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  • Haskell search an element on a List

    - by user1887556
    I want a function that changes (1 to 0) on a list, when number of 1's isn't even. I have done these functions: 1) Sees if the lines in a list are even or not: parityLine :: [[Int]] -> [Bool] parityLine [] =[] parityLine (x:xs) |sum(x) `mod` 2 == 0 = True:(parityLine(xs)) |otherwise = False:(parityLine(xs)) 2) Sum the corresponding elements on a list of lists: sumPositions :: [[Int]] -> [Int] sumPositions [] = [] sumPositions (x:xs) = foldl (zipWith (+)) (repeat 0) (x:xs) 3) Sees if the columns in a list are even or not: parityColumn :: [Int] -> [Bool] parityColumn [] = [] parityColumn (x:xs) |head(x:xs) `mod` 2 == 0 = True:parityColumn(xs) |otherwise = False:parityColumn(xs) 4) Does the operation or with two boolean lists: bol :: [Bool] -> [Bool] -> [[Bool]] bol [] _ = [] bol (x:xs) (y:ys)= (map (||x) (y:ys)):(bol xs (y:ys)) 5) Correct List: correct :: [[Int]] -> [[Bool]] correct [] = [] correct (x:xs)=(bol(parityLine (x:xs))(parityColumn(sumPositions(x:xs)))) So what I want is to alter the function correct to [[Int]]-[[Int]] that does this: My Int list(x:xs) With my correct function applied [[0,0,1,1], [[True,True,False,True], [1,0,1,1], [True,True,True,True], [0,1,0,1], [True,True,True,True] [1,1,1,1]] [True,True,True,True]] Now I can see that in the first line third column, False, so I have to correct that number 1 to have a number of 1's even. Result I want that function correct does: [[0,0,0,1], [1,0,1,1], [0,1,0,1], [1,1,1,1]] Thanks.

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  • Haskell lists difference

    - by user559354
    I'm trying make a lists difference. Found directly prelude operator \\\\ that makes lists difference. But errors Not in scope: '\\\\' occurs. Here is my simple from command line interpreter: Prelude> ([1,2,3] ++ [5,6]) -- works like expected [1,2,3,4,5,6] prelude> ([1,2,3] \\\\ [1,2]) -- erros occurs <interactive>:1:11: Not in scope: "\\\\" Thanks for explanation where I make a mistake.

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  • find if list 1 is a sequence of list 2 in haskell

    - by Isaak Wahb
    im trying to check if a given list is a subsequence of another list: here are example of lists which gives true: subseq "" "w" subseq "w" "w" subseq "ab" "cab" subseq "cb" "cab" subseq "aa" "xaxa" not (subseq "aa" "xax") not (subseq "ab" "ba") i just come to this but in some cases it gives a wrong result subseq :: Eq a => [a] -> [a] -> Bool subseq [] [] = True subseq [] ys = True subseq xs [] = False subseq (x:xs) (y:ys) = x == y || subseq xs ( 1 `drop` ys )

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  • best way to write a-> ..->[a] recursive functions in haskell

    - by Roman A. Taycher
    So I keep having this small problem where I have something like func :: a -> b -> [a] -- or basically any a-> ...-> [a] where ... is any types -> func x y = func' [x] y -- as long as they are used to generate a list of [a] from x func' :: [a] -> b -> [a] func = undefined --situation dependant generates a list from each element and returns it as one long list should I keep it like this? should I use func' hidden by a where? should I only use the [a] - b - [a] version and leave the responsibility of passing [variable] to the callee? I might well need to compose these functions and might want to mess around with the order so I'm leaning towards option 3. What do you think?

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  • haskell. words into binary numbers

    - by Katja
    I need to convert words into binary numbers. With a bit help of yours I got this blCo::String -> Integer blCo x = num2bin(lett2num x) blCo (x:xs) | x:xs = num2bin(lett2num x):blCo xs num2lett :: Int -> Char num2lett n | (n <= ord 'A') && (n <= ord 'Z') = chr(ord 'A'+ n - 1) | (n <= ord 'a') && (n <= ord 'Z') = chr(ord 'A'+ n - 1) num2bin :: Integer -> String num2bin n | n >= 0 = concatMap show (reverse ( n2b n)) | otherwise = error "num2bin: negative number" where n2b 0 = [] n2b n = n `mod` 2 : n2b (n `div` 2) he tells me a mistake.I dont undertsand it mistake: Couldn't match expected type `Char' against inferred type `String' In the first argument of `lett2num', namely `x' In the first argument of `num2bin', namely `(lett2num x)' In the expression: num2bin (lett2num x)

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  • Haskell Input & Passing Values to Functions

    - by Pradeep
    putStrLn "Enter the Artist Name" art <- getLine putStrLn "Enter the Number of CD's" num <- getLine let test= buyItem currentStockBase art num printListIO (showcurrentList test) the values i have to pass for buyItem is buyItem currentStockBase "Akon" 20 but i want to send "Akon" to art and for 20 i want to send num it gives me this error ERROR file:.\Project2.hs:126 - Type error in application *** Expression : buyItem currentStockBase art num *** Term : num *** Type : [Char] *** Does not match : Int please help me

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  • How do you solve this Haskell problem?

    - by Linda Cohen
    I want to define a function replicate to replicate a list of numbers by its value using only list comprehension, for example: replicate [5,1,3,2,8,1,2] output: [5,5,5,5,5,1,3,3,3,2,2,8,8,8,8,8,8,8,8,1,2,2] I know this would be easy to use the 'replicate' built in function but only list comprehension is allow, how can I do this? THANKS!

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  • Haskell type signature with multiple type somethings (predicates?, for example Eq a =>)

    - by Andrew
    I'm not sure if type predicates is the right term, in fact I've never learned the word for this, so an edit to correct would be helpful - I'm referring to when you give the tipe of function f :: a -> b and you want to say a is a Eq and you say f :: Eq a => a -> b, the name for Eq a => - this is the thing i called a type predicate. My question, though, is how to have multiple of these, so if A is an Eq and B is a Num, I could say either f :: Eq a => a -> b or f :: Num b => a -> b. So, how can I have Eq a => and Num b => at the same time? f :: Eq a => Num b => a -> b, f :: Eq a -> Num b => a -> b, and f :: Eq a, Num b => a -> b all didn't do what I wanted.

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  • Simple haskell splitlist

    - by js7354
    I have the following function which takes a list and returns two sublists split at a given element n. However, I only need to split it in half, with odd length lists having a larger first sublist splitlist :: [a] -> Int -> ([a],[a]) splitlist [] = ([],[]) splitlist l@(x : xs) n | n > 0 = (x : ys, zs) | otherwise = (l, []) where (ys,zs) = splitlist xs (n - 1) I know I need to change the signature to [a] - ([a],[a]), but where in the code should I put something like length(xs) so that I don't break recursion? Thank you.

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  • Haskell: list of elements with class restriction

    - by user1760586
    here's my question: this works perfectly: type Asdf = [Integer] type ListOfAsdf = [Asdf] Now I want to do the same but with the Integral class restriction: type Asdf2 a = (Integral a) => [a] type ListOfAsdf2 = (Integral a) => [Asdf2 a] I got this error: Illegal polymorphic or qualified type: Asdf2 a Perhaps you intended to use -XImpredicativeTypes In the type synonym declaration for `ListOfAsdf2' I have tried a lot of things but I am still not able to create a type with a class restriction as described above. Thanks in advance!!! =) Dak

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  • Nested/Sub data types in haskell

    - by Tom Carstens
    So what would be nice is if you could do something like the following (not necessarily with this format, just the general idea): data Minor = MinorA | MinorB data Major = Minor | MajorB isMinor :: Major -> Bool isMinor Minor = True isMinor _ = False So isMinor MinorA would report True (instead of an error.) At the moment you might do something like: data Major = MinorA | MinorB | MajorB isMinor :: Major -> Bool isMinor MinorA = True isMinor MinorB = True isMinor _ = False It's not terrible or anything, but it doesn't expand nicely (as in if Minor when up to MinorZ this would be terribly clunky). To avoid that problem you can wrap Minor: data Minor = MinorA | MinorB data Major = MajorA Minor | MajorB isMinor :: Major -> Bool isMinor (MajorA _) = True isMinor _ = False But now you have to make sure to wrap your Minors to use them as a Major... again not terrible; just doesn't really express the semantics I'd like very well (i.e. Major can be any Minor or MajorB). The first (legal) example is "Major can be MinorA..." but doesn't have any knowledge of Minor and the second is "Major can be MajorA that takes a Minor..." p.s. No, this isn't really about anything concrete.

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  • Webcast Q&A: Cisco's Platform Approach to Identity Management

    - by Tanu Sood
    Thanks to all who attended the live webcast we hosted on Cisco: Best Practices for a Platform Approach on Wed, March 14th. Those of you who couldn’t join us, the webcast replay is now available. Many thanks to our guest speaker, Ranjan Jain, Security Architect at Cisco for walking us through Cisco’s drivers and rationale for the platform approach, the implementation strategy, results, roadmap and recommendations. We greatly appreciate the insight he shared with us all on the deployment synergies with a platform approach to Identity Management. A forward looking organization, Cisco also has plans for secure cloud and mobile access enablement so it was interesting to learn how the Platform approach to Identity Management today is laying down the foundation for those future initiatives. While we tackled a good few questions during the webcast, we have captured the responses to those that we weren’t able to get to: Q.Can you provide insight into how you approached developing profiles for each user groupA. At Cisco, the user profile was already available to IT before the platform consolidation started. There is a dedicated business team that manages the user profiles. Q. What is the current version of Oracle Identity Manager in the market?A. Oracle Identity Manager 11gR1 is the latest version of our industry leading user provisioning/identity administration solution. Q. Is data resource segmentation part of the overall strategy at Cisco?A. It is but it is managed by the business teams and not at the IT level. Q. Does Cisco also have an Active Directoy LDAP? Do they sync AD from OID or do the provision to AD as another resource?[A. Yes, we do. AD is provisioned using in-house tools and not via Oracle Identity Manager (OIM). Q. If we already have a point IDM solution in place (SSO), can the platform approach still work?A. Yes, the platform approach calls for a seamless, standardized framework for identity management to support the enterprise’s entire infrastructure, both on-premise or in the cloud. Oracle Identity Management solutions are standards based so they can easily integrate and interoperate with existing Oracle or non-Oracle solutions. Hope you enjoyed the webcast and we look forward to having you join us for the next webcast in our Customers Talk: Identity as a Platform webcast series:ING: Scaling Role Management and Access Certification to Thousands of ApplicationsWednesday, April 11th at 10 am PST/ 1 pm ESTRegister Today We are also hosting a live event series in collaboration with the Aberdeen Group. To hear first-hand, the insights from the recently released Aberdeen Report and to discuss the merits of the Platform approach, do join us at this event. You can also connect with Oracle Identity Management SMEs and get your questions answered live. Aberdeen Group Live Event Series: IAM Integrated - Analyzing the "Platform" vs. "Point Solution" ApproachNorth America, April 10 - May 22Register for an event near you And here’s the slide deck from our Cisco webcast:   Oracle_Cisco identity platform approach_webcast View more presentations from OracleIDM

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  • Haskell: What is the difference between $ (dollar) and $! (dollar exclamation point)

    - by Jelle Fresen
    Can anybody explain the difference in Haskell between the operators ($) and ($!) (dollar sign vs dollar sign exclamation point)? I haven't seen the use of $! anywhere so far, but while browsing through the Haskell reference on www.zvon.org, I noticed its existence and that it has the exact same definition as $. When trying some simple statements in a Haskell interpreter (ghci), I couldn't find any difference, nor could I find any reference to the operator in the top listed tutorials when googling for haskell tutorial. So, just out of curiosity, what is the difference, if at all?

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  • Why does this Haskell code produce the "infinite type" error?

    - by Charlie Flowers
    I am new to Haskell and facing a "cannot construct infinite type" error that I cannot make sense of. In fact, beyond that, I have not been able to find a good explanation of what this error even means, so if you could go beyond my basic question and explain the "infinite type" error, I'd really appreciate it. Here's the code: intersperse :: a -> [[a]] -> [a] -- intersperse '*' ["foo","bar","baz","quux"] -- should produce the following: -- "foo*bar*baz*quux" -- intersperse -99 [ [1,2,3],[4,5,6],[7,8,9]] -- should produce the following: -- [1,2,3,-99,4,5,6,-99,7,8,9] intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:y:xs) = x:s:y:intersperse s xs And here's the error trying to load it into the interpreter: Prelude :load ./chapter.3.ending.real.world.haskell.exercises.hs [1 of 1] Compiling Main ( chapter.3.ending.real.world.haskell.exercises.hs, interpreted ) chapter.3.ending.real.world.haskell.exercises.hs:147:0: Occurs check: cannot construct the infinite type: a = [a] When generalising the type(s) for `intersperse' Failed, modules loaded: none. Thanks. EDIT: Thanks to the responses, I have corrected the code and I also have a general guideline for dealing with the "infinite type" error in Haskell: Corrected code intersperse _ [] = [] intersperse _ [x] = x intersperse s (x:xs) = x ++ s:intersperse s xs What the problem was: My type signature states that the second parameter to intersperse is a list of lists. Therefore, when I pattern matched against "s (x:y:xs)", x and y became lists. And yet I was treating x and y as elements, not lists. Guideline for dealing with the "infinite type" error: Most of the time, when you get this error, you have forgotten the types of the various variables you're dealing with, and you have attempted to use a variable as if it were some other type than what it is. Look carefully at what type everything is versus how you're using it, and this will usually uncover the problem.

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  • How to do i18n and create Windows Installer of Haskell programs?

    - by Aufheben
    I'm considering using Haskell to develop for a little commercial project. The program must be internationalized (to Simplified Chinese, to be specific), and my customer requests that it should be delivered in a one-click Windows Installer form. So basically these are the two problems I'm facing now: I18n of Haskell programs: the method described in Internationalization of Haskell programs did work (partially) if I change the command of executing the program from LOCALE=zh_CN.UTF-8 ./Main to LANG=zh_CN.UTF-8 ./Main (I'm working on Ubuntu 10.10), however, the Chinese output is garbled, and I've no idea why is that. Distribution on Windows: I'm used to work under Linux and build & package my Haskell programs using Cabal, but what is the most natural way to create a one-click Windows Installer from a cabalized Haskell package? Is the package bamse the right way to go? ------ Details for the first problem ------ What I did was: $ hgettext -k __ -o messages.pot Main.hs $ msginit --input=messages.pot --locale=zh_CN.UTF-8 (Edit the zh_CN.po file, adding Chinese translation) $ mkdir -p zh_CN/LC_MESSAGES $ msgfmt --output-file=zh_CN/LC_MESSAGES/hello.mo zh_CN.po $ ghc --make Main.hs $ LANG=zh_CN.UTF-8 ./Main And the output was like: This indicates gettext is actually working, but for some reason the generated zh_CN.mo file is broken (my guess). I'm pretty sure my zh_CN.po file is encoded in UTF-8. Plus, aside from using System.IO.putStrLn, I also tried System.IO.UTF8.putStrLn to output the string, which didn't work either.

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  • Openmatics Revolutionizes Fleet Management with Standards-Based Vehicle Telematics Platform

    - by Michael Snow
    Openmatics s.r.o. was founded in 2010 as a subsidiary of ZF Friedrichshafen AG, a global player in driveline and chassis technology. Oracle Customer:  Openmatics s.r.o.Location:  Pilsen, Czech RepublicIndustry:  AutomotiveEmployees:  70 Its goal was to develop and operate a flexible, open telematics platform for automotive applications, which is independent from vehicle and component suppliers—recognizing that the fragmented telematics market was not meeting today’s fleet management needs. Openmatics provides a rich product portfolio, and customers can extend the platform, as required, to meet their needs. Partners and third-parties can develop their own applications using the Openmatics’ software development kit and can sell them via the Openmatics app shop.ZF Friedrichshafen AG is a global player in driveline and chassis technology. With 121 production companies and 650 service partners in 26 countries, ZF is among the top 10 largest automotive suppliers worldwide. Founded in 1915 to develop and produce transmissions for airships and vehicles, the group’s product offerings now include transmissions and steering systems as well as chassis components and complete axle systems and modules.  A word from Openmatics s.r.o.  “Oracle WebCenter Portal, together with the underlying Oracle Application Development Framework, provided the fundamental infrastructure for the Openmatics platform. Fleet managers can now reduce fuel consumption and operating costs, and more efficiently manage vehicle usage, maintenance, and safety. The standards-based platform allows third-party suppliers to deploy their own vehicle telematics services as Openmatics apps and creates a de facto standard for the automotive industry, independent from a single manufacturer or service provider.” – Gero Strobel, Head of Development, Openmatics s.r.o. Challenges Create an industry standard for vehicle telematics by establishing a customizable platform that enables access to telematics information, such as current and past fuel consumption, through a web browser to better meet automotive market and customer needs Reduce fleet-management costs by eliminating the need to invest in isolated telematics hardware and software solutions per vehicle brand and vehicle component manufacturer Establish an open platform where third-party providers—such as original equipment manufacturers (OEM), insurers, fleet operators, and individual developers—can deploy their own vehicle telematics services Allow users to purchase targeted telematics services as single apps to reduce costs and ensure rapid growth of telematics services available on the platform Enable users to configure their telematics apps with ease to make sure the platform meets individual fleet management requirements, such as analyzing past and current fuel consumption of a truck fleet Solutions Deployed Oracle WebCenter Portal as a foundation for Openmatics, a standards-based automotive telematics platform that provides next-generation fleet management with unified digital communication from and to vehicles on the move Used Oracle Application Development Framework as the development framework for Oracle WebCenter Portal’s components and services, providing developers with ready-to-use software development kits with application programming interfaces, design templates, and visual tools that accelerated time to market Used Oracle Enterprise Pack for Eclipse to simplify telematics application development in Java Enabled fleet monitoring by recording vehicle data—such as fuel consumption information—through onboard units, delivering the information to Oracle Database, and making it accessible through a customizable app portfolio on any web browser Stored vehicle telematics data—sent as encrypted information—in Oracle Database, ensuring data integrity and immediate availability for the platform’s telematics applications Enabled a wide range of telematics services suppliers, from vehicle component manufacturers to fleet application developers, to offer vehicle telematics services on the Openmatics platform, ensuring platform independence from OEMs Provided Openmatics customers with the means to individually select the automotive telematics services that are relevant to their business requirements, eliminating the need to pay for superfluous information and reducing fleet management costs Oracle Products & Services Oracle Application Development Framework Oracle WebCenter Portal Oracle SOA Suite Oracle Enterprise Pack for Eclipse Oracle Database Oracle Consulting &amp;amp;amp;amp;amp;amp;amp;&amp;amp;amp;amp;amp;lt;span id=&amp;amp;amp;amp;amp;quot;XinhaEditingPostion&amp;amp;amp;amp;amp;quot;&amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;gt;amp;&amp;amp;amp;amp;amp;amp;lt;span id=&amp;amp;amp;amp;amp;amp;quot;XinhaEditingPostion&amp;amp;amp;amp;amp;amp;quot;&amp;amp;amp;amp;amp;amp;gt;&amp;amp;amp;amp;amp;amp;lt;/span&amp;amp;amp;amp;amp;amp;gt;lt;p&amp;amp;amp;amp;amp;amp;amp;amp;gt; &amp;amp;amp;amp;amp;amp;amp;amp;lt;/p&amp;amp;amp;amp;amp;amp;amp;amp;gt;

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  • Developing cross platform mobile application

    - by sohilv
    More and more mobile platforms are being launched and sdk's are available to developers. There are various mobile platform are available, Android,iOS,Moblin,Windows mobile 7,RIM,symbian,bada,maemo etc. And making of corss platform application is headache for developers. I am searching common thing across the platforms which will help to developers who want to port application to all platforms.Like what is the diff screen resolution, input methods, open gl support etc. please share details that you know for the any of platform . or is there possibilities , by writing code in html (widget type of thing) and load it into native application. I know about the android , in which we can add the web view into application. by calling setContentView(view) Please share the class details where we can add the html view into native application of different type of platforms that you know. Purpose of this thread is share common details across developers. marking as community wiki. Cross platform tools & library XMLVM and iSpectrum (cross compile Java code from an Android app or creating one from scratch Phone Gap (cross platform mobile apps) Titanium (to build native mobile and desktop apps with web technologies) Mono Touch ( C# for iphone ) rhomobile - http://rhomobile.com/ samples are here: http://github.com/rhomobile/rhodes-system-api-samples Sencha Touch - Sencha Touch is a HTML5 mobile app framework that allows you to develop web apps that look and feel native on Apple iOS and Google Android touchscreen devices. http://www.sencha.com/products/touch/ Corona - Iphone/Ipad / Android application cross platform library . Too awesome. http://anscamobile.com/corona/ A guide to port existing Android app to Windows Phone 7 http://windowsphone.interoperabilitybridges.com/articles/windows-phone-7-guide-for-iphone-application-developers

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  • portable cross-platform WebDAV Client

    - by theduke
    I am looking for a portable application that will allow me to do this: Browse a WebDAV share and open a file. Edit the file locally. Save the file, and automatically propagate the change to WebDAV. Is there any CROSS-PLATFORM application out there that will let me do this and exists as a portable? The reason I need this functionality is that I regularily have to access files via WebDAV from public machines where I do not have the neccessary permissions to natively mount a webdav share, or to install the neccessary components.

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  • Ur/Web new purely functional language for web programming?

    - by Phuc Nguyen
    I came across the Ur/Web project during my search for web frameworks for Haskell-like languages. It looks like a very interesting project done by one person. Basically, it is a domain-specific purely functional language for web programming, taking the best of ML and Haskell. The syntax is ML, but there are type classes and monad from Haskell, and it's strictly evaluated. Server-side is compiled to native code, client to Javascript. See the slides and FAQ page for other advertised advantages. Looking at the demos and their source code, I think the project is very promising. The latest version is something 20110123, so it seems to be under active development at this time. My question: Has anybody here had any further experience with it? Are there problems/annoyances compared to Haskell, apart from ML's slightly more verbose syntax? Even if it's not well known yet, I hope more people will know of it. OMG this looks very cool to me. I don't want this project to die!!

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  • OS choice for functional developing

    - by Carsten König
    I'm mainly a .NET developer so I normaly use Windows/VisualStudio (that means: I'm spoiled) but I'm enjoying Haskell and other (mostly functional) languagues in my spare time. Now for Haskell the windows-support is ok (you can get the Haskell-Platform) but latley I tried to get a basic Clojure/Scheme environment set up and it's just a pain on windows. So I'm thinking about trying out another OS for better tooling and languague support. Of course that leaves me with MacOS or some Linux distribution. I never used MacOS before and of course Linux would be cheaper (free) and I don't think I can parallel-boot MacOS on your normal PC-Hardware (can you?). PLUS: I don't have a clue about the tools you can use on those (to me) forign OSs. To make it short: I want to explore more Haskell, Clojure, Scala, Scheme and of course need at least good tooling for JavaScript/HTML5/Css. Support for .NET/Mono/F# would be great but for this I will still have my Win7 boot. So I like to know: - what is your prefered OS, Distribution (is Ubuntu viable?) - what Editor/IDE are you using Thank you for your help! PS: I'm not sure if this is the right place for this question but I surely hope so - if not please let me know where I should move this to (StackOverflow don't seem to be the right place IMHO)

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