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  • C++ require that one template type is derived from the other

    - by Will
    In a comparison operator: template<class R1, class R2> bool operator==(Manager<R1> m1, Manager<R2> m2) { return p1.internal_field == p2.internal_field; } Is there any way I could enforce that R1 and R2 must have a supertype or subtype relation? That is, I'd like to allow either R1 to be derived from R2, or R2 to be derived from R1, but disallow the comparison if R1 and R2 are unrelated types.

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  • c++ queue template

    - by Dalton Conley
    ALright, pardon my messy code please. Below is my queue class. #include <iostream> using namespace std; #ifndef QUEUE #define QUEUE /*---------------------------------------------------------------------------- Student Class # Methods # Student() // default constructor Student(string, int) // constructor display() // out puts a student # Data Members # Name // string name Id // int id ----------------------------------------------------------------------------*/ class Student { public: Student() { } Student(string iname, int iid) { name = iname; id = iid; } void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } private: string name; int id; }; // define a typedef of a pointer to a student. typedef Student * StudentPointer; template <typename T> class Queue { public: /*------------------------------------------------------------------------ Queue Default Constructor Preconditions: none Postconditions: assigns default values for front and back to 0 description: constructs a default empty Queue. ------------------------------------------------------------------------*/ Queue() : myFront(0), myBack(0) {} /*------------------------------------------------------------------------ Copy Constructor Preconditions: requres a reference to a value for which you are copying Postconditions: assigns a copy to the parent Queue. description: Copys a queue and assigns it to the parent Queue. ------------------------------------------------------------------------*/ Queue(const T & q) { myFront = myBack = 0; if(!q.empty()) { // copy the first node myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } /*------------------------------------------------------------------------ Destructor Preconditions: none Postconditions: deallocates the dynamic memory for the Queue description: deletes the memory stored for a Queue. ------------------------------------------------------------------------*/ ~Queue() { NodePointer prev = myFront, ptr; while(prev != NULL) { ptr = prev->next; delete prev; prev = ptr; } } /*------------------------------------------------------------------------ Empty() Preconditions: none Postconditions: returns a boolean value. description: returns true/false based on if the queue is empty or full. ------------------------------------------------------------------------*/ bool empty() const { return (myFront == NULL); } /*------------------------------------------------------------------------ Enqueue Preconditions: requires a constant reference Postconditions: allocates memory and appends a value at the end of a queue description: ------------------------------------------------------------------------*/ void enqueue(const T & value) { NodePointer newNodePtr = new Node(value); if(empty()) { myFront = myBack = newNodePtr; newNodePtr->next = NULL; } else { myBack->next = newNodePtr; myBack = newNodePtr; newNodePtr->next = NULL; } } /*------------------------------------------------------------------------ Display Preconditions: requires a reference of type ostream Postconditions: returns the ostream value (for chaining) description: outputs the contents of a queue. ------------------------------------------------------------------------*/ void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } /*------------------------------------------------------------------------ Front Preconditions: none Postconditions: returns a value of type T description: returns the first value in the parent Queue. ------------------------------------------------------------------------*/ T front() const { if ( !empty() ) return (myFront->data); else { cerr << "*** Queue is empty -- returning garbage value ***\n"; T * temp = new(T); T garbage = * temp; delete temp; return garbage; } } /*------------------------------------------------------------------------ Dequeue Preconditions: none Postconditions: removes the first value in a queue ------------------------------------------------------------------------*/ void dequeue() { if ( !empty() ) { NodePointer ptr = myFront; myFront = myFront->next; delete ptr; if(myFront == NULL) myBack = NULL; } else { cerr << "*** Queue is empty -- " "can't remove a value ***\n"; exit(1); } } /*------------------------------------------------------------------------ pverloaded = operator Preconditions: requires a constant reference Postconditions: returns a const type T description: this allows assigning of queues to queues ------------------------------------------------------------------------*/ Queue<T> & operator=(const T &q) { // make sure we arent reassigning ourself // e.g. thisQueue = thisQueue. if(this != &q) { this->~Queue(); if(q.empty()) { myFront = myBack = NULL; } else { myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } return *this; } private: class Node { public: T data; Node * next; Node(T value, Node * first = 0) : data(value), next(first) {} }; typedef Node * NodePointer; NodePointer myFront, myBack, queueSize; }; /*------------------------------------------------------------------------ join Preconditions: requires 2 queue values Postconditions: appends queue2 to the end of queue1 description: this function joins 2 queues into 1. ------------------------------------------------------------------------*/ template <typename T> Queue<T> join(Queue<T> q1, Queue<T> q2) { Queue<T> q1Copy(q1), q2Copy(q2); Queue<T> jQueue; while(!q1Copy.empty()) { jQueue.enqueue(q1Copy.front()); q1Copy.dequeue(); } while(!q2Copy.empty()) { jQueue.enqueue(q2Copy.front()); q2Copy.dequeue(); } cout << jQueue << endl; return jQueue; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a Queue of type T Postconditions: returns the ostream (for chaining) description: this function is overloaded for outputing a queue with << ----------------------------------------------------------------------------*/ template <typename T> ostream & operator<<(ostream &out, Queue<T> &s) { s.display(out); return out; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of type Student Postconditions: none description: this function is overloaded for outputing an object of type Student. ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, Student &s) { s.display(out); } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of a pointer to a Student object. Postconditions: none description: this function is overloaded for outputing pointers to Students ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, StudentPointer &s) { s->display(out); } #endif Now I'm having some issues with it. For one, when I add 0 to a queue and then I output the queue like so.. Queue<double> qdub; qdub.enqueue(0); cout << qdub << endl; That works, it will output 0. But for example, if I modify that queue in any way.. like.. assign it to a different queue.. Queue<double> qdub1; Queue<double> qdub2; qdub1.enqueue(0; qdub2 = qdub1; cout << qdub2 << endl; It will give me weird values for 0 like.. 7.86914e-316. Help on this would be much appreciated!

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  • Why is partial specialziation of a nested class template allowed, while complete isn't?

    - by drhirsch
    template<int x> struct A { template<int y> struct B {};. template<int y, int unused> struct C {}; }; template<int x> template<> struct A<x>::B<x> {}; // error: enclosing class templates are not explicitly specialized template<int x> template<int unused> struct A<x>::C<x, unused> {}; // ok So why is the explicit specialization of a inner, nested class (or function) not allowed, if the outer class isn't specialiced too? Strange enough, I can work around this behaviour if I only partially specialize the inner class with simply adding a dummy template parameter. Makes things uglier and more complex, but it works. Note: I need this feature for recursive templates of the inner class for a set of the outer class. To make things even more complicate, in reality I only need a template function instead of the inner class. But partial specialization of functions is generally disallowed somewhere else in the standard ^^

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  • Template function overloading with identical signatures, why does this work?

    - by user1843978
    Minimal program: #include <stdio.h> #include <type_traits> template<typename S, typename T> int foo(typename T::type s) { return 1; } template<typename S, typename T> int foo(S s) { return 2; } int main(int argc, char* argv[]) { int x = 3; printf("%d\n", foo<int, std::enable_if<true, int>>(x)); return 0; } output: 1 Why doesn't this give a compile error? When the template code is generated, wouldn't the functions int foo(typename T::type search) and int foo(S& search) have the same signature? If you change the template function signatures a little bit, it still works (as I would expect given the example above): template<typename S, typename T> void foo(typename T::type s) { printf("a\n"); } template<typename S, typename T> void foo(S s) { printf("b\n"); } Yet this doesn't and yet the only difference is that one has an int signature and the other is defined by the first template parameter. template<typename T> void foo(typename T::type s) { printf("a\n"); } template<typename T> void foo(int s) { printf("b\n"); } I'm using code similar to this for a project I'm working on and I'm afraid that there's a subtly to the language that I'm not understanding that will cause some undefined behavior in certain cases. I should also mention that it does compile on both Clang and in VS11 so I don't think it's just a compiler bug.

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  • EXSLT date:format-date template without document() XSLT 1.0

    - by DashaLuna
    Hello guys, I'm using date:format-date template EXSLT file I'm using XSLT 1.0 and MSXML3.0 as the processor. My date:format-date template EXSLT file's declaration is: <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxsl="urn:schemas-microsoft-com:xslt" xmlns:tui="http://www.travelbound.co.uk/" xmlns:date="http://exslt.org/dates-and-times" exclude-result-prefixes="msxsl tui date" version="1.0"> ... </xsl:stylesheet> I cannot use document() function due to the 3rd party restrictions. So I have changed the months and days (similarly) from XML snippet: <date:months> <date:month length="31" abbr="Jan">January</date:month> <date:month length="28" abbr="Feb">February</date:month> <date:month length="31" abbr="Mar">March</date:month> <date:month length="30" abbr="Apr">April</date:month> <date:month length="31" abbr="May">May</date:month> <date:month length="30" abbr="Jun">June</date:month> <date:month length="31" abbr="Jul">July</date:month> <date:month length="31" abbr="Aug">August</date:month> <date:month length="30" abbr="Sep">September</date:month> <date:month length="31" abbr="Oct">October</date:month> <date:month length="30" abbr="Nov">November</date:month> <date:month length="31" abbr="Dec">December</date:month> </date:months> to the variable: <xsl:variable name="months"> <month length="31" abbr="Jan">January</month> <month length="28" abbr="Feb">February</month> <month length="31" abbr="Mar">March</month> <month length="30" abbr="Apr">April</month> <month length="31" abbr="May">May</month> <month length="30" abbr="Jun">June</month> <month length="31" abbr="Jul">July</month> <month length="31" abbr="Aug">August</month> <month length="30" abbr="Sep">September</month> <month length="31" abbr="Oct">October</month> <month length="30" abbr="Nov">November</month> <month length="31" abbr="Dec">December</month> </xsl:variable> And correspondingly, I've changed the code that originally uses document() function from: [from month processing bit of EXSLT stylesheet] <xsl:variable name="month-node" select="document('')/*/date:months/date:month[number($month)]" /> to use MSXML3.0 node-set function: <xsl:variable name="month-node" select="msxsl:node-set($months)/month[number($month)]" /> So I assumed that this would work. According to the EXLT instructions "The format pattern string is interpreted as described for the JDK 1.1 SimpleDateFormat class." [I used current version]. I'm specifing the month in accordance to SimpleDateFormat class as 'dd MMMMM yyyy' so that the month will be the full month's name, for example January. But it doesn't work :( I've looked in EXSLT stylesheet and it has got the logic to do that. Also there is logic to display the name of the week for a day using 'E' pattern, which doesn't work for me. Maybe changing from using document() to variables broke it. Would really appreciate any help. Many thanks!

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  • Custom Template and Layered Navigation

    - by russjman
    I created a custom template for the category view that displays all subcategories for current category. When i set the current category as is_anchor = yes in the admin, the layered navigation filters show up in the side bar. The Sub categories is one of the filters are there as well, but when i click on one them the page still displays all subcategories. I would like to some how test for active filters in my custom template, which i assume there has to be a way to get this info from Magento. Below is my custom code. $_filters is how i am trying to access these filters, but it gives me nothing. Am i invoking this incorrectly, from the wrong place, in the wrong context? <?php $_helper = $this->helper('catalog/output'); $_filters = $this->getActiveFilters(); echo $_filters; if (!Mage::registry('current_category')) return ?> <?php $_categories=$this->getCurrentChildCategories() ?> <?php $_count = is_array($_categories)?count($_categories):$_categories->count(); ?> <?php if($_count): ?> <?php foreach ($_categories as $_category): ?> <?php if($_category->getIsActive()): ?> <?php $cur_category=Mage::getModel('catalog/category')->load($_category->getId()); $layer = Mage::getSingleton('catalog/layer'); $layer->setCurrentCategory($cur_category); $_imgHtml = ''; if ($_imgUrl = $this->getCurrentCategory()->getImageUrl()) { $_imgHtml = '<img src="'.$_imgUrl.'" alt="'.$this->htmlEscape($_category->getName()).'" title="'.$this->htmlEscape($_category->getName()).'" class="category-image" />'; $_imgHtml = $_helper->categoryAttribute($_category, $_imgHtml, 'image'); } echo $_category->getImageUrl(); ?> <div class="category-image-box"> <div class="category-description clearfix" > <div class="category-description-textbox" > <h2><span><?php echo $this->htmlEscape($_category->getName()) ?></span></h2> <p><?php echo $this->getCurrentCategory()->getDescription() ?></p> </div> <a href="<?php echo $this->getCategoryUrl($_category) ?>" class="collection-link<?php if ($this->isCategoryActive($_category)): ?> active<?php endif ?>" >See Entire Collection</a> <a href="<?php echo $this->getCategoryUrl($_category) ?>"><?php if($_imgUrl): ?><?php echo $_imgHtml ?><?php else: ?><img src="/store/skin/frontend/default/patio_theme/images/category-photo.jpg" class="category-image" alt="collection" /><?php endif; ?></a> </div> <?php echo '<pre>'.print_r($_category->getData()).'</pre>';?> </div> <?php endif; ?> <?php endforeach ?> <?php endif; ?>

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  • No Visual studio template information found. See application log in Event viewer for more details

    - by sathya
    I tried installing the .NET Framework 4.0 and ASP.NET MVC 2 Framework through the web platform installer. It took a long time and finally i had a restart in between for .NET 4 installation and after that due to my system hang problems had to do a couple of restarts. And after that tried installing the ASP.NET MVC 2 alone and it succeeded. (During this time i had all my VS instances closed).  I am having VS 2008 SP1. And finally after opening VS 2008 and clicking on new project it said the above error no template info found. and i dint have even a single template in the new project template selection window. So these are the steps that i did for recovering the same.  Start Menu --> Microsoft Visual Studio 2008 --> Visual Studio Tools. Right-click over the Visual Studio Command Prompt shortcut and make sure you select Run as Administrator. Once the VS Command Prompt comes up, execute the command 1. "devenv /installvstemplates" 2. "devenv /resetsettings"  And that worked out. No Visual studio template information found. See application log in Event viewer for more detail

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  • Where should instantiated classes be stored?

    - by Eric C.
    I'm having a bit of a design dilemma here. I'm writing a library that consists of a bunch of template classes that are designed to be used as a base for creating content. For example: public class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template() { //constructor } public void DoSomething() { //does something } ... } The problem is, not only is the library providing the templates, it will also supply quite a few predefined templates which are instances of these template classes. The question is, where do I put these instances of the templates? The three solutions I've come up with so far are: 1) Provide serialized instances of the templates as files. On the one hand, this solution would keep the instances separated from the library itself, which is nice, but it would also potentially add complexity for the user. Even if we provided methods for loading/deserializing the files, they'd still have to deal with a bunch of files, and some kind of config file so the app knows where to look for those files. Plus, creating the template files would probably require a separate app, so if the user wanted to stick with the files method of storing templates, we'd have to provide some kind of app for creating the template files. Also, this requires external dependencies for testing the templates in the user's code. 2) Add readonly instances to the template class Example: public class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template PredefinedTemplate { get { Template templateInstance = new Template(); templateInstance.Name = "Some Name"; templateInstance.Description = "A description"; ... return templateInstance; } } public Template() { //constructor } public void DoSomething() { //does something } ... } This method would be convenient for users, as they would be able to access the predefined templates in code directly, and would be able to unit test code that used them. The drawback here is that the predefined templates pollute the Template type namespace with a bunch of extra stuff. I suppose I could put the predefined templates in a different namespace to get around this drawback. The only other problem with this approach is that I'd have to basically duplicate all the namespaces in the library in the predefined namespace (e.g. Templates.SubTemplates and Predefined.Templates.SubTemplates) which would be a pain, and would also make refactoring more difficult. 3) Make the templates abstract classes and make the predefined templates inherit from those classes. For example: public abstract class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template() { //constructor } public void DoSomething() { //does something } ... } and public class PredefinedTemplate : Template { public PredefinedTemplate() { this.Name = "Some Name"; this.Description = "A description"; this.Attribute1 = "Some Value"; ... } } This solution is pretty similar to #2, but it ends up creating a lot of classes that don't really do anything (none of our predefined templates are currently overriding behavior), and don't have any methods, so I'm not sure how good a practice this is. Has anyone else had any experience with something like this? Is there a best practice of some kind, or a different/better approach that I haven't thought of? I'm kind of banging my head against a wall trying to figure out the best way to go. Thanks!

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  • iPhone web app from dashcode rss feed template works deployed on simulator but not on iphone

    - by Arge Anton
    iPhone web app from dashcode rss feed template works deployed on simulator but not on iphone. The web app is deployed at; http://www.alila.se/wordpress/index.html If i run the simulator and enter that adress, it fetches the rss feed and displays it. Everything fine. When i enter the adress into my iphone, same os 3.1.2 as the simulator, i just get the header part of the page. No rss feed. The rss feed is; alila.se/wordpress/?feed=rss2 and the source can be downloaded from: alila.se/rss_feed.zip

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  • Django cannot find my templatetags, even though it's in INSTALLED_APPS and has a __init__.py

    - by Vivian Short
    I just installed django-compress (http://code.google.com/p/django-compress) into /Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/compress. I added 'compress' to INSTALLED_APPS. In my template file, I wrote {% load compressed %}. I got the error: 'compressed' is not a valid tag library: Could not load template library from django.templatetags.compressed, No module named compressed I verified that there is an init.py in compress, as well as in compress/templatetags/. I tried putting the compress directory into PYTHONPATH. I ran python and wrote "import compress" and that worked. Your suggestions would be very appreciated! What else can I try?

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  • List display names from django models

    - by Ed
    I have an object: POP_CULTURE_TYPES = ( ('SG','Song'), ('MV', 'Movie'), ('GM', 'Game'), ('TV', 'TV'), ) class Pop_Culture(models.Model): name = models.CharField(max_length=30, unique=True) type = models.CharField(max_length=2, choices = POP_CULTURE_TYPES, blank=True, null=True) Then I have a function: def choice_list(request, modelname, field_name): mdlnm = get.model('mdb', modelname.lower()) mdlnm = mdlnm.objects.values_list(field_name, flat=True).distinct().order_by(field_name) return render_to_response("choice_list.html", { 'model' : modelname, 'field' : field_name, 'field_list' : mdlnm }) This gives me a distinct list of all the "type" entries in the database in the "field_list" variable passed in render_to_response. But I don't want a list that shows: SG MV I want a list that shows: Song Movie I can do this on an individual object basis if I was in the template object.get_type_display But how do I get a list of all of the unique "type" entries in the database as their full names for output into a template? I hope this question was clearly described. . .

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  • Good examples of MVVM Template

    - by jwarzech
    I am currently working with the Microsoft MVVM template and find the lack of detailed examples frustrating. The included ContactBook example shows very little Command handling and the only other example I've found is from an MSDN Magazine article where the concepts are similar but uses a slightly different approach and still lack in any complexity. Are there any decent MVVM examples that at least show basic CRUD operations and dialog/content switching? Everyone's suggestions were really useful and I will start compiling a list of good resources Frameworks/Templates WPF Model-View-ViewModel Toolkit MVVM Light Toolkit Prism Caliburn Cinch Useful Articles Data Validation in .NET 3.5 Using a ViewModel to Provide Meaningful Validation Error Messages Action based ViewModel and Model validation Dialogs Command Bindings in MVVM More than just MVC for WPF MVVM + Mediator Example Application Additional Libraries WPF Disciples' improved Mediator Pattern implementation(I highly recommend this for applications that have more complex navigation)

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  • Modification of a template has resulted in confusion...

    - by Dixon Crews
    Hello, I'm working on a site right now that has a short picture slideshow for the homepage. I purchased a template and I am modifying it to work for this situation. On modification, the thumbnail row under the slideshow is now separated from the slideshow and the thumbs are not centered. I can't seem to understand how to get this to get right under the slideshow and have them centered in the row. Any help for me? http://cormanroofinginc.com/ Thanks.

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  • WPF Custom Control - ItemsControl template not being applied.

    - by Patrick White
    I'm building a custom WPF control that derives from TabControl. In the ControlTemplate, I'm using a ItemsControl to display a list that is being bound from the template (an observable collection of type FileMenuItem). During program execution, I'm getting the following error in the output window: ItemTemplate and ItemTemplateSelector are ignored for items already of the ItemsControl's container type; Type='FileMenuItem' The type FileMenuItem is derived from MenuItem. I googled the error and couldn't find anything about it, has anyone run into this while developing custom controls? I can post more code if it would help. Thanks!

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  • Create multi-part message in MIME format Freemarker template

    - by Mat Banik
    How do you create email message that contains text and HTML version for the same content? Of course I would like to know how to setup the freemarker template or the header of the message that will be send. When I look on the source of message multi-part message in MIME format that I receive in inbox every once in while this is what is in there: This is a multi-part message in MIME format. ------=_NextPart_000_B10D_01CBAAA8.F29DB300 Content-Type: text/plain Content-Transfer-Encoding: 7bit ...Text here... ------=_NextPart_000_B10D_01CBAAA8.F29DB300 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <html><body> html code here ... </body></html>

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  • Resharper and Custom Live Template Not Working

    - by Bryce Fischer
    Working with Unity, I thought it would be a good idea to create some LiveTemplates to help out with creating configuration entries. For example, I want to create some typeAlias elements in a file called "unity.config": <typeAlias alias="QueryService" type="type,QueryAssembly"/> So, I created a live template: Shortcut: typeAlias Available "in all files" <typeAlias alias="$ALIAS$" type="$TYPE$,$ASSEMBLY$"/> the unity.config file is an XML file. I put the cursor in an empty spot and type "typeAlias" and then the tab key. Nothing happens. Any ideas?

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  • many1 no longer works with Parsec 3.x

    - by Zak
    After updating to Parsec 3.1 from 2.x, code using many1, such as word = many1 letter fails with No instance for (Stream s m Char) arising from a use of `letter' I found a mailing list post claiming that adding {-#LANGUAGE NoMonomorphismRestriction #-} to the top of the source file would solve the problem, but it did not.

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  • Make Custom Project template in Eclipse IDE

    - by Mohit Deshpande
    I have been using Eclipse IDE for a long time. Its a really great IDE for Java/C/C++ (and other languages with its THOUSANDS of plugins). Every once in a while, I get the need for creating a Javax interface. To do this normally, I would setup the new java project then add what I need. But, wouldn't it be nice if I could just make a template project to automatically include the code for the files. How would I go about doing this? It it even possible? The Eclipse CDT can make a new project type. So can the Google ADT and Google App engine. So I would imagine it is possible. But how?

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  • Parsec: backtracking not working

    - by Nathan Sanders
    I am trying to parse F# type syntax. I started writing an [F]Parsec grammar and ran into problems, so I simplified the grammar down to this: type ::= identifier | type -> type identifier ::= [A-Za-z0-9.`]+ After running into problems with FParsec, I switched to Parsec, since I have a full chapter of a book dedicated to explaining it. My code for this grammar is typeP = choice [identP, arrowP] identP = do id <- many1 (digit <|> letter <|> char '.' <|> char '`') -- more complicated code here later return id arrowP = do domain <- typeP string "->" range <- typeP return $ "("++domain++" -> "++range++")" run = parse (do t <- typeP eof return t) "F# type syntax" The problem is that Parsec doesn't backtrack by default, so > run "int" Right "int" -- works! > run "int->int" Left "F# type syntax" unexpected "-" expecting digit, letter, ".", "`" or end of input -- doesn't work! The first thing I tried was to reorder typeP: typeP = choice [arrowP, identP] But this just stack overflows because the grammar is left-recursive--typeP never gets to trying identP because it keeps trying arrowP over and over. Next I tried try in various places, for example: typeP = choice [try identP, arrowP] But nothing I do seems to change the basic behaviours of (1) stack overflow or (2) non-recognition of "-" following an identifier. My mistake is probably obvious to anybody who has successfully written a Parsec grammar. Can somebody point it out?

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  • Type error while trying to implement the (>>=) function in order to create a custom monad transforme

    - by CharlieP
    Hello, I'm trying to create a monad transformer for a future project, but unfortunately, my implementation of the Monad typeclasse's (=) function doesn't work. First of all, here is the underlying monad's implementation : newtype Runtime a = R { unR :: State EInfo a } deriving (Monad) Here, the implementation of the Monad typeclasse is done automatically by GHC (using the GeneralizedNewtypeDeriving language pragma). The monad transformer is defined as so : newtype RuntimeT m a = RuntimeT { runRuntimeT :: m (Runtime a) } The problem comes from the way I instanciate the (=) function of the Monad typeclasse : instance (Monad m) => Monad (RuntimeT m) where return a = RuntimeT $ (return . return) a x >>= f = runRuntimeT x >>= id >>= f The way I see it, the first >>= runs in the underlying m monad. Thus, runRuntimeT x >>= returns a value of type Runtime a (right ?). Then, the following code, id >>=, should return a value of type a. This value is the passed on to the function f of type f :: (Monad m) => a -> RuntimeT m b. And here comes the type problem : the f function's type doesn't match the type required by the (=) function. Jow can I make this coherent ? I can see why this doesn't work, but I can't manage to turn it into something functionnal. Thank you for you help, and do not hesitate to correct any flaws in my message, Charlie P.

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  • Removing the contents of a Chan or MVar in a single discrete step

    - by Bill
    I'm writing a discrete simulation where request values from multiple threads accumulate in a centralized queue. Every n milliseconds, a manager wakes up to process requests. When the manager wakes up, it should retrieve all of the contents of the central queue in a single discrete step. While processing these, any client threads attempting to submit to the queue should block. When processing completes, the queue reopens and the manager goes back to sleep. What's the best way to do this? The retry behavior of STM isn't really what I want. If I use a Chan or MVar, there's no way to prevent clients from enqueuing additional requests during processing. One approach is to use an MVar as a mutex on a Chan holding the queue. Are there other ways to do this?

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  • I'm working on Peano Axioms in Agda and I've hit a bit of a sticking point

    - by Schroedinger
    PA6 : ?{m n} -> m = n -> n = m is the axiom I am trying to solve and support, I've tried using a cong (from the core library) but am having troubles with the cong constructor PA6 = cong gets me nowhere, I know for cong I am required to supply a refl for equality and a type, but I'm, not sure what type I'm supposed to supply. Ideas? This is for a small assignment at University, so I'd rather someone demonstrate what I've missed rather than write the acutual answer, but I'd appreciate any degree of support.

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  • How to Convert Type in Tuples

    - by Pradeep
    how to convert a String type to a Int i have a tuple and i want to convert it to a tuple which has different types tupletotuple :: (String,String,String) ->(String,Int,Int) tupletotuple (a,b,c) = (a,read(b),read(c)) i get this Error Msg Project tupletotuple ("cha",4,3) ERROR - Cannot infer instance * Instance : Num [Char] * Expression : tupletotuple ("cha",4,3)

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  • VB Project Template for Monobjc in MonoDevelop?

    - by Ira Rainey
    After installing Monobjc and playing around with the Monobjc Application Project under C# in MonoDevelop, I noticed that there is only an empty Monobjc project under the VB section. Obviously this template adds all the correct references but doesn't add the basic files for the application to run. I've tried creating a class with: Imports System Imports Monobjc Imports Monobjc.Cocoa Class Application Public Sub Main(Byval args() As String) ObjectiveCRuntime.LoadFramework("Cocoa") ObjectiveCRuntime.Initialize() End Sub End Class Obviously I'm not loading the NIB there either, as I haven't added that in either, but if I try to build this I get: /Source/VB_Sample/VB_Sample/<MyGenerator>(1,1): Error VBNC30420: Could not find a 'Sub Main' in ''. (VBNC30420) (VB_Sample) Where should I be putting the Sub Main? Also if I add in a xib file from IB, how do I generate the designer code for the partial AppDelegate class? Any help would be appreciated.

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