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• car and cdr in Scheme are driving me crazy ...

  - by kristian Roger

  Hi Im facing a problem with the car and cdr functions for example: first I defined a list called it x (define x (a (bc) d ( (ef) g ) )) so x now is equal to (a (bc) d ( (ef) g ) ) now for example I need to get the g from this list using only car and cdr (!! noshortcuts as caddr cddr !!) the correct answer is: (car(cdr(car(cdr(cdr(cdr x)))))) BUT how ? :-( I work according to the rules (the car gives the head of list and cdr gives the tail) and instead of getting the answer above I keep reaching wrong answers. Can any one help me in understanding this ... give me step or a way to solve it step by step Thanks in advance. I'm really sick of Scheme.

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• PHP and Apache environment variables

  - by Simon

  Hello, I want to pass an environment variable in linux to apache on start up. export MYVAR=5 --I define my environment variable on the command line PassEnv MYVAR --set apache to import the variable in apache config file apachectl restart --when I restart apache I don't get an error message. However I have noticed that if I do not create the environment variable in my first step, I get a warning message, so must be working here echo $_SERVER['MYVAR'] --i try to access the environment variable within PHP but it is not defined I've observed that if I try to PassEnv an environment variable that already exits (one that I havn't created myself) it works fine. The SetEnv directive also works fine. I'd really like to pass an environment variable to apache on the fly without writing it in a file. Help much appreciated. I'm using CentOS, PHP5 and Apache2. Thanks.

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• Can I override a theme function with a .tpl file?

  - by Nick Lowman

  Hi everyone, How would I go around overriding a theme function with a .tpl file? I know how to override a .tpl file with a theme function but not the other way round. I can't seem to find anywhere that tells me so, so maybe it's not possible or not good practise. For example if there was a theme function defined in a module called super_results and registered with the theme registry, like the example below, how would I go around overriding it with super_results.tpl.php. 'super_results' => array( 'arguments' => array('title' => NULL, 'results' => NULL, 'votes' => NULL), ), function modulename_super_results($title, $results,$votes){ output HTML }

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• Why are difference lists more efficient than regular concatenation?

  - by Craig Innes

  I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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• How to update the following rows after the sum of the previous rows reach a threshold? MySQL

  - by Paulo Faria

  I want to update the following rows after the sum of the previous rows reach a defined threshold. I'm using MySQL, and trying to think of a way to solve this using SQL only. Here's an example. Having the threshold 100. Iterating through the rows, when the sum of the previous rows amount = 100, set the following rows to checked. Before the operation: | id | amount | checked | | 1 | 50 | false | | 2 | 50 | false | | 3 | 20 | false | | 4 | 30 | false | After the operation: | id | amount | checked | | 1 | 50 | false | | 2 | 50 | false | <- threshold reached (50 + 50 = 100) | 3 | 20 | true* | | 4 | 30 | true* | Is it possible to do it with just a SQL query? Do I need a stored procedure? How could I implement it using either solution?

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• Eclipse, Android ndk, source files, and library project dependencies

  - by Android Noob

  In Microsoft Visual Studio 2010, it is possible to create a Solution with multiple projects and set dependencies between projects. I'm trying to figure out if the same thing can be done using Eclipse via the NDK. More specifically, I want to know if it is possible to create C source files in an ordinary Android project that can reference C header files in an Android library project. For example: Android library project: Sockets Ordinary Android project: Socket_Server Sockets contains all the C header/source files that are needed to do socket I/O. Socket_Server contains test code that makes calls to the functions that are defined in Sockets library project. This test code requires a header file that contains the function declaration of all API calls. I already set the library dependencies between the projects via: Properties > Android > Library > Add

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• How to center drawableTop and text vertically on the Button in Android?

  - by Gaks

  I have the Button defined as follows: <Button android:drawableTop="@drawable/ico" android:gravity="center" android:id="@+id/StartButton2x2" android:text="@string/Widget2x2StartBtnLabel" android:layout_width="0dip" android:layout_height="fill_parent" android:layout_weight="1" android:background="@drawable/widgetbtn_bg" /> The problem is that 'drawableTop' image is aligned to the top border of the Button view. I would like to center it (together with text label) vertically on the button. 'android:gravity' seems to work only on text label. It does not affect 'drawableTop' positioning. I was able to center it vertically using 'android:paddingTop' - but that does not seem to be a good idea. I guess it would not work properly on different screen resolution/size.

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• Java hashcode based on identity

  - by hjfreyer

  The default behavior of Object.hashCode() is to return essentially the "address" of the object so that a.hashCode() == b.hashCode() if and only if a == b. How can I get this behavior in a user-defined class if a superclass already defines hashCode()? For instance: class A { public int hashCode() { return 0; } } class B extends A { public int hashCode() { // Now I want to return a unique hashcode for each object. // In pythonic terms, it'd look something like: return Object.hashCode(this); } } Ideas?

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• Why does my program occasionally segfault when out of memory rather than throwing std::bad_alloc?

  - by Bradford Larsen

  I have a program that implements several heuristic search algorithms and several domains, designed to experimentally evaluate the various algorithms. The program is written in C++, built using the GNU toolchain, and run on a 64-bit Ubuntu system. When I run my experiments, I use bash's ulimit command to limit the amount of virtual memory the process can use, so that my test system does not start swapping. Certain algorithm/test instance combinations hit the memory limit I have defined. Most of the time, the program throws an std::bad_alloc exception, which is printed by the default handler, at which point the program terminates. Occasionally, rather than this happening, the program simply segfaults. Why does my program occasionally segfault when out of memory, rather than reporting an unhandled std::bad_alloc and terminating?

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• Returning S_FALSE from a C# COM dll

  - by AntonyW

  I have a method defined in IDL as follows : interface IMyFunc : IDispatch { [id(1), helpstring("method GetNextFunction")] HRESULT GetNextFunction([in,out] long* lPos, [out, retval] BSTR* bstrName); } Using C++ I always implemented this as follows : STDMETHODIMP CMyFunc::GetNextFunction(long *nID, long *lPos, BSTR *bstrName) { if ( function to return ) { // setup return values; return S_OK; } else { // just exit return S_FALSE; } } Now I am implementing this in C# and have used tlbimp on the type library and ended up with : public string GetNextFunction(ref int nID, ref int lPos) I understand that this is because [out, retval] is used as the return type instead of the HRESULT as in C++. Is there a simple way to return the S_OK / S_FALSE values without changing the method definition? The only way I can see is that I have to use ildasm / ilasm to add preservesig so I end up with something like this : public int GetNextFunction(ref int nID, ref int lPos, ref string bstrName) I was wondering if there was some other way without doing the il compilation step.

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• Can pydoc/help hide the documentation for inherited class methods and attributes?

  - by EOL

  When declaring a class that inherits from a specific class: class C(dict): added_attribute = 0 the documentation for C lists all the methods of dict (either through help(C) or pydoc). Is there a way to hide the inherited methods from the automatically generated documentation (the documentation string can refer to the base class, for non-overwritten methods)? This would be useful: pydoc lists the functions defined in a module after its classes. Thus, when the classes have a very long documentation, a lot of less than useful information is printed before the new functions provided by the module are presented, which makes the documentation harder to exploit (you have to skip all the documentation for the inherited methods until you reach something specific to the module being documented).

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• How to make columns as wide as the widest entry?

  - by Helper Method

  For a gcc cheatsheet I'm writing, I want to create a table which should describe how gcc interprets different file endings. The table I created so far is defined as follows: |====================================================================== |.c |C source code which must be preprocessed. |.i |C source code which should not be preprocessed. |.h |C header file to be turned into a precompiled header. |.s |Assembler code. |other | An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. |====================================================================== The problem I have is that the table spans the total page width, but what I want is that each column only is as wide as it's widest entry, and that the table will span only as much witdh as it needs.

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• Question About Abstract Classes?

  - by IbrarMumtaz

  URL: Link (1) According to this wesbite .. you cannot implement Abstract classes but derive from them. This makes sense and I have read this many times. Like an interface, you cannot implement an instance of an abstract class, however you can implement methods, fields, and properties in the abstract class that can be used by the child class. But on MSDN URL: TextWriter CLass on MSDN TextWriter is an abstract class but it has two constructors defined ... and according to the MS 70-536 book, the following statement is valid: TextWriter tw = new File.CreateText("myFile.Txt") The static file class and it's CreateText method is fine by me as I have studied it on MSDN but can somebody explain this little contradiction I have found? Surely I am not the first? Why is instantaion of base abstract classes possible????

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• Using javascript with DITA

  - by team-ferrari22

  Hi All, How to use javascript with DITA ? •We can give 'javascript:URL' to the 'href' attribute of , and elements and it will execute it properly. ? ¦ e.g.Click here to get alert box •We tried to execute javascript user defined functions from href attribute but build fails. •We added .js files to .dita file resources and tried to refer a function from that file by href attribute.It is also not working. Before converting the DITA files into html using DITA toolkit,if we want to add JAVASCRIPT functionality which can be later used in html files, how it can be done? Please guide us. Regards.

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• Can I safely store UInt32 to NSUInteger?

  - by mystify

  In the header, it is defined like: #if __LP64__ || (TARGET_OS_EMBEDDED && !TARGET_OS_IPHONE) || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64 typedef long NSInteger; typedef unsigned long NSUInteger; #else typedef int NSInteger; typedef unsigned int NSUInteger; #endif So does an UInt32 fit without problems into an NSUInteger (an unsigned int)? Where's the difference between UInt32 and unsigned int? And I assume that an unsigned long is bigger than an unsigned int?

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• I18n - JSF variable value translation

  - by Yurish

  Hi! I am using Bundle Internationalization in my project. I have initialized bundle via <f:loadBundle basename="ui.all.bundles.AppResources_en" var="msg"/> When i need to translate some text, i am using a key to resourceBundle, to get a value of it, for example: #{msg.someText}. But, now i want to translate text, which key is a value of another variable. For example: I have variable String textToTransl. It`s value is status_booked. In my AppResources is defined, that status_booked means "It is booked!", so, when i am pointing it to #{msg.textToTransl} i need to see "It is booked!" How can i make it work?

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• Navigation Within TabController

  - by David.Chu.ca

  I am trying to use UITabController as may controller in my main window and add navigation controllers to some tab bar items. For example, the first tab has a navigation controller with table view: ![alt text][1] The SettingsViewController is associated with its own NIB file, where a table view is defined. Within that xib file, I have a table view and set it to the outlet of SettingsViewController class property myTableView. The problem is that in the main xib file, for the SettingsViewController navigation, there is one outlet myTableView. I am not sure if I have to set this to somewhere? The exception I get is "[UIViewController _loadViewFromNibNamed:bundle:] loaded the "SettingsViewController" nib but the view outlet was not set." [1]:

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• pinvoke to clutter function

  - by trampster

  I'm trying to pinvoke to a clutter function. The function is defined in the docs as ClutterActor * clutter_texture_new_from_actor (ClutterActor *actor); The code I have is as follows: [DllImport ("libclutter-glx-1.0.so.0")] private static extern IntPtr clutter_texture_new_from_file (string filename, IntPtr errorData); And I call it like this: IntPtr texture = clutter_texture_new_from_file("myImage.jpeg",IntPtr.Zero); however when called like this in monodevelop on ubuntu I get the following error. Unix Transport Error Eventally I would like to get the error reporting working so I can get the gerror result however firstly I need to get past the Unix Transport Error.

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• Website access per client and each client having multiple users Sample Application

  - by windson

  I'm interested in building a web application in .NET that is scalable to multiple Clients and each and every Client has users associated with them. Suppose that my website is xyz.com and I have 3 clients "abc", "klm", "pqr" and I want to give access to features of xyz.com under the link as follows www.xyz.com/abc www.xyz.com/klm www.xyz.com/pqr and Client abc has N users and I want to set 3 roles for every client's user role. Is there any sample application in .NET that support this kind of website access per client having multiple users? And If I use ASP.NET Membership will that be a suitable membership solution or Do I need to opt for any other type of Membership defined by my own or already available in open source market for .NET. Edit: All the clients will have same functionality. I would like to build a generic model for www.xyz.com/{whatever} so that in future if a new client want to register with me he/she just have to give client name and up on adding client name all the features avaiable to exising clients will be applicable.

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• Why are closures broken within exec?

  - by Devin Jeanpierre

  In Python 2.6, >>> exec "print (lambda: a)()" in dict(a=2), {} 2 >>> exec "print (lambda: a)()" in globals(), {'a': 2} Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<string>", line 1, in <module> File "<string>", line 1, in <lambda> NameError: global name 'a' is not defined >>> exec "print (lambda: a).__closure__" in globals(), {'a': 2} None I expected it to print 2 twice, and then print a tuple with a single cell. It is the same situation in 3.1. What's going on?

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• Access to an inner type

  - by sohum

  A colleague of mine posted a question on an internal forum which got me thinking about whether this was possible through C#. Basically, he's got an interface as follows: public interface IProvider<T> { T GetT(); } Is it possible to use something that implements that interface as a type parameter to another generic class and have access to the type T without re-specifying it? For example: public class Foo<P> where P : IProvider<T> { P p; T GetInnerT() { return p.GetT(); } } This does not compile, because the type T is not defined and hence can't be used as a parameter for IProvider. Is something like this even possible? Just curious!

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• How do I determine if my R installation on OS X has the "--enable-R-shlib" option enabled?

  - by Milktrader

  I've installed R on my OS X machine via the .pkg method. I'm trying to get a Ruby gem called RSRuby to work and though it installed correctly, it's throwing an error when I try to invoke the gem. Fatal error: R home directory is not defined Reading the documentation, R should be installed with the option --enable-R-shlib. But the R documentation states that the Mac OS X installation does this by default. How can you verify that this option is enabled on an installation if you don't know it was explicitly called during installation? I'm chasing down why RSRuby can't find R home directory and this seems like the most likely problem.

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• PostgeSQL: Arrays Data Type with PHP

  - by ArchJ

  I'm working on PostgeSQL with PHP and I know that PosrgeSQL allow columns of a table to be defined as arrays. So let's say I have a table like this: CREATE TABLE sal_emp ( a text ARRAY, b text ARRAY, c text ARRAY, ); These are my arrays: $a = array(aa,bb,cc); $b = array(dd,dd,aa); $c = array(bb,ff,ee); and I want to insert them into respective column each like this: a | b | c -----------+------------+------------ {aa,bb,cc} | {dd,dd,aa} | {bb,ff,ee} Can I insert it this way? $a = implode(',', $a); $b = implode(',', $b); $c = implode(',', $c); $a = array('a' => $a, 'b' => $b, 'c' => $c); pg_insert($dbconn, 'table', $a); Or is there a better way to achieve the same result?

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• How to configure a has_many association with non-ActiveRecord model

  - by Callmeed

  My Rails app has a normal ActiveRecord "Account" model stored in the database. The model will store the URL to a remote XML file which defines some other objects. For example, the Account has_many :galleries but the Gallery model is simply defined by nodes in the XML document. So how do I get /accounts/1/galleries to show the galleries from that account's XML? How do I setup this relationship? I know how to do basic non-AR models, but I'm not sure how to define the association or if I need to create a Gallery model at all.

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• Confusion about Nullable<T> constraints

  - by n535

  Greetings everybody. I am sorry, if this was already asked before (searched in vain) or is really very simple, but i just can't get it. The MSDN definition of a Nullable type, states, that it is defined in a following manner: [SerializableAttribute] public struct Nullable<T> where T : struct, new() So the question is quite straightforward: How is this definition possible? Or this is just a typo? Every value type already has a default constructor. Indeed, when i try to compile something like this, the compiler reasonably says, that it is illegal to apply both constraints at the same time, because the second one is implicitly included in a first one. Thanks in advance.

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