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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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• bytea type & nulls, Postgres

  - by Thanatos

  I'm using a bytea type in PostgreSQL, which, to my understanding, contains just a series of bytes. However, I can't get it to play well with nulls. For example: =# select length(E'aa\x00aa'::bytea); length -------- 2 (1 row) I was expecting 5. Also: =# select md5(E'aa\x00aa'::bytea); md5 ---------------------------------- 4124bc0a9335c27f086f24ba207a4912 (1 row) That's the MD5 of "aa", not "aa\x00aa". Clearly, I'm Doing It Wrong, but I don't know what I'm doing wrong. I'm also on an older version of Postgres (8.1.11) for reasons outside of my control. (I'll see if this behaves the same on the latest Postgres as soon as I get home...)

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• jQuery - How to combine has() and gt()

  - by KatieK

  With jQuery 1.4.2, I can't figure out how to combine has() with :gt. I'd like to select any ul which contains more than 3 lis, so here's what I've tried: $(document).ready(function(){ $("ul.collapse:has(li:gt(2))") .each( function() { $(this).css("border", "solid red 1px"); }); }); This does work with the 1.2.6 jQuery library, but not 1.3.2 or 1.4.2. I'd appreciate any help in understanding what's going on here. Thanks!

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• resetting the image in an NSView

  - by Josan

  I think this is a very simple question, but I’m new to programming so I may be going about it in a wrong-headed way. I have a basic understanding of Objective-C writing terminal applications and am teaching myself how to use the Cocoa GUI. I understand how to use IBOutlet and IBAction to connect a simple button to a method that will repeatedly send random numbers to a textfield . I understand how to add a NSView file, connect it to a custom view in interface builder and draw a path through random points in the view when the application launches. (I’ve been putting this code inside the - (void)drawRect:(NSRect)dirtyRect method that is declared when the file is created). What I can’t seem to figure out is how to connect a button to an action that will then ‘refresh’ the view – in this case repopulate it with another set of random points connected with a path. Looking at the documentation, I think I should somehow be using – (void) setNeedsDisplay(BOOL)flag but nothing I have tried so far had worked. Please tell me, what am I missing here?

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• why is there different id syntax in the Android docs?

  - by darren

  This page in the Android documentation defines an element id as follows: <TextView android:id="@+id/label" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Type here:" /> However this page defines it as: <EditText id="text" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:textColor="@color/opaque_red" android:text="Hello, World!" /> I thought I had a decent understanding of what was going on until I saw this second example. In the first case, you need the + character so that id 'label' is added to the R file, correct? In the second case, would the EditText's id not be added to the R file because it does not contain the + character? Also, the second example does not include the android namespace on the id. Does having or not having the Android namespace affect whether that id will be added to the R file? Thanks for any clarification.

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• Why should I use mock objects (Java)? Do all mocking frameworks serve the same purpose?

  - by Mehmet Yesin

  I'm preparing a presentation and I need to get a better understanding of what mocking is, what is the purpose of using it, what are the common situations that I should use mock objects? I found out that there are a bunch of mocking frameworks out there. Do they all do the same thing or do I use a specific framework for specific testing purpose? What are the differences between these frameworks? Which one would you recommend for testing Java? here are some stuff that I found: 1.MockingToolkitComparisonMatrix which seems biased. 2.What are mock objects in Java? This is a year old. I thought there might be some better answer today. Thank you.

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• BlackBerry project version number

  - by Seva Alekseyev

  I have a BlackBerry Java project in Eclipse. It has version number written down in four different spots: in the project properties, under "BlackBerry Project Settings/General" in the JAD file, under MIDlet-1 in the JAD file, under MIDlet-Version in the ALX file, under <version> And they seem uncorrelated. Changing either of these affects none of the rest. The third one is what the users sees during over-the-air setup and under Options/Advanced. Questions - why do we need all these? Are there contexts where numbers 1, 2, 4 come up? It's my understanding that the ALX is generated during compilation - where does the version # come from? Is there a way to learn at least one of those programmatically (without signing the app)?

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• Lifetime of javacript variables.

  - by The Machine

  What is the lifetime of a variable in javascript, declared with "var". I am sure, it is definitely not according to expectation. <script> function(){ var a; var fun=function(){ // a is accessed and modified } }(); </script> Here how and when does javascript garbage collect the variable a? Since 'a' is a part of the closure of the inner function, it ideally should never get garbage collected, since the inner function 'fun', may be passed as a reference to an external context.So 'fun' should still be able to access 'a', from the external context. If my understanding is correct, how does garbage collection happen then, and how does it ensure to have enough memory space, since keeping all variables in memory until the execution of the program might not be tenable ?

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• PHP namespaces and using the \ prefix in declaration

  - by Jason McCreary

  The following throws an error stating Exception can no be redeclared. namespace \NYTD\ReadingListBackend; class Exception extends \Exception { } However, removing the \ prefix in the namespace declaration does not: namespace NYTD\ReadingListBackend; I recently adopted PHP namespaces. My understanding is that namespaces prefixed with \ are a fully qualified name. So why can't I use the prefix in the namespace declaration? I can when referencing (e.g. new \NYTD\ReadingListBackend\Exception). Would appreciate a full explanation as I couldn't find anything in the docs.

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• Parsing and validating arbitrary date formats in ruby (on rails)

  - by Matt Briggs

  I have a requirement to handle custom date formats in an existing app. The idea is that the users have to do with multiple formats from outside sources they have very little control over. We will need to be able to take the format and both validate Dates against it, as well as parse strings specifically in that format. The other thing is that these can be completely arbitrary, like JA == January, FE == February, etc... to my understanding, chronic only handles parsing (and does it in a more magical way then I can use), and enter code here DateTime#strptime comes close, but doesn't really handle the whole two character month scenario, even with custom formatters. The 'nuclear' option is to write in custom support for edge cases like this, but I would prefer to use a library if something like this exists.

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• Including C header file with lots of global variables

  - by Costi

  I have an include file with 100+ global variables. It's being used in a library, but some programs that I'm linking the lib to also need to access the globals. The way it was built: // In one library .c file #define Extern // In the programs that use the globals #define Extern extern // In the .h file Extern int a,b,c; I had a hard time understanding why the original programmer did that so I removed that define Extern stuff. Now I think I understand the thing about TU with the help of stackoverflow: 1, 2, 3. Now I understand that I should define the global variables in one .c file in the library and use extern in the .h file. The problem is that I don't want to duplicate code. Should I go back to that #define Extern voodoo?

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• Android: stack management for views in a tab?

  - by wei

  I see some answers here prefer views over activities as contents of tabs. Correct me if I am wrong. My understanding is that by switching out views, it's possible to keep the navigation flow inside a tab (more user friendly, I think). But I wonder how to manage the view stack then in case of the back button events. Also this could cause one giant Activity with large amount of views, which might not be good. So I wish to know why exactly views as contents is preferred before I change my current application to this. Thanks,

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• Assigning a variable of a struct that contains an instance of a class to another variable

  - by xport

  In my understanding, assigning a variable of a struct to another variable of the same type will make a copy. But this rule seems broken as shown on the following figure. Could you explain why this happened? using System; namespace ReferenceInValue { class Inner { public int data; public Inner(int data) { this.data = data; } } struct Outer { public Inner inner; public Outer(int data) { this.inner = new Inner(data); } } class Program { static void Main(string[] args) { Outer p1 = new Outer(1); Outer p2 = p1; Console.WriteLine("p1:{0}, p2:{1}", p1.inner.data, p2.inner.data); p1.inner.data = 2; Console.WriteLine("p1:{0}, p2:{1}", p1.inner.data, p2.inner.data); p2.inner.data = 3; Console.WriteLine("p1:{0}, p2:{1}", p1.inner.data, p2.inner.data); Console.ReadKey(); } } }

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• Does importing of packages change visibility of classes?

  - by Roman

  I jsut learned that A class may be declared with the modifier public, in which case that class is visible to all classes everywhere. If a class has no modifier (the default, also known as package-private), it is visible only within its own package. This is a clear statement. But this information interfere with my understanding of importing of packages (which easily can be wrong). I thought that importing a package I make classes from the imported package visible to the importing class. So, how does it work? Are public classes visible to all classes everywhere under condition that the package containing the public class is imported? Or there is not such a condition? What about the package-private classes? They are invisible no mater if the containing package was imported or not? ADDED: It seems to me that I got 2 answers which are marked as good (up-voted) and which contradict eachother.

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• Which set(s) of video lectures for computer science?

  - by SebKom

  As most of you know a couple of top universities (MIT, Stanford, etc) around the world are now publishing videos of their lectures online. I am advancing to the third and final year of my computer science degree this September and I was thinking about spending some time during the summer to watch a couple of lectures, in order to improve my understanding of algorithms, complexity, programming, software engineering, etc. Now I don't have infinite time to spend so I can't watch all of the lectures from all of the universities so I was wondering if you could suggest me which sets to watch from each one (something like "Algorithms from MIT", "Programming from Yale", etc).

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• How do I configure WinCE to use wildcard SSL certificates?

  - by Robin M

  Our Windows CE 5.0 application has a problem with our wildcard SSL certificate (*.domain.com) - it won't accept it as valid. I understand that Windows Mobile 6.0 has support for wildcard certificates (earlier versions don't) and that is built on WinCE 5 which suggests it should be possible to change WinCE 5 to accept wildcard certificates (EDIT - apparently this shows my limited understanding of the environment and isn't a valid presumption!). Can anyone suggest how we go about this? The change needs to be programmatic so that we can roll it out to hundreds of existing clients. Help!

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• Improving the join of two wave file?

  - by kaki

  I have written a code for joining two wave files.It works fine when i am joining larger segments but as i need to join very small segments the clarity is not good. I have learned that the signal processing technique such a windowed join can be used to improve the joining of file. y[n] = w[n]s[n] Multiply value of signal at sample number n by the value of a windowing function hamming window w[n]= .54 - .46*cos(2*Pi*n)/L 0 I am not understanding how to get the value to signal at sample n and how to implement this?? the code i am using for joining is import wave m=['C:/begpython/S0001_0002.wav', 'C:/begpython/S0001_0001.wav'] i=1 a=m[i] infiles = [a, "C:/begpython/S0001_0002.wav", a] outfile = "C:/begpython/S0001_00367.wav" data= [] data1=[] for infile in infiles: w = wave.open(infile, 'rb') data1=[w.getnframes] data.append( [w.getparams(), w.readframes(w.getnframes())] ) #data1 = [ord(character) for character in data1] #print data1 #data1 = ''.join(chr(character) for character in data1) w.close() output = wave.open(outfile, 'wb') output.setparams(data[0][0]) output.writeframes(data[0][1]) output.writeframes(data[1][1]) output.writeframes(data[2][1]) output.close()

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• Moving to OOP hopefully!

  - by Luke

  So I am trying to understand OOP more and use it. The following code was written before i started using OOP. //loop through all the users $game = "$_POST[Game]_teams"; $result = mysql_query("SELECT username FROM `users`") or die(mysql_error()); while( $row=mysql_fetch_assoc($result) ) { $u[] = $row['username']; } I have put the query into my database page like following: function selectAllUsers() { $q = "SELECT username FROM ".TBL_USERS.""; mysql_query($q, $this->connection); } I'm a little confused about how the rest could be different? Would it be? Is it possible for anyone to help me without more code or understanding of my structure?

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• Wordpress & Django -- One domain, two servers. Possible?

  - by DomoDomo

  My question is about hosting Django and Wordpress under one domain, but two physical machines (actually, they are VMs but same diff). Let's say I have a Django webapp at example.com. I'd like to start a Wordpress blog about my webapp, so any blog page rank mojo flows back to my webapp, I'd like the blog address t be example.com/blog. My understanding is blog.example.com would not transfer said page rank mojo. Because I'm worried about Wordpress security flaws compromising my Django webapp, I want to host Django and Wordpress on two physically separate machines. Given all that, is it possible using re-write rules or a reverse proxy server to do this? I know the easy way is to make my Wordpress blog a subdomain, but I really don't want to do that. Has anyone done this in the past, is it stable? If I need a third server to be a dedicated reverse proxy, that's totally fine. Thanks!

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• After pip installing uWSGI there's no /etc/uwsgi/ directory - how can I use apps-enabled?

  - by orokusaki

  I've been using apt-get install uwsgi to install uWSGI. Today, I realized I needed a feature that's not available until uWSGI 1.1, and Ubuntu 12.04.1 doesn't have anything after 1.0.x, at least according to my apt-get install uwsgi=1.1 attempt. So, I used: pip install http://projects.unbit.it/downloads/uwsgi-lts.tar.gz After doing so, I get a message prescribing the use of /usr/local/bin/uwsgi to launch the program. I'm not a guru when it comes to compiling from source, but my understanding is that when you do so, nothing will be changed in the /etc/ directory. Is this correct? If not, why don't I have a /etc/uwsgi/ directory and, more specifically, a /etc/uwsgi/apps-enabled/ directory? Should I simply create the directories when installing uWSGI from source? I was hesitant to do so, considering there is no mention of this in the docs (I don't want something that accidentally works, etc.).

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• Why make anything internal?

  - by c-charp N00b

  I don't really see the point of making methods or classes internal. In my very limited understanding, all it does is make working with your code very difficult for other programmers. Say I write Big_Important_Class for Project A and make said class internal. Then Bob, working on Project B needs to use my class to have project B work with Project A, but since its internal he can't. As of now this is the only thing I have seen internals do, make things really complicated for the guy working on Project B. I know there has to be a good reason to use internals, but I don't see any. Could someone please explain how they can be a good thing?

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• Why for only some actions must I call setTarget?

  - by Max Pierce

  For most actions, I just click and drag in InterfaceBuilder to "wire up" a call from some interface object to my code. For example, if I want to know when the user single-clicks a row in a table, I drag a connection from the table's action to my controller's action. But now let's consider the user double-clicking a row. If I want one of my actions to be called when this happens, I need to call not only -[NSTableView setDoubleAction] but also -[NSControl setTarget]. Why? To be clear, I am not asking why Interface Builder doesn't support setDoubleAction. All tools have limitations. I am trying to gain a greater understanding about how and why setTarget doesn't seem to be necessary unless and until I want setDoubleAction to work. Another way to ask this question would be: Why don't I need to do anything in Interface Builder to set the target of the table's (single-click) action?

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• Has anyone been successful at a assembler based led blinker for an xcore?

  - by dwelch

  I am liking the http://www.xmos.com chips but want to get a lower level understanding of what is going on. Basically assembler. I am trying to sort out something as simple as an led blinker, set the led, count to N clear the led, count to N, loop forever. Sure I can disassemble a 10 line XC program, but if you have tried that you will see there is a lot of bloat in there that is in every program, what bits are to support the compiler output and what bits are actually setting up the gpio?

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• Different behaviour of browsers while caching the same file.

  - by Amrita

  I am trying to implement mod_disk_caching. i wrote a php code as shown in the example of the tutorial i was following. i fired the following in the terminal a2enmod cache a2enmod disk_cache /etc/init.d/apache2 force-reload then in the php code "; ? now i tried running it using firefox. In the first execution i got the following timestamp. 1308643975 here, when i press refresh, the timestamp changes (as the file is reloaded from the server) and remains the same when i click the link again (as the file is retrieved from the cache). Now i am trying the same with IExplorer. As per my understanding, the timestamp should be the same as the subsequent request for the file will be retrieved only from the cache. But i got a different timestamp. Can anyone explain me the reason for this? Why is it giving separate timestamps when the browsers are different? Thanks and Regards, AMJ

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• Cant see images on print preview

  - by Viren

  I been ask to lay a page where user can click on print option to print that page All the code is hooked up the print command works with one exception the images on web page arent getting reflected in print preview . there isnt any special stylesheet applied for printing to be specific the page has no stylesheet The code for print is given below <a href="javascript:window.print()">Print</a> Attaching the screenshot of the page And the print preview page for better understanding Note : Each images along with qrcode code is render using iframe so what you in web page contain 2 iframe each row to display qrode along with images of a products

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