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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • What are the reasons to select Object Oriented Programming over Procedural Programming?

    - by Starx
    Nowadays, Standard Coding has become Synonymous to Object Oriented Programming. But what are the reasons that forced classical procedural programming out of the way and rose the new concept of Object Oriented Programming. What were the limitations that Procedural Programming could not accomplish? and Does procedural language still hold some value in the field of programming? If yes, What are they, and What are there advantages over OOP?

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  • Adding metadata attributes to MySQL table

    - by Jack
    I would like to add custom attributes to a MySQL table which I can read via php. These attributes are not to interfere with the table itself - they are primarily accessed by php code during code generation time and these attributes HAVE to reside in the DB itself. Something similar in concept to .NET reflection. Does MySQL support anything like this? Thanks.

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  • Request is not generated fro m jsp page

    - by Hitesh Solanki
    Hiii.... I am developing small spring application. I have to store the details of the student information in the database. I have develop one simpleformcontroller. I have used netbeans + hibernate mapping + spring. when I submit the form, jsp page is redirect on the same page and control does not go to Formcontroller..

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  • AI opponent car logic in car race game.

    - by ashok patidar
    hello i want to develop AI car(opponent) in car race game what should be my direction to develop them with less complexity because i don't have any idea. because the player car is moving on the scrolling track plz suggest me should i have to use relative motion or way point concept but that should also be change on the scrolling track (i.e. player car movement)

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  • Autocomplete server-side implementation

    - by toluju
    What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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  • Zend Table Relationship Modeling with Composite Key

    - by emeraldjava
    I have a table with a composite primary key using four columns. mysql> describe leaguesummary; +------------------------+------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------------------+------------------+------+-----+---------+----------------+ | leagueid | int(10) unsigned | NO | PRI | NULL | auto_increment | | leaguetype | enum('I','T') | NO | PRI | NULL | | | leagueparticipantid | int(10) unsigned | NO | PRI | NULL | | | leaguestandard | int(10) unsigned | NO | | NULL | | | leaguedivision | varchar(5) | NO | PRI | NULL | | | leagueposition | int(10) unsigned | NO | | NULL | | I have the league object modelled as so (all plain enough mappings) <?php class Model_DbTable_League extends Zend_Db_Table_Abstract { protected $_name = 'league'; protected $_primary = 'id'; protected $_dependentTables = array('Model_DbTable_LeagueSummary'); And I've started like this on the new model class. I've mapped a simple reference map which returns all rows linked to the league id. // http://files.zend.com/help/Zend-Framework/zend.db.table.relationships.html // http://naneau.nl/2007/04/21/a-zend-framework-tutorial-part-one/ class Model_DbTable_LeagueSummary extends Zend_Db_Table_Abstract { protected $_name = "leaguesummary"; protected $_primary = array('leagueid', 'leaguetype','leagueparticipantid','leaguedivision'); protected $_referenceMap = array( 'Summary' => array( 'columns' => array('leagueid'), 'refTableClass' => 'Model_DbTable_League', 'refColumns' => array('id') ), ..... ); } ?> The simple case works when called from my controller public function listAction() { // action body $leagueTable = new Model_DbTable_League(); $this->view->leagues = $leagueTable->getLeagues(); $league = $leagueTable->getLeague(6); // work $summary = $league->findDependentRowset('Model_DbTable_LeagueSummary','Summary'); Zend_Debug::dump($summary,"",true); I'm not sure how i can define extra _referenceMap keys which will take extra contraint ket values. I would like to be able to define a set called 'MenA' in which the type and division values are hardcoded, and the league id is taken from the initial rowset. 'MenA' =>array( 'columns' => array('leagueid','leaguetype','leaguedivision'), 'refTableClass' => 'Model_DbTable_League', 'refColumns' => array("id","I","A") ) Is this style of mapping possible ie hardcoding the values into the 'refColumns'. The second crazy idea i had was to pass the variable values in as part of the third param of the findDependentRowset() method. $menA = $league->findDependentRowset('Model_DbTable_LeagueSummary','MenA',array("I","A")); Any suggestions on how I might use the Zend DB Table Relationship mapping correctly to do this would be appreciated. I'm not interested in the plain, old and ugly $db-select(a,b,c)-where(..) style solution.

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  • Parse URLs of major video streaming sites and generate appropriate code for embedding.

    - by Markus Lux
    Posting a video on tumblr.com allows you to just paste the URL of the video on youtube, vimeo, whatever and tumblr automatically does the embedding for you. I assume that this would be nothing more than a mapping between an URL-regex and the belonging HTML construct for embedding the video. Or it is just parsing the response of the URL and getting the construct from there. Is there already any utility, preferably in Java, for doing this? If not, how would you do it?

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  • Is key 'chord' functionality provided by Win32/.net?

    - by John
    Several MS apps support the concept of chords, like "CTRL+X,Y" which means "holding down CTRL, press X, then Y". Is this a bespoke thing they (and other companies) implement, or is it built into any APIs? It would be nice to be able to set up event handlers or accelerators based on chords rather than write code to do it.

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  • Can nullptr be emulated in gcc?

    - by nuzz
    I saw that nullptr was implemented in Visual Studio 2010. I like the concept and want to start using it as soon as possible; however GCC does not support it yet. My code needs to run on both (but doesn't have to compile with other compilers). Is there a way to "emulate" it? Something like: #define nullptr NULL (but obviously that wouldn't work well at all, I was simply showing what I meant).

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  • Explaining abstraction to a non-programmer.

    - by Dominic Bou-Samra
    Abstraction is a concept that seems difficult to explain, without reverting to using programming terminology. I've thought about it a lot, and I can't come up with a satisfactory answer. Does anyone have any very general, yet very pertinent explanations? Metaphors, similes etc are all welcome.

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  • What is the difference between "someValuesFrom" and "allValuesFrom"?

    - by ahmed
    In descriptive logic, what is the difference between "someValuesFrom" and "allValuesFrom"? In other words, the difference between (limited existential quantification) and (value restriction). For example, consider this picture: I have used the photoshop because I can't write some symbols. Is there any way to simplify the concept of somevaluefrom and allvaluesfrom?

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  • Meaning of Primary Key to Microsoft SQL Server 2008

    - by usr
    What meaning does the concept of a primary key have to the database engine of SQL Server? I don't mean the clustered/nonclustered index created on the "ID" column, i mean the constraint object "primary key". Does it matter if it exists or not? Alternatives: alter table add primary key clustered alter table create clustered index Does it make a difference?

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  • AJAX in Rails - doing simple looping to update information when available

    - by Acidburn2k
    I am trying to get put out a simple site, which would pool the database every few seconds and update the information on the page dynamicly, when theres something new inserted. I am farily new to ruby, but I understand the whole concept of RJS, link_to_function and soforth. The question is, what is the best way how to implement some kind of simple loop, which would run after the page is loaded and update the DOM if there is something new to display. Thanks in advance for any tips!

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  • linq groupby in strongly typed MVC View

    - by jason
    How do i get an IGrouping result to map to the view? I have this query: var groupedManuals = manuals.GroupBy(c => c.Series); return View(groupedManuals); What is the proper mapping for the ViewPage declaration? Inherits="System.Web.Mvc.ViewPage<IEnumerable<ProductManual>>"

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  • i recieved warning when set cookie

    - by jeya devan
    i used mvc concept for my project... i can set cookies index page... but i can not set cookies in view page,,, i received the following warning... Warning: Cannot modify header information - headers already sent by... thanks advance

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  • Wallet Underflow? [closed]

    - by David T. McKee
    I am a software engineer who would love to "disconnect" from the "company store" so-to-speak. This concept of Stack-Overflow is great...so, because I know that software engineers need coffee and food, how do you monetize this? Just wondering.

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  • Can lazy loading be considered an example of RAII?

    - by codemonkey
    I have been catching up on my c++ lately, after a couple years of exclusive Objective-C on iOS, and the topic that comes up most on 'new style' c++ is RAII To make sure I understand RAII concept correctly, would you consider Objective-C lazy loading property accessors a type of RAII? For example, check the following access method - (NSArray *)items { if(_items==nil) { _items=[[NSArray alloc] initWithCapacity:10]; } return _items } Would this be considered an example of RAII? If not, can you please explain where I'm mistaken?

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  • Spring Security 3 - Login is not working

    - by newbie
    I use Spring Security with Spring Framework 3 and when I tyr to login from homepage I get following error: 2010-04-26 12:16:39,525 [tomcat-http--2] WARN org.springframework.web.servlet.PageNotFound - No mapping found for HTTP request with URI [/AppName/app/j_spring_security_check] in DispatcherServlet with name 'Spring MVC Dispatcher Servlet' Spring Security is initialized as loggings tell and there are no errors. So what could be reason for this error? I have understood that j_spring_security_check is default url for Spring Security login chekeing servlet.

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  • asp.net: Where can I put my source files.

    - by David Sykes
    I am developing a web form using Visual Web Developer Currently I have class source files in the same directory as the web form, or in the App_Code folder. I'd like to organise the files into folders within the web form folder, but I can't find a way of adding a reference to the folders, and they don't seem to be being picked up automatically. These are files that are under constant development. What is the asp.net/c#'s equivalent concept to c++'s #include?

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