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• list permutations in haskell

  - by turingcomplete

  So I'm new to haskell and I've been playing with it for a while now. I want to get my function that outputs all list permutations to work. I have written 2 implementations, one works well, the other is giving me an error. Any help would be awesome. This is the first (working) implementation: permute [] = [[]] permute xs = [y| x <- xs, y <- map (x:) $ permute $ delete x xs] This one is giving me an error: permute [] = [[]] permute xs = map (\x -> map (x:) $ permute $ delete x xs) xs and here's the error message: Occurs check: cannot construct the infinite type: t0 = [t0] Expected type: [t0] Actual type: [[t0]] In the expression: map (x :) $ permute $ delete x xs In the first argument of `map', namely `(\ x -> map (x :) $ permute $ delete x xs)' I'd appreciate if someone could explain why I'm getting this error. Thanks

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• Initialization of array on heap

  - by Radek Šimko

  How do i manually initiate values in array on heap? If the array is local variable (in stack), it can be done very elegant and easy way, like this: int myArray[3] = {1,2,3}; Unfortunately, following code int * myArray = new int[3]; myArray = {1,2,3}; outputs an error by compiling error: expected primary-expression before ‘{’ token error: expected `;' before ‘{’ token Do i have to use cycle, or not-so-much-elegant way like this? myArray[0] = 1; myArray[1] = 2; myArray[2] = 3;

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• simple putStrLn in Haskell/Yampa with arrows syntax

  - by sisif

  i'm using Haskell with the Yampa FRP library which uses the arrows language extension. how can i do a simple putStrLn in a SF? mySF = proc x -> do y <- identity -< x*x putStrLn "Hello World!" ++ show y returnA -< y the arrow syntax complains about the expression not bein an arrow (of course), but even with arrows i get no output output <- identity -< putStrLn "Hello World!"

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• Pass property to access using .NET

  - by BitFiddler

  I'm fairly sure this is possible, but what I want to do is have a generic method where I can pass in an object along with a Expression that will tell the method which Property to use in it's logic. Can anyone get me started on the syntax for something like this? Essentially what I would like to code is something like: Dim firstNameMapper as IColumnMapper = new ColumnMapper(of Author)(Function(x) x.FirstName) Dim someAuthorObject as new Author() fistNameMapper.Map("Richard", someAuthorObject) Now the mapper object would know to set the FirstName property to "Richard". Now using a Function here won't work, I know this... I'm just trying to give an idea what I'm trying to work towards. Thanks for any help!

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• display image on a report based on two date

  - by Yongwei Xing

  Hi all I am using sql server 2005 reporting service to generate report base on a database. There are two columns which are datetime type ColumnA and ColumnB. The report would display a KPI image on this report by comparing these two columns.Below is the expression for selecting image SWITCH(DateDiff("d",Fields!ColumnA.Value,Fields!ColumnB.Value)<0,"kpi_r", DateDiff("d",Fields!ColumnA.Value,Fields!ColumnB.Value)>0,"kpi_g", DateDiff("d",Fields!ColumnA.Value,Fields!ColumnB.Value)=0,"kpi_y") For most of the records, the image is correct. Only for one record, the result is very strange. For this record ColumnA=2010-04-23 08:00:00 ColumnB=2010-04-22 17:00:00 It would display kpi_r, it displayed kpi_y. I have checked the value of DateDiff(d,Fields!ColumnA.Value,Fields!ColumnB.Value) in the SSMS, the value is -1. Why does it display kpi_y? Does anyone meet this problem before? Best Regards,

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• ASP.Net mysterious behaviour

  - by kalan

  Does anyone have any idea why this works (expression in the if-clause) if (!(childNode.Roles != null && !Helper.HasEqualElements((string[])childNode.Roles, System.Web.Security.Roles.GetRolesForUser()))) AddNode(childNode, parentNode); And this doesn't if (childNode.Roles == null || Helper.HasEqualElements((string[])childNode.Roles, System.Web.Security.Roles.GetRolesForUser())) AddNode(childNode, parentNode); The problem is that the second if-clause sometimes doesn't work. Though it always works in debug mode, but it sometimes fails while running. And the strange thing is that these two pieces of code seems absolutely equal for me.

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• Django: query spanning multiple many-to-many relationships

  - by Brant

  I've got some models set up like this: class AppGroup(models.Model): users = models.ManyToManyField(User) class Notification(models.Model): groups_to_notify = models.ManyToManyField(AppGroup) The User objects come from django's authentication system. Now, I am trying to get all the notifications pertaining to the groups that the current user is a part of. I have tried.. notifications = Notification.objects.filter(groups_to_notify=AppGroup.objects.filter(users=request.user)) But that gives an error: more than one row returned by a subquery used as an expression Which I suppose is because the groups_to_notify is checking against several groups. How can I grab all the notifications meant for the user based on the groups he is a part of?

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• Why "constructor-way" of declaring variable in "for-loop" allowed but in "if-statement" not allowed?

  - by PiotrNycz

  Consider this simple example: /*1*/ int main() { /*2*/ for (int i(7); i;){break;} /*3*/ if (int i(7)) {} /*4*/ } Why line-2 compiles just fine, whilst line-3 gives the error? This is little strange to me why if-statement is in this aspect treated worse than for-loop? If this is compiler specific - I tested with gcc-4.5.1: prog.cpp: In function 'int main()': prog.cpp:3:7: error: expected primary-expression before 'int' prog.cpp:3:7: error: expected ')' before 'int' I was inspired by this question [UPDATE] I know this compiles just fine: /*1*/ int main() { /*2*/ for (int i = 7; i;){break;} /*3*/ if (int i = 7) {} /*4*/ }

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• Why do I get null objects in a many-to-many bag?

  - by Jim Geurts

  I have a bag defined for a many-to-many list: <class name="Author" table="Authors"> <id name="Id" column="AuthorId"> <generator class="identity" /> </id> <property name="Name" /> <bag name="Books" table="Author_Book_Map" where="IsDeleted=0" fetch="join"> <key column="AuthorId" /> <many-to-many class="Book" column="BookId" where="IsDeleted=0" /> </bag> </class> If I return all author objects using something like the following, I will get what initially appeared to be duplicate Author records: Session.Query<Author>().List<Author>() The extra author objects are created when an author is mapped to Book objects that have IsDeleted = 1 and IsDeleted = 0. Rather than creating one Author object with an enumerable that contains only the books with IsDeleted = 0, it will create two author objects. The first author object has a Books enumerable that contains books with IsDeleted = 0. The second author object will contain an enumerable of null book objects. Similarly, if an object only has one book map, and that map points to a book with IsDeleted = 1, then an author object is returned with a Books collection having one null object. I'm thinking part of the problem stems from the map table objects linking to rows that satisfy the where condition on the bag object but do not meet the many-to-many where condition. This is happening with NHibernate version 3.0.0.4980. Is this a configuration issue or something else?

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• PHP Regex Question

  - by oyerli

  Hi, I am developing an application using PHP but I am new to regular expressions, I could not find a solution to my problem. I want to replace all occurences of #word with a link, i have written a preg_match for this: $text=preg_replace('~#([\p{L}|\p{N}]+)~u', '<a href="/?aranan=$1">#$1</a>', $text); The problem is, this regular expression also matches the html character codes like &#039; and gives corrupt output. I need to exclude the words starting with &# but i do not know how to do that using regular expressions. Thanks for your help.

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• UPDATE from SELECT complains about more that one value returned

  - by Álvaro G. Vicario

  I have this data structure: request ======= building_id lot_code building ======== building_id lot_id lot === lot_id lot_code The request table is missing the value for the building_id column and I want to fill it in from the other tables. So I've tried this: UPDATE request SET building_id = ( SELECT bu.building_id FROM building bu INNER JOIN lot lo ON bu.lot_id=lo.lot_id WHERE lo.lot_code = request.lot_code ); But I'm getting this error: Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , , = or when the subquery is used as an expression. Is it due to wrong syntax? The data model allows more than one building per lot but actual data doesn't contain such cases so there should be at most one building_id per lot_code.

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• arrays declaration and addressing

  - by avinash

  I have a few straightforward questions:- Is the following correct according to a normal c++ compiler? int arr[3][4]; void func(int *a, int m, int n) { int i,j; cin>>i>>j; cout<< a[i*n + j]; //is this way of addressing correct provided 0<=i<m and 0<=j<n } int main() { func((int*)arr, 3,4); } If the bounds of an array strictly has to be a constant expression, why doesn't the following generate compiler errors? int func(int m, int n) { int arr[m][n]; //m and n are not known until run time }

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• looking for a good vc++ profiler, already checked previous posts

  - by coreSOLO

  I'm looking for a good profiler for vs2008 professional edition, free or reasonably priced. I've already checked previous posts and tried about 8 profilers, but most of them are too basic or too detailed. Kindly suggest something, my requirements are as follows: It can be compiled, so that its well integrated with my application. I'm not shying away from instrumenting my methods. The output should be simple, i only need call count and time taken by methods and nothing else. I am mostly concerned about things INSIDE a method, you may call it line by line profiling. I want to select a method and know which line (expression / method call) is eating most of the time.

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• getElementByTagName does not return comment nodes in javascript

  - by Sourabh

  Hi , I want to retrieve all the nodes present in particular DIV element.see the below test page (firefox) <HTML> <HEAD> <TITLE> New Document </TITLE> <META NAME="Generator" CONTENT="EditPlus"> <META NAME="Author" CONTENT=""> <META NAME="Keywords" CONTENT=""> <META NAME="Description" CONTENT=""> <script> function processTags() { var chNodes = document.getElementById('foo').getElementsByTagName('*') ; console.log(chNodes); } </script> </HEAD> <BODY onload="processTags();"> <div id="foo"> <!-- this is a comment -->this is some text ? <span>this is inside span</span> <div><p>test</p>test<div> </div> </BODY> </HTML> But it does not give me comments tag.. what is the best way to retrieve all tags ??

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• I want to extract the video link out of youtube embed code, I am searching for a regex solution for

  - by Starx

  For example: an youtube embed code <object width="480" height="385"> <param name="movie" value="http://www.youtube.com/v/TFlzeO267qY&hl=en_US&fs=1&"></param> <param name="allowFullScreen" value="true"></param> <param name="allowscriptaccess" value="always"></param> <embed src="http://www.youtube.com/v/TFlzeO267qY&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed> </object> I want to extract http://www.youtube.com/v/TFlzeO267qY&hl=en_US&fs=1&" from this embed code but I dont know how to create a regex expression for this Thanks in Advance?

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• C# ToDictionary can valueSelector give null?

  - by Trimack

  Hi, I want to make a dictionary out of list in a way, that the list becomes keys and values would be empty. I have following code Dictionary<XmlTest, int?> testBattery = new XmlTests().GetRandomTestBattery(id). ToDictionary(k => k, v => null); But I am getting the error "Cannot convert lambda expression to type System.Collections.Generic.IEqualityComparer' because it is not a delegate type" Any ideas how could I fix it? (I know I could iterate through and fill the dict one element at a time, but I simply want to use something more elegant)

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• Linq To SQL: Retain list order when using .Contains

  - by rockinthesixstring

  I'm using Lucene.net to build a MyListOfIds As List(Of Integer) which I then pass on to my Linq service. I then search the database as follows Return _EventRepository.Read().Where(Function(e) MyListOfIds.Contains(e.ID)).ToList Now I know that Lucene is already ordering MyListOfIds based on the weight it gave each term. What sucks is that Linq is losing that order in it's SQL search. My Question: How can I retain that sort order when building my Lambda expression? I tried using LINQPad to see how the query is being built, but because I had to declare a variable LINQPad didn't show me the resultant SQL :-( Here's what I tried in LINQPad Dim i As New List(Of Integer) i.Add(1) i.Add(100) i.Add(15) i.Add(3) i.Add(123) Dim r = (From e In Events Where i.Contains(e.ID) Select e) note: my example is in VB.NET, but I don't mind if responses are in C#

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• Paperclip: Stay put on edit

  - by EricR

  When a user edits something in my application, they're forced to re-upload their image via paperclip even if they aren't changing it. Failing to do so will cause an error, since I validate_presence_of :image. This is quite annoying. How can I make it so Paperclip won't update its attributes if a user simply doesn't supply a new image on an edit? The photo controller is fresh out of Rails' scaffold generator. The rest of the source code is provided below. models/accommodation.rb class Accommodation < ActiveRecord::Base attr_accessible :photo validates_presence_of :photo has_one :photo has_many :notifications belongs_to :user accepts_nested_attributes_for :photo, :allow_destroy => true end controllers/accommodation_controller.rb class AccommodationsController < ApplicationController def index @accommodations = Accommodation.all end def show @accommodation = Accommodation.find(params[:id]) rescue ActiveRecord::RecordNotFound flash[:error] = "Accommodation not found." redirect_to :home end def new @accommodation = current_user.accommodations.build @accommodation.build_photo end def create @accommodation = current_user.accommodations.build(params[:accommodation]) if @accommodation.save flash[:notice] = "Successfully created your accommodation." redirect_to @accommodation else @accommodation.build_photo render :new end end def edit @accommodation = Accommodation.find(params[:id]) @accommodation.build_photo rescue ActiveRecord::RecordNotFound flash[:error] = "Accommodation not found." redirect_to :home end def update @accommodation = Accommodation.find(params[:id]) if @accommodation.update_attributes(params[:accommodation]) flash[:notice] = "Successfully updated accommodation." redirect_to @accommodation else @accommodation.build_photo render :edit end end def destroy @accommodation = Accommodation.find(params[:id]) @accommodation.destroy flash[:notice] = "Successfully destroyed accommodation." redirect_to :inkeep end end models/photo.rb class Photo < ActiveRecord::Base attr_accessible :image, :primary belongs_to :accommodation has_attached_file :image, :styles => { :thumb=> "100x100#", :small => "150x150>" } end

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• Advice on Linq to SQL mapping object design

  - by fearofawhackplanet

  I hope the title and following text are clear, I'm not very familiar with the correct terms so please correct me if I get anything wrong. I'm using Linq ORM for the first time and am wondering how to address the following. Say I have two DB tables: User ---- Id Name Phone ----- Id UserId Model The Linq code generator produces a bunch of entity classes. I then write my own classes and interfaces which wrap these Linq classes: class DatabaseUser : IUser { public DatabaseUser(User user) { _user = user; } public Guid Id { get { return _user.Id; } } ... etc } so far so good. Now it's easy enough to find a users phones from Phones.Where(p => p.User = user) but surely comsumers of the API shouldn't need to be writing their own Linq queries to get at data, so I should wrap this query in a function or property somewhere. So the question is, in this example, would you add a Phones property to IUser or not? In other words, should my interface specifically be modelling my database objects (in which case Phones doesn't belong in IUser), or are they actually simply providing a set of functions and properties which are conceptually associated with a User (in which case it does)? There seems drawbacks to both views, but I'm wondering if there is a standard approach to the problem. Or just any general words of wisdom you could share. My first thought was to use extension methods but in fact that doesn't work in this case.

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• Nhibernate Cannot delete the child object

  - by Daoming Yang

  I know it has been asked for many times, i also have found a lot of answers on this website, but i just cannot get out this problem. Can anyone help me with this piece of code? Many thanks. Here is my parent mapping file <set name="ProductPictureList" table="[ProductPicture]" lazy="true" order-by="DateCreated" inverse="true" cascade="all-delete-orphan" > <key column="ProductID"/> <one-to-many class="ProductPicture"/> </set> Here is my child mapping file <class name="ProductPicture" table="[ProductPicture]" lazy="true"> <id name="ProductPictureID"> <generator class="identity" /> </id> <property name="ProductID" type="Int32"></property> <property name="PictureName" type="String"></property> <property name="DateCreated" type="DateTime"></property> </class> Here is my c# code var item = _productRepository.Get(productID); var productPictrue = item.ProductPictureList .OfType<ProductPicture>() .Where(x => x.ProductPictureID == productPictureID); // reomve the finding item var ok = item.ProductPictureList.Remove(productPictrue); _productRepository.SaveOrUpdate(item); ok is false value and this child object is still in my database.

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• ASP.NET 3.5 Page character encoding problem

  - by Dorian McHensie

  Hello everyone. I have a problem in my asp.net 3.5 application (C#) when I try to render in my pages characters like 'è' which are shown in a very strange manner (if i'm lucky i get a ? mark in my web page). in fact Expression Web, when i open my web site, substitutes the è char with �... How can I tell asp.net that I want to use a particular charset so that i can write in the html source letters like è without using hexadecimal codes?????? I tried in the web.config this: inside the system.web namespace of the file but nothing works.... Can anyone tell me how to do? THANKS in advance

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• Would it be simply better to use the system's functions rather than use the language?

  - by Nullw0rm

  There are many scenarios where I've questioned PHP's performance with some of its functions, and whether I should build a complex class to handle specific things using its seemingly slow tools. For example, Complex regular expressions with sed and processing with awk would seemingly be exponential in performance rather than making PHP's regular expression and seemingly excessive functions parse and in time manage to finish it. If I were to do a lot of network tasks such as MX lookups/DIGging/retrieving simultaneously I would rather pass it via system() and let the OS handle it itself. There are simply too many functions in PHP, that are inefficient and result in slow pages or can be handled easier by the OS. What are your opinions? Do you think I should do the hard work with the OS in its own/custom functions?

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• extract number of A tags using jquery

  - by user1017268

  I am working on an enterprise application where I can have several links present in table or none depending on the data. The links appear in the table and have following code behind them <td class="Row"><span id='s_3_2_14_0' ><a href='JavaScript:SWETargetGotoURL("/eservice_enu/start.swe?SWECmd=GotoView&SWEView=Active+PO+Serial+View&SWEPostnApplet=Purchase+Order+List+Applet&SWEPostnRowId=1-KPBLOZ","_self")'>2001103009</a></span></td> I need to find all the A tags present in the page inside SPAN tag having following text SWEView=Active+PO+Serial+View&SWEPostnApplet=Purchase+Order+List+Applet I tried the following expression but it returns 0 $('a[href*="SWEView=Active+PO+Serial+View&SWEPostnApplet=Purchase+Order+List+Applet"').length;

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• Python text file processing speed issues

  - by Anonymouslemming

  Hi all, I'm having a problem with processing a largeish file in Python. All I'm doing is f = gzip.open(pathToLog, 'r') for line in f: counter = counter + 1 if (counter % 1000000 == 0): print counter f.close This takes around 10m25s just to open the file, read the lines and increment this counter. In perl, dealing with the same file and doing quite a bit more (some regular expression stuff), the whole process takes around 1m17s. Perl Code: open(LOG, "/bin/zcat $logfile |") or die "Cannot read $logfile: $!\n"; while (<LOG>) { if (m/.*\[svc-\w+\].*login result: Successful\.$/) { $_ =~ s/some regex here/$1,$2,$3,$4/; push @an_array, $_ } } close LOG; Can anyone advise what I can do to make the Python solution run at a similar speed to the Perl solution? I've tried just uncompressing the file and dealing with it using open instead of gzip.open, but that made a very small difference to the overall time.

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• Why size_t arguments in template declaration need to be const?

  - by ArunSaha

  I can have std::bitset< 10 > bitsetA; or const size_t LengthB = 20; std::bitset< LengthB > bitsetB; without any problem. But, if the length is not const size_t LengthC = 30; std::bitset< LengthC > bitsetC; // Line 30, say I face the following compilation error 'LengthC' cannot appear in a constant-expression template argument 1 is invalid What is the reason for that? What would be the problem, for compiler and for user code, if line 30 was to be accepted? Is it because LengthC might have some alias?

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