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  • What is a monad?

    - by kronoz
    Having briefly looked at Haskell recently I wondered whether anybody could give a brief, succinct, practical explanation as to what a monad essentially is? I have found most explanations I've come across to be fairly inaccessible and lacking in practical detail, so could somebody here help me?

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  • Ruby: intelligent patch/update

    - by Shyam
    Hi, After being blown away by the greatness of irb and rails console, I am loving the dynamical parts of the language more and more. Now, I wonder if it would be possible for a Ruby application to update itself on-the-fly (if the write permission allows it). Can a Ruby application fetch an update and refresh itself? I have seen this functionality a lot in Apple applications and I know updates and fixes are something you must anticipate for when deploying an application. Thank you for your feedback, comments and answers!

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  • StreamReader.EndOfStream produces IOException

    - by Ziplin
    I'm working on an application that accepts TCP connections and reads in data until an </File> marker is read and then writes that data to the filesystem. I don't want to disconnect, I want to let the client sending the data to do that so they can send multiple files in one connection. I'm using the StreamReader.EndOfStream around my outter loop, but it throws an IOException when the client disconnects. Is there a better way to do this? private static void RecieveAsyncStream(IAsyncResult ar) { TcpListener listener = (TcpListener)ar.AsyncState; TcpClient client = listener.EndAcceptTcpClient(ar); // init the streams NetworkStream netStream = client.GetStream(); StreamReader streamReader = new StreamReader(netStream); StreamWriter streamWriter = new StreamWriter(netStream); while (!streamReader.EndOfStream) // throws IOException { string file= ""; while (file!= "</File>" && !streamReader.EndOfStream) { file += streamReader.ReadLine(); } // write file to filesystem } listener.BeginAcceptTcpClient(RecieveAsyncStream, listener); }

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  • opencv image conversion from rgb to hsv

    - by kaushalyjain
    When I run this following code on a sample image ie an rgb image; and then execute it to display the converted hsv image, both appear to be different... can anyone explain why? or can you suggest a solution for this not to happen... coz its the same image afterall Mat img_hsv,img_rgb,red_blob,blue_blob; img_rgb = imread("pic.png",1); cvtColor(img_rgb,img_hsv,CV_RGB2HSV); namedWindow("win1", CV_WINDOW_AUTOSIZE); imshow("win1", img_hsv);

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  • Why does this IF statement fail?

    - by ChosenOne
    If variable path is empty, and editor.Text is not empty, the SaveFileDialog should be displayed. Now, why on earth is this damn thing failing??? I have tried this with many different variations of code with the same result: FAIL: if(path.Length >= 1) // path contains a path. Save changes instead of creating NEW file. { File.WriteAllText(path, content); } else { // no path defined. Create new file and write to it. using(SaveFileDialog saver = new SaveFileDialog()) { if(saver.ShowDialog() == DialogButtons.OK) { File.WriteAllText(saver.Filename, content); } } } At the top of code file I have: path = String.Empty; So why the heck it this failing every single time, even after trying all of the below variations? if(path.Length > 1) // path contains a path. Save changes instead of creating NEW file. { File.WriteAllText(path, content); } else { // no path defined. Create new file and write to it. using(SaveFileDialog saver = new SaveFileDialog()) { if(saver.ShowDialog() == DialogButtons.OK) { File.WriteAllText(saver.Filename, content); } } } and if(String.IsNullOrEmpty(path)) // path contains a path. Save changes instead of creating NEW file. { File.WriteAllText(path, content); } else { // no path defined. Create new file and write to it. using(SaveFileDialog saver = new SaveFileDialog()) { if(saver.ShowDialog() == DialogButtons.OK) { File.WriteAllText(saver.Filename, content); } } } and if(String.IsNullOrWhiteSpace(path)) // path contains a path. Save changes instead of creating NEW file. { File.WriteAllText(path, content); } else { // no path defined. Create new file and write to it. using(SaveFileDialog saver = new SaveFileDialog()) { if(saver.ShowDialog() == DialogButtons.OK) { File.WriteAllText(saver.Filename, content); } } } This is making me very angry. How could this fail? Setting a break point reveals that path is definitely null/"".

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  • What languages have a while-else type control structure, and how does it work?

    - by Dan
    A long time ago, I thought I saw a proposal to add an else clause to for or while loops in C or C++... or something like that. I don't remember how it was supposed to work -- did the else clause run if the loop exited normally but not via a break statement? Anyway, this is tough to search for, so I thought maybe I could get some CW answers here for various languages. What languages support adding an else clause to something other than an if statement? What is the meaning of that clause? One language per answer please.

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  • how to maintain multiple components for multiple client for multiple features?

    - by Dhana
    Basically my project is product based. Once we developed a project and catch the multiple client and deploy the application based on their needs. But We decided to put the new features and project dependent modules are as component. Now my application got many number of customer. Every customer needs a different features based on the component. But we have centralized component for all client . we move the components additional feature to client specific folder and deploy. My problem is , I am unable maintain the components features for multiple client. My component feature code is increased and I am unable to track the client features. Is there any solution for maintaining the multiple component features for multiple client ?

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  • More FP-correct way to create an update sql query

    - by James Black
    I am working on access a database using F# and my initial attempt at creating a function to create the update query is flawed. let BuildUserUpdateQuery (oldUser:UserType) (newUser:UserType) = let buf = new System.Text.StringBuilder("UPDATE users SET "); if (oldUser.FirstName.Equals(newUser.FirstName) = false) then buf.Append("SET first_name='").Append(newUser.FirstName).Append("'" ) |> ignore if (oldUser.LastName.Equals(newUser.LastName) = false) then buf.Append("SET last_name='").Append(newUser.LastName).Append("'" ) |> ignore if (oldUser.UserName.Equals(newUser.UserName) = false) then buf.Append("SET username='").Append(newUser.UserName).Append("'" ) |> ignore buf.Append(" WHERE id=").Append(newUser.Id).ToString() This doesn't properly put a , between any update parts after the first, for example: UPDATE users SET first_name='Firstname', last_name='lastname' WHERE id=... I could put in a mutable variable to keep track when the first part of the set clause is appended, but that seems wrong. I could just create an list of tuples, where each tuple is oldtext, newtext, columnname, so that I could then loop through the list and build up the query, but it seems that I should be passing in a StringBuilder to a recursive function, returning back a boolean which is then passed as a parameter to the recursive function. Does this seem to be the best approach, or is there a better one?

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  • PHP - Best practice to retain form values across postback

    - by Adam
    Hello, Complete PHP novice here, almost all my previous work was in ASP.NET. I am now working on a PHP project, and the first rock I have stumbled upon is retaining values across postback. For the most simple yet still realistic example, i have 10 dropdowns. They are not even databound yet, as that is my next step. They are simple dropdowns. I have my entire page inclosed in a tag. the onclick() event for each dropdown, calls a javascript function that will populate the corrosponding dropdowns hidden element, with the dropdowns selected value. Then, upon page reload, if that hidden value is not empty, i set the selected option = that of my hidden. This works great for a single postback. However, when another dropdown is changed, the original 1'st dropdown loses its value, due to its corrosponding hidden value losing its value as well! This draws me to look into using querystring, or sessions, or... some other idea. Could someone point me in the right direction, as to which option is the best in my situation? I am a PHP novice, however I am being required to do some pretty intense stuff for my skill level, so I need something flexable and preferribly somewhat easy to use. Thanks! -----edit----- A little more clarification on my question :) When i say 'PostBack' I am referring to the page/form being submitted. The control is passed back to the server, and the HTML/PHP code is executed again. As for the dropdowns & hiddens, the reason I used hidden variables to retain the "selected value" or "selected index", is so that when the page is submitted, I am able to redraw the dropdown with the previous selection, instead of defaulting back to the first index. When I use the $_POST[] command, I am unable to retrieve the dropdown by name, but I am able to retrieve the hidden value by name. This is why upon dropdown-changed event, I call javascript which sets the selected value from the dropdown into its corrosponding hidden.

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  • Sparse quadratic program solver

    - by Jacob
    This great SO answer points to a good sparse solver, but I've got constraints on x (for Ax = b) such that each element in x is >=0 an <=N. The first thing which comes to mind is an QP solver for large sparse matrices. Also, A is huge (around 2e6x2e6) but very sparse with <=4 elements per row. Any ideas/recommendations?

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  • DataGridView: how to make scrollbar in sync with current cell selection?

    - by David.Chu.ca
    I have a windows application with DataGridView as data presentation. Every 2 minutes, the grid will be refreshed with new data. In order to keep the scroll bar in sync with the new data added, I have to reset its ScrollBars: dbv.Rows.Clear(); // clear rows SCrollBars sc = dbv.ScrollBars; dbv.ScrollBars = ScrollBars.None; // continue to populate rows such as dbv.Rows.Add(obj); dbv.ScrollBars = sc; // restore the scroll bar setting back With above codes, the scroll bar reappears fine after data refresh. The problem is that the application requires to set certain cell as selected after the refresh: dbv.CurrentCell = dbv[0, selectedRowIndex]; With above code, the cell is selected; however, the scroll bar's position does not reflect the position of the selected cell's row position. When I try to move the scroll bar after the refresh, the grid will jump to the first row. It seems that the scroll bar position is set back to 0 after the reset. The code to set grid's CurrentCell does not cause the scroll bar to reposition to the correct place. There is no property or method to get or set scroll bar's value in DataGriadView, as far as I know. I also tried to set the selected row to the top: dbv.CurrentCell = dbv[0, selectedRowIndex]; dbv.FirstDisplayedScrollingRowIndex = selectedRowIndex; The row will be set to the top, but the scroll bar's position is still out of sync. Not sure if there is any way to make scroll bar's position in sync with the selected row which is set in code?

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  • Can any genius out there turn this code from generating permutation to generating combination?

    - by mark
    #include <string> int main(int,char**) { std::string default_str = "12345"; int perm=1, digits=default_str.size(); for (int i=1;i<=digits;perm*=i++); for (int a=0;a<perm;a++) { std::string avail=default_str; for (int b=digits,div=perm;b>0; b--) { div/=b; int index = (a/div)%b; printf("%c", avail[index] ); avail.erase(index,1) ; } printf("\n"); } printf("permutations:%d\n",perm); while(1); }

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  • Effects of the `extern` keyword on C functions

    - by Elazar Leibovich
    In C I did not notice any effect of the extern keyword used before function declaration. At first I thougth that when defining extern int f(); in a single file forces you to implement it outside of the files scope, however I found out that both extern int f(); int f() {return 0;} And extern int f() {return 0;} Compiles just fine, with no warnings from gcc. I used gcc -Wall -ansi, he wouldn't even accept // comments. Are there any effects for using extern before function definitions? Or is it just an optional keyword with no side effects for functions. In the latter case I don't understand why did the standard designers chose to litter the grammar with superfluous keywords. EDIT: to clarify, I know there's usage for extern in variables, but I'm only asking about extern in functions.

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  • Any way to separate unit tests from integration tests in VS2008?

    - by AngryHacker
    I have a project full of tests, unit and integration alike. Integration tests require that a pretty large database be present, so it's difficult to make it a part of the build process simply because of the time that it takes to re-initialize the database. Is there a way to somehow separate unit tests from integration tests and have the build server just run the unit tests? I see that there is an Ordered Unit test in VS2008, which allows you to pick and choose tests, but I can't make it just execute alone, without all the others. Is there a trick that I am missing? Or perhaps I could adorn the unit tests with an attribute? What are some of the approaches people are using? P.S. I know I could use mocking for integration tests (just to make them go faster) but then it wouldn't be a true integration test.

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  • Design time error - multiple controls with the same Id

    - by ilivewithian
    I'm using VS 2008, I have a very simple page that has a bunch of uniquely named controls. When I try to view it in design mode I get the following error: Error Rendering Control - Label12 An unhanded exception has occurred. Multiple controls with the same ID 'Label1' were found. FindControl requires that controls have unique IDs I've checked the HTML and the designer file and I can only see one control called Label1. What might be causing this? Also, here is the aspx markup I'm having trouble with? <%@ Page Language="vb" AutoEventWireup="false" CodeBehind="CoachingAppearanceReport.aspx.vb" Inherits="AcademyPro.CoachingAppearanceReport" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> </head> <body> <form id="form1" runat="server"> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <div id="appearanceDetail" class="Left CriteriaContainer"> <asp:Label ID="Label1" runat="server" Text="Appearance Type" AssociatedControlID="ddlAppearanceType" /> <asp:DropDownList ID="ddlAppearanceType" runat="server" CssClass="AppType" OnDataBound="ddlAppearanceType_DataBound" DataSourceID="odsAppearanceType" DataTextField="AppearanceType" DataValueField="AppearanceTypeCode"> </asp:DropDownList> <asp:RequiredFieldValidator ID="rfvAppearanceType" runat="server" ControlToValidate="ddlAppearanceType" InitialValue="" Text="*" ErrorMessage="The appearance type must be selected" /> <asp:Label ID="lblAppearanceType" runat="server" /> <br /> <div class="SubSettings"> <asp:Label ID="Label12" runat="server" Text="Subbed for" AssociatedControlID="ddlSubbedFor" /> <asp:DropDownList ID="ddlSubbedFor" runat="server" OnDataBound="ddlSubbedFor_DataBound" DataSourceID="odsPlayersInAgeGroup" DataTextField="PlayerName" DataValueField="PlayerID"> </asp:DropDownList> <asp:Label ID="lblSubbedFor" runat="server" /> <br /> <asp:Label ID="Label13" runat="server" Text="Mins" AssociatedControlID="txtSubMins" /> <asp:TextBox ID="txtSubMins" runat="server" MaxLength="3" CssClass="TinyWidth" /> <asp:Label ID="lblSubMins" runat="server" /> </div> </div> </ContentTemplate> </asp:UpdatePanel> </form> </body> </html>

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  • Delete Drag and Drop Behavior of IKImageBrowserView

    - by PF1
    Hi Everyone: By default (it seems), IKImageBrowserView enables drag and drop to locations in the Finder. I would like to turn off this behavior but am unsure of how to do so. I was thinking that perhaps implementing the NSDraggingDestination protocol and overriding it could solve this, but so far it hasn't worked for me. Thanks for any help!

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  • the name 'controlname' does not exist in the current context

    - by zohair
    Hi, I have a web application that I'm working on(ASP.NET2.0 with C#)[Using VS2005]. Everything was working fine, and all of a sudden I get the error: Error 1 The name 'Label1' does not exist in the current context and 43 others of the sort for each time that I used a control in my codebehind of the page. This is only happening for 1 page. And it's as if the codebehind isn't recognizing the controls. Another interesting thing is that the intellisense isn't picking up any of the controls either.. I have tried to clean the solution file, delete the obj file, exclude the files from the project then re-add them, close VS and restart it, and even restart my computer, but none of these have worked. Please Help. Thank you

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  • How do I program hardware?

    - by Arlen Beiler
    What would I need to program a piece of hardware to do something for me? Let's say I have something with 15 relays (or equivalent) and I want to tell it to turn off relay 10. Or better yet, when sensor 10 is activated, toggle relay 10.

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  • How To Get A Field Value Based On The Max Of Another Field In VFP v8.0

    - by DaveB
    So, I have a table and I want to get the value from one field in the record with the greatest DateTime() value in another field and where still another field is equal to a certain value. Example data: Balance Created MeterNumber 7924.252 02/02/2010 10:31:48 AM 2743800 7924.243 02/02/2010 11:01:37 AM 2743876 7924.227 02/02/2010 03:55:50 PM 2743876 I want to get the balance for a record with the greatest created datetime for a specific meter number. In VFP 7 I can use: SELECT a.balance ,MAX(a.created) FROM MyTable a WHERE a.meternumber = '2743876' But, in the VFP v8.0 OleDb driver I am using in my ASP.NET page I must conform to VFP 8 which says you must have a GROUP BY listing each non aggregate field listed in the SELECT. This would return a record for each balance if I added GROUP BY a.balance to my query. Yes, I could issue a SET ENGINEBEHAVIOR 70 but I wanted to know if this could be done without having to revert to a previous version?

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  • What is the difference between clearcase and vss in label a release?

    - by raj
    Hi, We are using clearcase as our SCM. I have not much experience with clearcase. Now we are about to release our code to production. I want to label my code as I have done using VSS in my previous projects. But in clearcase labeling is not as easy as in VSS. clearcase is asking to create a label type before label a folder in VOB. I don't understand the concept of creating label type? Any guidance on this will be highly appreciated.

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