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  • Are comonads a good fit for modeling the Wumpus world?

    - by Tim Stewart
    I'm trying to find some practical applications of a comonad and I thought I'd try to see if I could represent the classical Wumpus world as a comonad. I'd like to use this code to allow the Wumpus to move left and right through the world and clean up dirty tiles and avoid pits. It seems that the only comonad function that's useful is extract (to get the current tile) and that moving around and cleaning tiles would not use be able to make use of extend or duplicate. I'm not sure comonads are a good fit but I've seen a talk (Dominic Orchard: A Notation for Comonads) where comonads were used to model a cursor in a two-dimensional matrix. If a comonad is a good way of representing the Wumpus world, could you please show where my code is wrong? If it's wrong, could you please suggest a simple application of comonads? module Wumpus where -- Incomplete model of a world inhabited by a Wumpus who likes a nice -- tidy world but does not like falling in pits. import Control.Comonad -- The Wumpus world is made up of tiles that can be in one of three -- states. data Tile = Clean | Dirty | Pit deriving (Show, Eq) -- The Wumpus world is a one dimensional array partitioned into three -- values: the tiles to the left of the Wumpus, the tile occupied by -- the Wumpus, and the tiles to the right of the Wumpus. data World a = World [a] a [a] deriving (Show, Eq) -- Applies a function to every tile in the world instance Functor World where fmap f (World as b cs) = World (fmap f as) (f b) (fmap f cs) -- The Wumpus world is a Comonad instance Comonad World where -- get the part of the world the Wumpus currently occupies extract (World _ b _) = b -- not sure what this means in the Wumpus world. This type checks -- but does not make sense to me. extend f w@(World as b cs) = World (map world as) (f w) (map world cs) where world v = f (World [] v []) -- returns a world in which the Wumpus has either 1) moved one tile to -- the left or 2) stayed in the same place if the Wumpus could not move -- to the left. moveLeft :: World a -> World a moveLeft w@(World [] _ _) = w moveLeft (World as b cs) = World (init as) (last as) (b:cs) -- returns a world in which the Wumpus has either 1) moved one tile to -- the right or 2) stayed in the same place if the Wumpus could not move -- to the right. moveRight :: World a -> World a moveRight w@(World _ _ []) = w moveRight (World as b cs) = World (as ++ [b]) (head cs) (tail cs) initWorld = World [Dirty, Clean, Dirty] Dirty [Clean, Dirty, Pit] -- cleans the current tile cleanTile :: Tile -> Tile cleanTile Dirty = Clean cleanTile t = t Thanks!

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  • Javascript: Static member variable containing object instances

    - by tom
    I have the following: function Preferences() { } Preferences.players = { 'player1': new Player() } players is a static member variable of Preferences and I'm trying to make it an object containing an instance of a Player. However, it doesn't appear to let me do this. It seems like it will allow me to define players if I make it a non-static member variable however. Like so: function Preferences() { var players = { 'player1' : new Player() } } Is it possible to create a static member variable containing instances of an object in JS?

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  • GridView - set selected index by searching through data keys

    - by Cristian Boariu
    Hi, I have a GridView which has DataKey[0] as productId. If i have for instance productId = 54, is there any way to search through all GridView item and set as selected the one who has DataKEy[0] = 54? In drop down list i have : ddlProducts.Items.FindByValue(lblProduct.Text.ToString())).Selected = true Is anything similar for GridView? Thanks in advance.

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  • New to MVC. Actionscript 3.0 Appreciate your help.

    - by Combustion007
    Hello Everyone, I am new to design patterns and am trying to learn the MVC implementation. I have written four classes: DataModel DataView DataController Main Main serves as the application facade. The main FLA is called HelloWorld. I have a symbol called "Box" in HelloWorld. I just would like to add an instance of the "Box" on the stage. Eventually I would like to place a button and when the button is clicked, the Box instance color will be changed. I would appreciate any help, please help me figure out what am I doing wrong. Here are my Classes: DATAMODEL CLASS: package { import flash.events.*; public class DataModel extends EventDispatcher { public static const UPDATE:String = "modelUpdate"; private var _color:Number = (Math.round(Math.random()* 0xffffff)); public function DataModel() { trace("DATA MODEL INIT"); } public function get color():Number { return _color; } public function set color(p:Number):void { _color = p; notifyObserver(); } public function notifyObserver():void { dispatchEvent(new Event(DataModel.UPDATE)); } } } //DATACONTROLLER CLASS: package { import flash.events.; import flash.display.; import flash.errors.*; public class DataController { private var _model:DataModel; public function DataController(m:DataModel) { trace("DATACONTROLLER INIT"); _model = m; } } } DATAVIEW CLASS: package { import flash.events.; import flash.display.; import flash.errors.*; public class DataView extends Sprite { private var _model:DataModel; private var _controller:DataController; private var b:Box; public function DataView(m:DataModel, c:DataController) { _model = m; _controller = c; b = new Box(); b.x = b.y = 100; addChild(b); } } } And Finally THE FACADE: package { import flash.display.; import flash.events.; import flash.text.; import flash.errors.; public class Main extends Sprite { private var _model:DataModel; private var _controller:DataController; private var _view:DataView; public function Main(m:DataModel, c:DataController, v:DataView) { _model = m; _controller = c; _view = v; addChild(v); } } } When I test the movie: I get this error: ArgumentError: Error #1063: Argument count mismatch on Main(). Expected 3, got 0. Thanks alot.

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  • What is the best way to include other scripts?

    - by Aaron H.
    The way you would normally include a script in bash is source. For example: main #!/bin/bash source incl.bash echo "The main script" incl.bash echo "The included script" The output of executing ./main: The included script The main script Now, if you attempt to execute that shell script from another location, it can't find the include unless it's in your PATH. What's a good way to ensure that your script can find the included script, especially if for instance, the script needs to be portable?

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  • How to create a database binding using Windows Builder Pro?

    - by Tiago
    For the first time, I'm creating a Java Swing application. I'm using Windows Builder Pro in Eclipse, and a MySQL database (already setup up). Let's say I have a combo box, and I want (for instance) all 'name' fields from a 'certain' table appear. How can I setup that binding? I know how to programatically handle the connection and query code, what I would like to know is how to make that binding in Eclipse.

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  • Event to listen to attribute changes

    - by Luis
    I dont think this is possible but maybe someone knows a way to achieve this. I want to attach an event to an html element to listen to attribute change. So say for instance that I want something to happen when a visibility of a div changes. The reason is that I have no control over the javascript that is switching the visibility, hence the need for an event. Thanks

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  • Force update in Hibernate

    - by gubrutz
    How can I force Hibernate to update an entity instance even if the entity is not dirty? I'm using Hibernate 3.3.2 GA, Hibernate Annotations and Hibernate EntityManager btw. I really want Hibernate to execute the generic UPDATE statement even if no property on the entity has changed. I need this because some event listeners need to get invoked to do some additional work when the application runs for the first time. Thanks!

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  • Get color output in bash

    - by Werner
    Hi, when compiling some projects on linux terminal, I get usually a long output consisting of a lot of information. Usually this information is MONOCHROME. I wonder if bash can be modified somehow, so in all outputs or in some specific outputs (like from Makefile, etc) I can get different colors dependeing on, for instance: make[1]: Leaving directory or g++ -DHAVE_CONFIG_H -I. etc. Thanks

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  • Django save_m2m() and excluded field

    - by jul
    hi, in a ModelForm I replaced a field by excluding it and adding a new one with the same name, as shown below in AddRestaurantForm. When saving the form with the code shown below, I get an error in form.save_m2m() ("Truncated incorrect DOUBLE value"), which seems to be due to the function to attempt to save the tag field, while it is excluded. Is the save_m2m() function supposed to save excluded fields? Is there anything wrong in my code? Thanks Jul (...) new_restaurant = form.save(commit=False) new_restaurant.city = city new_restaurant.save() tags = form.cleaned_data['tag'] if(tags!=''): tags=tags.split(',') for t in tags: tag, created = Tag.objects.get_or_create(name = t.strip()) tag.save() new_restaurant.tag.add(tag) new_restaurant.save() form.save_m2m() models.py class Tag(models.Model): name = models.CharField(max_length=100, unique=True) class Restaurant(models.Model): name = models.CharField(max_length=50) city=models.ForeignKey(City) category=models.ManyToManyField(Category) tag=models.ManyToManyField(Tag, blank=True, null=True) forms.py class AddRestaurantForm(ModelForm): name = forms.CharField(widget=forms.TextInput(attrs=classtext)) city = forms.CharField(widget=forms.TextInput(attrs=classtext), max_length=100) tag = forms.CharField(widget=forms.TextInput(attrs=classtext), required=False) class Meta: model = Restaurant exclude = ('city','tag') Traceback: File "/var/lib/python-support/python2.5/django/core/handlers/base.py" in get_response 92. response = callback(request, *callback_args, **callback_kwargs) File "/home/jul/atable/../atable/resto/views.py" in addRestaurant 498. form.save_m2m() File "/var/lib/python-support/python2.5/django/forms/models.py" in save_m2m 75. f.save_form_data(instance, cleaned_data[f.name]) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in save_form_data 967. setattr(instance, self.attname, data) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in set 627. manager.add(*value) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in add 430. self._add_items(self.source_col_name, self.target_col_name, *objs) File "/var/lib/python-support/python2.5/django/db/models/fields/ related.py" in _add_items 497. [self._pk_val] + list(new_ids)) File "/var/lib/python-support/python2.5/django/db/backends/util.py" in execute 19. return self.cursor.execute(sql, params) File "/var/lib/python-support/python2.5/django/db/backends/mysql/ base.py" in execute 84. return self.cursor.execute(query, args) File "/var/lib/python-support/python2.5/MySQLdb/cursors.py" in execute 168. if not self._defer_warnings: self._warning_check() File "/var/lib/python-support/python2.5/MySQLdb/cursors.py" in _warning_check 82. warn(w[-1], self.Warning, 3) File "/usr/lib/python2.5/warnings.py" in warn 62. globals) File "/usr/lib/python2.5/warnings.py" in warn_explicit 102. raise message Exception Type: Warning at /restaurant/add/ Exception Value: Truncated incorrect DOUBLE value: 'a'

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  • empty sharepoint user profile property throw an exception

    - by James123
    I have a user profile property. user not assigned any value that property. If I use below code. It is thorwing exception " object reference not set to an instance of an object " userprof["OptOut"].ToString() I tried all types like if (userprof["OptOut"] != null) OR if(userprof["OptOut"].Value != null) nothing worked out for me. Here userProf object has value. userprof["OptOut"].Value is null How to handle this?

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  • Not sure what happens to my apps objects when using NSURLSession in background - what state is my app in?

    - by Avner Barr
    More of a general question - I don't understand the workings of NSURLSession when using it in "background session mode". I will supply some simple contrived example code. I have a database which holds objects - such that portions of this data can be uploaded to a remote server. It is important to know which data/objects were uploaded in order to accurately display information to the user. It is also important to be able to upload to the server in a background task because the app can be killed at any point. for instance a simple profile picture object: @interface ProfilePicture : NSObject @property int userId; @property UIImage *profilePicture; @property BOOL successfullyUploaded; // we want to know if the image was uploaded to out server - this could also be a property that is queryable but lets assume this is attached to this object @end Now Lets say I want to upload the profile picture to a remote server - I could do something like: @implementation ProfilePictureUploader -(void)uploadProfilePicture:(ProfilePicture *)profilePicture completion:(void(^)(BOOL successInUploading))completion { NSUrlSession *uploadImageSession = ..... // code to setup uploading the image - and calling the completion handler; [uploadImageSession resume]; } @end Now somewhere else in my code I want to upload the profile picture - and if it was successful update the UI and the database that this action happened: ProfilePicture *aNewProfilePicture = ...; aNewProfilePicture.profilePicture = aImage; aNewProfilePicture.userId = 123; aNewProfilePicture.successfullyUploaded = NO; // write the change to disk [MyDatabase write:aNewProfilePicture]; // upload the image to the server ProfilePictureUploader *uploader = [ProfilePictureUploader ....]; [uploader uploadProfilePicture:aNewProfilePicture completion:^(BOOL successInUploading) { if (successInUploading) { // persist the change to my db. aNewProfilePicture.successfullyUploaded = YES; [Mydase update:aNewProfilePicture]; // persist the change } }]; Now obviously if my app is running then this "ProfilePicture" object is successfully uploaded and all is well - the database object has its own internal workings with data structures/caches and what not. All callbacks that may exist are maintained and the app state is straightforward. But I'm not clear what happens if the app "dies" at some point during the upload. It seems that any callbacks/notifications are dead. According to the API documentation- the uploading is handled by a separate process. Therefor the upload will continue and my app will be awakened at some point in the future to handle completion. But the object "aNewProfilePicture" is non existant at that point and all callbacks/objects are gone. I don't understand what context exists at this point. How am I supposed to ensure consistency in my DB and UI (For instance update the "successfullyUploaded" property for that user)? Do I need to re-work everything touching the DB or UI to correspond with the new API and work in a context free environment?

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  • Django: Template should render 'description' not actual value

    - by Till Backhaus
    Hi, in a Model I have a CharField with choices: class MyModel(models.Model): THE_CHOICES=( ('val',_(u'Value Description')), ) ... myfield=models.CharField(max_length=3,choices=THE_CHOICES Now in the template I access an instance of MyModel: {{ my_instance.myfield }} Of course the gives me val instead of Value Description. How do I get the description? Thanks in advance!

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  • Serialize an object using DataContractJsonSerializer as a json array

    - by rekna
    I have a class which contains a list of items. I want to serialize an instance of this class to json using the DataContractJsonSerializer as a json array. eg. class MyClass { List<MyItem> _items; } class MyItem { public string Name {get;set;} public string Description {get;set;} } When serialized to json it should be like this : [{"Name":"one","Description":"desc1"},{"Name":"two","Description":"desc2"}]

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