- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Nice clean code example?
by Chris Wong 30 Jun '17

30 Jun '17

How about Hackagebot? https://github.com/lfairy/hircine/blob/master/brigitte/Hackagebot.hs https://github.com/lfairy/hircine/blob/master/brigitte/Utils.hs It involves a lot of concurrency, networking, and data structure manipulation -- all areas Haskell excels in. It avoids using advanced features as well (except maybe pattern synonyms, but those aren't visible in the code that uses them) Here are some numbers: its sibling Cargobot boasts 3+ months continuous uptime, with memory usage never going beyond 12 MB. It has never crashed. I expect Hackagebot to have similar metrics. On Jul 1, 2017 06:34, "Han Joosten" <han.joosten.han(a)gmail.com> wrote: I'd like to showoff some nice Haskell code to a CTO with no experience with FP. I promised to send him a small piece of Haskell so he could get an idea. The code should be easy to read, without obscure looking operators (so sorry, no lens, arrows stuff like that), optionally even do something interesting. Who has the nicest example laying around? (and yes, I need it by yesterday ;-) ) Thanks! _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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Dynamically linking frameworks on macOS
by Ryan Trinkle 30 Jun '17

30 Jun '17

Hi everyone, I'm trying to ensure that beginner-level code that uses reflex-dom can be built by simply calling 'ghc myFile.hs', provided that all the necessary libraries are available in ghc-pkg. This works on linux, but on macOS, it's currently necessary for the user to add '-dynamic' to the command line. In particular, without -dynamic, the linker fails to find "_OBJC_CLASS_$_NSURL", which is a symbol in the Foundation system framework. Apple doesn't support (and strongly discourages) statically linked executables[1], so it's not terribly surprising that this doesn't work. Is there anything I can do to avoid the need for -dynamic here? Thanks, Ryan [1] https://developer.apple.com/library/content/qa/qa1118/_index.html

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Domain specific error diagnosis in Haskell, a proposal
by Alejandro Serrano Mena 30 Jun '17

30 Jun '17

Dear Haskellers, Some days ago Jurriaan Hage posted a video of our work on adding custom type error diagnosis to GHC. Here is a GHC proposal for incorporating this support in the mainline compiler: https://github.com/ghc-proposals/ghc-proposals/pull/59 Suggestions, criticisms and ideas are welcome. Alejandro

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Source code location in IO?
by Tom Ellis 30 Jun '17

30 Jun '17

Is it compatible with the semantics of Haskell to have a function sourceLocation :: IO String which when run returns the source file location at which it is used? For example, suppose Main.hs is module Main where main = do putStrLn =<< sourceLocation putStrLn "Hello" putStrLn =<< sourceLocation It would print the following when run Main.hs:4 Hello Main.hs:6 and module Main where main = do let s = sourceLocation putStrLn =<< s putStrLn "Hello" putStrLn =<< s It would print the following when run Main.hs:4 Hello Main.hs:4 If this is not compatible with the semantics of Haskell, why not? I agree that the two programs must have the same denotation, but is there anything that requires them to have the same output when run? Tom

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Problem with pipe/Is there a function that "lifts" functions to Producers?
by Cody Goodman 30 Jun '17

30 Jun '17

Hi all, I have a function from Text -> Text which I want to apply to each line using pipes-text and pipes-group. I'm pretty sure my pipe is not doing what I expect. I'm going back over the pipes tutorial now, but I think I could use some help figuring it out. I have the following (buildable github project: https://github.com/codygman/fixedWidthToDelimited) code: import Data.Monoid import Pipes import qualified Pipes.Text as Text import qualified Pipes.Text.IO as Text import System.IO import Lens.Family import qualified Pipes.Group as Group import qualified Data.Text as T appendAt :: Int -> T.Text -> T.Text -> (T.Text,T.Text) appendAt i appendBS bs = let (first, rest) = T.splitAt i bs in (first <> appendBS <> rest,rest) -- TODO figure out how to test a pipe (I'm sure pipes-text or any other libraries test their pipes) toDelimPipe :: Monad m => [Int] -> Pipe T.Text T.Text m r toDelimPipe offsets = do chunk <- await let text = (fixedWidthLine offsets) chunk if T.null text then (toDelimPipe offsets) else do yield text cat fixedWidthLine :: [Int] -> T.Text -> T.Text fixedWidthLine offsets bs = fst $ go offsets ("" :: T.Text,bs) where go :: [Int] -> (T.Text,T.Text) -> (T.Text,T.Text) go [] x = x go (x:xs) (acc,rest) = let (newAcc,newRest) = T.splitAt x rest in go xs (acc <> (fst $ appendAt x "|" newAcc),newRest) {- got: runEffect $ over Text.lines (Group.maps (>-> toDelimPipe [2,2,2] )) (Text.fromLazy (LT.replicate 2 "x" <> LT.replicate 2 "y" <> LT.replicate 2 "z")) >-> Text.stdout xx|||yyzz Expected: xx|yy|zz| When I use fixedWidthLine alone with the same offsets I get: λ> fixedWidthLine [2,2,2] (T.replicate 2 "x" <> T.replicate 2 "y" <> T.replicate 2 "z") "xx|yy|zz|" I think my pipe is wrong -}

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on the {lambda way}
by marty.alain 29 Jun '17

29 Jun '17

Dear Haskell-Café mailing list, Please excuse me if the Haskell-Café is not the appropriate place to post this question in but, following the advice of M. Simon Peyton Jones, I would like to know if one of you could tell me his opinion about such a work - http://lambdaway.free.fr/lambdaway/data/lambdatalk_20170615.pdf a PDF file directly printed from this wiki page - http://lambdaway.free.fr/lambdaway/?view=oxford introducing an “iconoclastic” approach detailed in long in this workshop - http://lambdaway.free.fr/ transforming a web markup syntax into a small functional programming language that an eleven years old child could understand: - http://lambdaway.free.fr/lambdaway/?view=teaching Best regards Alain Marty engineer architect

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Issue 61 :: Haskell Weekly
by Taylor Fausak 29 Jun '17

29 Jun '17

\ Haskell Weekly \/\/ Issue 61 <https://haskellweekly.news/issues/61.html> Welcome to another issue of Haskell Weekly! Haskell is a purely functional programming language that focuses on robustness, concision, and correctness. This is a weekly summary of what's going on in its community. ## Featured ## - Haxl: Making concurrency unreasonably easy <http://events.techcast.com/bigtechday10/Garmisch-1345/> > Haxl is a big hammer for doing I/O concurrently, testing I/O, and modularity (caching & memoization). - Introduction to Brick <https://samtay.github.io/articles/brick.html> > I'm going to give a short introduction to Brick, a Haskell library for building terminal user interfaces. So far I've used brick to implement Conway's Game of Life and a Tetris clone. I'll explain the basics, walk through an example snake application, and then explain some more complicated scenarios. - Simplexhc: An STG to LLVM compiler <https://pixel-druid.com/blog/announcing-simplexhc/> > STG's lowering to C-- and the decisions taken when implementing it were based in the '90s. That's not to say that the GHC team hasn't done an awesome job keeping it up to date; they have! But, I wonder what a complete rewrite of this lowering would look like. Hence, I'm trying to experiment in this space and see what happens. - Front Row is hiring a senior backend Haskell engineer <https://frontrow.workable.com/j/463B843754> > Come change how 6.5+ million K-12 US students learn Math, Language Arts, Social Studies and more. Use data, advanced type systems, great product design and deep pedagogy to change lives. - Threading responsibly: `forkIO` considered harmful <http://mazzo.li/posts/threads-resources.html> > In this post I want to argue that threads are also a resource, in the sense that they require management after we've created them. A stray thread will consume memory, CPU cycles, and really whatever resource it might need to execute. - The `Has` type class pattern <https://medium.com/@jonathangfischoff/the-has-type-class-pattern-ca12adab70…> > The value in this approach is that I don't have to think about what functions to call to collect the images: it's always `images`. In the prior example, I had to think about the how to collect the images each time, and it took brain power better spent elsewhere. - A tale of two brackets <https://www.fpcomplete.com/blog/2017/06/tale-of-two-brackets> > I hope the primary thing you take away from it is a deeper understanding of how monad transformer stacks interact with operations in the base monad, and how monad-control works in general. - `RecordWildCards` and binary parsing <https://jship.github.io/posts/2017-06-24-record-wildcards-and-binary-parsin…> > `RecordWildCards` is a GHC extension that makes working with Haskell records more convenient. The extension has been blogged about in a few places already, so this post intends to provide a different motivating example: binary parsing. - On naming things: Library design <http://www.parsonsmatt.org/2017/06/23/on_naming_things.html> > I've written a few libraries now and have tried out different naming and exporting conventions. I've developed a bit of a feel for how it is to write and use them, and I'm going to put out my personal preferences and opinions on library design here. - Haskell Bits #6: A guide to mutable references <http://www.kovach.me/posts/2017-06-22-mutable-references.html> > There are quite a few ways to store mutable data in Haskell. Let's talk about some of them! Specifically, we will focus on mutable containers that store a single value that can be modified by one or more threads at any given time. I'm not going to go into a ton of detail here --- I just want to give an overview. - Interfaces and type classes: Number APIs in C# and Haskell <https://mzabani.wordpress.com/2017/06/22/interfaces-and-typeclasses-number-…> > In C# sometimes I sorely miss something like an `INumber<T>` interface with methods add, subtract, multiply, and others. The lack of this means it is cumbersome to write generic code on numbers. ## Package of the week ## This week's package of the week is data-has, a library that provides a simple extensible product system. <https://www.stackage.org/lts-8.20/package/data-has-0.2.1.0> ## In brief ## - Announcing haskus-system 0.7 <http://hsyl20.fr/home/posts/2017-06-29-announcing-haskussystem-07.html> - Defeating evil with data structures <https://mmhaskell.com/blog/2017/6/26/fun-with-data-structures> - stack2nix first public release <https://mailman.science.uu.nl/pipermail/nix-dev/2017-June/024011.html> - Streaming combinators and extracting flat parallelism <https://futhark-lang.org/blog/2017-06-25-futhark-at-pldi.html> - Typing Nix <https://www.tweag.io/posts/2017-05-23-typing-nix.html> - When competing with C, fudge the benchmark <https://medium.com/@n0mad/when-competing-with-c-fudge-the-benchmark-16d3a91…> ## Events ## - Berlin Functional Programming Group's first meeting July 1 <https://www.meetup.com/Berlin-Functional-Programming-Group/events/241040383/> - Haskell.SG's July meetup July 5 <https://www.meetup.com/HASKELL-SG/events/240959693/>

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dsl for atari 2600 vcs?
by Raoul Duke 29 Jun '17

29 Jun '17

Along the lines of atom & ivory & tower, has anyone (I haven't turned up any hits online so I guess not) worked on a dsl in haskell for generating racing-the-beam code? Feels like all the book keeping might be something haskell could do, giving a dsl that is more high level than manual mental cycle counting.

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[ANN] haskus-system 0.7
by Sylvain Henry 29 Jun '17

29 Jun '17

Hi all, I have released haskus-system 0.7. haskus-system <https://github.com/haskus/haskus-system> is a Haskell library for system programming on top of the Linux kernel. You can use it to build systems that only use: * the Linux kernel * the haskus-system library * your code This release features a new build tool that automatically downloads, configures and builds Linux, SysLinux, etc. It can also execute your system within QEMU, build ISO images and even create bootable devices. For instance, to test the Demo example from https://github.com/haskus/haskus-system-examples/ with QEMU, you just have to type: > haskus-system-build test --init Demo The full announce with some screenshots and a video: http://hsyl20.fr/home/posts/2017-06-29-announcing-haskussystem-07.html Cheers, Sylvain

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[ann] hp2pretty-0.8
by Claude Heiland-Allen 29 Jun '17

29 Jun '17

Hi all, hp2pretty is a program to graph heap profiles output by Haskell programs compiled by GHC. New features in this 0.8 release: * --sort size|stddev|name and --reverse to change output order * --trace [percent] and --bands [count] to adjust output bands * --pattern to fill with patterns instead of solid colour The last option should help a lot if you want to print without using too much ink. More information and pictures exhbiting the new features: https://mathr.co.uk/blog/2017-06-29_hp2pretty-0.8_released.html There were also minor changes in the 0.7 release (earlier this week): * parsing bugfix (don't use `read` to drop quotes) thanks to Pepe Iborra * don't stroke text (fill is enough) * use HTTPS in the packaging hp2pretty still misses features from hp2ps including: * monochrome output * multipage (separate page for key) * page size options * header size options * (encapsulated) Postscript support (hp2pretty is still SVG-only) Another feature that might be nice is: * choose font(s) from command line, to be consistent across a document Patches welcome, or even just votes for which features would be most useful to you so I can prioritise my efforts next time I feel like hacking on it. Thanks, Claude -- https://mathr.co.uk

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[ANN] Compose :: Melbourne, 2017, Call for Presentations Extension - Monday, 10th of July
by Lyndon Maydwell 29 Jun '17

29 Jun '17

Hi All! We're extending the Compose :: Melbourne CFP until Monday, 10th of July. Details follow: (Web version: http://www.composeconference.org/2017-melbourne/cfp/) # Compose :: Melbourne Call for Presentations Compose :: Melbourne - http://www.composeconference.org/ - was closing its call for presentations at the end of the month... BUT, now we are extending the CFP until Monday, 10th of July, 2017! Submit your presentation proposal here: https://easychair.org/conferences/?conf=cmc20170 ## About Compose :: Melbourne Compose :: Melbourne is a functional-programming conference returning for its second year which is focused on developing the community and bringing functional-programming to a wider audience. It is a 2-day event being held in Melbourne, Australia on the 28th and 29th of August 2017 at RMIT University. The first day will feature a single track of presentations followed by a second day of workshops and unconference. Compose :: Melbourne is the sister-conference of the NY based Compose :: Conference. # Important Dates - CFP Extended Until - Monday 10th July, 2017 - Notify Presenters - July 20th, 2017 - Conference Day 1: Presentations - Monday, 28th August, 2017 - Conference Day 2: Unconference - Tuesday, 29th August, 2017 # Talk and Workshop Submission ## Day 1 - Presentations Submit a Presentation Proposal via Easy Chair: https://easychair.org/conferences/?conf=cmc20170 ## Day 2 - Unconference and Workshops Contact us (composemel-admin(a)googlegroups.com) with your workshop proposals, or talk-ideas. Although we don't require ahead-of-time talk information, if you tell us about your unconference talk, we will promote it! # Submission Guidelines Talk slots will be 30 minutes: 25 minute talk and 5 minutes for questions. Provide sufficient detail in your submission to enable the reviewers to understand your proposal and clearly identify what an attendee will gain from attending your session. You should include the following information in the submission system: - Authors - The details of each of the presenters - Title - Title of the presentation (please keep it brief and specific) - Abstract - A 300-500 word description of your presentation, ideally including... - Description of the content - Keywords - List any keywords that will help the program committee and attendees categorise your presentation. For example: proofs, Haskell, music. Please keep the content of your talk on-topic and do not use this speaking opportunity as a sales pitch. # Feel We want Compose Melbourne to be all about the community. We're aiming to help foster the growth of Functional Programming in Melbourne and unite all interested parties to spark a unified presence and a feeling of camaraderie amongst FP and Theory proponents in this wonderful city! Talks should help inspire and promote this goal. # Audience Functional-Programming and Programming-Language-Theory professionals and enthusiasts. Newcomers, experts, anyone from other disciplines of fields who is interested in what FP is or how it could help them with their work, or simply make life more enjoyable! # Diversity Just like Compose-Conference, we would also like to put an emphasis on soliciting a diverse set of speakers - anything you can do to distribute information about this CFP and encourage submissions from under-represented groups would be greatly appreciated. We welcome *all* (new and established) contributions and encourage you to apply! # Day One ## Keynote Day One will kick-off with a mind-blowing excursion into the realm of function live-coded music artistry by the living legend, Andrew Sorensen! Look him up on YouTube! ## Talks All topics for proposals for presentations are invited, but not limited to explore the following topics: ## New Languages The development of new and emerging Functional Languages, and the toolsets around them. ## Libraries and Tools Exploring the use and development of new and underrepresented tools and libraries. ## Production Systems 2017 continues the trend of many previously undeployed languages and systems breaking through into production. We're looking for war-stories, success-stories and sob-stories! ## Theory Theory is the cutting edge of new functional programming. Show the world what is rising over the horizon. ## Art and Music Exciting and innovative usage of functional programming language in the arts! # Day Two The second day will be dedicated to workshops and unconference. ## Workshops If you wish to run a workshop on the second day of the conference, then please let us know. Alternatively, if there is a workshop that would interest you as an attendee, then please also let us know. Last year, there were 5 workshops, including: * Intro to Haskell * FreeMonad FreeApplicative FreeWorkshop * Writing games for Android in Haskell * Intro to Purescript * Intro to the J language ## Unconference Got something random you want to talk about? The unconference will run the second day. There will be a whiteboard with spaces where anyone can write their name down to speak. There's no need to bring anything but yourself and your ideas and speaking voice. # Sponsors We are seeking sponsors to support us in putting on this conference. If you or your company would like to sponsor us, please get in contact via composemel-admin(a)googlegroups.com. You can find info on our sponsorship tiers here: https://github.com/composeconference/Compose-Melbourne-2017/wiki/Sponsorshi… -- Compose Conference Melbourne Organising Committee http://www.composeconference.org/

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Any ideas on what this should generate and not generate...?
by Jurriaan Hage 28 Jun '17

28 Jun '17

We had a strange phenomenon while debugging a large compiler. This is the smallest example, but we have seen this behavior in our own monad. module TracEx where import Debug.Trace runit :: IO () runit = traceShow "Bla" $ do traceShow "Bloe” runit and this generates Bla Bloe and then it hangs. Nothing else is generated. We are guessing this has to do with optimisations of some kind. And what about runit :: IO () runit = traceShow "Bla" $ do n <- traceShow "Num" print 2 traceShow "Bloe” runit Now we get Bla Num 2 Bloe 2 Bloe 2 … No more Bla and no more Num. Any ideas whether this is a bug or a feature? Jur and Tibor

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Haskell Infrastructure Jobs @ Swift Navigation (SF)
by Bhaskar Mookerji 27 Jun '17

27 Jun '17

Hello! I work at Swift Navigation, a high-accuracy GPS receiver manufacturer in San Francisco. We are currently looking to grow out our platform infrastructure team in the next few months and have **several positions** open for experienced Haskell developers. We definitely are open to remote candidates. You can **apply through the posting** here: https://jobs.lever.co/swift-nav/eb80d943-8157-4c9b-afef-8fe98d287c28. The text of this is reproduced at the end of the email. If you have any questions, feel free to comment or email me directly at mookerji(a)swiftnav.com. * About the Work We are a very small team supporting a zoo of libraries and internal services at Swift, including a mature ETL pipeline for evaluating our hardware product, as well an upcoming real-time GPS data product. We open source our work where possible and appropriate (https://github.com/swift-nav?utf8=%E2%9C%93&q=&type=&language=haskell) The ideal candidate will have experience designing and implementing Haskell backends in a commercial web services environment. A Haskell open-source background or production experience using another functional programming language (Scala, Clojure, Erlang, etc.). would also work. We value good communication skills, technical fluency, and responsibility in our day-to-day, and would enjoy seeing these personal qualities in future contributors. * About the Company We design, test, manufacture, and sell a Linux-based GPS/GLONASS receiver for machine automation applications, specifically targeting the autonomous vehicle market. Our work environment is very multidisciplinary, with ~30 engineers covering many areas of engineering (electrical/firmware, embedded Linux, statistics, satellite navigation, web, etc.). You definitely don't need knowledge of these subjects to work here, but you may find it a refreshing change of pace from typical web app development. You can read more about the product here: https://www.swiftnav.com/sites/default/files/piksi_multi_product_summary.pdf Thanks, Buro ================= Swift Navigation is looking for an outstanding software engineer in web infrastructure. You will work with a small team to push the state of the art in satellite navigation technology, making high accuracy positioning ubiquitous and easy to use across a wide variety of industries and applications in unmanned aerial vehicles, robotics, and autonomous transportation. As a member of the infrastructure team, you'll contribute to software services for upcoming networking services as well as internal infrastructure shared broadly by Swift's R&D teams: * Services for Networked Sensors. Service-oriented architecture, scientific modeling services, and distributed message brokers for connected satellite navigation receivers. * Integration Infrastructure. Much of our current work involves rigorously demonstrating that our hardware product works as intended when leaving the lab for a variety of customer scenarios in real-world environments. You'll build and use automation frameworks and assemble instrumentation for hardware-in-the-loop testing, fault injection, and regression testing across these scenarios, as well as data analysis pipelines and metrics monitoring for test units under firmware and manufacturing validation. Candidates should have skills and experience with: - Software engineering in a production environment (commercial web services) - Algorithms, data structures, distributed systems, and relational databases - Haskell, or other typed functional programming languages - Amazon Web Services (AWS) and its related ecosystem (Docker, etc.) for application automation and monitoring - Exceptional problem solving, communication, and collaboration skills. Flexibility and enthusiasm for learning new programming languages, tools, and ideas. Strong candidates will also possess skills in one or more of - Infrastructure engineering for "real-time" sensor networks - Python / NumPy / SciPy / Pandas, R and other analysis/scripting platforms - Version control tools (git), software automation - Open-source development

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I think we should stop "fixing" other people's packages on Hackage silently
by Niklas Hambüchen 27 Jun '17

27 Jun '17

I'm writing this after having spent many hours of debugging why the packages "entropy" and "happy" have different compile-time behaviour when taken from Hackage vs when taken from their upstream git repositories. After lots of frustration, I finally figured out the problem: These packages have "Hackage revisions", where their cabal files were modified from its upstream equivalent: * https://hackage.haskell.org/package/happy-1.19.5/revisions/ * https://hackage.haskell.org/package/entropy-0.3.7/revisions/ Here, "setup-depends" were added to the cabal file, in order to make the package build correctly. These changes are on Hackage only, they cannot be found in the equivalent release of the upstream git repository. This is *extremely* confusing. The practice of "fixing up" other people's cabal files behind their back instead of making those fixes upstream prevents me to use their upstream git packages to reproduce my issues. It hides the fact that there is a problem with the upstream package. In the case of happy, there is not even any upstream fix in the master branch for the missing setup-depends: * https://hackage.haskell.org/package/happy-1.19.5/revision/2.cabal vs * https://github.com/simonmar/happy/blob/2d84ca0/happy.cabal So in this case, I suspect that the silent "fix" has prevented the upstream maintainer to even notice that there is a problem with his package, and so it will be broken again when he uploads the next version. I understand that the concept of Hackage revisions was introduced in a commendable effort to improve the package users' experience: Nobody likes when packages they want to use are broken. And it is clear that something has to be done when upstream authors don't reply to pull requests. But I believe this is not the case here. The upstream maintainers of "happy" and "entropy" are Simon Marlow and Thomas M. DuBuisson, who are very reliable getting stuff fixed (if they know about it!) and they apply PRs quickly and their repositories are well and alive. I believe we're shooting ourselves in the foot with these fixes: The time it takes to make an upstream fix and release it as a proper revision is dwarfed by the time it takes you to figure out bugs when the code you download from Hackage is not the code that the maintainer put there, and when package maintainers don't even notice that their packages are broken because of "silent fixing". So I would welcome if we could make use of the "Hackage revisions" feature only in the utmost necessary cases, or even better, never, and always make properly versioned releases, where a change to any file implies a bump of the version, so that one can clearly see if one is dealing with the unmodified upstream code or not. Greetings, Niklas

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+RTS -n option
by Ruben Astudillo 27 Jun '17

27 Jun '17

Dear list I got a doubt on how the -n flag works. With 2 capabilities, is -A2m -n512k equivalent to just -A512k and 4 less times the garbage collection? It seems a win on every situation. I know I am being naive, but I don't know what could be missing. Care to share your thought on this? -- -- Ruben Astudillo -- PGP: 4EE9 28F7 932E F4AD

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Domain specific error diagnosis in Haskell, a video recorded at Curry On!
by Jurriaan Hage 27 Jun '17

27 Jun '17

Dear Haskellers, The work of Alejandro Serrano Mena and myself on domain-specific error diagnosis in GHC was accepted for a presentation at Curry On! in Barcelona, co-located with ECOOP. I gave the talk last week on what you can do with our branch of GHC. A few well-known Haskellers were around. They had some good questions, and were generally quite positive. In case you missed it, there is a video of the whole affair on YouTube. Here is the link: https://www.youtube.com/watch?v=LuqSkWOcnSA&feature=youtu.be best regards, Jur

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Using Intero on latest MacOS
by Evžen Wybitul 27 Jun '17

27 Jun '17

I’m using the latest developer beta of MacOS High Sierra. There are some problems with new Clang/LLVM; I can’t install terminfo, because of this problem: https://ghc.haskell.org/trac/ghc/ticket/13805 <https://ghc.haskell.org/trac/ghc/ticket/13805>. It seems it's been already fixed (and that it can be fixed by passing an argument to CFLAGS) - I don’t really know what CFLAGS are, though, and I also don’t know how can I update my local Clang/LLVM to include the new patch. Is somebody in a similar situation? I’d welcome any help.

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Re: [Haskell-cafe] Dynamically linking frameworks on macOS (Ryan Trinkle)
by Thomas Jakway 26 Jun '17

26 Jun '17

You could provide a wrapper script around ghc to pass -dynamic automatically. Or when installing append alias ghc="ghc -dynamic" to their bashrc. Not elegant but it's probably easier than any other solution. On 06/24/2017 08:00 AM, haskell-cafe-request(a)haskell.org wrote: > Message: 1 > Date: Fri, 23 Jun 2017 11:31:37 -0400 > From: Ryan Trinkle<ryan.trinkle(a)gmail.com> > To: Haskell Cafe<haskell-cafe(a)haskell.org> > Subject: [Haskell-cafe] Dynamically linking frameworks on macOS > Message-ID: > <CAHNEpix8NeMNo%3Dur3FX_Hs4Li8RTx4t0KT7aUutVGcN4_J5XVQ(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Hi everyone, > > I'm trying to ensure that beginner-level code that uses reflex-dom can be > built by simply calling 'ghc myFile.hs', provided that all the necessary > libraries are available in ghc-pkg. This works on linux, but on macOS, > it's currently necessary for the user to add '-dynamic' to the command > line. In particular, without -dynamic, the linker fails to find > "_OBJC_CLASS_$_NSURL", which is a symbol in the Foundation system > framework. Apple doesn't support (and strongly discourages) statically > linked executables[1], so it's not terribly surprising that this doesn't > work. > > Is there anything I can do to avoid the need for -dynamic here? > > > Thanks, > Ryan > > [1]https://developer.apple.com/library/content/qa/qa1118/_index.html

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OpenCV Haskell: Missing C libraries (macOS)
by Geraldus 26 Jun '17

26 Jun '17

Hi folks! I'm trying to build opencv <http://lumiguide.github.io/haskell-opencv/doc/index.html> as dependency on my macOS Sierra. I stuck with missing _contrib and _legacy C libraries. I've installed OpenCV with contrib packages via brew. Here are the steps I've done. Installation I have installed opencv via brew (with some patches <http://www.pyimagesearch.com/2017/05/15/resolving-macos-opencv-homebrew-ins…> of brew formula): brew install opencv3 --with-contrib --with-python3 python Python 3.6.1 (default, Apr 4 2017, 09:40:21) [GCC 4.2.1 Compatible Apple LLVM 8.1.0 (clang-802.0.38)] on darwin Type "help", "copyright", "credits" or "license" for more information.>>> import cv2>>> cv2.__version__'3.2.0' I have not installed Python 2.7 bindings. Python 3.6 only. Now stack build need some attention too: stack build opencv-0.0.1.0: configure Progress: 1/2 -- While building package opencv-0.0.1.0 using: Configuring opencv-0.0.1.0... setup: Missing dependencies on foreign libraries: * Missing C libraries: opencv_calib3d, opencv_imgproc, opencv_contrib, opencv_legacy, This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. Following suggestion I've tried specify include and lib dirs: stack build --extra-lib-dirs=/usr/local/opt/opencv3/lib --extra-include-dirs=/usr/local/opt/opencv3/include opencv-0.0.1.0: configure Progress: 1/2 -- While building package opencv-0.0.1.0 using: Configuring opencv-0.0.1.0... setup: Missing dependencies on foreign libraries: * Missing C libraries: opencv_contrib, opencv_legacy, This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. I have no idea how to find where missing libraries are located. Would appreciate any help! Arthur!

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stack, git, directory structure
by Dennis Raddle 26 Jun '17

26 Jun '17

I have a few basic questions about my project organization using stack. I'm going to have several executables and a hierarchical library. For instance, let's say I'm going to call my overall system "cac" (computer aided composition). I'll have imports like import Cac.Util import Cac.Search import Cac.Search.Algo1 -- some modules that assist things import XDoc import XDoc.Parse and so on. I'll have executables named 'foo', 'bar', etc. So would the following be correct? - call the directory where I put all stack packages $PROJ - call the top level of my specific project $PROJ/cac, which will have $PROJ/cac/cac.cabal - I'll have the following files and dirs: - modules: - $PROJ/cac/src/Cac.hs - $PROJ/cac/src/Cac/ - $PROJ/cac/src/Cac/Util.hs - $PROJ/cac/src/Cac/Search.hs - $PROJ/cac/src/Cac/Search/ - $PROJ/cac/src/XDoc.hs - $PROJ/cac/src/XDoc/ - $PROJ/cac/src/XDoc/Parse.hs - executables: - $PROJ/app/foo.hs - $PROJ/app/bar.hs Also, if I'm going to use git, would my .git/ directory be at $PROJ/cac/.git/ ? thanks D

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External scripts for use in testing
by Ivan Lazar Miljenovic 26 Jun '17

26 Jun '17

I'm trying to write a test suite for a package, but to properly ensure it's working I need to have some sample script/program for it to interact with. What would be the best way to ship this script/program? I was considering using extra-source-files but the Paths_* support from Cabal doesn't seem to list those. So should I ship them as a data file (which could have an issue if they aren't marked executable and installed globally)? Or blindly trust that the test suite is being run from within the source directory and try to guess/determine it's location from that? Furthermore, what about if it's an actual (small) program that requires compilation? Or am I completely out of luck at this point? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Munich Haskell Meeting, 2017-06-27 @ 19:30
by Christian Neukirchen 25 Jun '17

25 Jun '17

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, June 27 at Hirschgarten (self-service area) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jun-2017/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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Proposal: Instance apartness guards
by Anthony Clayden 24 Jun '17

24 Jun '17

After years of pondering this idea (in various forms), and several rounds of discussion on several forums, I've written it up. "This proposal tackles the thorny topic of Overlapping instances, for both type classes and Type Families/Associated types, by annotating instance heads with type-level apartness Guards. Type-level disequality predicates appear in Sulzmann & Stuckey 2002; in the type-level case selection in HList 2004; and in various guises in Haskell cafe discussions in following years. This proposal builds on the apartness testing implemented as part of the Closed Type Families work." All feedback welcome. https://github.com/AntC2/ghc-proposals/blob/instance-apartness-guards/propo… AntC

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Implicit Multi Threading in Switch Case
by Yotam Ohad 23 Jun '17

23 Jun '17

Hi, After reading "Push-Pull Functional Reactive Programming <https://pdfs.semanticscholar.org/fb7a/879d639641341e025197b40afad9e21f0ce5.…>" I had an idea about deciding which, of two events, comes first. Instead of using forkIO, I tried something like the following: infi :: Maybe Int infi = infi stop :: Maybe Int stop = Nothing test :: Int test = case (infi, stop) of (Nothing, Just _) -> 1 (_, _) -> 2 Here, infi is an action that never ends, and stop a function that ends immediately. I thought that the compiler would see that stop evaluates immediately to Nothing and thus will return 2, but it tries to evaluate infi and get stuck. I think it happens because I am using a tuple to hold both values (but not really sure about it). Do you know a way to make this arrangement work? Yotam

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Why can't GHC infer record fields?
by Clinton Mead 23 Jun '17

23 Jun '17

I asked this below question on Stack Overflow <https://stackoverflow.com/questions/44714711/silly-duplicated-record-fields…> and I got an answer suggesting that GHC doesn't support type inference of overloaded record fields. But I'm wondering why this is the case. Consider the following: {-# LANGUAGE DuplicateRecordFields #-} data A = A { name :: String } data B = B { name :: String } main = print $ name (A "Alice") When compiled, I get the following message (on GHC 8.0.2) duplicatedrecords.hs:7:16: error: Ambiguous occurrence ‘name’ It could refer to either the field ‘name’, defined at duplicatedrecords.hs:5:14 or the field ‘name’, defined at duplicatedrecords.hs:3:14 But if I modify the main line as follows: main = print $ name ((A "Alice") :: A) Compilation proceeds successfully. I'm not sure why I need the :: A here, it seems to be clear that (A "Alice") is of type A due to the A constructor. It's worth noting that the following compiles fine: data A = A { a_name :: String }data B = B { b_name :: String } class Name t where name :: t -> String instance Name A where name = a_nameinstance Name B where name = b_name main = print $ name (A "Alice") We can even go further as follows, allowing different result types: {-# LANGUAGE TypeFamilies #-} data A = A { a_name :: String }data B = B { b_name :: Int } class Name t where type family T t name :: t -> T t instance Name A where type T A = String name = a_name instance Name B where type T B = Int name = b_name main = print $ name (A "Alice") It seems like GHC just has to mechanically add a class for each unique record name and an instance for each record in each data type. This will mean however that name x == name y not implying that the types of x and y are the same but I'd expect that when using this extension anyway. Just wondering if there's anything tricky I'm missing here regarding the implementation or that it just needs someone to implement it?

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exceptions, errors, random
by Dennis Raddle 23 Jun '17

23 Jun '17

I am wondering what exception/error and random classes I should use for my application. The application will be doing Monte Carlo backtracking search. I want it to be multithreaded and run on all four cores on my MacBook. I need detailed error messages in order to investigate errors. So I will throw errors or exceptions, then catch them in lower functions and annotate them with the parameters or computations within the lower function, then re-throw until finally the exception pops into the terminal. Because it's multi-threaded, at least some parts will needs to be in IO. Also, because it's a Monte Carlo algorithm it will need to make pseudorandom choices. Perhaps I should put everything in the IO monad? This will give me access to threads and the standard generator seed. But how about throwing, catching/rethrowing exceptions in IO? I have done this in pure code before: not sure if it's better to do it that way, in which case I could put some kind of state monad to hold the random seed together with an error monad and IO at the core of the monad stack. Any advice welcome. D

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Having trouble with this recursive Parsec parser
by Cody Goodman 23 Jun '17

23 Jun '17

Hi all, I'm having trouble with a recursive parsec parser that keeps recursing on one type of end tag and terminates on another type of end tag. I'm sure I'm stuck on something silly, but here's what I have so far. Git repo with stack/cabal project: https://github.com/codygman/megaparsectest/blob/master/library/Example.hs Code I have so far (I deleted a few different approaches I tried because I thought they would clutter things up and make it harder to assist me with this issue): {-# LANGUAGE QuasiQuotes #-} -- | An example module. module Example where import Text.Megaparsec import Text.RawString.QQ import Text.Megaparsec.String -- input stream is of the type ‘String’ import qualified Text.Megaparsec.Lexer as L import Control.Monad (void, join) ex :: String ex = [r| begin field1 string begin field11 int field12 string end subsection; // optional end; |] data Field = Field String String deriving Show data Block = Fields [Field] | Block [Field] deriving Show sc :: Parser () sc = L.space (void spaceChar) lineCmnt blockCmnt where lineCmnt = L.skipLineComment "//" blockCmnt = L.skipBlockComment "/*" "*/" field :: Parser Field field = dbg "field" $ do sc Field <$> someTill ((oneOf' (['a'..'z'] ++ ['0'..'9']))) spaceChar <*> some ((oneOf' (['a'..'z'] ++ ['0'..'9']))) endEof = do sc *> string "end" *> char ';' *> sc *> eof pure "" endIdent = do string "end" *> sc ident <- someTill ((oneOf' (['a'..'z'] ++ ['0'..'9']))) (char ';') sc *> eof pure ident block = error "TODO implement" -- Thanks, -- Cody

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Issue 60 :: Haskell Weekly
by Taylor Fausak 22 Jun '17

22 Jun '17

\ Haskell Weekly \/\/ Issue 60 <https://haskellweekly.news/issues/60.html> Welcome to another issue of Haskell Weekly! Haskell is a purely functional programming language that focuses on robustness, concision, and correctness. This is a weekly summary of what's going on in its community. ## Featured ## - Understanding ResourceT <https://www.fpcomplete.com/blog/2017/06/understanding-resourcet> > Instead of just teaching you how to use the library, this post will demonstrate why you need it and how it works internally, to help you avoid some of the potential pitfalls of the library. - Announcing Weeder: dead export detection <https://neilmitchell.blogspot.com/2017/06/announcing-weeder-dead-export-det…> > Most projects accumulate code over time. To combat that, I've written Weeder which detects unused Haskell exports, allowing dead code to be removed (pulling up the weeds). - Dhall is now a template engine <http://www.haskellforall.com/2017/06/dhall-is-now-template-engine.html> > Now you can use Dhall as a template engine with the newly released dhall-text library which provides a dhall-to-text executable for templating text. - Front Row is hiring a senior backend Haskell engineer <https://frontrow.workable.com/j/463B843754> > Come change how 6.5+ million K-12 US students learn Math, Language Arts, Social Studies and more. Use data, advanced type systems, great product design and deep pedagogy to change lives. - Testing PostgreSQL for fun <https://hackernoon.com/testing-postgresql-for-fun-af891047e5fc> > In this post I'll show how to make database programming fun by using packages that make testing easy. I'll walk through a example of building a durable queue backed with PostgreSQL. - Exceptional Servant handling <http://www.parsonsmatt.org/2017/06/21/exceptional_servant_handling.html> > There are various good reasons why you might want to strip ExceptT from your Servant handlers. There are various good reasons why you wouldn't want to do that. I'm in the first camp --- I don't want ExceptT over IO. - On competing with C using Haskell <https://two-wrongs.com/on-competing-with-c-using-haskell> > By writing very straight-forward pure, functional Haskell code without any special trickery, you can get performance equivalent to what you'd get by calling out to a C function, which is also in the same order of magnitude as the same algorithm implemented in a program completely written in C. - How well does it work? Profiling in Haskell <https://mmhaskell.com/blog/2017/6/19/profiling-in-haskell> > This is where benchmarking and profiling come in. We're going to take a specific problem and learn how we can use some Haskell tools to zero in on the problem point. - The chain in blockchain <http://haroldcarr.com/posts/2017-06-19-the-chain-in-blockchain.html> > This post develops a simple blockchain with the goal of understanding the basics of the chain. The most straightforward part of a blockchain is the chain itself, a sequence of blocks. - Mezzo: type-safe music composition <https://github.com/DimaSamoz/mezzo/blob/1d46c5edd5d7d360a027a614c618bb2830d…> > Its novelty is in the fact that it can enforce various rules of music composition statically, that is, at compile-time. This effectively means that if you write "bad" music, your composition will not compile --- think of it as a very strict spell-checker for music. - Linear types 101 and its relevance to streams <https://m0ar.github.io/safe-streaming/2017/06/19/linear-types-101.html> > It creates a resource aware type system, which not only knows types of values but also number of uses; a linearly typed value is guaranteed to only have one reference to it at any time, duplication or ignoring will not compile. ## Package of the week ## This week's package of the week is async, a library that allows you to run IO operations asynchronously and wait for their results. <https://www.stackage.org/lts-8.19/package/async-2.1.1.1> ## In brief ## - An alternate definition of Haskell's Functor type class <https://github.com/rampion/kinder-functor/blob/20e5c57/README.md> - Configurable data types <http://mazzo.li/posts/customizable-data-types.html> - Generic unification <https://ro-che.info/articles/2017-06-17-generic-unification> - The linearity monad <https://www.cis.upenn.edu/~jpaykin/papers/pz_linearity_monad_2017.pdf) (pdf> - A terminal interface for Tetris <https://github.com/samtay/tetris/blob/5d9c74c/README.md>

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DSLDI 2017: Call for Talk Proposals
by Lindsey Kuper 20 Jun '17

20 Jun '17

********************************************************************* FIRST CALL FOR TALK PROPOSALS DSLDI 2017 Fifth Workshop on Domain-Specific Language Design and Implementation October 22, 2017 Vancouver, Canada Co-located with SPLASH http://2017.splashcon.org/track/dsldi-2017 https://twitter.com/wsdsldi ********************************************************************* Deadline for talk proposals: 7th of August, 2017 Well-designed and implemented domain-specific languages (DSLs) can achieve both usability and performance benefits over general-purpose programming languages. By raising the level of abstraction and exploiting domain knowledge, DSLs can make programming more accessible, increase programmer productivity, and support domain-specific optimizations. ## Workshop Goal Domain-Specific Language Design and Implementation (DSLDI) is a workshop intended to bring together researchers and practitioners interested in discussing how DSLs should be designed, implemented, supported by tools, and applied in realistic contexts. The focus of the workshop is on all aspects of this process, from soliciting domain knowledge from experts, through the design and implementation of the language, to evaluating whether and how a DSL is successful. More generally, we are interested in continuing to build a community that can drive forward the development of modern DSLs. ## Workshop Format DSLDI is a single-day workshop and will consist of an invited speaker followed by moderated audience discussions structured around a series of short talks. The role of the talks is to facilitate interesting and substantive discussion. Therefore, we welcome and encourage talks that express strong opinions, describe open problems, propose new research directions, and report on early research in progress. Proposed talks should be on topics within DSLDI’s area of interest, which include but are not limited to: * solicitation and representation of domain knowledge * DSL design principles and processes * DSL implementation techniques and language workbenches * domain-specific optimizations * human factors of DSLs * tool support for DSL users * community and educational support for DSL users * applications of DSLs to existing and emerging domains * studies of usability, performance, or other benefits of DSLs * experience reports of DSLs deployed in practice ## Call for Talk Proposals We solicit talk proposals in the form of short abstracts (max. 2 pages). A good talk proposal describes an interesting position, open problem, demonstration, or early achievement. The submissions will be reviewed on relevance and clarity, and used to plan the mostly interactive sessions of the workshop day. Publication of accepted abstracts and slides on the website is voluntary. * Deadline for talk proposals: August 7th, 2017 * Notification: September 11th, 2017 * Workshop: October 22nd, 2017 * Submission website: https://dsldi17.hotcrp.com/ ## Workshop Organization Co-chairs: * Lindsey Kuper (lindsey(a)composition.al) Intel Labs * Eric Walkingshaw (eric.walkingshaw(a)oregonstate.edu) Oregon State University Follow us on Twitter at https://twitter.com/wsdsldi Program committee: * Nada Amin (EPFL/University of Cambridge) * Eric Holk (Google) * Gabriele Keller (Data61, CSIRO (formerly NICTA) and UNSW) * Rebekah Leslie-Hurd (Intel Labs) * Chris Martens (NCSU) * Lee Pike (Galois) * Jonathan Ragan-Kelley (UC Berkeley) * Jesús Sánchez Cuadrado (Autonomous University of Madrid) * Vincent St-Amour (Northwestern University) * Philip Wadler (University of Edinburgh)

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[Announcement] Haskell game for iOS
by Ivan Perez 20 Jun '17

20 Jun '17

Dear all (I hope this is not seen as spam. My sincere apologies if you see it as such.) This is just to let you know that we have released a Haskell game for iOS on the App Store. https://itunes.apple.com/us/app/magic-cookies/id1244709871 There is also an Android version [1]. It's the same Haskell code with just a few minor adaptations [2] (the iOS version is actually simpler). Issues with either version can be reported online [3]. I hope this is seen as yet another step reached by Haskell. This game is written in the FRP variant Yampa, and uses SDL2 for graphics. While the game is not open source, we've had to extend existing Haskell libraries and tools to make this possible. These changes will now be sent as pull requests to the corresponding projects. We have also developed in-house tooling to make the development, compilation and deployment process for mobile platforms smooth [4]. Recompiling and deploying a new version online is now automatic and takes less than 1 minute. These tools also run directly on Travis and publish new versions of our games directly to stores. We have already started distributing our toolchain to private users, and our plan is to release immediately. We'd like to thank all the users who tried the game before the release, many during Zurihac last weekend. Also, many thanks to the people who worked on GHC and the ARM backends over the years, and to all those who work daily to make Haskell better. We really mean that. Once again, I hope this is not seen as spam, but as something worth celebrating. And, also, that you enjoy playing. Best wishes Ivan -- Keera Studios [1] https://play.google.com/store/apps/details?id=uk.co.keera.games.magiccookies [2] https://www.facebook.com/keerastudios/photos/a.301326223216244.89053.300854… [3] https://github.com/keera-studios/magic-cookies [4] http://keera.co.uk/blog/2017/06/01/haskell-android-ios/

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Master programme with Haskell prospects
by Georgi Nakov 20 Jun '17

20 Jun '17

Hi all, I was pondering on Master programme with "good" Haskell-related prospects upon completion (regardless whether it's in academia or industry). Currently the only options available to me are Master in Logic at University of Amsterdam and Computing Science at Utrecht. The latter has more emphasis on FP and Haskell while the former seems more concerned with the mathematical/philosophical foundations. Any thoughts or direct observations on these programmes would be greatly appreciated. Thanks. Best regards, Georgi

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Vancouver Haskell Meetup session - Jun 22, 2017
by Román González 20 Jun '17

20 Jun '17

Dear All, I'm happy to announce there will be a Haskell Meetup that is going to be held at Unbounce HQ this Thursday, Jun 22, 2017 This is intended to be a Newcomer friendly session, so basics of Why Haskell and Haskell used in production will be the main topics of the event. If you live in Vancouver, would hope to see you there. https://www.meetup.com/Vancouver-Haskell-Unmeetup/ Cheers. Roman.-

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Re: [Haskell-cafe] MultiCase alternative
by Oleg 20 Jun '17

20 Jun '17

Richard A. O'Keefe wrote: > Let Pi be the pattern (i,_) | (_,i) > In SML, > fun f P1 ... Pn (0,0) = true > | f _ ... _ _ = false > > fun g () = f (1,1) (2,2) ... (n,n) (1,1) > > (So far it has taken 3 minutes on a fast machine to not > > finish compiling these 3 lines of code... I fear the worst.) I can't speak for SML, but I was curious to try your example in OCaml, which also supports OR patterns. Here is how it looks in OCaml: let f = function ((1,_)|(_,1)), ((2,_)|(_,2)), ((3,_)|(_,3)), ((4,_)|(_,4)), ((5,_)|(_,5)), ((6,_)|(_,6)), ((7,_)|(_,7)), ((8,_)|(_,8)), (0,0) -> true | _ -> false ;; let g () = f ((1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(1,1)) ;; let _ = g ();; It compiled instantly. I was curious what it is compiled to. Enclosed in the result, in an intermediate language called Lambda (before optimizations). It seems the size of the code is linear in n. Not too bad. BTW, match/1207 is the identifier called match with the timestamp 1207. The timestamps tell distinct identifiers with the same given name apart. Also, 1a means true and 0a means false (and also unit and the empty list). >From personal experience, OR patterns are quite handy when handing an AST where many of the alternatives are to be handled the same. That said, supporting OR patterns in MetaOCaml was responsible for some of the most complex code there. ocamlc -c -dlambda p.ml (setglobal P! (let (f/1199 = (function param/1206 (let (match/1207 =a (field 0 param/1206)) (catch (catch (if (!= (field 0 match/1207) 1) (if (!= (field 1 match/1207) 1) (exit 1) (exit 2)) (exit 2)) with (2) (let (match/1227 =a (field 1 param/1206)) (catch (if (!= (field 0 match/1227) 2) (if (!= (field 1 match/1227) 2) (exit 1) (exit 4)) (exit 4)) with (4) (let (match/1245 =a (field 2 param/1206)) (catch (if (!= (field 0 match/1245) 3) (if (!= (field 1 match/1245) 3) (exit 1) (exit 6)) (exit 6)) with (6) (let (match/1261 =a (field 3 param/1206)) (catch (if (!= (field 0 match/1261) 4) (if (!= (field 1 match/1261) 4) (exit 1) (exit 8)) (exit 8)) with (8) (let (match/1275 =a (field 4 param/1206)) (catch (if (!= (field 0 match/1275) 5) (if (!= (field 1 match/1275) 5) (exit 1) (exit 10)) (exit 10)) with (10) (let (match/1287 =a (field 5 param/1206)) (catch (if (!= (field 0 match/1287) 6) (if (!= (field 1 match/1287) 6) (exit 1) (exit 12)) (exit 12)) with (12) (let (match/1297 =a (field 6 param/1206)) (catch (if (!= (field 0 match/1297) 7) (if (!= (field 1 match/1297) 7) (exit 1) (exit 14)) (exit 14)) with (14) (let (match/1305 =a (field 7 param/1206)) (catch (if (!= (field 0 match/1305) 8) (if (!= (field 1 match/1305) 8) (exit 1) (exit 16)) (exit 16)) with (16) (let (match/1311 =a (field 8 param/1206)) (if (!= (field 0 match/1311) 0) (exit 1) (if (!= (field 1 match/1311) 0) (exit 1) 1a)))))))))))))))))) with (1) 0a))) g/1201 = (function param/1205 (apply f/1199 [0: [0: 1 1] [0: 2 2] [0: 3 3] [0: 4 4] [0: 5 5] [0: 6 6] [0: 7 7] [0: 8 8] [0: 1 1]]))) (seq (apply g/1201 0a) (makeblock 0 f/1199 g/1201))))

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Re: [Haskell-cafe] Probabilistic programming in Haskell with bali-phy
by dominic＠steinitz.org 19 Jun '17

19 Jun '17

> While we're mentioning Haskell-embedded languages for probabilistic > programming, there is yet another, Hakaru. > > github: https://github.com/hakaru-dev/hakaru > docs: https://hakaru-dev.github.io/ > hackage: https://hackage.haskell.org/package/hakaru-0.4.0 > > It can be used either embedded or via an external syntax. It can act as > a sampler, but also do code generation (to Haskell, to C, more coming), > simplification (via Maple if it is installed) and disintegration (aka > conditioning). > > It uses quite a number of advanced Haskell features (though works in 7.8 > onwards) to insure safety of the embedded language. See > https://hackage.haskell.org/package/hakaru-0.4.0/docs/Language-Hakaru-Synta… > if you are curious about that. > > Jacques There are production strength PPLs like Stan and PyMC3. They aren’t Haskell but if you actually want to model something then they are my “go to” tools. There’s also LibBI which uses Sequential Monte Carlo rather than Hamiltonian Monte Carlo. Stan and LibBI are C++ with interfaces (I use the word very loosely) from e.g. R, Python, Matlab, etc. PyMC3 as you might guess is entirely Python. Both have very good communities. In Haskell there is also monad-bayes https://github.com/adscib/monad-bayes <https://github.com/adscib/monad-bayes> and baysig, the latter sadly not publicly available (last time I checked). If you have a hidden state model (e.g. stochastic volatility) then there is also particle filtering (aka Sequential Monte Carlo) using https://hackage.haskell.org/package/kalman-1.0.0.2 <https://hackage.haskell.org/package/kalman-1.0.0.2>. I just looked at the commit log for monad-bayes and it seems to use HMC these days :) and supports ADVI. I spent a bit of time at the recent Zurihac with Alexander Vershilov making some very small steps towards a symplectic integrator package which could form the basis for HMC in Haskell. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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MultiCase alternative
by Baa 19 Jun '17

19 Jun '17

Hello, Everyone! As I understand "MultiCase" proposal was not approved, so my question is: is there alternatives to multi-case? I have code like: case x of A a -> .. B b -> .. C c -> --same-- D c -> --same-- and I want to merge code of "C c" with "D c" branch. Anywhere, in general: is any alternatives to make "OR"s in patterns? I don't see how to do it with pattern guards, pattern synonyms, views extensions and don't see another related extensions. Something like "(C|D) c -> ..." === Best regards, Paul

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Re: [Haskell-cafe] Probabilistic programming in Haskell with bali-phy
by Oleg 18 Jun '17

18 Jun '17

It seems worth mentioning then another Haskell embedded language for probabilistic programming http://okmij.org/ftp/kakuritu/Hakaru10/index.html It also lets us write probabilistic models as Haskell programs. It supports both discrete and continuous distributions, conditioning, as well as branching (mixing models). It takes care to statically preclude senseless models (forcing conditioning only on external data). The 'Model' is *not* a monad. Not everything can be or should be a monad. Hakaru10 also takes care to avoid the problems that are frequent in implementations of Wingate algorithms. It also uses incremental evaluation. As to semantic problems of probabilistic programming languages, http://okmij.org/ftp/kakuritu/index.html shows a couple of them.

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Announce: Probablistic programming in Haskell with bali-phy
by Benjamin Redelings 17 Jun '17

17 Jun '17

Hi, I'm working on a project to implement support for probabilistic programming with models written as Haskell programs. This is similar to Bayesian graphical models (e.g. BUGS, JAGS) and to full probabilistic programming systems like Church / Venture. http://www.bali-phy.org/models.php This project is not very mature, but it is used as the core of the MCMC software mentioned above, which is relatively mature. Probabilistic programs are written using the probability monad. I've implemented a Haskell interpreter in C++ that records execution traces of the Haskell programs. These execution traces depend on some number of (random) variables, and when one of the variables is changed (during MCMC), the parts of the execution trace that depend on the changed variables are invalidated and recomputed. This saves work by not recomputing the probability of the new state from scratch. I can provide DOT graphs of the execution traces if anyone is interested. The problem domain I've been focusing on is evolution of DNA sequences on binary trees. You can see some of the code for that problem domain here: https://github.com/bredelings/BAli-Phy/blob/master/modules/ The code for the interpreter is here: https://github.com/bredelings/BAli-Phy/blob/master/src/computation/ -BenRI

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Issue 59 :: Haskell Weekly
by Taylor Fausak 15 Jun '17

15 Jun '17

\ Haskell Weekly \/\/ Issue 59 <https://haskellweekly.news/issues/59.html> Welcome to another issue of Haskell Weekly! Haskell is a purely functional programming language that focuses on robustness, concision, and correctness. This is a weekly summary of what's going on in its community. ## Featured - Haskell on Android and iOS <http://keera.co.uk/blog/2017/06/01/haskell-android-ios/> > With our framework, writing professional Haskell apps and games becomes a reality. In minutes one can have the complete toolchain and see the first app running on a phone or published on the online store. If you weren't considering using Haskell yet, we hope you soon change your mind. - Translating a C++ parser to Haskell <http://www.haskellforall.com/2017/06/translating-c-parser-to-haskell.html> > Recently I translated Nix's derivation parser to Haskell and I thought this would make an instructive example for how C++ idioms map to Haskell idioms. This post targets people who understand Haskell's basic syntax but perhaps have difficulty translating imperative style to a functional style. - The `ReaderT` design pattern <https://www.fpcomplete.com/blog/2017/06/readert-design-pattern> > What many languages address via patterns, in Haskell we address via language features (like built-in immutability, lambdas, laziness, etc.). However, I believe there is still room for some high-level guidance on structuring programs, which I'll loosely refer to as a Haskell design pattern. - Front Row is hiring a senior backend Haskell engineer (ad) <https://frontrow.workable.com/j/463B843754> > Come change how 6.5+ million K-12 US students learn Math, Language Arts, Social Studies and more. Use data, advanced type systems, great product design and deep pedagogy to change lives. - 10 things Idris improved over Haskell <https://deque.blog/2017/06/14/10-things-idris-improved-over-haskell/> > This post describes some of the pleasant surprises you get trying out Idris, coming from the Haskell world. These pleasant surprises have nothing to do with the dependent typing features. They are simple yet impacting modifications, which improve the developer experience substantially. - Migrating text metrics to pure Haskell <https://markkarpov.com/post/migrating-text-metrics.html> > text-metrics-0.3.0 is written in pure Haskell, almost as fast as the previous versions (especially for not very long inputs), and is more correct (we handle characters represented as two `Word16` values properly). - ZuriHac 2017 recap <https://jship.github.io/posts/2017-06-11-zurihac-recap.html> > This was my first time attending ZuriHac and it was too much fun --- will definitely be back next year! Big thanks to Jasper Van der Jeugt, Simon Meier, and all of the HSR folks that made the event happen. Props to the Haskell community too for being friendly and inviting. - Haddock markup quick reference <https://github.com/aisamanra/haddock-cheatsheet/blob/c3485d33e6bb42beb41c97…> > This page is a single-page quick reference for the markup used in GHC's Haddock documentation format. It doesn't list all the details of the format, just the basic markup, so for the vagaries and edge-cases of the syntax, it would be helpful to consult the Haddock user guide. - Haskell Summer of Code <https://jaredweakly.com/blog/haskell-summer-of-code/> > The performance tests do two things: first, they make sure that when people change the compiler, they don't accidentally make it slower; secondly, they make sure that when people change the compiler, they don't accidentally make the generated code less efficient. - Use hpack <https://e.xtendo.org/haskell/hpack> > One of the remaining problems is that the `project.cabal` file is in a custom format. Custom formats are generally not good because you can't leverage the existing tools and free-ride other people's work. - Haskell taketh away: Limiting side effects for parallel programming <https://www.youtube.com/watch?v=lC5UWG5N8oY> > In designing parallel programming abstractions, taking away user capabilities is as important as granting them. In this talk, I'll explain the role of this idea in several different parallel programming libraries for Haskell, C++, and other languages --- spanning from shared memory to big data. ## Package of the week This week's package of the week is generic-lens, a library that exposes generic data structure operations as lenses. <https://hackage.haskell.org/package/generic-lens-0.2.0.0> ## In brief - Binary instances for GADTs (or: RTTI in Haskell) <https://www.well-typed.com/blog/2017/06/rtti/> - Data structures are antithetical to functional programming <http://degoes.net/articles/kill-data> - Drive-by Haskell contributions <http://ndmitchell.com/downloads/slides-drive-by_haskell_contributions-09_ju…> - On friendly contributing policies <https://ro-che.info/articles/2017-06-12-friendly-contributing-policies> - Taking a close look at lenses <https://mmhaskell.com/blog/2017/6/12/taking-a-close-look-at-lenses> - Teaching Haskell for understanding <https://docs.google.com/presentation/d/1_I5mYXivG5NbOHnICld_Xo41uOyAT57Yade…> - The Haskell Cast episode 14: Richard Eisenberg on dependent types <http://www.haskellcast.com/episode/014-richard-eisenberg-on-dependent-types…>

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Error-containing Maybes
by Ivan Lazar Miljenovic 15 Jun '17

15 Jun '17

The Maybe type is often (almost always?) used to indicate that a computation may fail; specifically, `Maybe a` typically indicates that it may not be possible to always produce a value of type `a`. However, there are times when the inverse of this is desirable (usually within a monadic/side-effectful context): if Nothing is returned then the computation was a success; otherwise, an error message is returned. Whilst this usage definitely fits the types, it breaks the mould of how we think/use Maybe in most cases and may at times cause confusion. As such, it may be advisable (and I know I've done this at least once) to define a `data Result e = Error e | Success` data type to model this behaviour. Is this a typical enough requirement that would make it worth adding such a datatype to base (despite my usual aversion to piling more things in there) or having a library up on Hackage just for this very simplistic type? (Another option would be to use `Either error ()`, which could be lifted better into an ExceptT result, albeit with the additional useless parameter/value in there.) -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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Re: [Haskell-cafe] Announce: Probablistic programming in Haskell with bali-phy
by Olaf Klinke 14 Jun '17

14 Jun '17

Benjamin, I'm also excited to see more probabilistic programming in Haskell. Adding to Sergiu's questions I'd like to know why you chose to implement a new interpreter instead of making an embedded domain-specific language. Are there C++ libraries that were convenient to use? As theorist I'm curious whether you have a denotational semantics in mind. Can you decribe the building blocks of your language? The examples show primitives for known families of distributions (e.g. beta). Then there is Observe, which seems to compute conditional distributions. What else is there beyond ordinary Haskell? Cheers, Olaf

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use of models in proving program properties
by Ben Franksen 12 Jun '17

12 Jun '17

This is something that has left me puzzled for years. My understanding is that a model is a concrete realization of an abstract structure in terms of some other mathematical structure, such that all the laws from the first are satisfied in the latter. A simple example might be the abstract (algebraic) structure "group" and a concrete realization e.g. the integers with addition. Finding models for abstract theories is certainly useful, for instance it shows that the theory is actually 'inhabited'; it may also shed light on the theory and give us ideas about new theorems that might generalize to the abstract setting. However, nobody would claim that from a theorem about integers I can deduce one for abstract groups in general. But exactly this kind of reasoning appears to be valid when proving things about e.g. the polymorphic lambda calculus (aka System F). For instance, in the famous "free theorems" paper by Wadler, the free theorems appear as a consequence of modeling types in system F as relations (this is most probably oversimplified, i can't remember the details but I think they are not important here). The question is: How can that imply anything about system F itself? Wouldn't it be necessary to prove that these free theorems hold for /all/ models of System F, not just one particular? Besides, if such proofs using a suitable model are really valid, why does it seem to be impossible to 'translate the proof back' from the model to the original system and thus arrive at a direct proof? I am sure there is something wrong with my understanding of these things but I can't figure out what. Cheers Ben

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1st CfP: IFL 2017 (29th Symposium on Implementation and Application of Functional Languages)
by publicityifl＠gmail.com 12 Jun '17

12 Jun '17

<div dir="ltr">Hello, Please, find below the first call for papers for IFL 2017. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL --- IFL 2017 - CALL FOR PAPERS ========================== 29th SYMPOSIUM ON IMPLEMENTATION AND APPLICATION OF FUNCTIONAL LANGUAGES ======================================================================== University of Bristol, UK In cooperation with ACM SIGPLAN Wednesday 30 August - Friday 1 September, 2017 <a href="http://iflconference.org/">http://iflconference.org/</a> Scope ----- The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2017 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Peer-review ----------- Following the IFL tradition, IFL 2017 will use a post-symposium review process to produce the formal proceedings. All participants of IFL 2017 are invited to submit either a draft paper or an extended abstract describing work to be presented at the symposium. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: <a href="http://www.sigplan.org/Resources/Policies/Republication">http://www.sigplan.org/Resources/Policies/Republication</a> The submissions will be screened by the program committee chair to make sure they are within the scope of IFL, and will appear in the draft proceedings distributed at the symposium. Submissions appearing in the draft proceedings are not peer-reviewed publications. Hence, publications that appear only in the draft proceedings are not subject to the ACM SIGPLAN republication policy. After the symposium, authors will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal review process. From the revised submissions, the program committee will select papers for the formal proceedings considering their correctness, novelty, originality, relevance, significance, and clarity. The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. Important dates --------------- Mon 31 July 2017 : Submission deadline draft papers Wed 2 August 2017 : Notification of acceptance for presentation Fri 4 August 2017 : Early registration deadline Fri 11 August 2017 : Late registration deadline Mon 21 August 2017 : Submission deadline for pre-symposium proceedings Wed 30 August 2017 - Fri 1 September 2017 : IFL Symposium Mon 4 December 2017 : Submission deadline for post-symposium proceedings Wed 31 January 2018 : Notification of acceptance for post-symposium proceedings Mon 12 March 2018 : Camera-ready version for post-symposium proceedings Submission details ------------------ Prospective authors are encouraged to submit papers or extended abstracts to be published in the draft proceedings and to present them at the symposium. All contributions must be written in English. Papers must use the new ACM two columns conference format, which can be found at: <a href="http://www.acm.org/publications/proceedings-template">http://www.acm.org/publications/proceedings-template</a> For the pre-symposium proceedings we adopt a 'weak' page limit of 12 pages. For the post-symposium proceedings the page limit of 12 pages is firm. Authors submit through EasyChair: <a href="https://easychair.org/conferences/?conf=ifl2017">https://easychair.org/conferences/?conf=ifl2017</a> Topics ------ IFL welcomes submissions describing practical and theoretical work as well as submissions describing applications and tools in the context of functional programming. If you are not sure whether your work is appropriate for IFL 2017, please contact the PC chair at <a href="mailto:nicolas.wu@bristol.ac.uk">nicolas.wu(a)bristol.ac.uk</a>. Topics of interest include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications Peter Landin Prize ------------------ The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. Programme committee ------------------- Chair: Nicolas Wu, University of Bristol, UK - Kenichi Asai, Ochanomizu University, Japan - Sandrine Blazy, University of Rennes 1, France - Carlos Camarao, Universidade Federal de Minas Gerais, Brazil - Stephen Dolan, University of Cambridge, UK - Jurriaan Hage, Utrecht University, Netherlands - Yukiyoshi Kameyama, University of Tsukuba, Japan - Benjamin Lerner, Brown University, USA - Bas Lijnse, Radboud University, Netherlands - Garrett Morris, University of Kansas, USA - Miguel Pagano, Universidad Nacional de C√≥rdoba, Argentina - Tomas Petricek, Alan Turing Institute, UK - Maciej Pir√≥g, University of Wroc≈Çaw, Poland - Exequiel Rivas, Universidad Nacional de Rosario, Argentina - Neil Sculthorpe, Nottingham Trent University, UK - Melinda T√≥th, E√∂tv√∂s Lor√°nd University, Hungary - Phil Trinder, Glasgow University, UK - Kanae Tsushima, National Institute of Informatics, Japan - Marcos Viera, Universidad de la Republica, Uruguay - Meng Wang, University of Kent, UK Venue ----- The IFL 2017 will be held in association with the Department of Computer Science, University of Bristol, UK. Bristol is located in South West England, and can be easily reached from Bristol Airport. See the website for more information on the venue. </div>  <a style='display: block; margin: 32px 0 40px 0; padding: 10px; font-size: 1em; text-align: center; border: 0; border-top: 1px solid gray; ' href='https://goo.gl/2ksdRv'>powered by GSM. Free mail merge and email marketing software for Gmail.</a>

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Re: [Haskell-cafe] ANNOUNCE: streaming-conduit
by Olaf Klinke 12 Jun '17

12 Jun '17

Dear Ivan, I'm confused. The package documentation states that the typical problem to avoid is extracting a long list from IO, which is bound to allocate too much memory. However, if I do preprocess :: IO [a] preprocess = fmap (map (parse :: String -> a) . lines) $ readFile filename then this may create a huge pile of thunks if the rest of the program is not written in a streaming style. But if done right, lazy IO will make sure only the necessary part of the list is kept im memory. For example, a strict function like postprocess :: [a] -> IO () postprocess = mapM (print . f) with some strict f would fit the bill. Did I get the concept of lazy IO wrong? What is the operational semantics of the following fragment? x:xs <- someIOaction :: IO [a] Control.DeepSeq.force x I used to think that xs is now a thunk which, when evalated further, may trigger more (read) IO actions. Hence, would behave as if someIOaction was one of your Streams. I do acknowledge, though, that the style above is easy to go wrong [*], whereas explicitly wrapping each list element in its own monadic action makes the intentions more verbose. Cheers, Olaf [*] If someIOaction needs to touch every list element in order to ensure the result has the shape _:_ then we will indeed have a huge list of thunks.

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Bug in GHC or cabal-install?
by Henk-Jan van Tuyl 11 Jun '17

11 Jun '17

L.S., I am trying the prerelease of GHC, version 8.2.0.20170507 I adapted wxHaskell to the new packages that come with the new GHC and it compiles now, but only the first time. If I compile it a second time, even if nothing has changed, the information from the custom-setup section of the wxc.cabal file seems to be forgotten. This section looks like this: custom-setup setup-depends: base, Cabal < 2, containers, bytestring, split, process, directory, filepath (I am using cabal-install 1.24.0.2) Output from the second time I try to install wxHaskell: > cabal install --force-reinstalls --reinstall wxdirect wxc wxcore wx [1 of 1] Compiling Main ( X:\Temp\wxHaskell\wxcore\dist\setup\setup.hs, X:\Temp\wxHaskell\wxcore\dist\setup\Main.o ) Linking X:\Temp\wxHaskell\wxcore\dist\setup\setup.exe ... [1 of 1] Compiling Main ( X:\Temp\wxHaskell\wxc\dist\setup\setup.hs, X:\Temp\wxHaskell\wxc\dist\setup\Main.o ) X:\Temp\wxHaskell\wxc\dist\setup\setup.hs:505:61: error: Variable not in scope: versionBranch :: Version -> [a0] | 505 | full_ver = (concat . intersperse "." . map show . versionBranch) ver | ^^^^^^^^^^^^^ This error message indicates that the wrong version of Cabal (2.0) is used to compile the wxcore setup.hs It looks like a cabal-install bug, but this does not happen when I use GHC 8.0.2; should I write a GHC bug ticket? Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://foldingathome.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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[ANN] Budapest Haskell Hackathon 2017, 29-30th July 2017
by Daniel Berecz 11 Jun '17

11 Jun '17

Hi everybody, I'm happy to announce that our local user group will hold a Haskell Hackathon in Budapest this year (this will be the second)! We will hold it from the 29th to the 30th of July (Saturday & Sunday). You can find out more on the following link: https://wiki.haskell.org/Budapest_Hackathon_2017 We will reguraly update the site with new information. If you decide to come, please fill out the following Google Form: https://goo.gl/forms/QjTNdXTD1aEOMEQU2 If you have a project, demo, or talk that you want to bring to the event please contact us, and we can talk about the details. You can find our contact info the events wiki site, or you can just contact me directly. The event will be open to people of all experience levels, from beginners to gurus. The only requisite is that you’re interested in the Haskell language, and want to hang out with us, and have a good time! Greetings from Daniel, and the other BP-HUG organizers.

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Last call for presentations: CUFP 2017, September 7-9, Oxford, UK
by Jasper Van der Jeugt 10 Jun '17

10 Jun '17

The deadline for CUFP presentations is this friday, the 9th of June. This CFP and the form for submitting presentations proposals can be found at: http://cufp.org/2017/call-for-presentations.html ------------------------------------------------------------------------ 2017 Call for Presentations Workshop for Commercial Users of Functional Programming 2017 Sponsored by SIGPLAN CUFP 2017 Co-located with ICFP 2017 Oxford, UK September 7-9 Talk Proposal Submission Deadline: 9 June 2017 The annual CUFP event is a place where people can see how others are using functional programming to solve real world problems; where practitioners meet and collaborate; where language designers and users can share ideas about the future of their favorite language; and where one can learn practical techniques and approaches for putting functional programming to work. ------------------------------------------------------------------------ Giving a CUFP Talk If you have experience using functional languages in a practical setting, we invite you to submit a proposal to give a talk at the event. We're looking for two kinds of talks: Retrospective reports are typically 25 minutes long. Now that CUFP has run for more than a decade, we intend to invite past speakers to share what they’ve learned after a decade spent as commercial users of functional programming. We will favour experience reports that include technical content. Technical talks are also 25 minutes long, and should focus on teaching the audience something about a particular technique or methodology, from the point of view of someone who has seen it play out in practice. These talks could cover anything from techniques for building functional concurrent applications, to managing dynamic reconfigurations, to design recipes for using types effectively in large-scale applications. While these talks will often be based on a particular language, they should be accessible to a broad range of programmers. We strongly encourage submissions from people in communities that are underrepresented in functional programming, including but not limited to women; people of color; people in gender, sexual and romantic minorities; people with disabilities; people residing in Asia, Africa, or Latin America; and people who have never presented at a conference before. We recognize that inclusion is an important part of our ission to promote functional programming. So that CUFP can be a safe environment in which participants openly exchange ideas, we abide by the SIGPLAN Conference Anti-Harassment Policy: http://www.sigplan.org/Resources/Policies/Anti-harassment If you are interested in offering a talk, or nominating someone to do so, please submit your presentation before 09 June 2017 via the CUFP 2017 Presentation Submission Form: https://goo.gl/forms/KPloANxHHwdiaoVj2 You do not need to submit a paper, just a short proposal for your talk. There will be a short scribe's report of the presentations and discussions but not of the details of individual talks, as the meeting is intended to be more of a discussion forum than a technical interchange. Nevertheless, presentations will be recorded and presenters will be expected to sign an ACM copyright release form. Note that we will need presenters to register for the CUFP workshop and travel to Oxford at their own expense. There are some funds available to would-be presenters who require assistance in this respect. ------------------------------------------------------------------------ Program Committee Alex Lang (Tsuru Capital), co-chair Rachel Reese (Mulberry Labs), co-chair Garrett Smith (Guild AI) Danielle Sucher (Jane Street) Jasper Van der Jeugt (Fugue) Yukitoshi Suzuki (Ziosoft) Evelina Gabasova (University of Cambridge) Brian Mitchell (Jet.com) ------------------------------------------------------------------------ More information For more information on CUFP, including videos of presentations from previous years, take a look at the CUFP website at http://cufp.org. Note that presenters, like other attendees, will need to register for the event. Acceptance and rejection letters will be sent out by July 15th. Guidance on giving a great CUFP talk Focus on the interesting bits: Think about what will distinguish your talk, and what will engage the audience, and focus there. There are a number of places to look for those interesting bits. Setting: FP is pretty well-established in some areas, including formal verification, financial processing, and server-side web services. An unusual setting can be a source of interest. If you're deploying FP-based mobile UIs or building servers on oil rigs, then the challenges of that scenario are worth focusing on. Did FP help or hinder in adapting to the setting? Technology: The CUFP audience is hungry to learn about how FP techniques work in practice. What design patterns have you applied, and to what areas? Did you use functional reactive programming for user interfaces, or DSLs for playing chess, or fault-tolerant actors for large-scale geological data processing? Teach us something about the techniques you used, and why we should consider using them ourselves. Getting things done: How did you deal with large-scale software development in the absence of pre-existing support tools that are often expected in larger commercial environments (IDEs, coverage tools, debuggers, profilers) and without larger, proven bodies of libraries? Did you hit any brick walls that required support from the community? Don't just be a cheerleader: It's easy to write a rah-rah talk about how well FP worked for you, but CUFP is more interesting when the talks also cover what doesn't work. Even when the results were all great, you should spend more time on the challenges along the way than on the parts that went smoothly.

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rts nursery and stopping the world minor gc
by Ruben Astudillo 09 Jun '17

09 Jun '17

I've been reading about garbage collection. I understand that is stop-the-world, parallel and generational. Per capability also exists "the nursery", which is a block of memory where new objects are allocated. When the nursery of a capability gets filled, do we have to stop-the-world just for that local nursery gc?. To me this is different than gen0 or gen1 gc because isn't really a shared resource. -- Ruben Astudillo.

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Haskell in Leipzig 2017: 1st call for papers
by Wolfgang Jeltsch 08 Jun '17

08 Jun '17

Event: Haskell in Leipzig 2017 Time: October 26–28, 2017 Place: HTWK Leipzig, Germany Homepage: https://hal2017.softbase.org/ About ===== Haskell is a modern functional programming language that allows rapid development of robust and correct software. It is renowned for its expressive type system, its unique approaches to concurrency and parallelism, and its excellent refactoring capabilities. Haskell is both the playing field of cutting-edge programming language research and a reliable base for commercial software development. The workshop series Haskell in Leipzig (HaL), now in its 12th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts, and Haskell beginners to listen to talks, take part in tutorials, join in interesting conversations, and hack together. To support the latter, HaL will include a one-day hackathon this year. The workshop will have a focus on functional reactive programming (FRP) this time, while continuing to be open to all aspects of Haskell. As in the previous year, the workshop will be in English. Contributions ============= Everything related to Haskell is on topic, whether it is about current research, practical applications, interesting ideas off the beaten track, education, or art, and topics may extend to functional programming in general and its connections to other programming paradigms. Contributions can take the form of * talks (about 30 minutes), * tutorials (about 90 minutes), * demonstrations, artistic performances, or other extraordinary things. Please submit an abstract that describes the content and form of your presentation, the intended audience, and required previous knowledge. We recommend a length of 2 pages, so that the program committee and the audience get a good idea of your contribution, but this is not a hard requirement. Please submit your abstract as a PDF document at https://easychair.org/conferences/?conf=hal2017 until Friday, August 4, 2017. You will be notified by Friday, August 25, 2017. Hacking Projects ================ Projects for the hackathon can be presented during the workshop. A prior submission is not needed for this. Program Committee ================= * Edward Amsden, Plow Technologies, USA * Heinrich Apfelmus, Germany * Jurriaan Hage, Utrecht University, The Netherlands * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Tallinn University of Technology, Estonia (chair) * Andres Löh, Well-Typed LLP, Germany * Keiko Nakata, SAP SE, Germany * Henrik Nilsson, University of Nottingham, UK * Ertuğrul Söylemez, Intelego GmbH, Germany * Henning Thielemann, Germany * Niki Vazou, University of Maryland, USA * Johannes Waldmann, HTWK Leipzig, Germany Questions ========= If you have any questions, please do not hesitate to contact Wolfgang Jeltsch at wolfgang-it(a)jeltsch.info.

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Arithmetic expressions with random operators
by Mahmoud Murad 08 Jun '17

08 Jun '17

I have the following problem, I want to randomly generate arithmetic expressions based on a number, for example: if I have n = 3, then the expression must have 3 operators like this (4)*(((3+5)-2)). Any advice or hint? I am relatively new to Haskell. Thanks.

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Issue 58 :: Haskell Weekly
by Taylor Fausak 08 Jun '17

08 Jun '17

\ Haskell Weekly \/\/ Issue 58 Welcome to another issue of Haskell Weekly! Haskell is a purely functional programming language that focuses on robustness, concision, and correctness. This is a weekly summary of what's going on in its community. - A Haskell cross compiler for iOS <https://medium.com/@zw3rk/a-haskell-cross-compiler-for-ios-7cc009abe208> So far we have built a Haskell cross compiler for Raspberry Pi, as well as a Haskell cross compiler for Android. To round this off, we will build a cross compiler for iOS as well. With the WWDC signaling the end of 32-bit devices, we will only build the 64-bit cross compiler. - Event sourced aggregates in Haskell <http://blog.akii.de/posts/2017-06-04-eventsourcing-in-haskell.html> In this first post I'll be digging into event sourced aggregates in Haskell. It basically means that instead of persisting some state like "Johns account balance is $100", you keep track of the changes to John's account: "First he deposited $125, then withdrew $25". - The round-trip property <http://teh.id.au/posts/2017/06/07/round-trip-property/index.html> We know that parsers and printers are supposed to be dual. We can simply treat this as a law, and write a property test to enforce it. This is both the simplest useful property test I can think of for a working engineer and the most likely to reliably identify bugs of consequence. - How well do you know your programming tools? Take the survey and test your skills! (ad) <http://vmob.me/DE3Q17Haskellweek> "It is a good survey which, in addition to remembering what I already knew, gave me new tools to learn about and work with." This is how developers feel about the Developer Economics survey. The survey also shows you how you compare to other developers in your country. Plus you may win an iPhone 7 or a Pixel 32GB phone. - Assume it worked and fix it later <https://hackernoon.com/assume-it-worked-and-fix-later-8436d18b7ed3> If your email service is down, it can be beneficial to have the signup succeed regardless. By decoupling the success of an email request from the success of account signup, you can improve the reliability of your application. - Flexible data with Aeson <https://mmhaskell.com/blog/2017/6/5/flexible-data-with-aeson> At a certain point, our Haskell programs have to be compatible with other programs running on the web. This is especially useful given the growing usage of micro-services as an architecture. Regardless, it's very common to be transferring data between applications on different stacks. - Tagless final encoding of a test language <https://wickstrom.tech/programming/2017/06/05/tagless-final-encoding-of-a-t…> I have experimented with a test language encoded in tagless final style, instead of algebraic data types, to support the typed combinators `beforeEach` and `beforeAll`. I want to share the Haskell prototype I ended up with, and explain how I got there. - Can't see the four-est for the trees <http://www.gigamonkeys.com/trees/> It's a fun puzzle so you may want to take a crack at it yourself before reading on. But this isn't really about that puzzle. This is about how sometimes when the mathematical insights aren't flowing it's good to be a programmer. - The Typeclassopedia is now up to date <https://byorgey.wordpress.com/2017/06/07/the-typeclassopedia-is-now-up-to-d…> The title pretty much says it all: I have finally finished (I hope) updating the Typeclassopedia to reflect various recent changes to the language and standard libraries (such as the AMP and BBP/FTP). Along the way I also added more links to related reading as well as more exercises. - Continuations from the ground up <http://blog.ielliott.io/continuations-from-the-ground-up/> It's difficult to learn functional programming without hearing about continuations. Often they're mentioned while talking about boosting the performance of pure functional code, sometimes there's talk of control flow, and occasionally with "time-travel" thrown in there to make it all seem more obscure. - How to send me a pull request <https://www.snoyman.com/blog/2017/06/how-to-send-me-a-pull-request> I find myself repeating a lot of the same comments in pull requests, so I decided to put together a list of what I consider the most important features of a good pull request. Other people will have different feelings on some of these, but the points below are what apply to my projects. Package of the week ------------------- This week's package of the week is Yesod, a web framework for productive development of type-safe, RESTful, high performance web applications. <https://www.stackage.org/package/yesod>

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