- Haskell-Cafe - Haskell.org

Prolog-style patterns
by Jan Stolarek 09 Apr '13

09 Apr '13

Hi all, consider this simple reimplementation of 'elem' function: member :: Eq a => a -> [a] -> Bool member _ [] = False member y (x:xs) | x == y = True | otherwise = member y xs If Haskell allowed to write pattern matching similar to Prolog then we could write this function like this: member :: Eq a => a -> [a] -> Bool member _ [] = False member x (x:_) = True member x (_:xs) = member x xs The meaning of pattern in the second equation is "match this equation if the first argument equals to head of the list". Many times I have found myself instinctively writing patterns in this way, only to get a compilation error. I was thinking about implementing language extension for GHC that would allow to write Prolog-style patterns. Would there be an interest in such an extension? Also, if I missed something obvious please let me know. Janek

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Can any hackage library do JWT signing
by Ryan Newton 09 Apr '13

09 Apr '13

I want to enable a Haskell benchmarking bot that would upload its data to a Google Fusion Table each time it runs. That seems to require the "service-to-service" mode for Google's OAuth2: https://developers.google.com/accounts/docs/OAuth2ServiceAccount There are a bunch of libraries on Hackage for different flavors of OAuth. But I haven't yet found one that handles this signing of JWT headers and claimsets. Is there something I'm missing? Thanks, -Ryan

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Re: [Haskell-cafe] [Caml-list] Vector Fabrics is hiring!
by Alexey Rodriguez 09 Apr '13

09 Apr '13

Hi Phil, I am posting this on behalf of Martijn Rutten. Cheers, Alexey 8-<--------------- Fair point. When we started the company in 2007, the experts in Silicon Valley told us that our ambition to develop tools to create an efficient, parallel embedded system from sequential C and C++ code is the "holy grail" of embedded system design. In the same sentence, they told us it could not be done. It is widely acknowledged as well as debated that there can be an order of magnitude difference between a real good and an average programmer (http://programmers.stackexchange.com/questions/14052/is-there-such-a-thing-…)) Often these talented programmers are called a "rockstar", "free electron" (http://www.randsinrepose.com/archives/2005/03/20/free_electron.html) or just plain "awesome" for their ability to quickly sort out the many trade-offs in software architecture and design. Without these talented programmers to design and implement the algorithms to make sense out of the literally millions of data dependencies that can make or break parallelism, our company's vision would still be just that: a vision. You are right, if the talent comes with a rockstar's ego, forget it. No matter how smart, you are always part of a team. As for craftsmanship, what we did learn is the huge difference between functional programming and imperative programming. Our analysis engine is fully written in OCaml. Obviously that allowed us to focus on the algorithmic problems at hand without ever wasting time in debugging stray pointers (the one week debugging such a Heisenbug was spent in the few hundred lines of C interfacing with OCaml). I am sure I am preaching to the choir here when I say we learned that thinking functionally allowed us to much better reason at the algorithmic level and we generally wrote significantly cleaner and more reliable code. My 2 cents, Martijn Rutten, Co-founder of Vector Fabrics. On Mon, Apr 8, 2013 at 10:09 PM, Phil Tomson <philtomson(a)gmail.com> wrote: > On Sunday, April 7, 2013 10:30:40 PM UTC-7, Stefan Holdermans wrote: > >> >> * Your friends and colleagues describe you as a "rockstar" programmer; >> >> your programming ability is way above average; >> > > I thought we (as in industry) were over this "rockstar programmer" thing? What does a "rockstar" do? S/He breaks guitars when not happy. Rockstars are petulant and hard to work with. We need less rockstars and more craftspeople. > > Just my 2 cents. > > Phil > -- Alexey Rodriguez Yakushev O +31 (0)40 8200960 | D + 31 (0)40 8200974 | F +31 (0)40 8200979 Vonderweg 22, 5616 RM | Eindhoven | The Netherlands www.vectorfabrics.com | alexey(a)vectorfabrics.com On Mon, Apr 8, 2013 at 10:09 PM, Phil Tomson <philtomson(a)gmail.com> wrote: > On Sunday, April 7, 2013 10:30:40 PM UTC-7, Stefan Holdermans wrote: > >> >> * Your friends and colleagues describe you as a "rockstar" programmer; >> >> your programming ability is way above average; >> > > I thought we (as in industry) were over this "rockstar programmer" thing? What does a "rockstar" do? S/He breaks guitars when not happy. Rockstars are petulant and hard to work with. We need less rockstars and more craftspeople. > > Just my 2 cents. > > Phil > -- Alexey Rodriguez Yakushev O +31 (0)40 8200960 | D + 31 (0)40 8200974 | F +31 (0)40 8200979 Vonderweg 22, 5616 RM | Eindhoven | The Netherlands www.vectorfabrics.com | alexey(a)vectorfabrics.com

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[Conduit] weird action of leftover.
by Magicloud Magiclouds 09 Apr '13

09 Apr '13

Say I have code like below. If I comment the leftover in main, I got (Just "L1\n", Just "L2\n", Just "L3\n", Just "L4\n"). But if I did not comment the leftover, then I got (Just "L1\n", Just "L1\n", Just "", Just "L2\n"). Why is not it (Just "L1\n", Just "L1\n", Just "L2\n", Just "L3\n")? takeLine :: (Monad m) => Consumer ByteString m (Maybe ByteString) takeLine = do mBS <- await case mBS of Nothing -> return Nothing Just bs -> case DBS.elemIndex _lf bs of Nothing -> return $ Just bs Just i -> do let (l, ls) = DBS.splitAt (i + 1) bs leftover ls return $ Just l main = do m <- runResourceT $ sourceFile "test.simple" $$ (do a <- takeLine leftover $ fromJust a b <- takeLine c <- takeLine d <- takeLine return (a, b, c, d)) print m -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

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[haskell.org Summer of Code 2013] We're In!
by Edward Kmett 08 Apr '13

08 Apr '13

We (haskell.org) have been officially accepted into the Google Summer of Code for 2013. We should show up in the mentoring organization list as soon as I get some information we need to finalize the listing. Shachaf Ben-Kiki has volunteered to help out as our backup org administrator this year. If you are thinking about joining up as a mentor or a student this year, now would be a good time to start brainstorming about project ideas! I'll follow up with more information as soon as the listing goes in. In the meantime there is the #haskell-gsoc channel on irc.freenode.net. Feel free to pester me (or Shachaf) with questions! -Edward Kmett

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llvm-3.0.1.0 installation on Mac
by Luke Evans 08 Apr '13

08 Apr '13

I'm trying to get LLVM 3.0 installed and then have the llvm-3.0.1.0 package install and bind against it with cabal. I'm on a recent 64 bit Mac which shows up in various messages like: "Target platform inferred as: x86_64-apple-darwin" I was advised on the Haskell IRC channel to install a 3.0 LLVM from a location like MacPorts first, then point cabal at the location where LLVM was installed with the appropriate config option. So, I did a "sudo ./port install llvm-3.0", and everything seemed to proceed fine. Then I did: cabal install llvm --configure-option=--with-llvm-prefix=/opt/local/libexec/llvm-3.0 This looks promising (compared to missing the config option), but eventually this happens: Building llvm-base-3.0.1.0... Preprocessing library llvm-base-3.0.1.0... dyld: Library not loaded: /Users/ian/zz64/ghc-7.4.2/libffi/build/inst/lib/libffi.5.dylib Referenced from: /private/var/folders/tz/vlbc03q5333897z201hkmcb40000gn/T/llvm-base-3.0.1.0-3941/llvm-base-3.0.1.0/dist/build/LLVM/FFI/Analysis_hsc_make Reason: image not found running dist/build/LLVM/FFI/Analysis_hsc_make failed (exit code 5) command was: dist/build/LLVM/FFI/Analysis_hsc_make >dist/build/LLVM/FFI/Analysis.hs Failed to install llvm-base-3.0.1.0 I have no idea where "/Users/ian/..." is coming from! My cabal-fu is extremely weak, so I'll plug on and see if I can figure out how cabal's analysis/build might be going wrong here. I'd be very grateful for any clues though! -- Luke

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%==%, :==: and type equality in the singletons library
by Paul Brauner 08 Apr '13

08 Apr '13

Hello, from the output of -ddump-splices I dont think it is the case but I'm asking anyway: is there any way to deduce a ~ b from a :==: b? Given data T = C1 | ... | Cn I can easily derive data EqT :: T -> T -> * where EqT :: a ~ b => EqT a b eqT :: ST a -> ST b -> Maybe (EqT a b) eqT SC1 SC1 = Just EqT ... eqT SCn SCn = Just EqT eqT _ _ = Nothing but this kind of replicates the boilerplate generated by the singletons library for %==%. However I can't see how to leverage %==% to inhabit eqT since I can't deduce a ~ b from a %==% b == STrue. Any idea? If there's no way to write eqT using what singletons generates, wouldn't it make sense for it to generate something that relates :==: and ~ ? Cheers, Paul

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Re: [Haskell-cafe] Prolog-style patterns
by Stephen Tetley 08 Apr '13

08 Apr '13

This is a recurring theme, see also here: http://www.haskell.org/pipermail/haskell-cafe/2009-May/061498.html On 8 April 2013 16:53, Tom Murphy <amindfv(a)gmail.com> wrote: > > Also, for some history, this was discussed a while back: > http://www.mail-archive.com/haskell@haskell.org/msg03721.html >

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My first Haskell program
by John Wood 08 Apr '13

08 Apr '13

Hello, Cafe I'm new to Haskell and the mailing list, and am wondering if I could get some feedback on my first program -- a Markov text generator. The code is posted here:http://codereview.stackexchange.com/questions/24791/haskell-markov-tex… Thanks, John;

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Vector Fabrics is hiring!
by Stefan Holdermans 08 Apr '13

08 Apr '13

[Apologies for multiple postings.] Vector Fabrics is hiring: we are looking for a top-notch programmer to extend our program-analysis and parallelization products. You design and implement algorithms to assist the programmer to create a parallel design from a sequential C or C++ program. You work with our international team of world-class computer scientists and experts in the Haskell / OCaml functional programming languages. Your work is at the forefront of technology, giving you the opportunity to publish your work in major conferences and directly cooperate with processor design companies and domain-specific application vendors. As we are a startup company, you will quickly have a major impact on our products and get to know all aspects of product creation. You will be part of a strongly committed development team and contribute to our agile development process and automated test suites. Interested? Send your CV, GitHub account or other proof of what you can do to jobs(a)vectorfabrics.com. RESPONSIBILITIES * Design and implement software optimization (e.g. parallelization) algorithms for CPUs and GPUs; * Thoroughly test your code, create automated test suites; * Contribute to our agile development planning and process; * Analyze complex customer applications for optimization opportunities and translate this to new analysis algorithms. PROFILE * Your friends and colleagues describe you as a "rockstar" programmer; your programming ability is way above average; * Demonstrable experience in design and implementation of complex software applications; prior experience in functional programming languages is preferred; * You continuously surprise us with your creative yet pragmatic solutions for complex software problems; * You are strongly committed to deliver working software as early as possible; * You work against very high quality standards. Refactoring is your bread and butter, pair-programming is how you prefer to review your code; * Whatever technologies, languages, or development environments you've been using, we expect you have mastered them in depth, and we expect that you will be able to master any technology, language, or development environment that we need in the future; * You are not afraid to get your hands dirty on low-level code, hijack a malloc() call in the standard C library, port the latest gdb debugger to Android on a jail-broken tablet? You get it done. * Excellent command of written and spoken English. EDUCATION MSc, MEng or PhD in Computer Science or significant relevant experience. ABOUT VECTOR FABRICS Vector Fabrics is a high-tech software company, developing tools for embedded multicore programming. Its technology and expertise is getting widespread recognition in the industry as being innovative and unique in their ability to address heterogeneous multicore application-specific silicon platforms. Due to the advanced nature of its tools, Vector Fabrics operates at the forefront of the next generation of embedded platforms for diverse markets ranging from supercomputers to automotive to cell phones. Vector Fabrics puts absolute priority on hiring top class individuals in key positions. Vector Fabrics’ team profile is exceptional and its ambition is to hire only individuals that match or surpass that profile. The company pays top salary and offers a challenging, engaging and stimulating work environment with a high degree of responsibility.

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