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  • Side effect-free interface on top of a stateful library

    - by beta
    In an interview with John Hughes where he talks about Erlang and Haskell, he has the following to say about using stateful libraries in Erlang: If I want to use a stateful library, I usually build a side effect-free interface on top of it so that I can the use it safely in the rest of my code. What does he mean by this? I am trying to think of an example of how this would look, but my imagination and/or knowledge is failing me.

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  • Why does this article state that graduate education liberate one from concerns like the efficiency of hardware-based integers?

    - by kadaj
    Quoting The Evolution of Haskell Programmer, graduate education tends to liberate one from petty concerns about, e.g., the efficiency of hardware-based integers What exactly does this suggest? Is it that after graduation, one gets more interested in abstract ideas so much that he does not think hardware is relevant? Or that hardware is also abstracted and one is more interested in algorithms? I am trying to understand on what grounds the sentence is based.

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  • ReSharper C# Live Template for Declaring Routed Event

    - by Bart Read
    Here's another WPF ReSharper Live Template for you. This one is for declaring standalone routed events of any type. Again, it's pretty simple:        #region $EVENTNAME$ Routed Event       public static readonly RoutedEvent $EVENTNAME$Event = EventManager.RegisterRoutedEvent(            "$EVENTNAME$",           RoutingStrategy.$ROUTINGSTRATEGY$,           typeof( $EVENTHANDLERDELEGATE$ ),           typeof( $DECLARINGTYPE$ ) );       public event $EVENTHANDLERDELEGATE$ $EVENTNAME$       {           add { AddHandler( $EVENTNAME$Event, value ); }           remove { RemoveHandler( $EVENTNAME$Event, value ); }       }       protected virtual void On$EVENTNAME$()       {           RaiseEvent( new $EVENTARGSTYPE$( $EVENTNAME$Event, this ) );           $END$       }       #endregion Here are my previous posts along the same lines: ReSharper C# Live Template for Read-Only Dependency Property and Routed Event Boilerplate ReSharper C# Live Template for Dependency Property and Property Change Routed Event Boilerplate Code Enjoy! Technorati Tags: resharper,live template,c#,routed event,wpf,boilerplate,code generation

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  • Can Haskell's Parsec library be used to implement a recursive descent parser with backup?

    - by Thor Thurn
    I've been considering using Haskell's Parsec parsing library to parse a subset of Java as a recursive descent parser as an alternative to more traditional parser-generator solutions like Happy. Parsec seems very easy to use, and parse speed is definitely not a factor for me. I'm wondering, though, if it's possible to implement "backup" with Parsec, a technique which finds the correct production to use by trying each one in turn. For a simple example, consider the very start of the JLS Java grammar: Literal: IntegerLiteral FloatingPointLiteral I'd like a way to not have to figure out how I should order these two rules to get the parse to succeed. As it stands, a naive implementation like this: literal = do { x <- try (do { v <- integer; return (IntLiteral v)}) <|> (do { v <- float; return (FPLiteral v)}); return(Literal x) } Will not work... inputs like "15.2" will cause the integer parser to succeed first, and then the whole thing will choke on the "." symbol. In this case, of course, it's obvious that you can solve the problem by re-ordering the two productions. In the general case, though, finding things like this is going to be a nightmare, and it's very likely that I'll miss some cases. Ideally, I'd like a way to have Parsec figure out stuff like this for me. Is this possible, or am I simply trying to do too much with the library? The Parsec documentation claims that it can "parse context-sensitive, infinite look-ahead grammars", so it seems like something like I should be able to do something here.

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  • How to functionally generate a tree breadth-first. (With Haskell)

    - by Dennetik
    Say I have the following Haskell tree type, where "State" is a simple wrapper: data Tree a = Branch (State a) [Tree a] | Leaf (State a) deriving (Eq, Show) I also have a function "expand :: Tree a - Tree a" which takes a leaf node, and expands it into a branch, or takes a branch and returns it unaltered. This tree type represents an N-ary search-tree. Searching depth-first is a waste, as the search-space is obviously infinite, as I can easily keep on expanding the search-space with the use of expand on all the tree's leaf nodes, and the chances of accidentally missing the goal-state is huge... thus the only solution is a breadth-first search, implemented pretty decent over here, which will find the solution if it's there. What I want to generate, though, is the tree traversed up to finding the solution. This is a problem because I only know how to do this depth-first, which could be done by simply called the "expand" function again and again upon the first child node... until a goal-state is found. (This would really not generate anything other then a really uncomfortable list.) Could anyone give me any hints on how to do this (or an entire algorithm), or a verdict on whether or not it's possible with a decent complexity? (Or any sources on this, because I found rather few.)

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  • Can Haskell's monads be thought of as using and returning a hidden state parameter?

    - by AJM
    I don't understand the exact algebra and theory behind Haskell's monads. However, when I think about functional programming in general I get the impression that state would be modelled by taking an initial state and generating a copy of it to represent the next state. This is like when one list is appended to another; neither list gets modified, but a third list is created and returned. Is it therefore valid to think of monadic operations as implicitly taking an initial state object as a parameter and implicitly returning a final state object? These state objects would be hidden so that the programmer doesn't have to worry about them and to control how they gets accessed. So, the programmer would not try to copy the object representing the IO stream as it was ten minutes ago. In other words, if we have this code: main = do putStrLn "Enter your name:" name <- getLine putStrLn ( "Hello " ++ name ) ...is it OK to think of the IO monad and the "do" syntax as representing this style of code? putStrLn :: IOState -> String -> IOState getLine :: IOState -> (IOState, String) main :: IOState -> IOState -- main returns an IOState we can call "state3" main state0 = putStrLn state2 ("Hello " ++ name) where (state2, name) = getLine state1 state1 = putStrLn state0 "Enter your name:"

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  • Haskell function composition (.) and function application ($) idioms: correct use.

    - by Robert Massaioli
    I have been reading Real World Haskell and I am nearing the end but a matter of style has been niggling at me to do with the (.) and ($) operators. When you write a function that is a composition of other functions you write it like: f = g . h But when you apply something to the end of those functions I write it like this: k = a $ b $ c $ value But the book would write it like this: k = a . b . c $ value Now to me they look functionally equivalent, they do the exact same thing in my eyes. However, the more I look, the more I see people writing their functions in the manner that the book does: compose with (.) first and then only at the end use ($) to append a value to evaluate the lot (nobody does it with many dollar compositions). Is there a reason for using the books way that is much better than using all ($) symbols? Or is there some best practice here that I am not getting? Or is it superfluous and I shouldn't be worrying about it at all? Thanks.

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  • How does Haskell do pattern matching without us defining an Eq on our data types?

    - by devoured elysium
    I have defined a binary tree: data Tree = Null | Node Tree Int Tree and have implemented a function that'll yield the sum of the values of all its nodes: sumOfValues :: Tree -> Int sumOfValues Null = 0 sumOfValues (Node Null v Null) = v sumOfValues (Node Null v t2) = v + (sumOfValues t2) sumOfValues (Node t1 v Null) = v + (sumOfValues t1) sumOfValues (Node t1 v t2) = v + (sumOfValues t1) + (sumOfValues t2) It works as expected. I had the idea of also trying to implement it using guards: sumOfValues2 :: Tree -> Int sumOfValues2 Null = 0 sumOfValues2 (Node t1 v t2) | t1 == Null && t2 == Null = v | t1 == Null = v + (sumOfValues2 t2) | t2 == Null = v + (sumOfValues2 t1) | otherwise = v + (sumOfValues2 t1) + (sumOfValues2 t2) but this one doesn't work because I haven't implemented Eq, I believe: No instance for (Eq Tree) arising from a use of `==' at zzz3.hs:13:3-12 Possible fix: add an instance declaration for (Eq Tree) In the first argument of `(&&)', namely `t1 == Null' In the expression: t1 == Null && t2 == Null In a stmt of a pattern guard for the definition of `sumOfValues2': t1 == Null && t2 == Null The question that has to be made, then, is how can Haskell make pattern matching without knowing when a passed argument matches, without resorting to Eq?

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  • Oracle Announces New Oracle VM Template for MySQL Enterprise Edition

    - by Zeynep Koch
     Oracle announces new Oracle VM template for MySQL Enterprise Edition enabling more efficient and lower cost deployments of virtualized MySQL environments. Here are some of the details and benefits: The new Oracle VM Template for MySQL helps eliminate manual configuration efforts and risks by providing a pre-installed, pre-configured and certified software stack that includes Oracle VM Server for x86, Oracle Linux with the Unbreakable Enterprise Kernel and MySQL Enterprise Edition. By pre-integrating the world’s most popular open source database with Oracle Linux and Oracle Virtualization technologies, enterprise users and ISVs can quickly and easily deploy and manage a virtualized MySQL database server for Web and cloud-based applications. Backed by Oracle’s world-class support organization and the result of extensive integration and quality assurance testing, the Oracle VM Template for MySQL Enterprise Edition further demonstrates Oracle’s investment in MySQL and allows users to benefit from a single point of contact for 24/7 technical support for all pre-configured components. Read more in this white paper. 

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  • Rendering CV template with XeLaTex

    - by jacob
    Installed kubuntu on thursday Installed LaTeX on my kubuntu machine, using full Compiled an old document and it worked fine Downloaded a CV template from http://www.latextemplates.com/template/two-column-one-page-cv Compiled it, got error Fatal fontspec error: "cannot-use-pdftex" The fontspec package requires either XeTeX or LuaTeX to function. You must change your typesetting engine to, e.g., "xelatex" or "lualatex" instead of plain "latex" or "pdflatex". See the fontspec documentation for further information. For immediate help type H . Installed XeLaTex using this guide http://ledgersmb.org/faq/xelatex i.e. 7 Installed texlive-xetex that includes xelatex apt-get install texlive-xetex apt-get install liblatex-{driver,encode,table}-perl apt-get install libtemplate-plugin-latex-per 8) Compiled CV template again, did not work. Related: No Xelatex in texlive 2012 Excuse me if my question is not clear enough, I'm new to linux.

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  • Annoying mistake when create web template in SharePoint 2010

    - by ybbest
    I get the error    Error occurred in deployment step ‘Add Solution’: Exception from HRESULT: 0x8107026E when deploying my web template project. It turns out that your name for the Web template name has to match the name of you WebTemplate section in the element.xml file. Please see the screenshot below, the highlighted two needs to be the same. It took me so long to figure out and I will keep here in case everybody else struggle. If you are a newbie with web template in SharePoint 2010, this blog post explains the details.

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  • Spring MVC vs raw servlets and template engine?

    - by Gigatron
    I've read numerous articles about the Spring MVC framework, and I still can't see the benefits of using it. It looks like writing even a simple application with it requires creating a big hodgepodge of XML files and annotations and other reams of code to conform to what the framework wants, a whole bunch of moving parts to accomplish a simple single task. Any time I look at a Spring example, I can see how I can write something with the same functionality using a simple servlet and template engine (e.g. FreeMarker, StringTemplate), in half the lines of code and little or no XML files and other artifacts. Just grab the data from the session and request, call the application domain objects if necessary, pass the results to the template engine to generate the resulting web page, done. What am I missing? Can you describe even one example of something that is actually made simpler with Spring than using a combination of raw servlets with a template engine? Or is Spring MVC just one of those overly complicated things that people use only because their boss tells them to use it?

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  • Effective template system

    - by Alex
    I'm building a content management system, and need advice on which theming structure should I adopt. A few options (This is not a complete list): Wordpress style: the controller decides what template to load based on the user request, like: home page / article archive / single article page etc. each of these templates are unrelated to other templates, and must exist within the theme the theme developer decides if (s)he want to use inner-templates (like "sidebar", "sidebar item"), and includes them manually where (s)he thinks are needed. Drupal style: the controller gives control to the theme developer only to inner-templates; if they don't exist it falls back internally to some default templates (I find this very restrictive) Funky style: the controller only loads a "index.php" template and provides the theme developer conditional tags, which he can use to include inner-templates if (s)he wants. Among these styles, or others what style of template system allows for fast development and a more concise design and implementation.

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  • Windows Phone 7 Design Template

    Expression Blend is a wonderful design environment for WP7 (Windows Phone 7) but for quickly visualizing a concept nothing beats Illustrator! I am excited about WP7 and decided that having a solid .ai template would prove invaluable. Some of the details of the WP7 UI Design and Interaction Guide are a bit fuzzy (literally) but I was able to generate some useful layout guides, character styles, and symbols. While the template does not cover every aspect of the guide I think it is a good launching point; if you find it useful and extend it please share your updates (I created the template in CS4, if you have problems in earlier versions let me know).Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • How to Choose a Web Developer to Create Your Online Template Site

    Online template systems are found online, and, typically offer you an "easy" and inexpensive way to build your website. Notice the quotations about easy. The actual process of building and maintaining the online template site might not feel like it's easy and inexpensive. The reality is that, in most cases, it really is easier to use an online template system than it is to start a new website from scratch. Also, you can get a site up much more quickly because the internal structure and background images of the site are already done. However, you should choose a developer that has some experience in this area.

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  • Referring EDMX file in Separate VS Project from T4 Template

    - by Paul Petrov
    In my project I needed to separate template generated entities, context in separate projects from the EDMX file. I’ve stumbled across this problem how to make template generator to find edmx file without hardcoding absolute path into the template. Using relative path directly (inputFile=@”..\ProjectFolder\DataModel.edmx”) generated error: Error      2              Running transformation: System.IO.DirectoryNotFoundException: Could not find a part of the path 'C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\ProjectFolder\DataModel.edmx' The code that worked well for me when placed in the beginning of the .tt file: … string rootPath = Host.ResolvePath(String.Empty); string relativePath = @"..\\ProjectDir\\DataModel.edmx"; string inputFile = Path.Combine(rootPath, relativePath); EdmItemCollection ItemCollection = loader.CreateEdmItemCollection(inputFile); …

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  • Template standard controls for an entirely new look and feel

    - by T
    This is the  Ineta Live player without the O’Data Feed.  It is a good example of taking the plain Media Player provided with the Encoder install and re-templating it to make it your own.  It also has a custom scrub control that is added in.  I generally put my tempates in a separate resource file.  On this project, I discovered that I had to include the template at the document level because I needed the ability to attach some code behind to fire change state behaviors.  I could not use the blend xaml behaviors for change state inside the template because the template can’ determine the TargetObject.   Version 1.01 – 6/10/09 (wow how did a week slip by)

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  • Template standard controls for an entirely new look and feel

    - by T
    This is the  Ineta Live player without the O’Data Feed.  It is a good example of taking the plain Media Player provided with the Encoder install and re-templating it to make it your own.  It also has a custom scrub control that is added in.  I generally put my tempates in a separate resource file.  On this project, I discovered that I had to include the template at the document level because I needed the ability to attach some code behind to fire change state behaviors.  I could not use the blend xaml behaviors for change state inside the template because the template can’ determine the TargetObject. Version 1.01 – 6/10/09 (wow how did a week slip by)

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  • OpenWorld Presentations and Anatomy of an RTF Template w/ files

    - by mdonohue
    For those who missed it ... or those who made it and couldn't get enough, check out the presentations delivered at OpenWorld: Overview and Roadmap The Reporting Platform for Oracle Applications Best Practices and even though it wasn't presented at OpenWorld an updated version of Anatomy of an RTF Template to include documented example files  (RTF template, Sub-Template and sample XML data) so you can re-use and play with the code directly.  Huge thanks to Tim and Hok-Min who did all the hard, original work on this example loaded with tips and tricks.  

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  • Are there any purely functional Schemes or Lisps?

    - by nickname
    Over the past few months, I've put a lot of effort into learning (or attempting to learn) several functional programming languages. I really like math, so they have been very natural for me to use. Simply to be more specific, I have tried Common Lisp, Scheme, Haskell, OCaml, and (a little bit of) Erlang. I did not like the syntax of OCaml and do not have enough Erlang knowledge to make a judgment on it yet. Because of its consistent and beautiful (non-)syntax, I really like Scheme. However, I really do appreciate the stateless nature of purely functional programming languages such as Haskell. Haskell looks very interesting, but the amount of inconsistent and non-extendable syntax really bothered me. In the interest of preventing a Lisp vs Haskell flame war, just pretend that I can't use Haskell for some other reason. Therefore, my question is: Are there any purely functional Schemes (or Lisps in general)?

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  • django-registration password reset custom template not loading

    - by ip.
    I'm using django-registration for registering users, however when I want to use my own template for password reset I get the admin template and not the template I created. My template is in myapp/templates/registration/password_reset_form.html and my template loaders are properly set: TEMPLATE_LOADERS = ( 'django.template.loaders.filesystem.Loader', 'django.template.loaders.app_directories.Loader', ) What could I be missing? I'm using Django 1.4

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  • Best way to convert between [Char] and [Word8]?

    - by cmars232
    I'm new to Haskell and I'm trying to use a pure SHA1 implementation in my app (Data.Digest.Pure.SHA) with a JSON library (AttoJSON). AttoJSON uses Data.ByteString.Char8 bytestrings, SHA uses Data.ByteString.Lazy bytestrings, and some of my string literals in my app are [Char]. This article seems to indicate this is something still being worked out in the Haskell language/Prelude: http // hackage.haskell.org/trac/haskell-prime/wiki/CharAsUnicode And this one lists a few libraries but its a couple years old: http //blog.kfish.org/2007/10/survey-haskell-unicode-support.html [Links broken because SO doesn't trust me -- whatever...] What is the current best way to convert between these types, and what are some of the tradeoffs? I don't want to pick something that is obsolete... Thanks!

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  • What does the `forall` keyword in Haskell/GHC do?

    - by JUST MY correct OPINION
    I've been banging my head on this one for (quite literally) years now. I'm beginning to kinda/sorta understand how the foreach keyword is used in so-called "existential types" like this: data ShowBox = forall s. Show s => SB s (This despite the confusingly-worded explanations of it in the fragments found all around the web.) This is only a subset, however, of how foreach is used and I simply cannot wrap my mind around its use in things like this: runST :: forall a. (forall s. ST s a) -> a Or explaining why these are different: foo :: (forall a. a -> a) -> (Char,Bool) bar :: forall a. ((a -> a) -> (Char, Bool)) Or the whole RankNTypes stuff that breaks my brain when "explained" in a way that makes me want to do that Samuel L. Jackson thing from Pulp Fiction. (Don't follow that link if you're easily offended by strong language.) The problem, really, is that I'm a dullard. I can't fathom the chicken scratchings (some call them "formulae") of the elite mathematicians that created this language seeing as my university years are over two decades behind me and I never actually had to put what I learnt into use in practice. I also tend to prefer clear, jargon-free English rather than the kinds of language which are normal in academic environments. Most of the explanations I attempt to read on this (the ones I can find through search engines) have these problems: They're incomplete. They explain one part of the use of this keyword (like "existential types") which makes me feel happy until I read code that uses it in a completely different way (like runST, foo and bar above). They're densely packed with assumptions that I've read the latest in whatever branch of discrete math, category theory or abstract algebra is popular this week. (If I never read the words "consult the paper whatever for details of implementation" again, it will be too soon.) They're written in ways that frequently turn even simple concepts into tortuously twisted and fractured grammar and semantics. (I suspect that the last two items are the biggest problem. I wouldn't know, though, since I'm too much a dullard to comprehend them.) It's been asked why Haskell never really caught on in industry. I suspect, in my own humble, unintelligent way, that my experience in figuring out one stupid little keyword -- a keyword that is increasingly ubiquitous in the libraries being written these days -- are also part of the answer to that question. It's hard for a language to catch on when even its individual keywords cause years-long quests to comprehend. Years-long quests which end in failure. So... On to the actual question. Can anybody completely explain the foreach keyword in clear, plain English (or, if it exists somewhere, point to such a clear explanation which I've missed) that doesn't assume I'm a mathematician steeped in the jargon?

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  • rsyslog - template - regex data for insertion into db

    - by Mike Purcell
    I've been googling around the last few days looking for a solid example of how to regex a log entry for desired data, which is then to be inserted into a database, but apparently my google-fu is lacking. What I am trying to do is track when an email is sent, and then track the remote mta response, specifically the dsn code. At this point I have two templates setup for each situation: # /etc/rsyslog.conf ... $Template tpl_custom_header, "MPurcell: CUSTOM HEADER Template: %msg%\n" $Template tpl_response_dsn, "MPurcell: RESPONSE DSN Template: %msg%\n" # /etc/rsyslog.d/mail if $programname == 'mail-myapp' then /var/log/mail/myapp.log if ($programname == 'mail-myapp') and ($msg contains 'X-custom_header') then /var/log/mail/test.log;tpl_custom_header if ($programname == 'mail-myapp') and ($msg contains 'dsn=') then /var/log/mail/test.log;tpl_response_dsn & ~ Example log entries: MPurcell: CUSTOM HEADER Template: D921940A1A: prepend: header X-custom_header: 101 from localhost[127.0.0.1]; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<localhost>: headername: message-id MPurcell: RESPONSE DSN Template: D921940A1A: to=<[email protected]>, relay=gmail-smtp-in.l.google.com[2607:f8b0:400e:c02::1a]:25, delay=2, delays=0.12/0.01/0.82/1.1, dsn=2.0.0, status=sent (250 2.0.0 OK 1372378600 o4si2828280pac.279 - gsmtp) From the CUSTOM HEADER Template I would like to extract: D921940A1A, and X-custom_header value; 101 From the RESPONSE DSN Template I would like to extract: D921940A1A, and "dsn=2.0.0"

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