CSU-AM

  Alright so I'm using Microsoft's Web Services and AJAX to get information from a SQL database for use with java script on the client side. And I'm wondering what the best method is. Before I started working on the project, the web services were setup to return a C# List filled with some objects. Those objects variables (ints, strings, etc.) contain the data I want to use. Of course, java script can't do much with this, to the best of my knowledge. I then modified the web service to return a 2D Array, but java script got confused, and to the best of my knowledge can't handle 2D array's returned from C#. I then tried to use a regular array, but then a found the length property of an array in JS doesn't carry over, so I couldn't preform a for loop through all the items, because there wasn't anyway of knowing how many elements there were. The only other thing I can thing of is returning a string with special char's to separate the data, but this seems way too convoluted. Any suggestions? Thanks in advance!

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• PHP MySQLi isn't letting me alter a table (adding a new column)

  - by asdasd

  Well thats pretty much it. This is my query: $query = 'ALTER TABLE permissions ADD '.$name.' INT NOT NULL DEFAULT \'0\''; Where $name is already checked to exist with only lower case alpha letters, and not more than 20 length. Im just starting this out with very simple names. The next 4 lines of code after that one are: if($stmt = $db -> prepare($query)) { $success = $stmt -> execute(); $stmt -> close(); if(!$success) echo 'ERROR: Unsuccessful query: ',$db->error,PHP_EOL; } And I get back, every time ERROR: Unsuccessful query: And no error message. Is there a way to get more error messages so I can see what is failing? I can add new columns through phpmyadmin, but that really doesnt help me at all. The $db is fine, i do lots of stuff before and after this one section. It is only adding new column to the table that fails. side question: prepare() rejected my query every time when i tried to make those 2 variables, the $name and the 0 value as ? ? prepared statement values. Thats why they are in the real query and not bound later. If i could change that too I would like that.

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• Can we have a component-scoped bean in a JSF2 composite component?

  - by Pradyumna

  Hi, I was wondering how I could create "component-scoped" beans, or so-to-say, "local variables inside a composite component" that are private to the instance of the composite component, and live as long as that instance lives. Below are more details, explained with an example: Suppose there is a "calculator" component - something that allows users to type in a mathematical expression, and evaluates its value. Optionally, it also plots the associated function. I can make a composite component that has: a text box for accepting the math expression two buttons called "Evaluate", and "Plot" another nested component that plots the function It is evidently a self-contained piece of function; so that somebody who wants to use it may just say <math:expressionEvaluator /> But obviously, the implementation would need a java object - something that evaluates the expression, something that computes the plot points, etc. - and I imagine it can be a bean - scoped just for this instance of this component, not a view-scoped or request-scoped bean that is shared across all instances of the component. How do I create such a bean? Is that even possible with composite components?

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• Does everything after my try statement have to be encompassed in that try statement to access variab

  - by Mithrax

  I'm learning java and one thing I've found that I don't like, is generally when I have code like this: import java.util.*; import java.io.*; public class GraphProblem { public static void main(String[] args) { if (args.length < 2) { System.out.println("Error: Please specify a graph file!"); return; } FileReader in = new FileReader(args[1]); Scanner input = new Scanner(in); int size = input.nextInt(); WeightedGraph graph = new WeightedGraph(size); for(int i = 0; i < size; i++) { graph.setLabel(i,Character.toString((char)('A' + i))); } for(int i = 0; i < size; i++) { for(int j = 0; j < size; j++) { graph.addEdge(i, j, input.nextInt()); } } // .. lots more code } } I have an uncaught exception around my FileReader. So, I have to wrap it in a try-catch to catch that specific exception. My question is does that try { } have to encompass everything after that in my method that wants to use either my FileReader (in) or my Scanner (input)? If I don't wrap the whole remainder of the program in that try statement, then anything outside of it can't access the in/input because it may of not been initialized or has been initialized outside of its scope. So I can't isolate the try-catch to just say the portion that intializes the FileReader and close the try statement immediately after that. So, is it the "best practice" to have the try statement wrapping all portions of the code that are going to access variables initialized in it? Thanks!

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• VS2010 - Using <Import /> to share properties between setup projects?

  - by arex1337

  Why doesn't it work to <Import /> this file, when it works when I replace the statement with just copy-pasting the three properties? ../../Setup.Version.proj <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"> <PropertyGroup> <InstallerMajorVersion>7</InstallerMajorVersion> <InstallerMinorVersion>7</InstallerMinorVersion> <InstallerBuildNumber>7</InstallerBuildNumber> </PropertyGroup> </Project> Works: <?xml version="1.0" encoding="utf-8"?> <Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"> <PropertyGroup> <InstallerMajorVersion>7</InstallerMajorVersion> <InstallerMinorVersion>7</InstallerMinorVersion> <InstallerBuildNumber>7</InstallerBuildNumber> <OutputName>asdf-$(InstallerMajorVersion).$(InstallerMinorVersion).$(InstallerBuildNumber)</OutputName> <OutputType>Package</OutputType> Doesn't work: <?xml version="1.0" encoding="utf-8"?> <Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"> <Import Project="../../Setup.Version.proj" /> <PropertyGroup> <OutputName>asdf-$(InstallerMajorVersion).$(InstallerMinorVersion).$(InstallerBuildNumber)</OutputName> <OutputType>Package</OutputType> Here the variables just evaulate to empty strings... :( I'm certain the path to the imported project is correct.

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• Need advanced mod_rewrite assistance

  - by user1647719

  This is driving me bananas. I have tried multiple fixes, and have even found a generator (generateit.net/mod-rewrite/) to create my .htaccess files, but I cannot get this to work. The .htaccess file is being read - if I put garbage characters in, I get a 500 server error. Also, mod rewrite was working in a simpler format, but the client wants even more SEO, so here I am. My intention: Take the url of brinkofdesign.com/portfolio/123/456/some_seo_text.html and send it to brinkofdesign.com/brink_portfolio.php?catid=123&locationid=456. The full contents of my .htaccess file are: Options +FollowSymlinks RewriteEngine on RewriteBase / RewriteRule ^portfolio([^/]*)/([^/]*)/([^/]*)\.html$ /portfolio_brink.php?catid=$1&locationid=$2&page=$3 [NC,L] RewriteRule ^(.*)blog(.+)([0-9+])(.+).html$ blog.php?blogid=$3 [NC,L] RewriteRule ^blog.xml$ blogfeed.php The blog and blogfeed parts work fine. If it matters, I do have an actual portfolio.php page - could this be breaking it? There is no actual /portfolio/ folder - this is just part of the SEO nme. Also, the host is 1and1.com. Real life tests: brinkofdesign.com/portfolio/1/1/birmingham_al_corporate_branding.html loads my actual portfolio.php page - which is supposed to be a landing page for the portfolio, as opposed to the brink_portfolio.php page, which is my detail record page. No variables are passed (echoing out the contents of the $_GET array gives an empty array). Typing in an non SEO link like brinkofdesign.com/brink_portfolio.php?catid=1&locationid=1 does work correctly. Gurus, please help me!

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• How to programmatically create a node in Drupal 8?

  - by chapka

  I'm designing a new module in Drupal 8. It's a long-term project that won't be going public for a few months at least, so I'm using it as a way to figure out what's new. In this module, I want to be able to programmatically create nodes. In Drupal 7, I would do this by creating the object, then calling "node_submit" and "node_save". These functions no longer exist in Drupal 8. Instead, according to the documentation, "Modules and scripts may programmatically submit nodes using the usual form API pattern." I'm at a loss. What does this mean? I've used Form API to create forms in Drupal 7, but I don't get what the docs are saying here. What I'm looking to do is programmatically create at least one and possibly multiple new nodes, based on information not taken directly from a user-presented form. I need to be able to: 1) Specify the content type 2) Specify the URL path 3) Set any other necessary variables that would previously have been handled by the now-obsolete node_object_prepare() 4) Commit the new node object I would prefer to be able to do this in an independent, highly abstracted function not tied to a specific block or form. So what am I missing?

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• WPF Binding to variable / DependencyProperty

  - by Peter

  I'm playing around with WPF Binding and variables. Apparently one can only bind DependencyProperties. I have come up with the following, which works perfectly fine: The code-behind file: public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } public string Test { get { return (string)this.GetValue(TestProperty); } set { this.SetValue(TestProperty, value); } //set { this.SetValue(TestProperty, "BBB"); } } public static readonly DependencyProperty TestProperty = DependencyProperty.Register( "Test", typeof(string), typeof(MainWindow), new PropertyMetadata("CCC")); private void button1_Click(object sender, RoutedEventArgs e) { MessageBox.Show(Test); Test = "AAA"; MessageBox.Show(Test); } } XAML: <Window x:Class="WpfApplication3.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase" Title="MainWindow" Height="350" Width="525" DataContext="{Binding RelativeSource={RelativeSource Self}}"> <Grid> <TextBox Height="31" HorizontalAlignment="Left" Margin="84,86,0,0" Name="textBox1" VerticalAlignment="Top" Width="152" Text="{Binding Test, Mode=TwoWay, diag:PresentationTraceSources.TraceLevel=High}"/> <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="320,85,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" /> <TextBox Height="31" HorizontalAlignment="Left" Margin="84,138,0,0" Name="textBox2" Text="{Binding Test, Mode=TwoWay}" VerticalAlignment="Top" Width="152" /> </Grid> The two TextBoxes update one an other. And the Button sets them to "AAA". But now I replaced the Setter function with the one that is commented out (simulating some manipulation of the given value). I would expect that whenever the property value is changed it will be reset to "BBB". It does so when you press the button, that is when you set the property in code. But it does for some reason not affect the WPF Bindings, that is you can change the TextBox contents and thus the property, but apparently the Setter is never called. I wonder why that is so, and how one would go about to achive the expected behaviour.

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• Why does this Haskell code produce the "infinite type" error?

  - by Charlie Flowers

  I am new to Haskell and facing a "cannot construct infinite type" error that I cannot make sense of. In fact, beyond that, I have not been able to find a good explanation of what this error even means, so if you could go beyond my basic question and explain the "infinite type" error, I'd really appreciate it. Here's the code: intersperse :: a -> [[a]] -> [a] -- intersperse '*' ["foo","bar","baz","quux"] -- should produce the following: -- "foo*bar*baz*quux" -- intersperse -99 [ [1,2,3],[4,5,6],[7,8,9]] -- should produce the following: -- [1,2,3,-99,4,5,6,-99,7,8,9] intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:y:xs) = x:s:y:intersperse s xs And here's the error trying to load it into the interpreter: Prelude :load ./chapter.3.ending.real.world.haskell.exercises.hs [1 of 1] Compiling Main ( chapter.3.ending.real.world.haskell.exercises.hs, interpreted ) chapter.3.ending.real.world.haskell.exercises.hs:147:0: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `intersperse' Failed, modules loaded: none. Thanks. EDIT: Thanks to the responses, I have corrected the code and I also have a general guideline for dealing with the "infinite type" error in Haskell: Corrected code intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:xs) = x ++ s:intersperse s xs What the problem was: My type signature states that the second parameter to intersperse is a list of lists. Therefore, when I pattern matched against "s (x:y:xs)", x and y became lists. And yet I was treating x and y as elements, not lists. Guideline for dealing with the "infinite type" error: Most of the time, when you get this error, you have forgotten the types of the various variables you're dealing with, and you have attempted to use a variable as if it were some other type than what it is. Look carefully at what type everything is versus how you're using it, and this will usually uncover the problem.

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• Universal oAuth for objective-c class?

  - by phpnerd211

  I have an app that connects to 6+ social networks via APIs. What I want to do is transfer over my oAuth calls to call directly from the phone (not from the server). Here's what I have (for tumblr): // Set some variables NSString *consumerKey = CONSUMER_KEY_HERE; NSString *sharedSecret = SHARED_SECRET_HERE; NSString *callToURL = @"https://tumblr.com/oauth/access_token"; NSString *thePassword = PASSWORD_HERE; NSString *theUsername = USERNAME_HERE; // Calculate nonce & timestamp NSString *nonce = [[NSString stringWithFormat:@"%d", arc4random()] retain]; time_t t; time(&t); mktime(gmtime(&t)); NSString *timestamp = [[NSString stringWithFormat:@"%d", (int)(((float)([[NSDate date] timeIntervalSince1970])) + 0.5)] retain]; // Generate signature NSString *baseString = [NSString stringWithFormat:@"GET&%@&%@",[callToURL urlEncode],[[NSString stringWithFormat:@"oauth_consumer_key=%@&oauth_nonce=%@&oauth_signature_method=HMAC-SHA1&oauth_timestamp=%@&oauth_version=1.0&x_auth_mode=client_auth&x_auth_password=%@&x_auth_username=%@",consumerKey,nonce,timestamp,thePassword,theUsername] urlEncode]]; NSLog(@"baseString: %@",baseString); const char *cKey = [sharedSecret cStringUsingEncoding:NSASCIIStringEncoding]; const char *cData = [baseString cStringUsingEncoding:NSASCIIStringEncoding]; unsigned char cHMAC[CC_SHA256_DIGEST_LENGTH]; CCHmac(kCCHmacAlgSHA256, cKey, strlen(cKey), cData, strlen(cData), cHMAC); NSData *HMAC = [[NSData alloc] initWithBytes:cHMAC length:sizeof(cHMAC)]; NSString *signature = [HMAC base64EncodedString]; NSString *theUrl = [NSString stringWithFormat:@"%@?oauth_consumer_key=%@&oauth_nonce=%@&oauth_signature=%@&oauth_signature_method=HMAC-SHA1&oauth_timestamp=%@&oauth_version=1.0&x_auth_mode=client_auth&x_auth_password=%@&x_auth_username=%@",callToURL,consumerKey,nonce,signature,timestamp,thePassword,theUsername]; From tumblr, I get this error: oauth_signature does not match expected value I've done some forum scouring, and no oAuth for objective-c classes worked for what I want to do. I also don't want to have to download and implement 6+ social API classes into my project and do it that way.

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• Any problems with this C++ const reference accessor interface idiom?

  - by mskfisher

  I was converting a struct to a class so I could enforce a setter interface for my variables. I did not want to change all of the instances where the variable was read, though. So I converted this: struct foo_t { int x; float y; }; to this: class foo_t { int _x; float _y; public: foot_t() : x(_x), y(_y) { set(0, 0.0); } const int &x; const float &y; set(int x, float y) { _x = x; _y = y; } }; I'm interested in this because it seems to model C#'s idea of public read-only properties. Compiles fine, and I haven't seen any problems yet. Besides the boilerplate of associating the const references in the constructor, what are the downsides to this method? Any strange aliasing issues? Why haven't I seen this idiom before?

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