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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Have unit test generators helped you when working with legacy code?

  - by Duncan Bayne

  I am looking at a small (~70kLOC including generated) C# (.NET 4.0, some Silverlight) code-base that has very low test coverage. The code itself works in that it has passed user acceptance testing, but it is brittle and in some areas not very well factored. I would like to add solid unit test coverage around the legacy code using the usual suspects (NMock, NUnit, StatLight for the Silverlight bits). My normal approach is to start working through the project, unit testing & refactoring, until I am satisfied with the state of the code. I've done this many times in the past, and it's worked well. However, this time I'm thinking of using a test generator (in particular Pex) to create the test framework, then manually fleshing it out. My question is: have you used unit test generators in the past when commencing work on a legacy codebase, and if so, would you recommend them? My fear is that the generated tests will miss the semantic nuances of the code-base, leading to the dreaded situation of having tests for the sake of the coverage metric, rather than tests which clearly express the intended behaviour in code.

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• Capitalizing on JavaScript's prototypal inheritance

  - by keithjgrant

  JavaScript has a class-free object system in which objects inherit properties directly from other objects. This is really powerful, but it is unfamiliar to classically trained programmers. If you attempt to apply classical design patterns directly to JavaScript, you will be frustrated. But if you learn to work with JavaScript's prototypal nature, your efforts will be rewarded. ... It is Lisp in C's clothing. -Douglas Crockford What does this mean for a game developer working with canvas and HTML5? I've been looking over this question on useful design patterns in gaming, but prototypal inheritance is very different than classical inheritance, and there are surely differences in the best way to apply some of these common patterns. For example, classical inheritance allows us to create a moveableEntity class, and extend that with any classes that move in our game world (player, monster, bullet, etc.). Sure, you can strongarm JavaScript to work that way, but in doing so, you are kind of fighting against its nature. Is there a better approach to this sort of problem when we have prototypal inheritance at our fingertips?

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• New partnership allows auto-transposition of client/server application to Windows Azure

  - by Webgui

  The economics of IT is changing rapidly, and organizations are searching to widen and secure availability of their systems and at the same time lower costs which is exactly what the cloud meant to do. Running your systems on Microsoft’s Windows Azure cloud for example would improve and secure the availability, accessibility and scalability (both up and down) of your systems and support the new IT economics. However, in order to take advantage of the cloud's promise of lower cost of ownership, the applications must be built or adjusted to work on that platform and in most cases this is not a simple task.  Even existing web applications cannot always be transferred to Azure without some changes, and for client/server applications, the task is way more challenging even to the point where it seems impossible. The reason is the gaps between the client/server desktop technology and the cloud's. For that reason, most of the known methodologies to migrate existing client/server applications actually involve rewrite of the desktop systems for the cloud. A unique approach is introduced by Visual WebGui which creates a virtualization layer atop ASP.Net web server, it moves the transformed or generated .Net code to that layer, and then using a patent pending protocol it renders a user interface within a plain browser. The end result is pure .NET code that is a base code for a pure rich web application and now due to a collaboration with Microsoft Windows Azure Visual WebGui provides the shortest path from client/server to the Azure cloud by being able to handle close to 95% of the transformation to the cloud platform in an automatic way. Application Migration to Azure without migraines More information about the Instant CloudMove Azure solution here.

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• Be liberal in what you accept... or not?

  - by Matthieu M.

  [Disclaimer: this question is subjective, but I would prefer getting answers backed by facts and/or reflexions] I think everyone knows about the Robustness Principle, usually summed up by Postel's Law: Be conservative in what you send; be liberal in what you accept. I would agree that for the design of a widespread communication protocol this may make sense (with the goal of allowing easy extension), however I have always thought that its application to HTML / CSS was a total failure, each browser implementing its own silent tweak detection / behavior, making it near impossible to obtain a consistent rendering across multiple browsers. I do notice though that there the RFC of the TCP protocol deems "Silent Failure" acceptable unless otherwise specified... which is an interesting behavior, to say the least. There are other examples of the application of this principle throughout the software trade that regularly pop up because they have bitten developpers, from the top off my head: Javascript semi-colon insertion C (silent) builtin conversions (which would not be so bad if it did not truncated...) and there are tools to help implement "smart" behavior: name matching phonetic algorithms (Double Metaphone) string distances algorithms (Levenshtein distance) However I find that this approach, while it may be helpful when dealing with non-technical users or to help users in the process of error recovery, has some drawbacks when applied to the design of library/classes interface: it is somewhat subjective whether the algorithm guesses "right", and thus it may go against the Principle of Least Astonishment it makes the implementation more difficult, thus more chances to introduce bugs (violation of YAGNI ?) it makes the behavior more susceptible to change, as any modification of the "guess" routine may break old programs, nearly excluding refactoring possibilities... from the start! And this is what led me to the following question: When designing an interface (library, class, message), do you lean toward the robustness principle or not ? I myself tend to be quite strict, using extensive input validation on my interfaces, and I was wondering if I was perhaps too strict.

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• Groovy Debugging

  - by Vijay Allen Raj

  Groovy Debugging - An Overview:ADF BC developers may express snippets of business logic (like the following) as embedded groovy expressions: default / calculated attribute valuesvalidation rules / conditionserror message tokensLOV input values (VO) This approach has the advantages that: Groovy has a compact, EL-like syntax for expressing simple logicADF has extended this syntax to provide useful built-insembedded Groovy expressions are customizableGroovy debugging support helps improve maintainability of business logic expressed in Groovy.Following is an example how groovy debugging works.Example:This example shows how a script expression validator can be created and the groovy script debugged. It shows Step over, breakpoint functionalities as well as syntax coloring.Let us create a ADFBC application based on Emp and Dept tables, and add a script expression validator based on the script:  if (Sal >= 5000){ //If EmpSal is greater than a property value set on the custom //properties on the root AM //raise a custom exception else raise a custom warning if (Sal >= source.DBTransaction.rootApplicationModule.propertiesMap.salHigh) { adf.error.raise("ExcGreaterThanApplicationLimit"); } else { adf.error.warn("WarnGreaterThan5000"); } } else if (EmpSal <= 1000) { adf.error.raise("ExcTooLow"); }return true;In the Emp.xml Flat editor, place breakpoints at various locations as shown below:Right click the appmodule and click Debug. Enter a value greater than 5000 and click next. You can see the debugging work as shown below:  The code can be also be stepped over and debugged.

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• Does the use of mongodb enhance extending/changing database driven applications?

  - by developer10214

  When an application is created which need to store data, an SQL database is used very often. So did I in a lot of asp.net applications. The resulting applications have often an ORM like the entity framework and maybe a business layer. So when such an application needs to be extended(let's say you have to add a comment property to an object), you have to change/extend the database, then the ORM and the business layer and so on. To deploy the changes you have to update the target database and the application. I know that things like code first and fluent can make this approach easier. I tried mongodb, I only used the standard driver and I had to extend some objects and all I had to do was changing the code. So it feels that such approaches are much easier to realize when using mongodb. I don't have much experience with larger applications an mongodb. I know that a SQL database or mongodb doesn't fit for all needs and both have their pros and cons. I want to know if my feeling is right, if yes I would choose rather choose mongodb than SQL database.

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• PostgreSQL, Ubuntu, NetBeans IDE (Part 3)

  - by Geertjan

  To complete the picture, let's use the traditional (that is, old) Hibernate mechanism, i.e., via XML files, rather than via the annotations shown yesterday. It's definitely trickier, with many more places where typos can occur, but that's why it's the old mechanism. I do not recommend this approach. I recommend the approach shown yesterday. The other players in this scenario include PostgreSQL, as outlined in the previous blog entries in this series. Here's the structure of the module, replacing the code shown yesterday: Here's the Employee class, notice that it has no annotations: import java.io.Serializable; import java.util.Date; public class Employees implements Serializable {         private int employeeId;     private String firstName;     private String lastName;     private Date dateOfBirth;     private String phoneNumber;     private String junk;     public int getEmployeeId() {         return employeeId;     }     public void setEmployeeId(int employeeId) {         this.employeeId = employeeId;     }     public String getFirstName() {         return firstName;     }     public void setFirstName(String firstName) {         this.firstName = firstName;     }     public String getLastName() {         return lastName;     }     public void setLastName(String lastName) {         this.lastName = lastName;     }     public Date getDateOfBirth() {         return dateOfBirth;     }     public void setDateOfBirth(Date dateOfBirth) {         this.dateOfBirth = dateOfBirth;     }     public String getPhoneNumber() {         return phoneNumber;     }     public void setPhoneNumber(String phoneNumber) {         this.phoneNumber = phoneNumber;     }     public String getJunk() {         return junk;     }     public void setJunk(String junk) {         this.junk = junk;     } } And here's the Hibernate configuration file: <?xml version="1.0"?> <!DOCTYPE hibernate-configuration PUBLIC       "-//Hibernate/Hibernate Configuration DTD 3.0//EN"     "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration>     <session-factory>         <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>         <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/smithdb</property>         <property name="hibernate.connection.username">smith</property>         <property name="hibernate.connection.password">smith</property>         <property name="hibernate.connection.pool_size">1</property>         <property name="hibernate.default_schema">public"</property>         <property name="hibernate.transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property>         <property name="hibernate.current_session_context_class">thread</property>         <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>         <property name="hibernate.show_sql">true</property>         <mapping resource="org/db/viewer/employees.hbm.xml"/>     </session-factory> </hibernate-configuration> Next, the Hibernate mapping file: <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC       "-//Hibernate/Hibernate Mapping DTD 3.0//EN"       "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping>     <class name="org.db.viewer.Employees"            table="employees"            schema="public"            catalog="smithdb">         <id name="employeeId" column="employee_id" type="int">             <generator class="increment"/>         </id>         <property name="firstName" column="first_name" type="string" />         <property name="lastName" column="last_name" type="string" />         <property name="dateOfBirth" column="date_of_birth" type="date" />         <property name="phoneNumber" column="phone_number" type="string" />         <property name="junk" column="junk" type="string" />             </class>     </hibernate-mapping> Then, the HibernateUtil file, for providing access to the Hibernate SessionFactory: import java.net.URL; import org.hibernate.cfg.AnnotationConfiguration; import org.hibernate.SessionFactory; public class HibernateUtil {     private static final SessionFactory sessionFactory;         static {         try {             // Create the SessionFactory from standard (hibernate.cfg.xml)             // config file.             String res = "org/db/viewer/employees.cfg.xml";             URL myURL = Thread.currentThread().getContextClassLoader().getResource(res);             sessionFactory = new AnnotationConfiguration().configure(myURL).buildSessionFactory();         } catch (Throwable ex) {             // Log the exception.             System.err.println("Initial SessionFactory creation failed." + ex);             throw new ExceptionInInitializerError(ex);         }     }         public static SessionFactory getSessionFactory() {         return sessionFactory;     }     } Finally, the "createKeys" in the ChildFactory: @Override protected boolean createKeys(List list) {     Session session = HibernateUtil.getSessionFactory().getCurrentSession();     Transaction transac = null;     try {         transac = session.beginTransaction();         Query query = session.createQuery("from Employees");         list.addAll(query.list());     } catch (HibernateException he) {         Exceptions.printStackTrace(he);         if (transac != null){             transac.rollback();         }     } finally {         session.close();     }     return true; } Note that Constantine Drabo has a similar article here. Run the application and the result should be the same as yesterday.

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• How to handle a player's level and its consequent privileges?

  - by Songo

  I'm building a game similar to Mafia Wars where a player can do tasks for his gang and gain experience and thus advancing his level. The game is built using PHP and a Mysql database. In the game I want to limit the resources allowed to player based on his level. For example: ________| (Max gold) | (Max army size) | (Max moves) | ... Level 1 | 1000 | 100 | 10 | ... Level 2 | 1500 | 200 | 20 | ... Level 3 | 3000 | 300 | 25 | ... . . . In addition certain features of the game won't be allowed until a certain level is reached such as players under Level 10 can't trade in the game market, players under Level 20 can't create alliances,...etc. The way I have modeled it is by implementing a very loooong ACL (Access Control List) with about 100 entries (an entry for each level). However, I think there may be a simpler approach to this seeing that this feature have been implemented in many games before.

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• Single Responsibility Principle - How Can I Avoid Code Fragmentation?

  - by Dean Chalk

  I'm working on a team where the team leader is a virulent advocate of SOLID development principles. However, he lacks a lot of experience in getting complex software out of the door. We have a situation where he has applied SRP to what was already quite a complex code base, which has now become very highly fragmented and difficult to understand and debug. We now have a problem not only with code fragmentation, but also encapsulation, as methods within a class that may have been private or protected have been judged to represent a 'reason to change' and have been extracted to public or internal classes and interfaces which is not in keeping with the encapsulation goals of the application. We have some class constructors which take over 20 interface parameters, so our IoC registration and resolution is becoming a monster in its own right. I want to know if there is any 'refactor away from SRP' approach we could use to help fix some of these issues. I have read that it doesn't violate SOLID if I create a number of empty courser-grained classes that 'wrap' a number of closely related classes to provide a single-point of access to the sum of their functionality (i.e. mimicking a less overly SRP'd class implementation). Apart from that, I cannot think of a solution which will allow us to pragmatically continue with our development efforts, while keeping everyone happy. Any suggestions ?

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• best way to enlarge system partition

  - by yuvi

  I have a problem - I need to enlarge my system partition. I mean - when I initially installed Ubuntu, I split the partition so I have 15GB for system and the rest (around 400) pointed at /home/. This is very useful if anything goes wrong someday and I want to format and completely re-install Ubuntu without losing any of my actual data. The problem is, 15GB isn't enough, so it seems. I already moved /var/ and /opt/ folder to /home/, adding symlinks at root, but I'm still at 86% usage and I'm having performance issues (mostly when booting or running a VM). I can use Ubuntu on a flash drive and externally enlarge the partition, but I'm really afraid with going forward with that plan. Also, despite what I said before, I'd like to avoid re-installing the system if at all possible. Any advice, suggestions or ideas on how to best approach this? Any warnings I should heed? Thanks in advance! update Here's the gparted screenshot - as you can see, there's windows on dual boot (sda1-5 are all related to the windows system), then I have a linux swap, 14GB (so uh... not even 15) of system and 435 of for /home.

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• Z Order in 2D with orthographic projection and texture atlas

  - by Carbon Crystal

  I am working with a 2D game in OpenGL ES and have a question about z-order together with a texture atlas. I am using an orthographic projection because I want pixel-perfect rendering of 2D sprites, however from what I can determine the draw order is really the only thing that will determine which textures (sprites) appear above or below their neighbors. That is, the "z-index" is a function of the order in which the textures are drawn as opposed to the z coordinate on the vertex array being drawn. So.. I have a texture atlas to save binding multiple textures for each draw call but this immediately creates a problem if there is more than one atlas in play. If I need to draw textures from more than one atlas (typically the case if I have too many sprites to fit in a single atlas of a reasonable size), then I can't maintain a "draw order" across atlases unless I want to bind/unbind the atlas textures more than once.. which kinda defeats the purpose. Does anyone have any clues as to what the best approach is here? Currently I'm running under an assumption that I will have to declare different fixed "depths" (e.g foreground, background etc) in my 2D scene and assume that the z-order for sprites at a given depth is the same. Then I can have as many atlases as I need at each depth and simply draw the depths in order (along with their associated atlases) I'd love to hear what other people are doing.

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• How do I use depth testing and texture transparency together in my 2.5D world?

  - by nbolton

  Note: I've already found an answer (which I will post after this question) - I was just wondering if I was doing it right, or if there is a better way. I'm making a "2.5D" isometric game using OpenGL ES (JOGL). By "2.5D", I mean that the world is 3D, but it is rendered using 2D isometric tiles. The original problem I had to solve was that my textures had to be rendered in order (from back to front), so that the tiles overlapped properly to create the proper effect. After some reading, I quickly realised that this is the "old hat" 2D approach. This became difficult to do efficiently, since the 3D world can be modified by the player (so stuff can appear anywhere in 3D space) - so it seemed logical that I take advantage of the depth buffer. This meant that I didn't have to worry about rendering stuff in the correct order. However, I faced a problem. If you use GL_DEPTH_TEST and GL_BLEND together, it creates an effect where objects are blended with the background before they are "sorted" by z order (meaning that you get a weird kind of overlap where the transparency should be). Here's some pseudo code that should illustrate the problem (incidentally, I'm using libgdx for Android). create() { // ... // some other code here // ... Gdx.gl.glEnable(GL10.GL_DEPTH_TEST); Gdx.gl.glEnable(GL10.GL_BLEND); } render() { Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); Gdx.gl.glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA); // ... // bind texture and create vertices // ... } So the question is: How do I solve the transparency overlap problem?

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• Generating Deep Arrays: Shallow to Deep, Deep to Shallow or Bad idea?

  - by MobyD

  I'm working on an array structure that will be used as the data source for a report template in a web app. The data comes from relatively complex SQL queries that return one or many rows as one dimensional associative arrays. In the case of many, they are turned into two dimensional indexed array. The data is complex and in some cases there is a lot of it. To save trips to the database (which are extremely expensive in this scenario) I'm attempting to get all of the basic arrays (1 and 2 dimension raw database data) and put them, conditionally, into a single, five level deep array. Organizing the data in PHP seems like a better idea than by using where statements in the SQL. Array Structure Array of years( year => array of types( types => array of information( total => value, table => array of data( index => db array ) ) ) ) My first question is, is this a bad idea. Are arrays like this appropriate for this situation? If this would work, how should I go about populating it? My initial thought was shallow to deep, but the more I work on this, the more I realize that it'd be very difficult to abstract out the conditionals that determine where each item goes in the array. So it seems that starting from the most deeply nested data may be the approach I should take. If this is array abuse, what alternatives exist?

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• Splitting big request in multiple small ajax requests

  - by Ionut

  I am unsure regarding the scalability of the following model. I have no experience at all with large systems, big number of requests and so on but I'm trying to build some features considering scalability first. In my scenario there is a user page which contains data for: User's details (name, location, workplace ...) User's activity (blog posts, comments...) User statistics (rating, number of friends...) In order to show all this on the same page, for a request there will be at least 3 different database queries on the back-end. In some cases, I imagine that those queries will be running quite a wile, therefore the user experience may suffer while waiting between requests. This is why I decided to run only step 1 (User's details) as a normal request. After the response is received, two ajax requests are sent for steps 2 and 3. When those responses are received, I only place the data in the destined wrappers. For me at least this makes more sense. However there are 3 requests instead of one for every user page view. Will this affect the system on the long term? I'm assuming that this kind of approach requires more resources but is this trade of UX for resources a good dial or should I stick to one plain big request?

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• Common way of animating 'motion' for walk cycle animations

  - by Ben Hymers

  I've just posted this at the Blender artists' forums before realising I would probably get a better response from a more game development-specific audience, so apologies for cross-posting! It's for the right reasons :) I'm a programmer trying to animate a character walking for a game project, using Ogre. I've made a very simple walk cycle in Blender and exported it to Ogre, and it plays just fine. By fine, I mean it works, but there's terrible foot sliding. This is because I just animated the walk in-place (at the origin) in Blender, and of course I don't know what "speed of walk" that corresponds to, so when I move the character in-game the motion doesn't necessarily match up with the movement of the feet in the animation. So my question is: what's the normal approach for this kind of thing? At work we use Maya, and the animators either animate a special 'moveTrans' node that represents the "position" of the character (or have the exporter generate it for them from the movement of the root node), then the game can read this to know how fast the animation moves the character. So in the Maya file, the character will walk forward for one cycle and this extra node will follow along with them by their feet. I've not seen anything like this in open-source land, and there's certainly no provision for that in the Ogre Exporter script. What do you chaps normally do for this?

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• Preventing Users From Copying Text From and Pasting It Into TextBoxes

  Many websites that support user accounts require users to enter an email address as part of the registration process. This email address is then used as the primary communication channel with the user. For instance, if the user forgets her password a new one can be generated and emailed to the address on file. But what if, when registering, a user enters an incorrect email address? Perhaps the user meant to enter [email protected], but accidentally transposed the first two letters, entering [email protected]. How can such typos be prevented? The only foolproof way to ensure that the user's entered email address is valid is to send them a validation email upon registering that includes a link that, when visited, activates their account. (This technique is discussed in detail in Examining ASP.NET's Membership, Roles, and Profile - Part 11.) The downside to using a validation email is that it adds one more step to the registration process, which will cause some people to bail out on the registration process. A simpler approach to lessening email entry errors is to have the user enter their email address twice, just like how most registration forms prompt users to enter their password twice. In fact, you may have seen registration pages that do just this. However, when I encounter such a registration page I usually avoid entering the email address twice, but instead enter it once and then copy and paste it from the first textbox into the second. This behavior circumvents the purpose of the two textboxes - any typo entered into the first textbox will be copied into the second. Using a bit of JavaScript it is possible to prevent most users from copying text from one textbox and pasting it into another, thereby requiring the user to type their email address into both textboxes. This article shows how to disable cut and paste between textboxes on a web page using the free jQuery library. Read on to learn more! Read More >

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• My father is a doctor. He is insisting on writing a database to store non-critical patient information, with no programming background

  - by Dominic Bou-Samra

  So, my father is currently in the process of "hacking" together a database using FileMaker Pro, a GUI based databasing tool for his small (4 doctor) practice. The database will be used to help ease the burden on reporting from medical machines, streamlining quite a clumsy process. He's got no programming background, and seems to be doing everything in his power to not learn things correctly. He's got duplicate data types, no database-enforced relationships (foreign/primary key constraints) and a dozen other issues. He's doing it all by hand via GUI tool using Youtube videos. My issue is, that whilst I want him to succeed 100%, I don't think it's appropriate for him to be handling these types of decisions. How do I convince him that without some sort of education in these topics, a hacked together solution is a bad idea? He's can be quite stubborn and I think he sees these types of jobs as "childs play" How should I approach this? Is it even that bad an idea - or am I correct in thinking he should hire a proper DBA/developer to handle this so that it doesn't become a maintenance nightmare? NB: I am a developer consultant of 4 years and I've seen my share of painful customer implementations.

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• Automatic Appointment Conflict Resolution

  - by Thomas

  I'm trying to figure out an algorithm for resolving appointment times. I currently have a naive algorithm that pushes down conflicting appointments repeatedly, until there are no more appointments. # The appointment list is always sorted on start time appointment_list = [ <Appointment: 10:00 -> 12:00>, <Appointment: 11:00 -> 12:30>, <Appointment: 13:00 -> 14:00>, <Appointment: 13:30 -> 14:30>, ] Constraints are that appointments: cannot be after 15:00 cannot be before 9:00 This is the naive algorithm for i, app in enumerate(appointment_list): for possible_conflict in appointment_list[i+1:]: if possible_conflict.start < app.end: difference = app.end - possible_conflict.start possible_conflict.end += difference possible_conflict.start += difference else: break This results in the following resolution, which obviously breaks those constraints, and the last appointment will have to be pushed to the following day. appointment_list = [ <Appointment: 10:00 -> 12:00>, <Appointment: 12:00 -> 13:30>, <Appointment: 13:30 -> 14:30>, <Appointment: 14:30 -> 15:30>, ] Obviously this is sub-optimal, It performs 3 appointment moves when the confict could have been resolved with one: if we were able to push the first appointment backwards, we could avoid moving all the subsequent appointments down. I'm thinking that there should be a sort of edit-distance approach that would calculate the least number of appointments that should be moved in order to resolve the scheduling conflict, but I can't get the a handle on the methodology. Should it be breadth-first or depth first solution search. When do I know if the solution is "good enough"?

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• Dependency injection: what belongs in the constructor?

  - by Adam Backstrom

  I'm evaluating my current PHP practices in an effort to write more testable code. Generally speaking, I'm fishing for opinions on what types of actions belong in the constructor. Should I limit things to dependency injection? If I do have some data to populate, should that happen via a factory rather than as constructor arguments? (Here, I'm thinking about my User class that takes a user ID and populates user data from the database during construction, which obviously needs to change in some way.) I've heard it said that "initialization" methods are bad, but I'm sure that depends on what exactly is being done during initialization. At the risk of getting too specific, I'll also piggyback a more detailed example onto my question. For a previous project, I built a FormField class (which handled field value setting, validation, and output as HTML) and a Model class to contain these fields and do a bit of magic to ease working with fields. FormField had some prebuilt subclasses, e.g. FormText (<input type="text">) and FormSelect (<select>). Model would be subclassed so that a specific implementation (say, a Widget) had its own fields, such as a name and date of manufacture: class Widget extends Model { public function __construct( $data = null ) { $this->name = new FormField('length=20&label=Name:'); $this->manufactured = new FormDate; parent::__construct( $data ); // set above fields using incoming array } } Now, this does violate some rules that I have read, such as "avoid new in the constructor," but to my eyes this does not seem untestable. These are properties of the object, not some black box data generator reading from an external source. Unit tests would progressively build up to any test of Widget-specific functionality, so I could be confident that the underlying FormFields were working correctly during the Widget test. In theory I could provide the Model with a FieldFactory() which could supply custom field objects, but I don't believe I would gain anything from this approach. Is this a poor assumption?

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• In Scrum, should you split up the backlog in a functional backlog and a technical backlog or not?

  - by Patrick

  In our Scrum teams we use a backlog, which mostly contains functional topics, but also sometimes contains technical topics. The advantage of having 1 backlog is that it becomes easy to choose the topics for the next sprint, but I have some questions: First, to me it seems more logical to have a separate technical backlog, where developers themselves can add pure technical items, like: we could improve performance in this method, this class lacks some technical documentation, ... By having one backlog, all developers always have to pass via the product owner to have their topics added to the backlog, which seems additional, unnecessary work for the product owner. Second, if you have a product owner that only focuses on the pure-functional items, the pure-technical items (like missing technical documentation, code that erodes and should be refactored, classes that always give problems during debugging because they don't have a stable foundation and should be refactored, ...) always end up at the end of the list because "they don't serve the customer directly". By having a separate technical backlog, and time reserved in every sprint for these pure technical items, we can improve the applications functionally, but also keep them healthy inside. What is the best approach? One backlog or two?

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• What does your Lisp workflow look like?

  - by Duncan Bayne

  I'm learning Lisp at the moment, coming from a language progression that is Locomotive BASIC - Z80 Assembler - Pascal - C - Perl - C# - Ruby. My approach is to simultaneously: write a simple web-scraper using SBCL, QuickLisp, closure-html, and drakma watch the SICP lectures I think this is working well; I'm developing good 'Lisp goggles', in that I can now read Lisp reasonably easily. I'm also getting a feel for how the Lisp ecosystem works, e.g. Quicklisp for dependencies. What I'm really missing, though, is a sense of how a seasoned Lisper actually works. When I'm coding for .NET, I have Visual Studio set up with ReSharper and VisualSVN. I write tests, I implement, I refactor, I commit. Then when I'm done enough of that to complete a story, I write some AUATs. Then I kick off a Release build on TeamCity to push the new functionality out to the customer for testing & hopefully approval. If it's an app that needs an installer, I use either WiX or InnoSetup, obviously building the installer through the CI system. So, my question is: as an experienced Lisper, what does your workflow look like? Do you work mostly in the REPL, or in the editor? How do you do unit tests? Continuous integration? Packaging & deployment? When you sit down at your desk, steaming mug of coffee to one side and a framed photo of John McCarthy to the other, what is it that you do? Currently, I feel like I am getting to grips with Lisp coding, but not Lisp development ...

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• Using XSLT for messaging instead of marshalling/unmarshalling Java message objects

  - by Joost van Stuijvenberg

  So far I have been using either handmade or generated (e.g. JAXB) Java objects as 'carriers' for messages in message processing software such as protocol converters. This often leads to tedious programming, such as copying/converting data from one system's message object to an instance of another's system message object. And it sure brings in lots of Java code with getters and setters for each message attribute, validation code, etc. I was wondering whether it would be a good idea to convert one system's XML message into another system's format - or even convert requests into responses from the same system - using XSLT. This would mean I would no longer have to unmarshall XML streams to Java objects, copy/convert data using Java and marshall the resulting message object to another XML stream. Since each message may actually have a purpose I would 'link' the message (and the payload it contains in its properties or XML elements/attributes) to EXSLT functions. This would change my design approach from an imperative to a declarative style. Has anyone done this before and, if so, what are your experiences? Does the reduced amount of Java 'boiler plate' code weigh up to the increased complexity of (E)XSLT?

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• Jump handling and gravity

  - by sprawl

  I'm new to game development and am looking for some help on improving my jump handling for a simple side scrolling game I've made. I would like to make the jump last longer if the key is held down for the full length of the jump, otherwise if the key is tapped, make the jump not as long. Currently, how I'm handling the jumping is the following: Player.prototype.jump = function () { // Player pressed jump key if (this.isJumping === true) { // Set sprite to jump state this.settings.slice = 250; if (this.isFalling === true) { // Player let go of jump key, increase rate of fall this.settings.y -= this.velocity; this.velocity -= this.settings.gravity * 2; } else { // Player is holding down jump key this.settings.y -= this.velocity; this.velocity -= this.settings.gravity; } } if (this.settings.y >= 240) { // Player is on the ground this.isJumping = false; this.isFalling = false; this.velocity = this.settings.maxVelocity; this.settings.y = 240; } } I'm setting isJumping on keydown and isFalling on keyup. While it works okay for simple use, I'm looking for a better way handle jumping and gravity. It's a bit buggy if the gravity is increased (which is why I had to put the last y setting in the last if condition in there) on keyup, so I'd like to know a better way to do it. Where are some resources I could look at that would help me better understand how to handle jumping and gravity? What's a better approach to handling this? Like I said, I'm new to game development so I could be doing it completely wrong. Any help would be appreciated.

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• Formal definition for term "pure OO language"?

  - by Yauhen Yakimovich

  I can't think of a better place among SO siblings to pose such a question. Originally I wanted to ask "Is python a pure OO language?" but considering troubles and some sort of discomfort people experience while trying to define the term I decided to start with obtaining a clear definition for the term itself. It would be rather fair to start with correspondence by Dr. Alan Kay, who has coined the term (note the inspiration in biological analogy to cells or other living objects). There are following ways to approach the task: Give a comparative analysis by listing programming languages that exhibits certain properties unique and sufficient to define the term (although Smalltalk and Java are passing examples but IMO this way seems neither really complete or nor fruitful) Give a formal definition (or close to it, e.g. in more academic or mathematical style). Give a philosophical definition that would totally rely on semantical context of concrete language or a priori programming experience (there must be some chance of successful explanation by the community). My current version: "If a certain programing (formal) language that can (grammatically) differentiate between operations and operands as well as infer about the type of each operand whether this type is an object (in sense of OOP) or not then we call such a language an OO-language as long as there is at least one type in this language which is an object. Finally, if all types of the language are also objects we define such language to be pure OO-language." Would appreciate any possible improvement of it. As you can see I just made the definition dependent on the term "object" (often fully referenced as class of objects).

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