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• Getting a handle on GIS math, where do I start?

  - by Joshua

  I am in charge of a program that is used to create a set of nodes and paths for consumption by an autonomous ground vehicle. The program keeps track of the locations of all items in its map by indicating the item's position as being x meters north and y meters east of an origin point of 0,0. In the real world, the vehicle knows the location of the origin's lat and long, as it is determined by a dgps system and is accurate down to a couple centimeters. My program is ignorant of any lat long coordinates. It is one of my goals to modify the program to keep track of lat long coords of items in addition to an origin point and items' x,y position in relation to that origin. At first blush, it seems that I am going to modify the program to allow the lat long coords of the origin to be passed in, and after that I desire that the program will automatically calculate the lat long of every item currently in a map. From what I've researched so far, I believe that I will need to figure out the math behind converting to lat long coords from a UTM like projection where I specify the origin points and meridians etc as opposed to whatever is defined already for UTM. I've come to ask of you GIS programmers, am I on the right track? It seems to me like there is so much to wrap ones head around, and I'm not sure if the answer isn't something as simple as, "oh yea theres a conversion from meters to lat long, here" Currently, due to the nature of DGPS, the system really doesn't need to care about locations more than oh, what... 40 km? radius away from the origin. Given this, and the fact that I need to make sure that the error on my coordinates is not greater than .5 meters, do I need anything more complex than a simple lat/long to meters conversion constant? I'm knee deep in materials here. I could use some pointers about what concepts to research. Thanks much!

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• Modify XML existing content in C#

  - by Nano HE

  Purpose: I plan to Create a XML file with XmlTextWriter and Modify/Update some Existing Content with XmlNode SelectSingleNode(), node.ChildNode[?].InnerText = someting, etc. After I created the XML file with XmlTextWriter as below. XmlTextWriter textWriter = new XmlTextWriter("D:\\learning\\cs\\myTest.xml", System.Text.Encoding.UTF8); I practiced the code below. But failed to save my XML file. XmlDocument doc = new XmlDocument(); doc.Load("D:\\learning\\cs\\myTest.xml"); XmlNode root = doc.DocumentElement; XmlNode myNode; myNode= root.SelectSingleNode("descendant::books"); .... textWriter.Close(); doc.Save("D:\\learning\\cs\\myTest.xml"); I found it is not good to produce like my way. Is there any suggestion about it? I am not clear about the concepts and usage of both XmlTextWriter and XmlNode in the same project. Thank you for reading and replies.

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• Opengl: fit a quad to screen, given the value of Z.

  - by hytparadisee

  Short Version of the question: I will put a quad. I know the width and height of the screen in window coordinates, i know the Z-coordinates of the quad in 3D. I know the FOVY, I know the aspect. The quad will be put along Z-axis, My camera doesn't move (placed at 0, 0, 0). I want to find out the width and height of the quad IN 3D COORDINATES that will fit exactly onto my screen. Long Version of the question: I would like to put a quad along the Z-axis at the specified offset Z, I would like to find out the width and height of the quad that will exactly fill the entire screen. I used to have a post on gamedev.net that uses a formula similar to the following: *dist = Z * tan ( FOV / 2 )* Now I can never find the post! Though it's similar, it is still different, because I remembered in that working formula, they do make use of screenWidth and screenHeight, which are the width and height of the screen in window coordinates. I am not really familiar with concepts like frustum, fov and aspect so that's why I can't work out the formula on my own. Besides, I am sure I don't need gluUnproject (I tried it, but the results are way off). It's not some gl calls, it's just a math formula that can find out the width and height in 3D space that can fill the entire screen, IF Z offset, width in window coordinates, and height in window coordinates, are known. Thanks all in advance.

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• Some clarification needed about synchronous versus asynchronous asio operations

  - by Old newbie

  As far as I know, the main difference between synchronous and asynchronous operations. I.e. write() or read() vs async_write() and async_read() is that the former, don't return until the operation finish -or error-, and the last ones, returns inmediately. Due the fact that the asynchronous operations are controlled by an io_service.run() that does not finish until the controlled operations has finalized. It seems to me that in sequencial operations as those involved in TCP/IP connections with protocols such as POP3, in which the operaton is a sequence such as: C: <connect> S: Ok. C: User... S: Ok. C: Password S: Ok. C: Command S: answer C: Command S: answer ... C: bye S: <close> The difference between synchronous/asynchronous opperatons does not make much sense. Of course, in both operations there is allways the risk that the program flow stops indefinitely by some circunstance -there the use of timers-, but I would like know some more authorized opinions in this matter. I must admit that the question is rather ill-defined, but I like hear some advices about when use one or other, because I've problems in debugging with MS Visual Studio, asynchronous SSL operations in a POP3 client in wich I'm working now -about some of who surely I would write here soon-, and sometimes think that perhaps is a bad idea use asynchronous in this. Not to say that I'm an absolute newbie with this librarys, that additionally to the difficult with the idioma, and some obscure concepts in the STL, must suffer the brevity of the asio documentation.

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• Old fashioned html onclick return false doesnt in IE work when jquery script included

  - by user292662

  Ok, so im quite new to jquery but found this bizzar problem just now, If we ignore jquery for a second and consider this scenario, if i have two links like below both with an href and both with and onclick event. The first link will not follow the href because the onclick returns false, and the second link will because the onclick returns true. <a href="/page.html" onclick="return false;">Dont follow</a> <a href="/page.html" onclick="return false;">Follow</a> This works just hunky dory in every browser as it should, the thing is, as soon as i include the jQuery script on the page this stops working in all versions of IE which then always follows the href whether the onclick returns false or not. (it continues to work fine in other browsers) Now if i add an event using jquery and call .preventDefault() on the event object instead of doing it the old fashioned way this behaves correctly, and you may say, well just do that then? But i have a site with thousands of lines of code and i am adding jquery support, i dont want to run the risk that i might miss an already defined html onclick="" and break the website. I cant see why jQuery should prevent perfectly normal javascript concepts from working, so is this a jQuery bug or am I missing something?

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• Webforms vs. MVC. Once you start using MVC.. Do you ever go back to webforms?

  - by punkouter

  I checked out MVC months ago and didn't really get it.. but recently as I have become a better programmer I think it is making sense.. Here is my theory.. tell me if I got it Right In the 90s for Microsoft Devs we had Classic ASP. This mixed VBscript and HTML on the same page. So you needed to create all the HTML yourself and mix HTML and VBScript. This was not considered Ideal. Then .NET came along and everyone liked it because it was similiar to event driven VB 6 style programming. It created this abstraction of binding data to ASP Servier controls. It made getting Enumerated data easy to get on the screen with one line. Then recently Jquery and SOA concepts are mixed together.. Now people think.. Why create this extra layer of abstraction when I can just directly use .NET as a data provider and use jquery AJAX calls to get the data and create the HTML with it directly .. no need for the Webforms abstraction layer.. Sowe are back to creating HTML directly like we did in 1999. So MVC is all about saying Stop pretending like WEb programming is a VB6 app! Generate HTML directly! Am I missing anything? So I wonder.. for you people out there using MVC... is it the sort of things that once you get used to it you never want to go back to webforms??

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• Agile language for 2d game prototypes?

  - by instanceofTom

  Occasionally ( read: when my fiancé allows ) I like to prototype different game or game-like ideas I have. Usually I use Java or C# (not xna yet) because they are the languages I have the most practice with. However I would like to learn something more suited to agile development; a language in which it would be easier to knock out quick prototypes. At my job I have recently been working with looser (weak/dynamically typed) languages, specifically python and groovy, and I think something similar would fit what I am looking for. So, my question is: What languages (and framework/engine) would be good for rapidly developing prototypes of 2d game concepts? A few notes: I don't need blazing fast bitcrunching performance. In this case I would strongly prefer ease of development over performance. I'd like to use a language with a healthy community, which to me means a fair amount of maintained 3rd party, libraries. I'd like the language to be cross-platform friendly, I work on a variety of different operating systems and would like something that is portable with minimum effort. I can't imagine myself using a language with out decent options for debugging and editor syntax highlighting support. Note: If you are aware of a Java or C# library/framework that you think streamlines producing game prototypes I open to learning something new for those languages too

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• Sorting out POCO, Repository Pattern, Unit of Work, and ORM

  - by CoffeeAddict

  I'm reading a crapload on all these subjects: POCO Repository Pattern Unit of work Using an ORM mapper ok I see the basic definitions of each in books, etc. but I can't visualize this all together. Meaning an example structure (DL, BL, PL). So what, you have your DL objects that contain your CRUD methods, then your BL objects which are "mapped" using an ORM back to your DL objects? What about DTOs...they're your DL objects right? I'm confused. Can anyone really explain all this together or send me example code? I'm just trying to put this together. I am determining whether to go LINQ to SQL or EF 4 (not sure about NHibrernate yet). Just not getting the concepts as in physical layers and code layers here and what each type of object contains (just properties for DTOs, and CRUDs for your core DL classes that match the table fields???). I just need some guidance here. I'm reading Fowler's books and starting to read Evans but just not all there yet.

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• How is a referencing environment generally implemented for closures?

  - by Alexandr Kurilin

  Let's say I have a statically/lexically scoped language with deep binding and I create a closure. The closure will consist of the statements I want executed plus the so called referencing environment, or, to quote this post, the collection of variables which can be used. What does this referencing environment actually look like implementation-wise? I was recently reading about ObjectiveC's implementation of blocks, and the author suggests that behind the scenes you get a copy of all of the variables on the stack and also of all the references to heap objects. The explanation claims that you get a "snapshot" of the referencing environment at the point in time of the closure's creation. Is that more or less what happens, or did I misread that? Is anything done to "freeze" a separate copy of the heap objects, or is it safe to assume that if they get modified between closure creation and the closure executing, the closure will no longer be operating on the original version of the object? If indeed there's copying being made, are there memory usage considerations in situations where one might want to create plenty of closures and store them somewhere? I think that misunderstanding of some of these concepts might lead to tricky issues like the ones Eric Lippert mentions in this blog post. It's interesting because you'd think that it wouldn't make sense to keep a reference to a value type that might be gone by the time the closure is called, but I'm guessing that in C# the compiler will figure out that the variable is needed later and put it into the heap instead. It seems that in most memory-managed languages everything is a reference and thus ObjectiveC is a somewhat unique situation with having to deal with copying what's on the stack.

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• How to call a function from another class file

  - by Guy Parker

  I am very familiar with writing VB based applications but am new to Xcode (and Objective C). I have gone through numerous tutorials on the web and understand the basics and how to interact with Interface Builder etc. However, I am really struggling with some basic concepts of the C language and would be grateful for any help you can offer. Heres my problem… I have a simple iphone app which has a view controller (FirstViewController) and a subview (SecondViewController) with associated header and class files. In the FirstViewController.m have a function defined @implementation FirstViewController (void) writeToServer:(const uint8_t ) buf { [oStream write:buf maxLength:strlen((char)buf)]; } It doesn't really matter what the function is. I want to use this function in my SecondViewController, so in SecondViewController.m I import FirstViewController.h import "SecondViewController.h" import "FirstViewController.h" @implementation SecondViewController -(IBAction) SetButton: (id) sender { NSString *s = [@"Fill:" stringByAppendingString: FillLevelValue.text]; NSString *strToSend = [s stringByAppendingString: @":"]; const uint8_t *str = (uint8_t *) [strToSend cStringUsingEncoding:NSASCIIStringEncoding]; FillLevelValue.text = strToSend; [FirstViewController writeToServer:str]; } This last line is where my problem is. XCode tells me that FirstViewController may not respond to writeToServer. And when I try to run the application it crashes when this function is called. I guess I don't fully understand how to share functions and more importantly, the relationship between classes. In an ideal world I would create a global class to place my functions in and call them as required. Any advice gratefully received.

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• How is a functional programming-based javascript app laid out?

  - by user321521

  I've been working with node.js for awhile on a chat app (I know, very original, but I figured it'd be a good learning project). Underscore.js provides a lot of functional programming concepts which look interesting, so I'd like to understand how a functional program in javascript would be setup. From my understanding of functional programming (which may be wrong), the whole idea is to avoid side effects, which are basically having a function which updates another variable outside of the function so something like var external; function foo() { external = 'bar'; } foo(); would be creating a side effect, correct? So as a general rule, you want to avoid disturbing variables in the global scope. Ok, so how does that work when you're dealing with objects and what not? For example, a lot of times, I'll have a constructor and an init method that initializes the object, like so: var Foo = function(initVars) { this.init(initVars); } Foo.prototype.init = function(initVars) { this.bar1 = initVars['bar1']; this.bar2 = initVars['bar2']; //.... } var myFoo = new Foo({'bar1': '1', 'bar2': '2'}); So my init method is intentionally causing side effects, but what would be a functional way to handle the same sort of situation? Also, if anyone could point me to either a python or javascript source code of a program that tries to be as functional as possible, that would also be much appreciated. I feel like I'm close to "getting it", but I'm just not quite there. Mainly I'm interested in how functional programming works with traditional OOP classes concept (or does away with it for something different if that's the case).

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• What makes people think that NNs have more computational power than existing models?

  - by Bubba88

  I've read in Wikipedia that neural-network functions defined on a field of arbitrary real/rational numbers (along with algorithmic schemas, and the speculative `transrecursive' models) have more computational power than the computers we use today. Of course it was a page of russian wikipedia (ru.wikipedia.org) and that may be not properly proven, but that's not the only source of such.. rumors Now, the thing that I really do not understand is: How can a string-rewriting machine (NNs are exactly string-rewriting machines just as Turing machines are; only programming language is different) be more powerful than a universally capable U-machine? Yes, the descriptive instrument is really different, but the fact is that any function of such class can be (easily or not) turned to be a legal Turing-machine. Am I wrong? Do I miss something important? What is the cause of people saying that? I do know that the fenomenum of undecidability is widely accepted today (though not consistently proven according to what I've read), but I do not really see a smallest chance of NNs being able to solve that particular problem. Add-in: Not consistently proven according to what I've read - I meant that you might want to take a look at A. Zenkin's (russian mathematician) papers after mid-90-s where he persuasively postulates the wrongness of G. Cantor's concepts, including transfinite sets, uncountable sets, diagonalization method (method used in the proof of undecidability by Turing) and maybe others. Even Goedel's incompletness theorems were proven in right way in only 21-st century.. That's all just to plug Zenkin's work to the post cause I don't know how widespread that knowledge is in CS community so forgive me if that did look stupid. Thank you!

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• what is file verification system for php project or licence checking the configuration files

  - by Jayapal Chandran

  Hi, My colleague asked me a question like "license check to config file". when i searched i got this http://www.google.com/search?q=file+verification+system&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a and in the result i got this http://integrit.sourceforge.net/texinfo/integrit.html but could not grasp much of its idea. Here is my thoughts... Our project is written in codeigniter. The project owner is providing it to their customer. The owner is a business partner with that concept. Besides, the owner needs control of the project code so that the customer will not break rules with him like changing the code or moving it go another server or validity. So the owner needs a system to enable disable the site. Let me give an example... owner.com will have an admin panel where he can either disable or enable the client.com. when he disables the client.com should display a custom message instead of loading the files. client.com is written i a way that i will process requests from owner.com and also the other way round. so, here i want a list of the concepts with which we can implement the ownership and control over client.com any suggestions, links, references, answers will be helpful. If i am missing something in my question i will update my question according to your comments if any so that the users can give in their idea without confusing of what i had asked. THX

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• How to prepare data for display on a silverlight chart using WCF RIA Services + Entity Framework

  - by Banford

  I've used WCF RIA services with Entity Framework to build a simple application which can display and updates data about school courses. This was done by following the Microsoft tutorials. Now I would like to have a chart which shows a count for how many courses are on a key stage. Example: Key Stage 3 - 20 courses Key Stage 4 - 32 courses Key Stage 5 - 12 courses Displayed on any form of chart. I have no problem binding data to the chart in XAML. My problem is that I do not know how to correct way of getting the data into that format. The generated CRUD methods are basic. I have a few thoughts about possible ways, but don't know which is correct, they are: Create a View in SQL server and map this to a separate Entity in the Entity Data Model. Generating new CRUD methods for this automatically. Customise the read method in the existing DomainService using .Select() .Distinct() etc. Don't know this syntax very well labda expressions/LINQ??? what is it? Any good quickstarts on it? Create a new class to store only the data required and create a read method for it. Tried this but didn't know how to make it work without a matching entity in the entity model. Something I am not aware of. I'm very new to this and struggling with the concepts so if there are useful blogs or documentation I've missed feel free to point me towards them. But I'm unsure of the terminology to use in my searches at the moment.

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• emacs lisp mapcar doesn't apply function to all elements?

  - by Stephen

  Hi, I have a function that takes a list and replaces some elements. I have constructed it as a closure so that the free variable cannot be modified outside of the function. (defun transform (elems) (lexical-let ( (elems elems) ) (lambda (seq) (let (e) (while (setq e (car elems)) (setf (nth e seq) e) (setq elems (cdr elems))) seq)))) I call this on a list of lists. (defun tester (seq-list) (let ( (elems '(1 3 5)) ) (mapcar (transform elems) seq-list))) => ((10 1 8 3 6 5 4 3 2 1) ("a" "b" "c" "d" "e" "f")) It does not seem to apply the function to the second element of the list provided to tester(). However, if I explicitly apply this function to the individual elements, it works... (defun tester (seq-list) (let ( (elems '(1 3 5)) ) (list (funcall (transform elems) (car seq-list)) (funcall (transform elems) (cadr seq-list))))) => ((10 1 8 3 6 5 4 3 2 1) ("a" 1 "c" 3 "e" 5)) If I write a simple function using the same concepts as above, mapcar seems to work... What could I be doing wrong? (defun transform (x) (lexical-let ( (x x) ) (lambda (y) (+ x y)))) (defun tester (seq) (let ( (x 1) ) (mapcar (transform x) seq))) (tester (list 1 3)) => (2 4) Thanks

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• Bitwise operators and converting an int to 2 bytes and back again.

  - by aKiwi

  first time user, Hi guys! So hopefully someone can help.. My background is php so entering the word of lowend stuff like, char is bytes, which are bits.. which is binary values.. etc is taking some time to get the hang of ;) What im trying to do here is sent some values from an Ardunio board to openFrameWorks (both are c++). What this script currently does (and works well for one sensor i might add) when asked for the data to be sent is.. int value_01 = analogRead(0); // which outputs between 0-1024 unsigned char val1; unsigned char val2; //some Complicated bitshift operation val1 = value_01 &0xFF; val2 = (value_01 >> 8) &0xFF; //send both bytes Serial.print(val1, BYTE); Serial.print(val2, BYTE); Apparently this is the most reliable way of getting the data across.. So now that it is send via serial port, the bytes are added to a char string and converted back by.. int num = ( (unsigned char)bytesReadString[1] << 8 | (unsigned char)bytesReadString[0] ); So to recap, im trying to get 4 sensors worth of data (which im assuming will be 8 of those serialprints?) and to have int num_01 - num_04... at the end of it all. Im assuming this (as with most things) might be quite easy for someone with experience in these concepts.. Any help would be greatly appreciated. Thanks

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• Understanding Hibernate saveOrUpdate and the Persistence Life Cycle

  - by Stephano

  The books that I've read regarding hibernate are, at best, reference tomes. They very seldom have good code examples, so I tend to use online resources for those needs. However, I've always had a problem understanding the basic idea of hibernate persistence. I've read the books and understand the concepts, but in practice, I often see results that I don't understand. Perhaps you all can help, as you have in the past. Let's look at a simple example of a dog and a cat that are friends. This isn't a rare occurrence. It also has the benefit of being much more interesting than my business case. We want a function called "saveFriends" that takes a dog name and a cat name. We'll save the Dog and then the Cat. For this example to work, the cat is going to have a reference back to the dog. I understand this isn't an ideal example, but it's cute and works for our purposes. FriendService.java public int saveFriends(String dogName, String catName) { Dog fido = new Dog(); Cat felix = new Cat(); fido.name = dogName; fido = animalDao.saveDog(fido); felix.name = catName; [ex.A]felix.friend = fido; [ex.B]felix.friend = animalDao.getDogByName(dogName); animalDao.saveCat(felix); } AnimalDao.java (extends HibernateDaoSupport) public Dog saveDog(Dog dog) { getHibernateTemplate().saveOrUpdate(dog); return dog } public Cat saveCat(Cat cat) { getHibernateTemplate().saveOrUpdate(cat); return cat; } public Dog getDogByName(String name) { return (Dog) getHibernateTemplate().find("from Dog where name=?", name).get(0); } Now, assume for a minute that I would like to use either example A or example B to save my friend. Is one better than the other to use? I'll understand if neither of those examples work, but please explain why.

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• Something about Stream

  - by sforester

  I've been working on something that make use of streams and I found myself not clear about some stream concepts( you can also view another question posted by me at http://stackoverflow.com/questions/2933923/about-redirected-stdout-in-system-diagnostics-process ). 1.how do you indicate that you have finished writing a stream, writing something like a EOF? 2.follow the previous question, if I have written a EOF(or something like that) to a stream but didn't close the stream, then I want to write something else to the same stream, can I just start writing to it and no more set up required? 3.if a procedure tries to read a stream(like the stdin ) that no one has written anything to it, the reading procedure will be blocked,finally some data arrives and the procedure will just read till the writing is done,which is indicated by getting a return of 0 count of bytes read rather than being blocked, and now if the procedure issues another read to the same stream, it will still get a 0 count and return immediately while I was expecting it will be blocked since no one is writing to the stream now. So does the stream holds different states when the stream is opened but no one has written to it yet and when someone has finished a writing session? I'm using Windows the .net framework if there will by any thing platform specific. Thanks a lot!

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• Help me write my LISP :) LISP environments, Ruby Hashes...

  - by MikeC8

  I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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• How do I cast a void pointer to a struct in C?

  - by Rowhawn

  In a project I'm writing code for, I have a void pointer, "implementation", which is a member of a "Hash_map" struct, and points to an "Array_hash_map" struct. The concepts behind this project are not very realistic, but bear with me. The specifications of the project ask that I cast the void pointer "implementation" to an "Array_hash_map" before I can use it in any functions. My question, specifically is, what do I do in the functions to cast the void pointers to the desired struct? Is there one statement at the top of each function that casts them or do I make the cast every time I use "implementation"? Here are the typedefs the structs of a Hash_map and Array_hash_map as well as a couple functions making use of them. typedef struct { Key_compare_fn key_compare_fn; Key_delete_fn key_delete_fn; Data_compare_fn data_compare_fn; Data_delete_fn data_delete_fn; void *implementation; } Hash_map; typedef struct Array_hash_map{ struct Unit *array; int size; int capacity; } Array_hash_map; typedef struct Unit{ Key key; Data data; } Unit; functions: /* Sets the value parameter to the value associated with the key parameter in the Hash_map. */ int get(Hash_map *map, Key key, Data *value){ int i; if (map == NULL || value == NULL) return 0; for (i = 0; i < map->implementation->size; i++){ if (map->key_compare_fn(map->implementation->array[i].key, key) == 0){ *value = map->implementation->array[i].data; return 1; } } return 0; } /* Returns the number of values that can be stored in the Hash_map, since it is represented by an array. */ int current_capacity(Hash_map map){ return map.implementation->capacity; }

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• How can I execute an ANTLR parser action for each item in a rule that can match more than one item?

  - by Chris Farmer

  I am trying to write an ANTLR parser rule that matches a list of things, and I want to write a parser action that can deal with each item in the list independently. Some example input for these rules is: $(A1 A2 A3) I'd like this to result in an evaluator that contains a list of three MyIdentEvaluator objects -- one for each of A1, A2, and A3. Here's a snippet of my grammar: my_list returns [IEvaluator e] : { $e = new MyListEvaluator(); } '$' LPAREN op=my_ident+ { /* want to do something here for each 'my_ident'. */ /* the following seems to see only the 'A3' my_ident */ $e.Add($op.e); } RPAREN ; my_ident returns [IEvaluator e] : IDENT { $e = new MyIdentEvaluator($IDENT.text); } ; I think my_ident is defined correctly, because I can see the three MyIdentEvaluators getting created as expected for my input string, but only the last my_ident ever gets added to the list (A3 in my example input). How can I best treat each of these elements independently, either through a grammar change or a parser action change? It also occurred to me that my vocabulary for these concepts is not what it should be, so if it looks like I'm misusing a term, I probably am. EDIT in response to Wayne's comment: I tried to use op+=my_ident+. In that case, the $op in my action becomes an IList (in C#) that contains Antlr.Runtime.Tree.CommonTree instances. It does give me one entry per matched token in $op, so I see my three matches, but I don't have the MyIdentEvaluator instances that I really want. I was hoping I could then find a rule attribute in the ANTLR docs that might help with this, but nothing seemed to help me get rid of this IList. Result... Based on chollida's answer, I ended up with this which works well: my_list returns [IEvaluator e] : { $e = new MyListEvaluator(); } '$' LPAREN (op=my_ident { $e.Add($op.e); } )+ RPAREN ; The Add method gets called for each match of my_ident.

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• How can I help fellow students struggling in programming classes?

  - by David Barry

  I'm a computer science student finishing up my second semester of programming classes. I've enjoyed them quite a bit, and learned a lot, but it seems other students are struggling with the concepts and assignments more than I am. When an assignment is due, the inevitable group email comes out the day or two before with people needing some help either with a specific part of the problem, or sometimes people just seem to have a hard time knowing where to start. I'd really like to be able to help out, but I have a hard time thinking of the right way to give them help without giving them the answer. When I'm having trouble understanding a concept, a code snippet can go along way to helping me, but at the same time if it makes a lot of sense, it can be difficult to think of another way to go about it. Plus the Academic Integrity section of each assignment is always looming overhead warning against sharing code with others. I've tried using pseudo code to help give others an idea on program flow, leaving them to figure out how to implement certain aspects of it, but I didn't get too much feedback and don't know how much it actually helped them out, or if it just confused them further. So I'm basically looking to see if anyone has experience with this, or good ways that I can help out other students to nudge them in the right direction or help them think about the problem in the right way.

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• ecommerce platform or from scratch? customer specific catalogs and purchase orders

  - by rafi

  I have a possible freelance job in front of me for a distributor who wants product ordering set up but the orders are all P.O.s basically - no actual credit card or paypal transaction. The customer is simply billed and the order archived. Customers will need to login to this site and each customer will have their own custom catalog of a few dozen products which have been setup via a control panel this distributor uses. So there will be a master catalog of over 1,000 products (perhaps browsable but not to be ordered from on the site) but each customer will only be able to order from the products specified for their accounts. I know I can build this from scratch but I figured it's worth looking into what ecommerce platforms would get me a nice head start. Obviously shopping cart, order history, catalog management are concepts that I can reuse but are any of the ecommerce systems out there also capable of handling custom catalogs (maybe as multi-stores?) or transactions billed to accounts without credit card? The more I could reuse the better. I've messed with OSCommerce (way back) and a little Zen Cart more recently. I've also worked on a number of totally custom e-commerce sites. But my knowledge of the open source e-commerce tools is pretty limited and I'm trying to keep the effort as simple as I possibly can on this. I'm pretty flexible on the language of the platform by the way. Thanks in advance.

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• I can learn either C or Java, which one should I choose first? Should I take them concurrently?

  - by GR1000

  I realize this is a subject of hot debate, but I'm interested in opinions that relate to my specific situation. I want to learn the basics and fundamentals of programming, so I'm already taking a college course in general programming concepts. It isn't covering a specific language, but it's giving me a solid foundation that I can build upon when I move on to a class that teaches a specific language. My two options for a specific language are Java and C because those are the two languages taught at the college I want to take classes from. What I want to do is learn a complex language so that I can apply that knowledge to languages that I use, or will eventually use, in my current job building web pages: XHTML, CSS, JavaScript, PHP, XML, ActionScript. I'm not necessariy interested in becoming a Java developer or a C developer in the immediate future, but I do have aspirations of developing web applications and iPod/iPhone applications. So, basically, I'm looking for answers to these questions and the reasoning behind them: Do I take the introductory course in Java first, and then take the intro course in C, or Do I take C first and then take Java? Is there any reason not to take them concurrently? Should I skip C altogether as Java covers everything I need to know? EDIT: Thanks everyone for your thoughtful and insightful responses.

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• How I May Have Taken A Wrong Path in Programming

  - by Ygam

  I am in a major stump right now. I am a BSIT graduate, but I only started actual programming less than a year ago. I observed that I have the following attitude in programming: I tend to be more of a purist, scorning unelegant approaches to solving problems using code I tend to look at anything in a large scale, planning everything before I start coding, either in simple flowcharts or complex UML charts I have a really strong impulse on refactoring my code, even if I miss deadlines or prolong development times I am obsessed with good directory structures, file naming conventions, class, method, and variable naming conventions I tend to always want to study something new, even, as I said, at the cost of missing deadlines I tend to see software development as something to engineer, to architect; that is, seeing how things relate to each other and how blocks of code can interact (I am a huge fan of loose coupling) i.e the OOP thinking I tend to combine OOP and procedural coding whenever I see fit I want my code to execute fast (thus the elegant approaches and refactoring) This bothers me because I see my colleagues doing much better the other way around (aside from the fact that they started programming since our first year in college). By the other way around I mean, they fire up coding, gets the job done much faster because they don't have to really look at how clean their codes are or how elegant their algorithms are, they don't bother with OOP however big their projects are, they mostly use web APIs, piece them together and voila! Working code! CLients are happy, they get paid fast, at the expense of a really unmaintainable or hard-to-read code that lacks structure and conventions, or slow executions of certain actions (which the common reasoning against would be that internet connections are much faster these days, hardware is more powerful). The excuse I often receive is clients don't care about how you write the code, but they do care about how long you deliver it. If it works then all is good. Now, did my "purist" approach to programming may have been the wrong way to start programming? Should I just dump these purist concepts and just code the hell up because I have seen it: clients don't really care how beautifully coded it is?

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