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• Haskell: Pattern Matching with Lists

  - by user1670032

  I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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• Design issue with ATG CommercePipelineManager

  - by user1339772

  The definition of runProcess() method in PipelineManager is public PipelineResult runProcess(String pChainId, Object pParam) throws RunProcessException This gives me an impression that ANY object can be passed as the second param. However, ATG OOTB has PipelineManager component referring to CommercePipelineManager class which overrides the runProcess() method and downcast pParam to map and adds siteId to it. Basically, this enforces the client code to send only Map. Thus, if one needs to create a new pipeline chain, has to use map as data structure to pass on the data. Offcourse, one can always get around this by creating a new PipelineManager component, but I was just wondering the thought behind explicitly using map in CommercePipelineManager

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• Designing different Factory classes (and what to use as argument to the factories!)

  - by devoured elysium

  Let's say we have the following piece of code: public class Event { } public class SportEvent1 : Event { } public class SportEvent2 : Event { } public class MedicalEvent1 : Event { } public class MedicalEvent2 : Event { } public interface IEventFactory { bool AcceptsInputString(string inputString); Event CreateEvent(string inputString); } public class EventFactory { private List<IEventFactory> factories = new List<IEventFactory>(); public void AddFactory(IEventFactory factory) { factories.Add(factory); } //I don't see a point in defining a RemoveFactory() so I won't. public Event CreateEvent(string inputString) { try { //iterate through all factories. If one and only one of them accepts //the string, generate the event. Otherwise, throw an exception. return factories.Single(factory => factory.AcceptsInputString(inputString)).CreateEvent(inputString); } catch (InvalidOperationException e) { throw new InvalidOperationException("No valid factory found to generate this kind of Event!", e); } } } public class SportEvent1Factory : IEventFactory { public bool AcceptsInputString(string inputString) { return inputString.StartsWith("SportEvent1"); } public Event CreateEvent(string inputString) { return new SportEvent1(); } } public class MedicalEvent1Factory : IEventFactory { public bool AcceptsInputString(string inputString) { return inputString.StartsWith("MedicalEvent1"); } public Event CreateEvent(string inputString) { return new MedicalEvent1(); } } And here is the code that runs it: static void Main(string[] args) { EventFactory medicalEventFactory = new EventFactory(); medicalEventFactory.AddFactory(new MedicalEvent1Factory()); medicalEventFactory.AddFactory(new MedicalEvent2Factory()); EventFactory sportsEventFactory = new EventFactory(); sportsEventFactory.AddFactory(new SportEvent1Factory()); sportsEventFactory.AddFactory(new SportEvent2Factory()); } I have a couple of questions: Instead of having to add factories here in the main method of my application, should I try to redesign my EventFactory class so it is an abstract factory? It'd be better if I had a way of not having to manually add EventFactories every time I want to use them. So I could just instantiate MedicalFactory and SportsFactory. Should I make a Factory of factories? Maybe that'd be over-engineering? As you have probably noticed, I am using a inputString string as argument to feed the factories. I have an application that lets the user create his own events but also to load/save them from text files. Later, I might want to add other kinds of files, XML, sql connections, whatever. The only way I can think of that would allow me to make this work is having an internal format (I choose a string, as it's easy to understand). How would you make this? I assume this is a recurrent situation, probably most of you know of any other more intelligent approach to this. I am then only looping in the EventFactory for all the factories in its list to check if any of them accepts the input string. If one does, then it asks it to generate the Event. If you find there is something wrong or awkward with the method I'm using to make this happen, I'd be happy to hear about different implementations. Thanks! PS: Although I don't show it in here, all the different kind of events have different properties, so I have to generate them with different arguments (SportEvent1 might have SportName and Duration properties, that have to be put in the inputString as argument).

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• Efficiently Serving Dynamic Content in Google App Engine

  - by awegawef

  My app on google app engine returns content items (just text) and comments on them. It works like this (pseudo-ish code): query: get keys of latest content #query to datastore for each item in content if item_dict in memcache: use item_dict else: build_item_dict(item) #by fetching from datastore store item_dict in memcache send all item_dicts to template Sorry if the code isn't understandable. I get all of the content dictionaries and send them to the template, which uses them to create the webpage. My problem is that if the memcache has expired, for each item I want to display, I have to (1) lookup item in memcache, (2) since no memcache exists I must fetch item from the datastore, and (3) store the item in memcache. These calls build up quickly. I don't set an expire time for the entries to the memcache, so this really only happens once in the morning, but the webpage takes long enough to load (~1 sec) that the browser reports it as not existing. Regularly, my webpages take about 50ms to load. This approach works decently for frequent visits, but it has its flaws as shown above. How can I remedy this? The entries are dynamic enough that I don't think it would be in my best interest to cache my initial request. Thanks in advance

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• Is a "Confirm Email" input good practice when user changes email address?

  - by dibson

  My organization has a form to allow users to update their email address with us. It's suggested that we have two input boxes for email: the second as an email confirmation. I always copy/paste my email address when faced with the confirmation. I'm assuming most of our users are not so savvy. Regardless, is this considered a good practice? I can't stand it personally, but I also realize it probably isn't meant for me. If someone screws up their email, they can't login, and they must call to sort things out.

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• Can we create a class from a xml file ?

  - by panzerschreck

  Hello, Is it possible to create a class dynamically by reading an xml file ( in java preferably) ? if yes, please provide pointers on how to do it. In the process of development, we have come up with a class that has 5 attributes, all these attributes correspond to an entry in the xml file, now if the user adds/modifies the xml entry the object corresponding to it must change automatically, one approach would be generate the source code, before compile time.Is there any other way ? Is there any common pattern to model such changes in the system ? Thanks,

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• What is the best way to identify which form has been submitted?

  - by Rupert

  Currently, when I design my forms, I like to keep the name of the submit button equal to the id of the form. Then, in my php, I just do if(isset($_POST['submitName'])) in order to check if a form has been submitted and which form has been submitted. Firstly, are there any security problems or design flaws with this method? One problem I have encountered is when I wish to overlay my forms with javascript in order to provide faster validation to the user. For example, whilst I obviously need to retain server side validation, it is more convenient for the user if an error message is displayed inline, upon blurring an input. Additionally, it would be good to provide entire form validation, upon clicking the submit button. Therefore, when the user clicks on the form's submit button, I am stopping the default action, doing my validation, and then attempting to renable the traditional submit functionality, if the validation passes. In order to do this, I am using the form.submit() method but, unfortunately, this doesn't send the submit button variable (as it should be as form.submit() can be called without any button being clicked). This means my PHP script fails to detect that the form has been submitted. What is the correct way to work around this? It seems like the standard solution is to add a hidden field into the form, upon passing validation, which has the name of form's id. Then when form.submit() is called, this is passed along in place of the submit button. However, this solution seems very ungraceful to me and so I am wondering whether I should: a) Use an alternative method to detect which form has been submitted which doesn't rely rely on passing the submit button. If so what alternative is there? Obviously, just having an extra hidden field from the start isn't any better. b) Use an alternative Javascript solution which allows me to retain my non-Javascript design. For example, is there an alternative to form.submit() which allows me to pass in extra data? c) Suck it up and just insert a hidden field using Javascript.

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• A .Net4 Gem: The ConcurrentDictionary - Tips & Tricks

  - by SDReyes

  Hi guys, I started to use the new ConcurrentDictionary from .Net4 yesterday to implement a simple caching for a threading project. But I'm wondering what I have to take care of/be careful about when using it? What have been your experiences using it?

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• What is the best way to manage application screens in SWT?

  - by parxier

  I'm creating a standalone SWT desktop application that has around 10 different screens (few wizards, help, forms, etc). Some elements on screen don't change at all (like header, background, etc) and there is a working area that changes depending on what is clicked, etc. What is the best way to manage application screens? Do I need to create all screen at startup and then show/hide them depending on what is clicked? Or do I need to create those screens dynamically? Also, I couldn't find any way to show/hide a Composite, do I need to dispose it and then create again? What is the best practice? I'm new to SWT developing outside of Eclipse so any help would be beneficial.

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• Using GET instead of POST to delete data behind authenticated pages

  - by Matt Spradley

  I know you should use POST whenever data will be modified on a public website. There are several reasons including the fact that search engines will follow all the links and modify the data. My question is do you think it is OK to use GET behind authenticated pages in something like an admin interface? One example would be a list of products with a delete link on each row. Since the only way to get to the page is if you are logged in, is there any harm in just using a link with the product ID in the query string?

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• Pattern for null settings

  - by user21243

  Hi, I would like to hear your thoughts and ideas about this one. in my application i have controls that are binded to objects properties. but.. the controls always looks like that: a check box, label that explain the settings and then the edited control (for ex: text box) when unchecking the checkbox i disable the text box (using binding) when the checkbox is unchecked i want the property to contain null, and when it is checked i would like the property to contain the text box's text. Of course text box can be NumericUpDown, ComboBox, DatePicker etc.. Do you have any smart way of doing it using binding or do i have to do everything on code; I really would like to a build a control that supports that and re-use it all over Ideas? Thanks,

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• Would ViewModels fit in the Model View Presenter pattern?

  - by Jonn

  Having used ViewModels in MVC, I was wondering if applying the same to the MVP pattern is practical. I only have a few considerations, one being that MVP is already fairly hard to implement (with all the additional coding, not much on the seeming complexity) or that ViewModels already have a slightly similar way of modeling data or entities. Would adding another layer in the form of ViewModels be redundant or is it a logical abstraction that I, as one implementing the MVP pattern, should adhere to?

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• What's the best way to unit test code that generates random output?

  - by Flynn1179

  Specifically, I've got a method picks n items from a list in such a way that a% of them meet one criterion, and b% meet a second, and so on. A simplified example would be to pick 5 items where 50% have a given property with the value 'true', and 50% 'false'; 50% of the time the method would return 2 true/3 false, and the other 50%, 3 true/2 false. Statistically speaking, this means that over 100 runs, I should get about 250 true/250 false, but because of the randomness, 240/260 is entirely possible. What's the best way to unit test this? I'm assuming that even though technically 300/200 is possible, it should probably fail the test if this happens. Is there a generally accepted tolerance for cases like this, and if so, how do you determine what that is?

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• Handling Dialogs in WPF with MVVM

  - by Ray Booysen

  In the MVVM pattern for WPF, handling dialogs is one of the more complex operations. As your view model does not know anything about the view, dialog communication can be interesting. I can expose an ICommand that when the view invokes it, a dialog can appear. Does anyone know of a good way to handle results from dialogs? I am speaking about windows dialogs such as MessageBox. One of the ways we did this was have an event on the viewmodel that the view would subscribe to when a dialog was required. public event EventHandler<MyDeleteArgs> RequiresDeleteDialog; This is OK, but it means that the view requires code which is something I would like to stay away from.

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• Should my validator have access to my entire model?

  - by wb

  As the title states I'm wondering if it's a good idea for my validation class to have access to all properties from my model. Ideally, I would like to do that because some fields require 10+ other fields to verify whether it is valid or not. I could but would rather not have functions with 10+ parameters. Or would that make the model and validator too coupled with one another? Here is a little example of what I mean. This code however does not work because it give an infinite loop! Class User Private m_UserID Private m_Validator Public Sub Class_Initialize() End Sub Public Property Let Validator(value) Set m_Validator = value m_Validator.Initialize(Me) End Property Public Property Get Validator() Validator = m_Validator End Property Public Property Let UserID(value) m_UserID = value End property Public Property Get UserID() UserID = m_Validator.IsUserIDValid() End property End Class Class Validator Private m_User Public Sub Class_Initialize() End Sub Public Sub Initialize(value) Set m_User = value End Sub Public Function IsUserIDValid() IsUserIDValid = m_User.UserID > 13 End Function End Class Dim mike : Set mike = New User mike.UserID = 123456 mike.Validator = New Validator Response.Write mike.UserID If I'm right and it is a good idea, how can I go a head and fix the infinite loop with the get property UserID? Thank you.

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• Is Abstract Factory Pattern implemented correctly for given scenario.... ???

  - by Amit

  First thing... I am novice to pattern world, so correct me if wrong anywhere Scenario: There are multiple companies providing multiple products of diff size so there are 3 entities i.e. Companies, Their Product and size of product I have implement Abstract Pattern on this i.e. so that I will create instance of IProductFactory interface to get desired product... Is below implementation of Abstract Factory Pattern correct ??? If not then please correct the approach + Also tell me if any other pattern can be used for such scenario Thanks in advance... public enum Companies { Samsung = 0, LG = 1, Philips = 2, Sony = 3 } public enum Product { PlasmaTv = 0, DVD = 1 } public enum ProductSize { FortyTwoInch, FiftyFiveInch } interface IProductFactory { IPhilips GetPhilipsProduct(); ISony GetSonyProduct(); } interface ISony { string CreateProducts(Product product, ProductSize size); } interface IPhilips { string CreateProducts(Product product, ProductSize size); } class ProductFactory : IProductFactory { public IPhilips GetPhilipsProduct() { return new Philips(); } public ISony GetSonyProduct() { return new Sony(); } } class Philips : IPhilips { #region IPhilips Members public string CreateProducts(Product product, ProductSize size) {// I have ingnore size for now.... string output = string.Empty; if (product == Product.PlasmaTv) { output = "Plasma TV Created !!!"; } else if (product == Product.DVD) { output = "DVD Created !!!"; } return output; } #endregion } class Sony : ISony {// I have ingnore size for now.... #region ISony Members public string CreateProducts(Product product, ProductSize size) { string output = string.Empty; if (product == Product.PlasmaTv) { output = "Plasma TV Created !!!"; } else if (product == Product.DVD) { output = "DVD Created !!!"; } return output; } #endregion } IProductFactory prodFactory = new ProductFactory(); IPhilips philipsObj = prodFactory.GetPhilipsProduct(); MessageBox.Show(philipsObj.CreateProducts(Product.DVD, ProductSize.FortyTwoInch)); or //ISony sonyObj = prodFactory.GetSonyProduct(); //MessageBox.Show(sonyObj.CreateProducts(Product.DVD, ProductSize.FortyTwoInch));

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• Tips for documenting a web application?

  - by Pandiya Chendur

  I know that I can take my asp.net application and get it reversed to a UML document, but that doesn't tell the whole story of things like who can use what, what it calls in the way of stored procedures, what pages call what pages etc. etc. Does anyone know of an article where someone has a comprehensive way to document a web application/site? Or shall I just make up my own way?

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• Some good websites to learn about JavaScript and programming architecture?

  - by Jack Roscoe

  I'm not sure if 'architecture' is the correct term, but I've been looking for some articles online which talk about programming design and more about how best to use languages such as JavaScript in a code design sense rather than the actual syntax itself. I have found many websites but a lot seem to be very out dated, and I'm not sure what developments have taken place with JavaScript over the years so do not know how old is too old. If anybody could suggest some great websites, or maybe specific articles you think would be useful, that would be highly appreciated. I am a beginner programmer currently using JavaScript with XML and of course HTML & CSS, and I'm currently trying to get further into and learn more about web development.

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• Applying the Decorator Pattern to Forms

  - by devoured elysium

  I am trying to apply the Decorator Design Pattern to the following situation: I have 3 different kind of forms: Green, Yellow, Red. Now, each of those forms can have different set of attributes. They can have a minimize box disabled, a maximized box disabled and they can be always on top. I tried to model this the following way: Form <---------------------------------------FormDecorator /\ /\ |---------|-----------| |----------------------|-----------------| GreenForm YellowForm RedForm MinimizeButtonDisabled MaximizedButtonDisabled AlwaysOnTop Here is my GreenForm code: public class GreenForm : Form { public GreenForm() { this.BackColor = Color.GreenYellow; } public override sealed Color BackColor { get { return base.BackColor; } set { base.BackColor = value; } } } FormDecorator: public abstract class FormDecorator : Form { private Form _decoratorForm; protected FormDecorator(Form decoratorForm) { this._decoratorForm = decoratorForm; } } and finally NoMaximizeDecorator: public class NoMaximizeDecorator : FormDecorator { public NoMaximizeDecorator(Form decoratorForm) : base(decoratorForm) { this.MaximizeBox = false; } } So here is the running code: static void Main() { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(CreateForm()); } static Form CreateForm() { Form form = new GreenForm(); form = new NoMaximizeDecorator(form); form = new NoMinimizeDecorator(form); return form; } The problem is that I get a form that isn't green and that still allows me to maximize it. It is only taking in consideration the NoMinimizeDecorator form. I do comprehend why this happens but I'm having trouble understanding how to make this work with this Pattern. I know probably there are better ways of achieving what I want. I made this example as an attempt to apply the Decorator Pattern to something. Maybe this wasn't the best pattern I could have used(if one, at all) to this kind of scenario. Is there any other pattern more suitable than the Decorator to accomplish this? Am I doing something wrong when trying to implement the Decorator Pattern? Thanks

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• Multiple Actions (Forms) on one Page - How not to lose master data, after editing detail data?

  - by nWorx

  Hello all, I've got a form where users can edit members of a group. So they have the possibilty to add members or remove existing members. So the Url goes like ".../Group/Edit/4" Where 4 is the id of the group. the view looks like this <% using (Html.BeginForm("AddUser", "Group")) %> <%{%> <label for="newUser">User</label> <%=Html.TextBox("username")%> <input type="submit" value="Add"/> </div> <%}%> <% using (Html.BeginForm("RemoveUser", "Group")) %> <%{%> <div class="inputItem"> <label for="groupMember">Bestehende Mitglieder</label> <%= Html.ListBox("groupMember", from g in Model.GetMembers() select new SelectListItem(){Text = g}) %> <input type="submit" value="Remove" /> </div> <%}%> The problem is that after adding or removing one user i lose the id of the group. What is the best solution for solving this kind of problem? Should I use hidden fields to save the group id? Thanks in advance.

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• Why should GoTos be bad?

  - by lisn

  I'm using gotos and a lot of them. C++, PHP or COBOL - I use them on nearly all occasions where everybody else would use functions or even classes. Yet my code is Clear Maintainable Bug-free Fast So why does everybody I meet tell me about how bad gotos are? Are there any facts that show that they are "bad"?

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• Send through Email, or store in database?

  - by user156814

  I have wondered when it is best to send an email, and when its best to store data in a database/log file. Everytime a user wants to contact me or inform me of soething, I suppose an email is best.. but is an email always preferred over other ways, and in what cases. Possible reasons for being contacted I can think of are questions, suggestions, feedback, reporting abuse, advertising, etc... I assume email, "why add unnecessary things to the DB?", but I figure data in DB would be a lot easier to manage. Whats the better/best way to be informed of things like this.. What is the best way for you (webmaster) to be informed of something by users? through email, or some other way

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• syntax for binding multiple variables within text

  - by danke

  When binding multiple variables value1 value2 value3 in the same text field, do I do this: text="{some text value1 other text value2 and other text value3}" or text="some text {value1} other text {value2} and other text {value3}" I noticed both work, but which is the right way to do it and will work all the time.

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• What is the difference between a private and public funtion?

  - by Kyle

  I am a new programmer, and I started in C and am now starting to enjoy JavaScript and a tiny bit of PHP more. Lately I've heard the terms 'private' and 'public' functions a lot. Could anybody give an explanation of the both and how they are of use to a programmer? And I'm probably totally wrong here... but is a (function(){}) in javascript a private function?

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• overflow-x AND Middle Mouse Button Moving

  - by Rad The Mad

  My Page is 980px in Width, but I have a few design elements (which belong with the background). I positioned them with position: absolute;. This creates a horizontal scrollbar for those who have a =< 1024 resolution. I disabled that scrollbar with overflow-x:hidden on (and for IE7 and etc). However, when I hold my middle mouse button,(i think this applies to laptop touchpads as well) it let's me move around to the right, is it possible to fix this with anything? (javascript, css)? Tested this issues in Chrome, IE, Firefox.

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