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  • Has anyone ever encountered a Monad Transformer in the wild?

    - by martingw
    In my area of business - back office IT for a financial institution - it is very common for a software component to carry a global configuration around, to log it's progress, to have some kind of error handling / computation short circuit... Things that can be modelled nicely by Reader-, Writer-, Maybe-monads and the like in Haskell and composed together with monad transformers. But there seem to some drawbacks: The concept behind monad transformers is quite tricky and hard to understand, monad transformers lead to very complex type signatures, and they inflict some performance penalty. So I'm wondering: Are monad transformers best practice when dealing with those common tasks mentioned above?

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  • [NEWVERSION]algorithm || method to write prog[UNSOLVED] [closed]

    - by fatai
    I am one of the computer science student. Everyone solve problem with a different or same method, ( but actually I dont know whether they use method or I dont know whether there are such common method to approach problem.) if there are common method, What is it ? If there are different method, which method are you using ? All teacher give us problem which in simple form sometimes, but they donot introduce any approach or method(s) so that we cannot make a decision to choose the method then apply that one to problem , afterward find solution then write code.No help from teacher , push us to find method to solve homework. Ex: my friend is using no method , he says "I start to construct algorithm while I try to write prog." I have found one method when I failed the course, More accurately, my method: When I counter problem in language , I will get more paper and then ; first, input/ output step ; my prog will take this / these there argument(s) and return namely X , ex : in c, input length is not known and at same type , so I must use pointer desired output is in form of package , so use structure second, execution part ; in that step , I am writing all step which are goes to final output ex : in python ; 1.) [ + , [- , 4 , [ * , 1 , 2 ]], 5] 2.) [ + , [- , 4 , 2 ],5 ] 3.) [ + , 2 , 5] 4.) 7 ==> return 7 third, I will write test code ex : in c++ input : append 3 4 5 6 vector_x remove 0 1 desired output vector_x holds : 5 6 now, my other question is ; What is/are other method(s) which have/has been; used to construct class :::: for c++ , python, java used to communicate classes / computers used for solving embedded system problem ::::: for c by other user? Some programmer uses generalized method without considering prog-language(java , perl .. ), what is this method ? Why I wonder , because I learn if you dont costruct algorithm on paper, you may achieve your goal. Like no money no lunch , I can say no algorithm no prog therefore , feel free when you write your own method , a way which is introduced by someone else but you are using and you find it is so efficient

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  • How to reference a specific object in an array of objects using jTemplates

    - by Travis
    I am using the excellent jTemplates plugin to generate content. Given a data object like this... var data = { name: 'datatable', table: [ {id: 1, name: 'Anne'}, {id: 2, name: 'Amelie'}, {id: 3, name: 'Polly'}, {id: 4, name: 'Alice'}, {id: 5, name: 'Martha'} ] }; ..I'm wondering if it is possible to directly specify an object in an array of objects using $T. (I'm hoping there is something like $T.table:3 available) Currently the only way I can think of to access a specific object in an array is to do something like this... {#foreach $T.table as record} {#if $T.record$iteration == 3} This is record 3! Name: {$T.record.name} {#/if} {#/for} However that seems clumsy... Any suggestions? Thanks

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  • Java library class to handle scheduled execution of "callbacks"?

    - by Hanno Fietz
    My program has a component - dubbed the Scheduler - that lets other components register points in time at which they want to be called back. This should work much like the Unix cron service, i. e. you tell the Scheduler "notify me at ten minutes past every full hour". I realize there are no real callbacks in Java. Here's my approach, is there a library which already does this stuff? Feel free to suggest improvements, too. Register call to Scheduler passes: a time specification containing hour, minute, second, year month, dom, dow, where each item may be unspecified, meaning "execute it every hour / minute etc." (just like crontabs) an object containing data that will tell the calling object what to do when it is notified by the Scheduler. The Scheduler does not process this data, just stores it and passes it back upon notification. a reference to the calling object Upon startup, or after a new registration request, the Scheduler starts with a Calendar object of the current system time and checks if there are any entries in the database that match this point in time. If there are, they are executed and the process starts over. If there aren't, the time in the Calendar object is incremented by one second and the entreis are rechecked. This repeats until there is one entry or more that match(es). (Discrete Event Simulation) The Scheduler will then remember that timestamp, sleep and wake every second to check if it is already there. If it happens to wake up and the time has already passed, it starts over, likewise if the time has come and the jobs have been executed. Edit: Thanks for pointing me to Quartz. I'm looking for something much smaller, however.

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  • When is it better to use a method versus a property for a class definition?

    - by ccomet
    Partially related to an earlier question of mine, I have a system in which I have to store complex data as a string. Instead of parsing these strings as all kinds of separate objects, I just created one class that contains all of those objects, and it has some parser logic that will encode all properties into strings, or decode a string to get those objects. That's all fine and good. This question is not about the parser itself, but about where I should house the logic for the parser. Is it a better choice to put it as a property, or as a method? In the case of a property, say public string DataAsString, the get accessor would house the logic to encode all of the data into a string, while the set accessor would decode the input value and set all of the data in the class instance. It seems convenient because the input/output is indeed a string. In the case of a method, one method would be Encode(), which returns the encoded string. Then, either the constructor itself would house the logic for the decoding a string and require the string argument, or I write a Decode(string str) method which is called separately. In either case, it would be using a method instead of a property. So, is there a functional difference between these paths, in terms of the actual running of the code? Or are they basically equivalent and it then boils down to a choice of personal preference or which one looks better? And in that kind of question... which would look cleaner anyway?

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  • Strategy Pattern with Type Reflection affecting Performances ?

    - by Aurélien Ribon
    Hello ! I am building graphs. A graph consists of nodes linked each other with links (indeed my dear). In order to assign a given behavior to each node, I implemented the strategy pattern. class Node { public BaseNodeBehavior Behavior {get; set;} } As a result, in many parts of the application, I am extensively using type reflection to know which behavior a node is. if (node.Behavior is NodeDataOutputBehavior) workOnOutputNode(node) .... My graph can get thousands of nodes. Is type reflection greatly affecting performances ? Should I use something else than the strategy pattern ? I'm using strategy because I need behavior inheritance. For example, basically, a behavior can be Data or Operator, a Data behavior can IO, Const or Intermediate and finally an IO behavior can be Input or Output. So if I use an enumeration, I wont be able to test for a node behavior to be of data kind, I will need to test it to be [Input, Output, Const or Intermediate]. And if later I want to add another behavior of Data kind, I'm screwed, every data-testing method will need to be changed.

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  • Is it bad practice to make a setter return "this"?

    - by Ken Liu
    Is it a good or bad idea to make setters in java return "this"? public Employee setName(String name){ this.name = name; return this; } This pattern can be useful because then you can chain setters like this: list.add(new Employee().setName("Jack Sparrow").setId(1).setFoo("bacon!")); instead of this: Employee e = new Employee(); e.setName("Jack Sparrow"); ...and so on... list.add(e); ...but it sort of goes against standard convention. I suppose it might be worthwhile just because it can make that setter do something else useful. I've seen this pattern used some places (e.g. JMock, JPA), but it seems uncommon, and only generally used for very well defined APIs where this pattern is used everywhere. Update: What I've described is obviously valid, but what I am really looking for is some thoughts on whether this is generally acceptable, and if there are any pitfalls or related best practices. I know about the Builder pattern but it is a little more involved then what I am describing - as Josh Bloch describes it there is an associated static Builder class for object creation.

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  • Separating weakly linked database schemas

    - by jldugger
    I've been tasked with revisiting a database schema we designed and use internally for various ticketing and reporting systems. Currently there exists about 40 tables in one Oracle database schema supporting perhaps six webapps. However, there's one unifying relationship amongst them all: a rooms table describing the room. Room name, purpose and other data are thrown into a shared table for each app. My initial idea was to pull each of these applications into a separate database, and perform joins between a given database and the room database. But I've discovered this solution prevents foreign key constraints in SQL Server 2005. It seems silly to duplicate one table for each app and keep those multiple copies synchronized. Should I just leave everything in one large DB, or is there something else I can do separate the tables without losing FK constraints?

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  • Common one-to-many table for multiple entities

    - by Ben V
    Suppose I have two tables, Customer and Vendor. I want to have a common address table for customer and vendor addresses. Customers and Vendors can both have one to many addresses. Option 1 Add columns for the AddressID to the Customer and Vendor tables. This just doesn't seem like a clean solution to me. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID AddressID1 AddressID1 Street AddressID2 AddressID2 City... Option 2 Move the foreign key to the Address table. For a Customer, Address.CustomerID will be populated. For a Vendor, Address.VendorID will be populated. I don't like this either - I shouldn't need to modify the address table every time I want to use it for another entity. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID CustomerID VendorID Option 3 I've also seen this - only 1 foreign key column on the Address table with another column to identify which foreign key table the address belongs to. I don't like this one because it requires all the foreign key tables to have the same type of ID. It also seems messy once you start coding against it. Customer Vendor Address -------- --------- --------- CustomerID VendorID AddressID FKTable FKID So, am I just too picky, or is there something I haven't thought of?

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  • FWA for CSS based sites

    - by weotch
    Does anyone have a favorite style site that posts the latest and greatest sites constructed with CSS + HTML + JS? I'm thinking of something like thefwa.com but not for all flash microsites. Trying to find the definitive portal.

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  • Need some help understanding this problem about maximizing graph connectivity

    - by Legend
    I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. I am not sure if this is a really a problem but I somehow have a feeling that there might exist more than one order in which case, it is required to choose the best order. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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  • Modeling Tools that understand both Relational and LDAP

    - by jm04469
    I am looking to do some modeling and would like to have a tool that can capture not only a relational model like ERWIN but also allow us to easily port to LDAP as an option. NOTE: Visio can connect to an existing LDAP server and draw, but does not allow for you to model first and then deploy, unlike its relational capabilities.

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  • Architecting ASP.net MVC App to use repositories and services

    - by zaladane
    Hello, I recently started reading about ASP.net MVC and after getting excited about the concept, i started to migrate all my webform project to MVC but i am having a hard time keeping my controller skinny even after following all the good advices out there (or maybe i just don't get it ... ). The website i deal with has Articles, Videos, Quotes ... and each of these entities have categories, comments, images that can be associated with it. I am using Linq to sql for database operations and for each of these Entities, i have a Repository, and for each repository, i create a service to be used in the controller. so i have - ArticleRepository ArticleCategoryRepository ArticleCommentRepository and the corresponding service ArticleService ArticleCategoryService ... you see the picture. The problem i have is that i have one controller for article,category and comment because i thought that having ArticleController handle all of that might make sense, but now i have to pass all of the services needed to the Controller constructor. So i would like to know what it is that i am doing wrong. Are my services not designed properly? should i create Bigger service to encapsulate smaller services and use them in my controller? or should i have an articleCategory Controller and an articleComment Controller? A page viewed by the user is made of all of that, thee article to be viewed,the comments associated with it, a listing of the categories to witch it applies ... how can i efficiently break down the controller to keep it "skinny" and solve my headache? Thank you! I hope my question is not too long to be read ...

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  • Should we denormalize database to improve performance?

    - by Groo
    We have a requirement to store 500 measurements per second, coming from several devices. Each measurement consists of a timestamp, a quantity type, and several vector values. Right now there is 8 vector values per measurement, and we may consider this number to be constant for needs of our prototype project. We are using HNibernate. Tests are done in SQLite (disk file db, not in-memory), but production will probably be MsSQL. Our Measurement entity class is the one that holds a single measurement, and looks like this: public class Measurement { public virtual Guid Id { get; private set; } public virtual Device Device { get; private set; } public virtual Timestamp Timestamp { get; private set; } public virtual IList<VectorValue> Vectors { get; private set; } } Vector values are stored in a separate table, so that each of them references its parent measurement through a foreign key. We have done a couple of things to ensure that generated SQL is (reasonably) efficient: we are using Guid.Comb for generating IDs, we are flushing around 500 items in a single transaction, ADO.Net batch size is set to 100 (I think SQLIte does not support batch updates? But it might be useful later). The problem Right now we can insert 150-200 measurements per second (which is not fast enough, although this is SQLite we are talking about). Looking at the generated SQL, we can see that in a single transaction we insert (as expected): 1 timestamp 1 measurement 8 vector values which means that we are actually doing 10x more single table inserts: 1500-2000 per second. If we placed everything (all 8 vector values and the timestamp) into the measurement table (adding 9 dedicated columns), it seems that we could increase our insert speed up to 10 times. Switching to SQL server will improve performance, but we would like to know if there might be a way to avoid unnecessary performance costs related to the way database is organized right now. [Edit] With in-memory SQLite I get around 350 items/sec (3500 single table inserts), which I believe is about as good as it gets with NHibernate (taking this post for reference: http://ayende.com/Blog/archive/2009/08/22/nhibernate-perf-tricks.aspx). But I might as well switch to SQL server and stop assuming things, right? I will update my post as soon as I test it.

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  • Unexpected space between DIV elements, no - not padding and not margins

    - by jon
    my code for the php page displaying the divs <?php session_start(); require_once("classlib/mainspace.php"); if (isset($_SESSION['username'])==FALSE) { header("location:login.php"); } $user = new User($_SESSION['username']); ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="style/style.css" /> <title>SimpleTask - Home</title> </head> <body> <div id="main"> <div id="menu"> <div id="items"> <ul> <li><a href="home.php">home</a></li> <li>&bull;</li> <li><a href="projects.php">my projects</a></li> <li>&bull;</li> <li><a href="comments.php">my comments</a></li> </ul> </div> <div id="user"> <p>Welcome, <?php echo $user->GetRealName(); ?><br/><a href="editprofile.php">edit profile</a> &bull; <a href="logout.php">logout</a></p> </div> </div> <div id="content"> <h1>HOME</h1> </div> <div id="footer"> <p>footer text goes here here here here</p> </div> </div> </body> </html> and you can find my CSS here http://tasker.efficaxdevelopment.com/style/style.css and to view the live page go here http://tasker.efficaxdevelopment.com/login.php username:admin password:password

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  • C#, weird optimization

    - by Snake
    Hi, I'm trying to read my compiled C# code. this is my code: using(OleDbCommand insertCommand = new OleDbCommand("...", connection)) { // do super stuff } But! We all know that a using gets translated to this: { OleDbCommand insertCommand = new OleDbCommand("...", connection) try { //do super stuff } finally { if(insertCommand != null) ((IDisposable)insertCommand).Dispose(); } } (since OleDbCommand is a reference type). But when I decompile my assembly (compiled with .NET 2.0) I get this in Resharper: try { insertCommand = new OleDbCommand("", connection); Label_0017: try { //do super stuff } finally { Label_0111: if ((insertCommand == null) != null) { goto Label_0122; } insertCommand.Dispose(); Label_0122:; } I'm talking about this line: if ((insertCommand == null) != null). True is not null, it never is, nor is false. So how is my object disposed properly? WTF? Thanks! -Kristof

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  • PHP Classes Extend

    - by John
    I have two classes that work seperate from another, but they extend the same class. Is it possible to have them work the same instance of the extended class. I'm wanting the constructor of the extended class to run only once. I know this isn't right but something like this: <?php $oApp = new app; class a extends $oApp {} class b extends $oApp {}

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  • Resources on wordpress theme-development

    - by Espenhh
    What are the best resources for Wordpress theme-development? I am currently in the phase of starting my own blog, and don't want to use one of the many free themes. I already have a theme for my website, so I want to read about best-practices. Any advice on how to get started would be very welcome :) I have now created my theme (wohoo!), and thought I should summarize the best resources I found. Lets see.. Resources: ThemeTation's three-part guide to create a wordpress-theme from scratch Nettuts.com's guide: How to Create a Wordpress Theme from Scratch (And Part 2) Didn't actually use this, it's a quite new article, but anyway - it's great. It will get a follow-up in the next few days too.. Wordpress.org's own guide on templates Definatly a must-read for everyone new to wordpress-designing.. "The loop" Essential knowledge, also a must-read Directory of all the template tags Used by wordpress to actually output blog-content.. Inspiration: Smashing Magazine's lists: first, one more, yet another one Wordpress.org's theme-directory

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  • Natural vs surrogate keys on support tables

    - by Bugeo
    I have read many articles about the battle between natural versus surrogate primary keys. I agree in the use of surrogate keys to identify records of tables whose contents are created by the user. But in the case of supporting tables what should I use? For example, in a hypothetical table "orderStates". If you use a natural key would have the following data: TABLE ORDERSTATES {ID: "NEW", NAME: "New"} {ID: "MANAGEMENT" NAME: "Management"} {ID: "SHIPPED" NAME: "Shipped"} If I use a surrogate key would have the following data: TABLE ORDERSTATES {ID: 1 CODE: "NEW", NAME: "New"} {ID: 2 CODE: "MANAGEMENT" NAME: "Management"} {ID: 3 CODE: "SHIPPED" NAME: "Shipped"} Now let's take an example: a user enters a new order. In the case in which use natural keys, in the code I can write this: newOrder.StateOrderId = "NEW"; With the surrogate keys instead every time I have an additional step. stateOrderId_NEW = .... I retrieve the id corresponding to the recod code "NEW" newOrder.StateOrderId = stateOrderId_NEW; The same will happen every time I have to move the order in a new status. So, in this case, what are the reason to chose one key type vs the other one?

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  • Uses of the Apache commons-proxy library?

    - by Adrian
    I'm looking at the Apache commons-proxy library to implement some Proxy patterns in my current project. The Javadocs are all very well, but I'd really like to see some tutorials or just a project that uses the library so I can get more of a feel for it. Alas, searching for such things just tends to net you a lot of pages about setting up HTTP proxies using Apache. So I'm hoping that people here can help me.

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  • correct approach to store in database

    - by John
    I'm developing an online website (using Django and Mysql). I have a Tests table and User table. I have 50 tests within the table and each user completes them at their own pace. How do I store the status of the tests in my DB? One idea that came to my mind is to create an additional column in User table. That column containing testid's separated by comma or any other delimiter. userid | username | testscompleted 1 john 1, 5, 34 2 tom 1, 10, 23, 25 Another idea was to create a seperate table to store userid and testid. So, I'll have only 2 columns but thousands of rows (no of tests * no of users) and they will always continue to increase. userid | testid 1 1 1 5 2 1 1 34 2 10

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  • Updating Linking Tables

    - by Sasha
    I've currently adding a bit of functionality that manages holiday lettings on top of a CMS that runs on PHP and MySQL. The CMS stores the property details on a couple of tables, and I'm adding a third table (letting_times) that will contain information about when people are staying at the property. Basic functionality would allow the user to add new times when a guest is staying, edit the times that the guest is staying and remove the booking if the guest no longer wants to stay at the property. Right now the best way that I can think of updating the times that the property is occupied is to delete all the times contained in the letting_times database and reinsert them again. The only other way that I can think to do this would be to include the table's primary key and do an update if that is present and has a value, otherwise do an insert, but this would not delete rows of data if they are removed. Is there a better way of doing this?

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