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  • functional dependencies vs type families

    - by mhwombat
    I'm developing a framework for running experiments with artificial life, and I'm trying to use type families instead of functional dependencies. Type families seems to be the preferred approach among Haskellers, but I've run into a situation where functional dependencies seem like a better fit. Am I missing a trick? Here's the design using type families. (This code compiles OK.) {-# LANGUAGE TypeFamilies, FlexibleContexts #-} import Control.Monad.State (StateT) class Agent a where agentId :: a -> String liveALittle :: Universe u => a -> StateT u IO a -- plus other functions class Universe u where type MyAgent u :: * withAgent :: (MyAgent u -> StateT u IO (MyAgent u)) -> String -> StateT u IO () -- plus other functions data SimpleUniverse = SimpleUniverse { mainDir :: FilePath -- plus other fields } defaultWithAgent :: (MyAgent u -> StateT u IO (MyAgent u)) -> String -> StateT u IO () defaultWithAgent = undefined -- stub -- plus default implementations for other functions -- -- In order to use my framework, the user will need to create a typeclass -- that implements the Agent class... -- data Bug = Bug String deriving (Show, Eq) instance Agent Bug where agentId (Bug s) = s liveALittle bug = return bug -- stub -- -- .. and they'll also need to make SimpleUniverse an instance of Universe -- for their agent type. -- instance Universe SimpleUniverse where type MyAgent SimpleUniverse = Bug withAgent = defaultWithAgent -- boilerplate -- plus similar boilerplate for other functions Is there a way to avoid forcing my users to write those last two lines of boilerplate? Compare with the version using fundeps, below, which seems to make things simpler for my users. (The use of UndecideableInstances may be a red flag.) (This code also compiles OK.) {-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances, UndecidableInstances #-} import Control.Monad.State (StateT) class Agent a where agentId :: a -> String liveALittle :: Universe u a => a -> StateT u IO a -- plus other functions class Universe u a | u -> a where withAgent :: Agent a => (a -> StateT u IO a) -> String -> StateT u IO () -- plus other functions data SimpleUniverse = SimpleUniverse { mainDir :: FilePath -- plus other fields } instance Universe SimpleUniverse a where withAgent = undefined -- stub -- plus implementations for other functions -- -- In order to use my framework, the user will need to create a typeclass -- that implements the Agent class... -- data Bug = Bug String deriving (Show, Eq) instance Agent Bug where agentId (Bug s) = s liveALittle bug = return bug -- stub -- -- And now my users only have to write stuff like... -- u :: SimpleUniverse u = SimpleUniverse "mydir"

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  • Whats a good E-Commerce Cart

    - by s32ialx
    Whats a good Shopping Cart possibly free i know there oscommerce, xcart etc but whats a good one? and fairly easily to implement maintain and edit possibly merge with in my sites current theme. If you mean technology as in web language which I hope you do than it's php. other then that i have no clue what you mean apache/mysql? amd? lol

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  • how to develop complete software suite/platform ?

    - by fwfwfw
    here's an example of a company selling complete software suite/platform www.ql2.com/technology/platform.php i wonder how are such suite/platforms developped ? do you have to use J2EE ? i am more interested in how this company is able to produce their own proprietary WebQL language. www.automationanywhere.com/products/AAServer.htm is another similar company selling "servers"....how are such proprietary servers developped with Java technology ?

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  • Expert R users, what's in your .Rprofile?...

    - by gappy
    This question is maybe a little too cute, but I have always found startup profile files of other people both useful and instructive about the language. Moreover, while I have some customization for bash and vim, I have nothing for R. For example, one thing I always wanted is different colors for input and output text in a window terminal, and maybe even syntax highlighting.

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  • How to use Spanish characters in Handlebars templates

    - by Jon Rose
    I am wondering what the idiomatic way to render special language characters is using Handlebars.js templates. When I render the normal html I can use something like the Spanish lowercase e, &#233, and it renders as expected. When I pass the same text as a string to my Handlebars template I just see the characters &#233. I have tried creating a Handlebars helper that used jquery to render the text using .html() then returning the .html() of the tmp element and I get the same results.

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  • MySQL ODBC 3.51 Driver UTF-8 encoding

    - by kesava
    Currently I am migrating MSSQL to MYSQL.I am using the MySQL ODBC 3.51 driver to connect to mysql using odbc connectivity.I have telugu language charectors stored in the table.They are not showing properly while using the mysql odbc driver, but they are showing up properly while using the sqlserver odbc driver. Here is my connetion string Driver={MySQL ODBC 3.51 Driver};Server=localhost;Database=dbtest; User=user1;Password=mysql;Option=3;CharSet=utf8; Please suggest a solution to fix this.

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  • Recommendation on C# books

    - by Oliver Bayes-Shelton
    Hi, I am looking to buy my first c# book. At the moment amazon have a special offer on two titles: Sams Teach Yourself the C# Language Sams Teach Yourself Visual C# 2008 Is their a difference between visual C# and C#? Also which book would be better for an intro to C#?

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  • What quality, parser-generator options exist for ruby?

    - by cartoonfox
    What open source (preferably gem-based) parser-generator options do I have in Ruby? I've used (flex&bison)|(lex&yacc) from C in the past, and I'm comfortable with BNF-style specifications. I've heard of treetop, but it looks a bit alien and verbose compared to yacc... Purpose: I want to convert my text markup language to a BNF and generate the parsing code. I think it's a better strategy than my first-order solution: http://github.com/dafydd/semantictext/blob/master/lib/semantictext/rich_text_parser.rb

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  • Cant get description rss tag data with javascript

    - by AdamB
    I'm currently making a widget to take and display items from a feed. I have this working for the most part, but for some reason the data within the tag within the item comes back as empty, but I get the data in the and tags no problem. feed is and xmlhttp.responseXML object. var items = feed.getElementsByTagName("item"); for (var i=0; i<10; i++){ container = document.getElementById('list'); new_element = document.createElement('li'); title = items[i].getElementsByTagName("title")[0].firstChild.nodeValue; link = items[i].getElementsByTagName("link")[0].firstChild.nodeValue; alert(items[i].getElementsByTagName("description")[0].firstChild.nodeValue); new_element.innerHTML = "<a href=\""+link+"\">"+title+"</a> "; container.insertBefore(new_element, container.firstChild); } I have no idea why it wouldn't be working for the tag and would be for the other tags. Here is an example of the rss feed its trying to parse: <rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/"> <channel> <title>A title</title> <link>http://linksomehwere</link> <description>The title of the feed</description> <language>en-us</language> <item> <pubDate>Fri, 10 Jul 2009 11:34:49 -0500</pubDate> <title>Awesome Title</title> <link>http://link/to/thing</link> <guid>http://link/to/thing</guid> <description> <![CDATA[ <p>some html crap</p> blah blah balh ]]> </description> </item> </channel> </rss>

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  • read-only memory and heap memory

    - by benjamin button
    hi, AFAIK, string literals are stored in read only memory in case of C language. where is this actually present on the hardware. as per my knowledge heap is on RAM.correct me if i am wrong. how different is heap from read only memory? is it OS dependant?

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  • How can I demonstrate the benefits of abstractions to an old-time C programmer?

    - by Zaban Khuli
    Hi, there's this senior developer in my company that programs in C. I happen to be from functional background (ML, to be specific). This senior C programmer refuses to use abstractions because "abstraction is for lame programmers and _real_ programmers do not need it." I can not seem to convince him otherwise Is it a problem with only this programmer or do all C (and other lower level language) programmers have this opinion that abstraction is for lame programmers?

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  • How can I implement a site with ASP.NET MVC without using Visual Studio?

    - by Cheeso
    I have seen ASP.NET MVC Without Visual Studio, which asks, Is it possible to produce a website based on ASP.NET MVC, without using Visual Studio? And the accepted answer is, yes. Ok, next question: how? Here's an analogy. If I want to create an ASP.NET Webforms page, I load up my favorite text editor, create a file named Something.aspx. Then I insert into that file, some boilerplate: <%@ Page Language="C#" Debug="true" Trace="false" Src="Sourcefile.cs" Inherits="My.Namespace.ContentsPage" %> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>Title goes here </title> <link rel="stylesheet" type="text/css" href="css/style.css"></link> <style type="text/css"> #elementid { font-size: 9pt; color: Navy; ... more css ... } </style> <script type="text/javascript" language='javascript'> // insert javascript here. </script> </head> <body> <asp:Literal Id='Holder' runat='server'/> <br/> <div id='msgs'></div> </body> </html> Then I also create the Sourcefile.cs file: namespace My.Namespace { using System; using System.Web; using System.Xml; // etc... public class ContentsPage : System.Web.UI.Page { protected System.Web.UI.WebControls.Literal Holder; void Page_Load(Object sender, EventArgs e) { // page load logic here } } } And that is a working ASPNET page, created in a text editor. Drop it into an IIS virtual directory, and it's working. What do I have to do, to make a basic, hello, World ASPNET MVC app, in a text editor? (without Visual Studio) Suppose I want a basic MVC app with a controller, one view, and a simple model. What files would I need to create, and what would go into them?

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  • Is learncpp.com good for beginners?

    - by Dream Lane
    In my search for a good, freely available resource that will teach me C++ I stumbled on http://www.learncpp.com/. My question is for intermediate to experienced C++ programmers... Does this site seem to be a good resource for a beginner to learn C++ from? I've gone through the first few section of the site, and I feel like I am starting to grasp the language, but being a beginner in C++ I really could be learning things all wrong and have no idea.

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  • Can Visual Studio 2010 Test .net 3.5 SP1 Projects?

    - by Michael Stum
    I have some projects in a solution that are running on .net 3.5 SP1 (and can never ever be updated to 4.0 as they are SharePoint projects). When I try to create a new Visual C# Test Project in VS2010 Premium, I have to choose .net 4.0 which is apparently intended. Now I don't care about what my Unit Test project is (don't have to care about VS2008 users), but I do care if I can safely test 3.5 Projects in it due to the different CLRs and slight C# language differences?

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  • Rhino.Commons and it won't compile

    - by nandarya
    I get this very strange error message when trying to use Rhino.Commons with my asp.net mvc application. Error 3 'Rhino.Commons.Repository<Web.Models.Poll>.FindAll()' is not supported by the language C:\frank\dev\SampleApplication\Web\Models\Repositories\IPollRepository.cs 15 20 Web Someone got any experience with this error?

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  • Simple web general localization/translation backend (using mysql)?

    - by Hendrik
    Hi is there a free avaible translation backend with database avaible which can handle multiple users(no login needed), multiple languages (UTF-8) and provides automatic google translation? I just need this tool to fill a database (preferable mysql) with simple tables like this: language | label | text english | _helloworld | Hello World! german | _helloworld | Hallo Welt! I don't care about export since this will have to be created anyways.. Thanks it would be a real timesaver if something with an usable UI exists already.

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  • Where are the java swing String for me to translate?

    - by Tom Brito
    The JFileChooser don't provide support for my language, I'd translate strings defined in the file http://www.rgagnon.com/javadetails/JavaUIDefaults.txt with the UIManager.put(), but I'm not finding the popup strings ("view", "refresh" and "new folder" options when you right-click). Does anyone know where can I find them to translate?

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  • best algorithm for swapping?

    - by ashish yadav
    i have heard from a friend of mine that the best algorithm for swapping is " (a^=b^=a^=b)" where a and b are two integers to be swapped. but when i applied this using c language it resulted in crashing. can anyone of you fine people explain the possible reason for that? please suggest the best algorithm for swapping. thank you!!!!

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  • meaning of the returned list of python json

    - by fmsf
    Hey, I'm new to python so I really don't know the language very well. the following example was taken from here http://docs.python.org/library/json.html >>> import json >>> json.loads('["foo", {"bar":["baz", null, 1.0, 2]}]') [u'foo', {u'bar': [u'baz', None, 1.0, 2]}] what does the u mean? and how do i know which elements are available in the dictionary?

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