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• Implementing simple business model in Haskell

  - by elmes

  Supose we have a very simple model: Station has at least one Train Train has at least two Stations The model has to allow to check what stations any given train visits and to check what trains visit a particular station. How to model it in Haskell? I am a Haskell newbie, so please correct me: once an object is created, you cannot modify it - you can only make a new object based on that one (~immutability). Am I right? If so, I'll have to create a lot of temporary variables with semi-initialized objects (during deserialization or even in unit tests). Basically what I need is an example of modeling domain classes in Haskell - after reading "Learn you a haskell.." I still have no idea how to use this language.

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• Are returned locals automatically xvalues

  - by mark

  Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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• [ANT] Not able to invoke remote script in windows from linux using SSHEXEC

  - by jpegu

  Hi, I have set up OpenSSH in my windows environment and wants to invoke a ANT script from a Linux environment. But i'm getting the following error: $ ant -f invoke.xml Buildfile: /home/inysi/jpegu/cdt/tmp/invoke.xml run: [sshexec] Connecting to ****** [sshexec] cmd : ant -f build.xml [sshexec] uname: not found [sshexec] basename: not found [sshexec] dirname: not found [sshexec] Error: JAVA_HOME is not defined correctly. [sshexec] We cannot execute java [sshexec] which: not found BUILD SUCCESSFUL Total time: 2 seconds But, i can invoke the remote ANT script in Linux environment using SSHEXEC from windows. Can you please let me know, what could be the issue. JAVA_HOME is set in the windows environment variables. Where to set JAVA_HOME in the windows environment. Is there something similar to .bash_profile in windows. So that ANT process can pick it up.

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• C: Incompatible types?

  - by Airjoe

  #include <stdlib.h> #include <stdio.h> struct foo{ int id; char *bar; char *baz[6]; }; int main(int argc, char **argv){ struct foo f; f.id=1; char *qux[6]; f.bar=argv[0]; f.baz=qux; // Marked line return 1; } This is just some test code so ignore that qux doesn't actually have anything useful in it. I'm getting an error on the marked line, incompatible types when assigning to type ‘char *[6]’ from type ‘char **’ but both of the variables are defined as char *[6] in the code. Any insight?

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• Why do C++ streams use char instead of unsigned char?

  - by Johannes Schaub - litb

  I've always wondered why the C++ Standard library has instantiated basic_[io]stream and all its variants using the char type instead of the unsigned char type. char means (depending on whether it is signed or not) you can have overflow and underflow for operations like get(), which will lead to implementation-defined value of the variables involved. Another example is when you want to output a byte, unformatted, to an ostream using its put function. Any ideas? Note: I'm still not really convinced. So if you know the definitive answer, you can still post it indeed.

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• Static vs Non Static constructors

  - by Neil N

  I can't think of any reasons why one is better than the other. Compare these two implementations: public class MyClass { public myClass(string fileName) { // some code... } } as opposed to: public class MyClass { private myClass(){} public static Create(string fileName) { // some code... } } There are some places in the .Net framework that use the static method to create instances. At first I was thinking, it registers it's instances to keep track of them, but regular constructors could do the same thing through the use of private static variables. What is the reasoning behind this style?

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• How to create a GUI inside a function in Matlab?

  - by Paperflyer

  Is there a possibility to write a GUI from inside a function? The Problem is: The callback of all GUI-functions work in the global workspace. But functions have their own workspace and can not access variables in the global workspace. Is there a possibility to make the GUI-functions use the workspace of the function? function myvar = myfunc() myvar = true; h_fig = figure; % create a useless button uicontrol( h_fig, 'style', 'pushbutton', ... 'string', 'clickme', ... 'callback', 'myvar = false' ); % wait for the button to be pressed while myvar pause( 0.2 ); end close( h_fig ); disp( 'this will never be displayed' ); end This event-loop will run indefinitely, since the callback will not modify myvar in the function. Instead it will create a new myvar in the global workspace.

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• Mutual Information / Entropy Calculation Help

  - by Fillip

  Hi, Hoping someone can give me some pointers with this entropy problem. Say X is chosen randomly from the uniform integer distribution 0-32 (inclusive). I calculate the entropy, H(X) = 32 bits, as each Xi has equal probability of occurring. Now, say the following pseudocode executes. int r = rand(0,1); // a random integer 0 or 1 r = r * 33 + X; How would I work out the mutual information between the two variables r and X? Mutual Information is defined as I(X; Y) = H(X) - H(X|Y) but I don't really understand how to apply the conditional entropy H(X|Y) to this problem. Thanks

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• Xcodebuild failing to pick up environment values from project file?

  - by egrunin

  I'm using Xcode 3.2.6, MacOSX. I have a globally visible environment setting: ICU_SRC=~/Documents/icu/source This really is an environment setting, it's set at login time. When I open up Terminal, it's there. In my project, under Header Search Paths I've added this: $(ICU_SRC)/i18n $(ICU_SRC)/common These expand correctly when I compile inside the IDE. When I look at the build results, I see this: -I/Users/eric.grunin/Documents/icu/source/i18n -I/Users/eric.grunin/Documents/icu/source/common When I build from the command line, however, it fails. What I see is this: -I/i18n -I/common Here's the command I'm using to compile: /usr/bin/env -i xcodebuild -project my_project.xcodeproj -target "my_program" -configuration Release -sdk macosx10.6 build What am I doing wrong? Edited to add: Apple explains Setting environment variables for user processes

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• R: how can I concatenate a list?

  - by John

  I'm trying to produce a single variable which is a concatenation of two chars e.g to go from "p30s4" "p28s4" to "p30s4 p28s4". I've tried cat and paste as shown below. Both return empty variables. What am I doing wrong? > blah = c("p30s4","p28s4") > blah [1] "p30s4" "p28s4" > foo = cat(blah) p30s4 p28s4 > foo NULL > foo = paste(cat(blah)) p30s4 p28s4 > foo character(0)

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• passing self data into a recursive function

  - by user272689

  I'm trying to set a function to do something like this def __binaryTreeInsert(self, toInsert, currentNode=getRoot(), parentNode=None): where current node starts as root, and then we change it to a different node in the method and recursivly call it again. However, i cannot get the 'currentNode=getRoot()' to work. If i try calling the funcion getRoot() (as above) it says im not giving it all the required variables, but if i try to call self.getRoot() it complains that self is an undefined variable. Is there a way i can do this without having to specify the root while calling this method?

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• Does retrieving an object from Doctrine2 cause __construct() of the model class to run?

  - by jiewmeng

  When I retrieve an object say by $em->find('Application\Models\User', 1); or other methods like DQL, findBy*() cause the __construct() of the model class to run? I am having a problem where I set variables there like reference to EntityManager and I find that its not set. I tried putting a die() in __construct() and it doesn't halt the application. Can I say that if I want to set other properties/fields like EntityManager $em I have to do it some other way? Perhaps something like protected function getEm() { if (!isset($this->em)) { $this->em = \Zend_Registry::get('em'); } return $this->em; }

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• C++ class initialisation containing class variable initialization

  - by Phil Hannent

  I noticed some code of a colleague today that initialized class variables in the initialization. However it was causing a warning, he says because of the order they are in. My question is why is it better to do variable initialization where it currently is and not within the curly brackets? DiagramScene::DiagramScene( int slideNo, QRectF screenRect, MainWindow* parent ) : QGraphicsScene( screenRect, parent ), myParent( parent ), slideUndoImageCurrentIndex(-1), nextGroupID(0), m_undoInProgress(false), m_deleteItemOnNextUndo(0) line(0), path(0) { /* Setup default brush for background */ scDetail->bgBrush.setStyle(Qt::SolidPattern); scDetail->bgBrush.setColor(Qt::white); setBackgroundBrush(scDetail->bgBrush); }

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• How to Communicate between minifb and a GAE-Hosted Silverlight Client

  - by Nick Gotch

  I have a minifb app (technically gminifb) running on Google App Engine with a bunch of handlers for processing all kinds of requests from a Silverlight client. What's the recommended approach for adding the FB GET variables, such as fb_sig, to the HTTP requests? I believe I can technically pass the session key and uid directly and get things to work but it seems there's probably a much better way to do this. I was reading about FBJS AJAX and I'm trying to figure out how I can use it to proxy the HTTP requests from the Silverlight client through it. Is this a good way to do it? And if so, how would I go about doing so? Any other recommendations would be appreciated too. Thanks,

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• Issue with plotting daily data using ggplot

  - by user1723765

  I tried to plot daily data from 9 variables in ggplot, but the graph I get cannot handle the date variable properly. The x axis is unreadable and its impossible to read the plot. I'm guessing there's an issue with the handling of dates. Here's the data: https://dl.dropbox.com/u/22681355/su.csv Here's the code I've been using: su=read.csv(file="su.csv", head=TRUE) meltdf=melt(su) ggplot(meltdf, aes(x=Date, y=value, colour=variable, group=variable))+geom_line() and here's the output: https://dl.dropbox.com/u/22681355/output.jpg here's the same plot done in excel, why does it look completely different?

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• match 'article' in url RewriteRule

  - by daniel Crabbe

  hello there. building a site which has content for each section. urls range from; /work/ /work/print/ /work/print/folders etc. however, at any point a user can click on an article so; /work/article/1066 /work/print/article/1066 /work/print/folders/article/1066 using .htaccess i need to detect when there is 'article' in the url and set some different variables. RewriteRule ^([a-zA-Z0-9\-]+)/([a-zA-Z0-9\-]+)/([a-zA-Z0-9\-]+)/([a-zA-Z0-9\-]+)/$ sets index.php?level1=$1&level2=$2&level3=$3&level4=$4 but if 'article/([0-9-]+)' is in the url, say /work/print/article/1066 return index.php?level1=$1&level2=$2&articleID=1066 basically the amount of levels will always be different but i'd like to return those as needed. another example would /work/print/folder/archive/article/1066 return index.php?level1=$1&level2=$2&level3=$3&level4=$4&articleID=1066 any help appreciated! Dan

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• Integers in JavaScript

  - by muntoo

  I'm a beginner to Javascript so forgive me if I sound dumb because I learned some Javascript from W3Fools (which are really difficult tutorials - they don't explain anything I want to know, but everything I probably can guess from my experience with C++). I may be switching over to MDN, but if you can recommend any other tutorials, that be great. Anyways, so here's my question: I just read a few lines of this, and apparently: Numbers in JavaScript are "double-precision 64-bit format IEEE 754 values", according to the spec. This has some interesting consequences. There's no such thing as an integer in JavaScript, so you have to be a little careful with your arithmetic if you're used to math in C or Java. I've already seen that there are few of the data types (for variables) I'm used to from C++. But I didn't expect all numbers to automatically be floats. Isn't there any way to use integers, not float? Will a future version of JavaScript support ints?

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• MySQL encoding problem

  - by heffaklump

  I use Java and JDBC to save japanese characters and it works perfectly on my local MySQL. But when I tried doing the same thing on my web hotels MySQL i get ????? instead of japanese characters. I have made the exact same tables and use exact same code. The only difference I have found is SHOW VARIABLES LIKE 'CHAR%' character_set_client utf8 character_set_connection utf8 character_set_database latin1 character_set_filesystem binary character_set_results utf8 character_set_server latin1 character_set_system utf8 character_sets_dir /s/usr-local/share/mysql/charsets/ character_set_datbase is set to latin1. But I can't change it! Any tips?

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• Alternative to nesting for loops in Python

  - by davenz

  I've read that one of the key beliefs of Python is that flat nested. However, if I have several variables counting up, what is the alternative to multiple for loops? My code is for counting grid sums and goes as follows: def horizontal(): for x in range(20): for y in range(17): temp = grid[x][y: y + 4] sum = 1 for n in temp: sum += int(n) return sum This seems to me like it is too heavily nested. Firstly, what is considered to many nested loops in Python ( I have certainly seen 2 nested loops before). Secondly, if this is too heavily nested, what is an alternative way to write this code?

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• saving a records containing a member of type string to a file (Delphi, Windows)

  - by wonderer

  I have a record that looks similar to: type TNote = record Title : string; Note : string; Index : integer; end; Simple. The reason I chose to set the variables as string (as opposed to an array of chars) is that I have no idea how long those strings are going to be. They can be 1 char long, 200 or 2000. Of course when I try to save the record to a type file (file of...) the compiler complains that I have to give a size to string. Is there a way to overcome this? or a way to save those records to an untyped file and still maintain a sort of searchable way? Please do not point me to possible solutions, if you know the solution please post code. Thank you

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• PHP session values lost after redirect on one script but preserved after redirection on another.

  - by Iuhiz

  On my registration script i have: // Save registration information into the database // Set sessions $_SESSION['var1'] = 'somevalue'; $_SESSION['var2'] = 'anothervalue'; header('Location: /somewhere'); exit(); Then on my login script i have: // Check if user provided correct login credentials if (correct) { $_SESSION['var1'] = 'somevalue'; $_SESSION['var2'] = 'anothervalue'; } header('Location: /somewhere'); exit(); What happened is that the session variables were lost after the header redirect in the registration script but they were preserved after the redirect in the login script. I've checked session_id() at both pages and they have the same value, included session_start() at the top of every page and basically tried the solutions to this common problem found on Stackoverflow but somehow nothing seemed to work. I'm beginning to wonder if it is something to do with my server configuration instead of my code.

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• UISegemnted COntrol - selecting 3rd segment activates second segment

  - by diggers25

  I have a segmented control with 3 defined segments. i am looking to capture the segment index so I can use it in an if statement to update variables accordingly as such: -(IBAction)numPlayers:(id)sender; { numPlayersSegment = [(UISegmentedControl *)sender retain]; if (numPlayersSegment.selectedSegmentIndex == 0) { numOfPlayers = 2; } else if (numPlayersSegment.selectedSegmentIndex = 1) { numOfPlayers = 3; } else if (numPlayersSegment.selectedSegmentIndex = 2) { numOfPlayers = 4; } else if (numPlayersSegment.selectedSegmentIndex = -1) { numOfPlayers = 0; } NSLog(@"Players selected = %d", numPlayersSegment.selectedSegmentIndex); However whenever I press the third segment (index 2) it returns the value of the second segment (index 1) and also highlights the 2nd segment. I can see nothing untoward in IB. Has anybody seen this and have any suggestions. I am using xcode 3.2.1 on snow leopard thanks

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• Good code visualization / refactoring tools for C++?

  - by Paul D.

  I've found myself coming across a lot of reasonably large, complicated codebases at work recently which I've been asked to either review or refactor or both. This can be extremely time consuming when the code is highly concurrent, makes heavy use of templates (particularly static polymorphism) and has logic that depends on callbacks/signals/condition variables/etc. Are there any good visualization tools for C++ period, and of those are there any that actually play well with "advanced" C++ features? Anything would probably be better than my approach now, which is basically pen+paper or stepping through the debugger. The debugger method can be good for following a particular code path, but isn't great for seeing the big picture you really need when doing serious refactoring. EDIT: I should mention that Visual Studio plugins aren't going to be a lot of help to me, since our stuff is mostly Linux-only.

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• Is there any way to do a WER "Request Additional Files" for the windows temp directory?

  - by Jason Mathison

  My company has had numerous crashes reported to windows error reporting due to what looks like an install problem. The logs for our installs are typically in the windows\temp directory. I would like to include the install log file as a "Request Additional Files" entry, however there doesn't seem to be any way to get to a subdirectory of the list of environmental Variables that are provided. The windows temp directory is not in the list of values that you can work from, so I am stuck. In general, I don't understand how it is possible to get at almost anything of use via the "Request Additional Files". For example, the %programfiles% directory shouldn't contain any useful files, they should be in a subdirectory for your product. What am I missing?

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• PHP Looping....need some advice

  - by Homer_J

  Hi all, I have the following code: $q1 = $_POST["q1"]; $q2 = $_POST["q2"]; $q3 = $_POST["q3"]; $q4 = $_POST["q4"]; $q5 = $_POST["q5"]; $q6 = $_POST["q6"]; $q7 = $_POST["q7"]; $q8 = $_POST["q8"]; At the moment, this is hard coded and I need to manually change it each time, I'd like to use variables instead so that it's not a manual process. Is it a case of using a loop, while or foreach? If I had the the information $q and q in an array would that help? Thanks, Homer.

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