- Haskell-Cafe - Haskell.org

Let's plan BayHac 2018
by Dan Burton 09 Oct '17

09 Oct '17

I'm thinking late February this time. How is that looking for everyone? I am also hoping to cut down a touch on the talks and focus a little more on the hacking. Maybe bring back the old koans, or write some new ones. Location has not yet been decided. Obviously it will be somewhere in the San Francisco Bay Area or Silicon Valley. Over the next month or so I will be reviewing the data from the last survey and reaching out to those who expressed interest in organizing the event. Regardless of whether you filled out the survey or not, please feel free to contact me if you are interested in assisting with the planning and organizing of BayHac 2018.

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Kyiv Haskell Learning Group Meetups
by Kostiantyn Rybnikov 09 Oct '17

09 Oct '17

Hi! We're starting a Haskell Learning Group in Kyiv, Ukraine. First Meetup will be at 17 October (Tuesday) and will continue on weekly basis at the Institute of Mathematics. See full info about the first meetup at https://www.meetup.com/Kyiv-Haskell-Learning-Group/events/243945548/ Info about the course itself (in Ukrainian): https://github.com/KyivHaskell/haskell-study-startup See you there!

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ANN: hmep -- genetic multi expression programming package
by masterdeZign 09 Oct '17

09 Oct '17

Dear Haskell community, I am delighted to contribute a new package for the first time. Today, I am happy to announce `hmep` http://hackage.haskell.org/package/hmep/ bringing Multi Expression Programming to Haskell. Multi Expression Programming is a genetic programming variant encoding multiple solutions in the same chromosome. A chromosome is a computer program. Each gene is featuring code reuse. The latest version is of course on GitHub https://github.com/masterdezign/hmep Thank you for your kind attention, Happy Monday, Bogdan Penkovsky

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 09 Oct '17

09 Oct '17

Dear all, If you or one of your students recently completed a PhD in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, open access, deadline 31st October 2017. Please share! Best wishes, Graham ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 31st October 2017 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the PhD student and PhD advisor/supervisor although we encourage them to coordinate. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 31st October 2017. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of PhD award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 1000 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting in the abstract, but do get in touch if this causes significant problems) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Deprecating STM invariant mechanism
by Ben Gamari 09 Oct '17

09 Oct '17

tl;dr. Do you use Control.Monad.STM.always? If so say so on this [1] proposal otherwise the interface may be removed. Hello everyone, GHC's STM subsystem has long had the ability to run user-specified invariant checks when committing transactions, embodied by the Control.Monad.STM.always and alwaysSucceeds functions. However, if Hackage is any indication this feature has seen very little use of the past ten years. In fact, it has very likely been quite broken (#14310) for this entire duration. Consequently, I suggest that we begin deprecating the mechanism. See the deprecation Proposal [1] for full details. Please leave a comment if you object. Cheers, - Ben [1] https://github.com/ghc-proposals/ghc-proposals/pull/77

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CoqPL 2018: Call for Presentations
by Sergey, Ilya 06 Oct '17

06 Oct '17

==================================================================== CoqPL 2018 Coq for Programming Languages -- A Coq users and developers meeting 13 January 2018, co-located with POPL (as usual) Los Angeles, California, United States CALL FOR PRESENTATIONS https://popl18.sigplan.org/track/CoqPL-2018 ==================================================================== Workshop Overview ----------------- The series of CoqPL workshops provide an opportunity for programming languages researchers to meet and interact with one another and members from the core Coq development team. At the meeting, we will discuss upcoming new features, see talks and demonstrations of exciting current projects, solicit feedback for potential future changes, and generally work to strengthen the vibrant community around our favourite proof assistant. Topics in scope include but are no limited to: * General purpose libraries and tactic language extensions; * Domain-specific libraries for programming language formalization and verification; * IDEs, profilers, tracers, debuggers, and testing tools; * Reports on ongoing proof efforts conducted via (or in the context of) the Coq proof assistant; * Experience reports from Coq usage in educational or industrial contexts. To foster open discussion of cutting edge research which can later be published in full conference proceedings, we will not publish papers from the workshop. Workshop Format --------------- The workshop format will be driven by members of the Coq community. We will solicit abstracts for talks and proposals for demonstrations and flesh out format details based on responses. We expect the final program to include experiment reports, panel discussions, and invited talks. Talks will be selected according to relevance to the workshop, based on the submission of an extended abstract. Submission Details ------------------ * Abstract Submission : Monday, October, 16th, 2017 * Author Notification : Monday, November 6th, 2017 * Workshop : Saturday, January 13th, 2018 Submissions should be extended abstracts of 1-2 pages in portable document format (PDF). Submission is via EasyChair: https://easychair.org/conferences/?conf=coqpl2018 Program Committee ----------------- * Yves Bertot, INRIA (Workshop Co-chair) * Ilya Sergey, University College London (Workshop Co-chair) * Andrew Appel, Princeton University * Benjamin Delaware, Purdue University * Xinyu Feng, University of Science and Technology of China * Hugo Herbelin, INRIA * Chantal Keller, Université Paris-Sud * Ekaterina Komendantskaya, Heriot-Watt University * Beta Ziliani, Universidad Nacional de Córdoba Contact ----------------- For any queries, please contact : coqpl2018 at easychair.org<http://easychair.org>

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claiming maintainer position of a HackageDB package
by Guillaume Hoffmann 06 Oct '17

06 Oct '17

Hi, I would like to submit a new version of the following package: https://hackage.haskell.org/package/mime-string Unfortunately, I only received private consent from the current maintainer that I would become the maintainer of this package, more than one month ago. Since then I had not received any answer to my request and I cannot upload a new version to HackageDB. Is there a procedure I could summon to become the maintainer of this package on HackageDB? Thanks Guillaume PS: for the anecdote, darcsden needs this new version of mime-string.

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claiming maintainership of bsd-sysctl package
by info＠maximka.de 06 Oct '17

06 Oct '17

I'm still interested to take over the package. Regards, Alexei > ---------- Original Message ---------- > From: Alexei Pastuchov <info(a)maximka.de> > To: admin(a)hackage.haskell.org > Cc: mhenrion(a)gmail.com, info(a)maximka.de > Date: 31 January 2017 at 22:04 > Subject: bsd-sysctl 1.0.7 > > Hi, > the installation of bsd-sysctl v1.0.7 ends in exception: > Not in scope: `catch' > > I created a pull request for the bug at the end of 2015 and short time later the author/maintainer asked me if I'm interested in taking over the maintainership. > > As described in https://wiki.haskell.org/Taking_over_a_package I asked him to add my hackage account 'palik' to the maintainer group in my last message a couple of months ago and I'm going to ask you for the maintainer permissions. > > Here the aforementioned pull request https://bitbucket.org/mux/bsd-sysctl/pull-requests/ > > Best regards, > Alexei

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[Call for Contributions] Haskell Communities and Activities Report, November 2017 edition (33rd edition)
by Mihai Maruseac 06 Oct '17

06 Oct '17

Dear all, We would like to collect contributions for the 33rd edition of the ============================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 5 November 2017 (please send your contributions to hcar at haskell.org, in plain text or LaTeX format, both are equally accepted) ============================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, please write a short entry and submit it. Even if the project is very small or unfinished or you think it is not important enough --- please reconsider and submit an entry anyway! * If you are interested in an existing project related to Haskell that has not previously been mentioned in the HCAR, please tell us, so that we can contact the project leaders and ask them to submit an entry. * If you are working on a project that is looking for contributors, please write a short entry and submit it, mentioning that your are looking for contributors. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming six months. If you have only recently been exposed to Haskell, it might be a good idea to browse the previous edition --- you will find interesting projects described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the submission deadline. They will then be compiled into a coherent report that is published online as soon as it is ready. As always, this is a great opportunity to update your webpages, make new releases, announce or even start new projects, or to talk about developments you want every Haskeller to know about! Looking forward to your contributions, Mihai Maruseac FAQ: Q: What format should I write in? A: The usual format is a LaTeX source file, adhering to the template that is available at: http://haskell.org/communities/11-2017/template.tex There is also a LaTeX style file at http://haskell.org/communities/11-2017/hcar.sty that you can use to preview your entry. If you do not know LaTeX or don't want to use it or don't have time to translate your entry into it, then please use plain text, it is better to have an entry in plain-text which we will translate than not have it at all. If you modify an old entry that you have written for an earlier edition of the report, you should soon receive your old entry as a template (provided we have your valid email address). Please modify that template, rather than using your own version of the old entry as a template. Q: Can I include Haskell code? A: Yes. Please use lhs2tex syntax (http://www.andres-loeh.de/lhs2tex/) The report is compiled in mode polycode.fmt. Q: Can I include images? A: Yes, you are even encouraged to do so. Please use .jpg or .png format, then. PNG is preferred for simplicity. Q: Should I send files in .zip archives or similar? A: No, plain file attachments are the way. Q: How much should I write? A: Authors are asked to limit entries to about one column of text. A general introduction is helpful. Apart from that, you should focus on recent or upcoming developments. Pointers to online content can be given for more comprehensive or "historic" overviews of a project. Images do not count towards the length limit, so you may want to use this opportunity to pep up entries. There is no minimum length of an entry! The report aims for being as complete as possible, so please consider writing an entry, even if it is only a few lines long. Q: Which topics are relevant? A: All topics which are related to Haskell in some way are relevant. We usually had reports from users of Haskell (private, academic, or commercial), from authors or contributors to projects related to Haskell, from people working on the Haskell language, libraries, on language extensions or variants. We also like reports about distributions of Haskell software, Haskell infrastructure, books and tutorials on Haskell. Reports on past and upcoming events related to Haskell are also relevant. Finally, there might be new topics we do not even think about. As a rule of thumb: if in doubt, then it probably is relevant and has a place in the HCAR. You can also simply ask us. Q: Is unfinished work relevant? Are ideas for projects relevant? A: Yes! You can use the HCAR to talk about projects you are currently working on. You can use it to look for other developers that might help you. You can use HCAR to ask for more contributors to your project, it is a good way to gain visibility and traction. Q: If I do not update my entry, but want to keep it in the report, what should I do? A: Tell us that there are no changes. The old entry will typically be reused in this case, but it might be dropped if it is older than a year, to give more room and more attention to projects that change a lot. Do not resend complete entries if you have not changed them. Q: Will I get confirmation if I send an entry? How do I know whether my email has even reached its destination, and not ended up in a spam folder? A: Prior to publication of the final report, we will send a draft to all contributors, for possible corrections. So if you do not hear from us within two weeks after the deadline, it is safer to send another mail and check whether your first one was received. -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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Determine instance method from class method callsite
by Robin Palotai 06 Oct '17

06 Oct '17

Sorry, I messed up subject and mailing list. Copying to both list now after the mistake (wanted only ghc-devs for specificity). Thanks! 2017-09-19 7:36 GMT+02:00 Robin Palotai <palotai.robin(a)gmail.com>: > Hello GHC devs, > > Before inventing the wheel, want to check if there is a GHC API way to > look up the (fully) resolved instance method from a class method. > > For example, given a code > > data Foo Int deriving Show > > bar = show (Foo 3) > > when inspecting the Typechecked AST for bar's show call, I would like to > get to the Name / Id of 'show' of the 'Show' typeclass. > > I believe I could use splitHsSigmaTy on the HsType of the function call to > get the context, and then evaluate the HsWrapper somehow to find out what > instance dictionary is applied to the class restriction in the context, and > then look up the instance method from the dictionary.. > > Two questions: > > 1) Is there maybe functionality for this? > > 2) If not, is there any guarantee about the constraint order in the > context, at the method call? So I could more easily determine which > constraint's application to look for.. > > Any hints welcome && Thank you! > Robin >

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Cabal hell (8.2.1,/Haskell Package/MacOS X)
by Stuart A. Kurtz 06 Oct '17

06 Oct '17

Dear Cafe, I've had my first extended visit into cabal hell... ghc: 8.2.1 (Haskell Platform) cabal: 2.0.0.2 cabal-install: 2.0.0.0 OS: MacOS X 10.13 (High Sierra) I have problems around trying to install some standard packages: hlint, aeson. A typical error reported by cabal is <command line>: cannot satisfy -package-id hashable-1.2.6.1-14fEJP30YhAG9w115PODz0: hashable-1.2.6.1-14fEJP30YhAG9w115PODz0 is unusable due to shadowed dependencies: text-1.2.2.2-EGUst8sqNAZCw1xLPcmcMH FWIW, the versions of these packages reported by ghc-pkg are hashable-1.2.6.1 text-1.2.2.2 Suggestions welcome... Peace, Stu

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Job opportunity at Scrive
by Jonathan Jouty 05 Oct '17

05 Oct '17

Hey! We have a "full stack" Haskell position that just opened up: https://stackoverflow.com/jobs/156727/haskell-full-stack-developer-scrive Please apply directly on Stack Overflow. I'll be at Haskell eXchange in London next week if you want to meet, otherwise send an email. Cheers. -- Jonathan Jouty *Lead Developer* at *Scrive* www.scrive.com

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Re: [Haskell-cafe] Cabal hell (8.2.1,/Haskell Package/MacOS X)
by Stuart A. Kurtz 05 Oct '17

05 Oct '17

Dear Imants, > Is it possible that some ghc version is installed with /usr prefix, and another with /usr/local > ? > > If yes - try uninstalling the older versions. > You may need to clean up the obsolete library folders. Joy! Which is to say, after several unsuccessful attempts involving progressively more draconian deletion strategies, ending with % uninstall-hs all --remove and reinstalling the Core Platform from the installer, which finally worked. Many thanks! Peace, Stu

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Functional Languages Beat Procedural/Object-Oriented
by Gregory Guthrie 05 Oct '17

05 Oct '17

Functional Languages Beat Procedural/Object-Oriented Application Development Trends David Ramel October 3, 2017 Researchers at the University of Virginia and the University of California, Davis say they have completed a study evaluating the impact of programming languages on software quality, and found functional languages are superior to procedural/object-oriented languages in some respects. The team analyzed more than 700 GitHub projects containing about 63 million lines of source code. The researchers note empirically assessing software quality is complex, shaped by numerous interacting variables. "By triangulating findings from different methods, and controlling for confounding effects such as team size, project size, and project history, we report that language design does have a significant, but modest effect on software quality," the team says. Among their findings is that disallowing type confusion seems to offer an improvement over permitting it, while static typing is somewhat better than dynamic in functional languages. The team also found functional languages are associated with fewer defects than procedural/scripting languages, and that managed memory usage is better than unmanaged. The research was published in the October edition of Communications of the ACM. https://orange.hosting.lsoft.com/trk/click?ref=znwrbbrs9_6-17370x31326fx040… ---------------------------------------------------------------

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Haskell in Leipzig 2017: 2nd call for participation
by Wolfgang Jeltsch 04 Oct '17

04 Oct '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. Invited Speaker =============== * Ivan Perez, University of Nottingham, UK Invited Performer ================= * Lennart Melzer, Robert-Schumann-Hochschule Düsseldorf, Germany Registration ============ Registration information is available on the web page of the local organizers at http://nfa.imn.htwk-leipzig.de/HAL2017/. 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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Loading a csv file with ~200 columns into Haskell Record
by Guru Devanla 04 Oct '17

04 Oct '17

Hello All, I am in the process of replicating some code in Python in Haskell. In Python, I load a couple of csv files, each file having more than 100 columns into a Pandas' data frame. Panda's data-frame, in short is a tabular structure which lets me performs on bunch of joins, and filter out data. I generated different shapes of reports using these operations. Of course, I would love some type checking to help me with these merge, join operations as I create different reports. I am not looking to replicate the Pandas data-frame functionality in Haskell. First thing I want to do is reach out to the 'record' data structure. Here are some ideas I have: 1. I need to declare all these 100+ columns into multiple record structures. 2. Some of the columns can have NULL/NaN values. Therefore, some of the attributes of the record structure would be 'MayBe' values. Now, I could drop some columns during load and cut down the number of attributes i created per record structure. 3. Create a dictionary of each record structure which will help me index into into them.' I would like some feedback on the first 2 points. Seems like there is a lot of boiler plate code I have to generate for creating 100s of record attributes. Is this the only sane way to do this? What other patterns should I consider while solving such a problem. Also, I do not want to add too many dependencies into the project, but open to suggestions. Any input/advice on this would be very helpful. Thank you for the time! Guru

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Catch-all considered harmful?
by Vilem-Benjamin Liepelt 03 Oct '17

03 Oct '17

Catch-all considered harmful? ============================= I have been thinking about a potential source of bugs from catch-all pattern matches on sum types and would like to know your thoughts. Motivation ---------- Totality is usually a desirable property of a function and the catch-all can conveniently buy us totality. But at what price? I have been indoctrinated that rigour goes above convenience (think along the lines of: "Once we indulge in the impurities of I/O, there is no redemption.") I would like to evaluate the trade-offs between convenience for the programmer and a potential source of bugs. My questions to the community— 1. Are there real world examples of bugs caused by catch-alls? 2. Do you think that a language extension that disallows catch-alls (and annotations to opt back in at pattern match sites or type declaration) could be useful for certain code bases? 3. If this is a potential problem, then can you think of any better solutions a compiler could provide (i.e. that don't rely on an IDE / structured editing) other than disallowing catch-alls? Feel free to chip in with your 2p (or 2¢), but please only if you have any concrete experience (or compelling theoretical evidence). Example ------- Consider the sum type: data Answer = No | Yes and the function: foo : Answer -> String foo Yes = "Woo-hoo!" foo _ = "Bother." Say we need to extend our sum type: data Answer = No | Perhaps | Yes However, we forget to handle the new case appropriately in `foo`. The compiler is happy, but at runtime `foo Perhaps` would evaluate to `"Bother."`—with potentially catastrophic consequences. (Please imagine this happening in a large codebase with several contributors, no single one of whom knows the entire codebase.)

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CfP: Dutch FP-day 2018
by Arjen 03 Oct '17

03 Oct '17

Dear all, The next Dutch Functional Programming day will take place on Friday 5th of January 2018, at the Walter Bos Complex of the Dutch Tax Service at the John F. Kennedylaan 8, Apeldoorn. This is the first call for presentations, and we apologize if you received multiple copies. If you would like to give a presentation, please send an e-mail to a.van.weelden(a)belastingdienst.nl with a title, abstract, name of the speaker and expected duration of the talk. We'll try our best to make a proper program out of it with various subjects related to functional programming. Please note that to the nature of the location, registration in advance is required. As well as matching identification (passport, driver's license, or similar) before entering the venue! Photography and/or setting up a local WiFi network is explicitly not allowed. A dinner (pizza's) and drinks will be provided free of charge at the end of the day at the same location. Given that registration is mandatory this time, we'll assume that you stay around for this unless you specify otherwise. More information about registering for attendance and a website with information about the schedule and location will follow soon(ish). Feel free to invite other people who might take an interest. Best regards and looking forward to seeing you, Betsy Pepels and Arjen van Weelden

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Re: [Haskell-cafe] Loading a csv file with ~200 columns into Haskell Record
by dominic＠steinitz.org 03 Oct '17

03 Oct '17

I don’t know if this helps but here’s something I created in 5 minutes yesterday. Once you have the data you can convert to e.g. frames with all the help that types can give. I once used frames on a file with 10,000 columns and it worked (probably I shouldn’t have done this). Also an option is in Chris Done’s blog: https://www.fpcomplete.com/blog/2016/09/data-haskell PS My script below will fail if I have missing data but then I can use something better than read. > {-# OPTIONS_GHC -Wall #-} > > import qualified Data.Vector as V > import qualified Data.ByteString.Lazy as BL > import qualified Data.ByteString.Lazy.Char8 as BLC > import Data.Csv > import Data.List > import Plots > import Diagrams.Prelude > import Diagrams.Backend.Rasterific > > main :: IO () > main = do > evalsCsv <- BLC.readFile "/Users/dom/.local/share/simwork/data/Models/Lorenz.csv" > let records :: Either String (V.Vector (V.Vector BL.ByteString)) > records = decode NoHeader $ BLC.unlines $ BLC.lines evalsCsv > case records of > Left err -> putStrLn err > Right evals -> do > let hdrs :: V.Vector String > hdrs = V.map BLC.unpack $ V.head evals > let zss :: [[Double]] > zss = map (map read) $ map (map BLC.unpack) $ > transpose $ V.toList $ V.map V.toList $ V.drop 1 evals > renderRasterific "diagrams/lorenz.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!1)) > renderRasterific "diagrams/lorenz1.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!2)) > renderRasterific "diagrams/lorenz2.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!0) (zss!!3)) > renderRasterific "diagrams/lorenz3.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!1) (zss!!2)) > renderRasterific "diagrams/lorenz4.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!1) (zss!!3)) > renderRasterific "diagrams/lorenz5.png" (dims2D 500.0 500.0) > (renderAxis $ jSaxis (zss!!2) (zss!!3)) > > jSaxis :: [Double] -> [Double] -> Axis B V2 Double > jSaxis ts xs = r2Axis &~ do > linePlot' $ zip ts xs Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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EduHaskell
by erwig 02 Oct '17

02 Oct '17

Dear Haskell aficionados, We will be using Haskell in an introductory course to computer science for college freshmen. From my past experience in using Haskell for students, the biggest hurdle and source of frustration is the type checker, or more precisely, the error messages generated. I see three major kinds of errors that get in the way of a smoother programming experience: * Errors resulting from overloading * Errors due to undefined type class instances (specifically, Eq and Show) * Errors in the context of parametric polymorphism While these problems are not unsurmountable, having to talk about these errors is a distraction from the major goal of explaining basics of (functional) programming. It would be great to have a Haskell compiler that offers the following features (and maybe others): * Type classes and overloading could be turned off * Eq and Show (and maybe Ord) instances would be automatically defined for any data type definition (when type classes are enabled) My questions are: (1) Does there exist a good solution to this problem already? Should one use Helium? I haven't checked lately, but it used to avoid type classes. This might have the disadvantage of having to switch to GHC in case one wants to use overloading. (I have used Helium in the past, and while I admire the effort, I am not sure it's the best option.) Are there versions of the Prelude available that accomplish some of this? (2) Are there other Haskellers out there who also want a simpler, more educationally suited version of GHCi? (3) If the answer to (1) is NO and to (2) is YES, is there any interest in forming a group for creating something like "EduHaskell"? I'd be grateful for any comments or suggestions! Thanks, Martin

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hs-bibutils 6.2 candidate package
by Václav Haisman 02 Oct '17

02 Oct '17

Hi. I have created a candidate package for hs-bibutils 6.2. This synchronizes the hs-bibutils with Bibutils which it wraps. The candidate is at https://hackage.haskell.org/package/hs-bibutils-6.2/candidate. Please check it out and test it if you are interested. -- VH

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ANN: hledger 1.4
by Simon Michael 01 Oct '17

01 Oct '17

Aloha! I'm pleased to announce hledger 1.4. Thank you release contributors: Nicholas Niro, Hans-Peter Deifel, Jakub Zárybnický, Felix Yan, Mark Hansen, Christian G. Warden, Nissar Chababy and Peter Simons. Also, if I haven't already mentioned it: this year hledger turns 10! Here's the first commit, from January 27 2007: https://github.com/simonmichael/hledger/commit/85864b41 We have come a way, but there is much yet to look forward to. Onward and upward! The next major release is scheduled for 2017/12/31. What is hledger ? ----------------- hledger (http://hledger.org) is an evolving, dependable, robust, cross-platform program for tracking money, time, or any other commodity, using double-entry accounting and a simple plain text file format. It is a haskell reimplementation of Ledger and the plain text accounting concept, providing command-line, curses and web interfaces. hledger aims to be a pleasant and practical tool for personal, business or institutional finance and time tracking. What's new ? ------------ The full release notes are at http://hledger.org/release-notes#hledger-1.4 . Some highlights: - Easy install script: we have a new installation method for the hledger tools, intended to dodge common pitfalls and just-work more often. Building on the stack team's install script, this bash script is cross platform, uses cabal or stack, installs stack and GHC if needed, and installs the latest release of all major hledger packages. See http://hledger.org/download for details. - More batteries included: most experimental addon commands formerly shipped in bin/ are now built in and work out of the box. - New commands: balancesheetequity (a balance sheet including equity), tags (list tags in use), import (detects new transactions in multiple input files and adds them to the main journal, particularly useful with CSV downloads). - Balance reports can be sorted by amount - makes those high expenses easy to spot. - CLI conveniences: @ARGSFILE is expanded to the set of args/flags in ARGSFILE. depth:2 or --depth=2 can be written as -2. - Help improvements: reorganized docs page, a more useful commands list, a smarter help command, --help and -h are the same again (by popular demand), Getting started --------------- See http://hledger.org/download for all install methods. To get the latest hledger release, you may need to build it yourself using stack or cabal. But don't worry, this is.. getting quite painless. The new hledger installer requires only bash and will install everything you need in one step: the hledger tools in $HOME/.local/bin/, and (if required) stack and GHC in $HOME/.stack/. Run it like so: $ curl -sSLO http://hledger.org/hledger-install.sh $ less hledger-install.sh # review script, for the security conscious $ bash hledger-install.sh # install the latest hledger tools Ensure $HOME/.local/bin is in your $PATH. Now try some commands: $ hledger -h # quick help $ hledger help # list built-in manuals $ hledger add # record some transactions $ hledger # list available commands Now perhaps work through the tutorial at http://hledger.org/step-by-step.html Or review the fine documents, presentations etc. at http://hledger.org and http://plaintextaccounting.org Or say hello and ask questions in the #hledger IRC channel on Freenode: http://irc.hledger.org If you have been finding hledger useful, I invite you to become a sponsor or contributor to make it stronger. Donate using one of the funding links on the home page, give feedback, report bugs, send pull requests, write about it, or help in some other way. Thanks for your support! I hope to meet you online. -Simon

3 2

Mutable data structures and asynchronous exceptions
by Станислав Черничкин 30 Sep '17

30 Sep '17

It's quite hard to implement mutable data structures in presence of asynchronous exceptions. Since exception can arise at any point, it is not possible to guarantee atomicity of operation, hence mutable data structure may remain in incorrect state in case of interruption. One can certainly use maskAsyncExceptions# and friends to protect critical regions, but masking function are living in IO, mutable data structures on other hand trend to be state-polymorphic (to allow it usage in ST). This lead to conflicting requirements: - One should not care about asynchronous exceptions inside ST (it is not possible to catch exception in ST, hence not possible to use something in invalid state). More over, it is not even possible to do write “exception-safe” code, because masking functions not available. - One should provide accurate masking then using same data structures in IO. So I want do discuss several questions topics on this case. 1. Impact. Are async exceptions really common? Would not be easier to say: “ok, things can go bad if you combine async exceptions with mutable data structures, just don't do it”. 2. Documentation. Should library authors explicitly mention async exceptions safety? For example https://hackage.haskell.org/package/hashtables – is it async exceptions safe when used in IO? Or even worse https://hackage.haskell.org/package/ghc-prim-0.5.1.0/docs/GHC-Prim.html#v:r… - what will happened in case of async exception? This functions is sate-polimorphic, will it implicitly mask exceptions if used from IO? 3. Best practices. How should we deal with problem? Is creating separate versions of code for ST and IO is the only way? Probably it is possible to add “mask” to something like https://hackage.haskell.org/package/primitive-0.6.2.0/docs/Control-Monad-Pr… emit mask in IO instance and NOOP in ST version? Or maybe somebody know better patterns for async exeption safe code? -- Sincerely, Stanislav Chernichkin.

5 5

Reinventing the wheel? Does any existing package provide an applicatively lifted (>>) ?
by Viktor Dukhovni 28 Sep '17

28 Sep '17

When generating a report file from a database I found it much more efficient (significantly shorter runtime) to represent each row by an I/O action that prints the row, rather than to construct a Row object that to print and throw away. But the naive way to construct the I/O action can be tedious to maintain once the column count gets appreciably high: newtype Foo = Foo { _foo :: IO () } instance FromRow Foo where fromRow = Foo <$> (rowPrinter <$> field <*> field <*> field <*> ... <*> field) where rowPrinter :: Type1 -> Type2 -> Type3 -> ... -> TypeN -> IO () rowPrinter p1 p2 p3 ... pN = do printP1 printP2 printP3 ... printPN So I decided to applicatively decompose the rowPrinter function (with the actual name of "andthen" to be determined later) as: rowPrinter = (printP1 <$> field) `andthen` (printP2 <$> field) `andthen` (printP3 <$> field) `andthen` ... (printPN <$> field) which avoids the need to package the column printers explicitly into a single function, and may be somewhat more efficient a well. What was not immediately obvious to me was whether there's an "off the shelf" implementation of "andthen" I could just reuse. The necessary operator satisfies: andthen (f (m a)) (f (m b)) = f (ma >> mb) or, equivalently: a `andthen` b = (>>) <$> a <*> b for which http://pointree.io dutifully gives me: andthen = (<*>) . ((>>) <$>) Its type signature is: Prelude> :set prompt "l> " l> :m + Control.Applicative l> :m + Control.Monad l> :t ((<*>) . ((>>) <$>)) ((<*>) . ((>>) <$>)) :: (Monad m, Applicative f) => f (m a) -> f (m b) -> f (m b) l> It seems to me that this would have been done before, and the operator would already be present in some package, but I'm having trouble finding it. (Due to the hidden constructors of FromRow defining a Semigroup does not work out here, so I can't use (<>), which also inconveniently conflicts with Monoid (<>)). So my question is whether the operator in question is already available, under some name in some package, or else suggested names for it if new. -- Viktor.

5 6

[ANN] brittany-0.8.0.3
by lennart spitzner 28 Sep '17

28 Sep '17

- Support for ghc-8.2.1 - Fix quadratic performance bug full changelog at https://hackage.haskell.org/package/brittany-0.8.0.3/changelog -- lennart

1 0

[hs-bibutils] intention to take over package
by Václav Haisman 28 Sep '17

28 Sep '17

Hi. I would like to take over the hs-bibutils Hackage package. It has not been updated since 2014, the listed maintainer is not responsive to emails, and listed home page is 404 page. -- VH

1 1

Re: [Haskell-cafe] EduHaskell
by erwig 25 Sep '17

25 Sep '17

Thanks for all the useful hints and suggestions! Maybe I should have explained the constraints (and where they come from) in more detail. First, the course is NOT an introduction to programming, but an introduction to computer science more generally and thus also discusses several topics not typically addressed by a programming course. Second, computing concepts are introduced with the help of stories, and programming will only take place in the second half of the course (more details about the approach can be found at web.engr.oregonstate.edu/~erwig/SBT) Thus the goal of minimizing the need for explaining advanced type system features. Also, we have already created Haskell code, so that's why Elm, although a really nice language, is currently not an option because of its different syntax. Code.world is also a cool system, but we do currently require a REPL. I definitely will take another look a Helium. Again, thanks for all the responses so far! I'm still wondering which, if any, of the existing alternative preludes would potentially be a good substitute for educational purposes. -- Martin

2 1

(no subject)
by Vladyslav Nikolayevich 25 Sep '17

25 Sep '17

1 0

deploy wxHaskell app on Windows
by Olaf Klinke 25 Sep '17

25 Sep '17

Dear Cafe, I need help deploying a wxHaskell application on Windows. (The gui(a)haskell.org list seems to be dormant, as is wxhaskell-users on sourceforge.) I am explicitly CC-ing some people who recently posted about wxHaskell on this list. TL;DR: How to deploy a wxHaskell application on several Windows machines? Option (a): Automate the installation of DLLs and tweaking of PATH Option (b): Build static libs of wxWidgets to be linked into a static binary. I don't know how to do either. I developed a GUI application based on wxWidgets. I love the wx package, since wxWidgets provides all the high-level dialogs I need, like file and date pickers. The necessary installations on my Linux development machine went like a charm. Next I tried a Windows 10 machine. I installed stack, which installed a ghc.exe in %HOME%/AppData/Local/Programs/.../bin/ and cabal and stack binaries in %HOME%/AppData/Roaming/local/bin/. I downloaded a wx-config.exe binary and placed it in the latter directory and added that to the PATH. I downloaded wxInstall-Achelanne-64.0.1 and after adding the above path to ghc.exe to it's Install.bat, the Installation completed. Install.bat suggested to add two directories to the PATH, which I did. I set WXWIN to wxInstall-Achelanne-64.0.1/wxWidgets and WXCFG to gcc_dll/mswu With this, wx-config outputs some flags if requested. Next, I added %WXWIN%/include to extra-include-dirs and %WXWIN%/lib/gcc_dll to extra-lib-dirs in my stack.yaml. I also added %WXWIN%/DLLs to the extra-lib-dirs in the .cabal file. %WXWIN%/include/wx/platform.h mentions wx/setup.h which is not there. Remedy: Copy %WXWIN%/include/wx/msw/setup.h to %WXWIN%/include/wx/setup.h I believe I did set SHARED=0 in the wxWidgets config but there are no .lib, only .dll files in %WXWIN%, so I can not use ghc -optl-static. Hence the binaries produced by stack need to be told the place of the DLLs via the PATH environment variable. This is something I'd like to avoid on all the machines. Any suggestions welcome. Olaf

3 3

Re: [Haskell-cafe] EduHaskell
by Johannes Waldmann 24 Sep '17

24 Sep '17

Dear Martin, I use Haskell for teaching as well (not for beginners) [1]. I do use ghci in lab classes. For the problems you mention, I have these sort-of work-arounds: > Errors resulting from overloading numerical literals, arithmetical operators? avoid built-in (Prelude) numbers and the Num class. stuff that's been generalized from list to Foldable (e.g., length)? avoid built-in (Prelude) lists [2] > Errors due to undefined type class instances > (specifically, Eq and Show) I think these classes are somewhat easy to motivate - at least Eq is (we need "==" to notate and test properties of programs, not every type has decidable equality (functions have not), so we need to mark the types that do) For Show, it's not that nice (ghci uses "show" but implicitly - then why do we need to write the Show instance explicitly) Still, adding "deriving (Eq, Show)" after each data declaration is not too much of a burden. I agree it is a distraction. > Errors in the context of parametric polymorphism Well, it's an important concept to teach, so it is natural that it takes some time and work. (slightly tangential - I think it would already help if it would be easier to declare types of identifiers - to remove unwanted polymorphism. E.g., "\ (x::Bool) (y::Bool) -> x || y" currently requires a language pragma (!) whose name mentions type variables (!!) ) - Johannes. [1] https://www.imn.htwk-leipzig.de/~waldmann/talk/17/wflp [2] https://www.imn.htwk-leipzig.de/~waldmann/etc/untutorial/list-or-not-list/

1 0

3rd International Workshop on Real World Domain Specific Languages (RWDSL'18)
by Rob Stewart 22 Sep '17

22 Sep '17

CALL FOR PAPERS ================================= 3rd International Workshop on Real World Domain Specific Languages https://sites.google.com/site/realworlddsl In conjunction with The International Symposium on Code Generation and Optimisation 2018. http://cgo.org/cgo2018/ Vienna, Austria, 24 February, 2018 ==================================== As the use of computers proliferates, the complexity and variety of systems continues to grow. As a result, it is becoming increasingly inflexible to "hard wire" behaviours into software. Software developers can enable more control over their software configurations by exploiting Domain Specific Languages (DSLs). Such DSLs provide a systematic way to structure the underlying computational components: to coin a phrase, a DSL is a library with syntax. There is an enormous variety of DSLs for a very wide range of domains. Most DSLs are highly idiosyncratic, reflecting both the specific natures of their application domains and their designers' own preferences. This workshop will bring together constructors of DSLs for "real world" domains; that is, DSLs intended primarily to aid in building software to solve real world problems rather than to explore the more theoretical aspects of language design and implementation. We are looking for submissions that present the motivation, design, implementation, use and evaluation of such DSLs. ================================= Key Dates: ---------------- Paper submission deadline : 15th December2017 Author notification: 26th January 2018 Final manuscript due: 9th February 2018 Workshop: 24th February 2018 ---------------- Submission Instructions: The EasyChair submission page for this workshop is: https://easychair.org/conferences/?conf=rwdsl18 We anticipate that accepted submissions will be published in the ACM Digital Library within its International Conference Proceedings Series, as were RWSDL'16 and RWDSL'17. Submissions should be 8-10 pages in ACM double-column format. Authors should follow the information for formatting ACM SIGPLAN conference papers, which can be found at http://www.acm.org/publications/proceedings-template. Full submission details are on the workshop web page. ================================= Program Chairs Rob Stewart, Heriot-Watt University, UK Greg Michaelson, Heriot-Watt University, UK PC Members Riyadh Baghdadi, MIT, USA Allin Cottrell, Wake Forest University, USA Nina Dethlefs, University of Hull, UK And Gill, X - The Moonshot Factory, USA Kevin Hammond, University of St Andrews, UK Patrick Maier, University of Glasgow, UK Mathijs Schuts, Phillips Healthcare, Netherlands Simon Thompson, University of Kent, UK Phil Trinder, University of Glasgow, UK Contact Please email inquiries concerning the workshop to: R.Stewart(a)hw.ac.uk

1 0

Munich Haskell Meeting, 2017-09-25 @ 19:30
by Christian Neukirchen 22 Sep '17

22 Sep '17

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, September 25 at Max Emanuel Brauerei 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-sep-2017/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

1 0

Curious why there's no ioe_description accessor in System.IO.Error?
by Viktor Dukhovni 21 Sep '17

21 Sep '17

The IOError type re-exported from GHC.IO.Exception by System.IO.Error has accessors for some of the error elements fields, but is notably missing an accessor for ioe_description, which is only available as "ioeGetErrorString" for UserError, for all other errors you just get the string form of the error type: ioeGetErrorType :: IOError -> IOErrorType ioeGetErrorString :: IOError -> String ioeGetLocation :: IOError -> String ioeGetHandle :: IOError -> Maybe Handle ioeGetFileName :: IOError -> Maybe FilePath ioeGetErrorString ioe | isUserErrorType (ioe_type ioe) = ioe_description ioe | otherwise = show (ioe_type ioe) the real ioe_description for other error types can only be brought into scope by importing GHC.IO.Exception instead, or alternatively via the System.IO.Error.Lens: -- | Error type specific information. description :: Lens' IOException String description f s = f (ioe_description s) <&> \e -> s { ioe_description = e } {-# INLINE description #-} I am curious why ioeGetDescription was left out of System.IO.Error, and/or why it should not be added? Somehow it feels "wrong" to import GHC.IO.Exception instead of System.IO.Error just to get at the specific error text... Is it the case that, given all the other language extensions my code depends on, I should not have any qualms about importing GHC.* modules? Or perhaps is it the case that one should just start using lens, and so adding "missing" record accessors just delays migration to the right way and is no longer a priority? -- Viktor.

1 0

Traversable instance for ((->) a)?
by David Banas 20 Sep '17

20 Sep '17

Is there a Traversable instance for ((->) a)? -db

2 1

Re: [Haskell-cafe] Why is Haskell so slow (comparing to Java/Scala)?
by Saurabh Nanda 20 Sep '17

20 Sep '17

Intresting. Wont using "void" or "_ <- forM blah" have the same effect? Why not? On 20-Sep-2017 9:37 PM, "Nick Smallbone" <nick(a)smallbone.se> wrote: Hi Stanislav, Станислав Черничкин <schernichkin(a)gmail.com> writes: > I've wrote simple Haskell benchmark program, which populated primitive vector > from vector package: > > ... > void $ for [0..1000000 - 1] $ flip (P.unsafeWrite v) (1 :: Int) 'for' is a variant of 'map' - it returns a list of results (in this case a list of a million () values). Instead you should use 'forM_' (note the underscore) from Control.Monad, which discards the result - that cuts the runtime by a huge amount when I try it. (And make sure to compile with -O too.) Nick _______________________________________________ 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.

3 2

Call for Contributions: BOB 2018 - Berlin, Feb 23, 2018
by Matthias Fischmann 20 Sep '17

20 Sep '17

BOB Conference 2018 "What happens when we use what's best for a change?" http://bobkonf.de/2018/en/cfp.html Berlin, February 23 Call for Contributions Deadline: October 29, 2017 You are actively engaged in advanced software engineering methods, implement ambitious architectures and are open to cutting-edge innovation? Attend this conference, meet people that share your goals, and get to know the best software tools and technologies available today. We strive to offer a day full of new experiences and impressions that you can use to immediately improve your daily life as a software developer. If you share our vision and want to contribute, submit a proposal for a talk or tutorial! Topics ------ We are looking for talks about best-of-breed software technology, e.g.: - functional programming - persistent data structures and databases - types - formal methods for correctness and robustness - abstractions for concurrency and parallelism - metaprogramming - probabilistic programming - math and programming - controlled side effects - beyond REST and SOAP - effective abstractions for data analytics - ... everything really that isn’t mainstream, but you think should be. Presenters should provide the audience with information that is practically useful for software developers. We’re especially interested in experience reports. But this could also take other forms, e.g.: - introductory talks on technical background - overviews of a given field - demos and how-tos Requirements ------------ We accept proposals for presentations of 45 minutes (40 minutes talk + 5 minutes questions), as well as 90 minute tutorials for beginners. The language of presentation should be either English or German. Your proposal should include (in your presentation language of choice): - an abstract of max. 1500 characters. - a short bio/cv - contact information (including at least email address) - a list of 3-5 concrete ideas of how your work can be applied in a developer’s daily life - additional material (websites, blogs, slides, videos of past presentations, ...) Submit here: https://docs.google.com/forms/d/e/1FAIpQLSdjgwulSMpaITJ6q6cK_ndrfR1FlEs_HQl… Organisation - direct questions to contact at bobkonf dot de - proposal deadline: October 29, 2017 - notification: November 13, 2017 - program: December 1, 2017 NOTE: The conference fee will be waived for presenters, but travel expenses will not be covered. Speaker Grants -------------- BOB has Speaker Grants available to support speakers from groups under-represented in technology. We specifically seek women speakers and speakers who are not be able to attend the conference for financial reasons. Details are here: http://bobkonf.de/2018/en/speaker-grants.html Shepherding ----------- The program committee offers shepherding to all speakers. Shepherding provides speakers assistance with preparing their sessions, as well as a review of the talk slides. Program Committee ----------------- (more information here: http://bobkonf.de/2018/en/programmkomitee.html) - Matthias Fischmann, zerobuzz UG - Matthias Neubauer, SICK AG - Nicole Rauch, Softwareentwicklung und Entwicklungscoaching - Michael Sperber, Active Group - Stefan Wehr, factis research Scientific Advisory Board - Annette Bieniusa, TU Kaiserslautern - Torsten Grust, Uni Tübingen - Peter Thiemann, Uni Freiburg

1 0

Haskell job opportunity at RELEX Solutions in Helsinki, Finland
by samuli.thomasson＠paivola.fi 19 Sep '17

19 Sep '17

Would you like to get paid for writing Haskell? And do you live in Helsinki, Finland area (or could re-locate)? If yes, please read on. RELEX Solutions is Europe’s fastest growing provider of integrated retail and supply chain planning solutions. We are now hiring one or two Haskell programmers in Helsinki, Finland to join our small but impactful group of Haskellers to develop our internal tools. You would be working pretty much exclusively in Haskell and Elm. Exact role is somewhat flexible, depending on what other skills you might bring to the table. Read more and apply now here: https://www.relexsolutions.com/open-positions/#op-209192-haskell-and-elm-en… A good working knowledge of general Haskell programming is preferred, although eager learners can and should apply as well - if it's a good match, you just pick up the skills on the job. Unfortunately, we can't accept full remote for this position, so you should be able to be be present at the Helsinki office at least some days every week. Other details are largely negotiable. Note that the deadline for applications is quite soon, by October 2nd. Regards, Samuli Thomasson

1 0

Eindhoven Haskell Meetup session - Oct 3, 2017
by Damian Nadales 19 Sep '17

19 Sep '17

Dear All, A new edition of our Haskell meetup will be held in Eindhoven: https://www.meetup.com/preview/Eindhoven-Haskell-Meetup/events/243342181 I would like to invite all the people that might be around this area. Also if you don't live close by, but you're visiting and want to give a talk please let me know, as we can always use a speaker. And at the same time I want to thank to the speakers that came (and will come) from far away to support his meetup (the Haskell community is -in my experience- great!). Kind regards, Damian.

1 0

Haskell Programmers Wanted
by Brian Hurt 19 Sep '17

19 Sep '17

Code Haskell. Build great things. We’re Wrinkl, a well-funded startup working closely with Obsidian Systems to build a powerful new communications platform. We use Haskell on both the backend and the frontend (using GHCJS and Reflex). And we’re looking to hire Haskell developers, preferably in the Philly area or willing to relocate to Philly. If this sounds interesting, visit https://www.wrinkl.com/jobs/ for more info. Women and minorities strongly encouraged to apply. Brian

1 0

ghc-devs@haskell.org
by Robin Palotai 19 Sep '17

19 Sep '17

Hello GHC devs, Before inventing the wheel, want to check if there is a GHC API way to look up the (fully) resolved instance method from a class method. For example, given a code data Foo Int deriving Show bar = show (Foo 3) when inspecting the Typechecked AST for bar's show call, I would like to get to the Name / Id of 'show' of the 'Show' typeclass. I believe I could use splitHsSigmaTy on the HsType of the function call to get the context, and then evaluate the HsWrapper somehow to find out what instance dictionary is applied to the class restriction in the context, and then look up the instance method from the dictionary.. Two questions: 1) Is there maybe functionality for this? 2) If not, is there any guarantee about the constraint order in the context, at the method call? So I could more easily determine which constraint's application to look for.. Any hints welcome && Thank you! Robin

1 0

Haskell in Leipzig 2017: 1st call for participation
by Wolfgang Jeltsch 18 Sep '17

18 Sep '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. Invited Speaker =============== * Ivan Perez, University of Nottingham, UK Invited Performer ================= * Lennart Melzer, Robert-Schumann-Hochschule Düsseldorf, Germany Registration ============ Registration information is available on the web page of the local organizers at http://nfa.imn.htwk-leipzig.de/HAL2017/. 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.

1 0

Cabal: updating environment variable in a dependency
by aditya siram 17 Sep '17

17 Sep '17

Hi all, I have two separate packages, a library and an app. In the library's Setup.hs I set the LIBRARY_PATH environment variable to a place where I install a custom C shared library, but when the app is built LIBRARY_PATH is empty. I realize that GHC can build and link C code but for the purposes of this project that wasn't workable. So is there a way to make this environment variable hack work or, even better, a good way a dependency can pass custom information to its dependents? Thanks! -deech

1 0

Maintenance of streaming and streaming-bytestring
by Andrew Martin 16 Sep '17

16 Sep '17

David Feuer brought this up two weeks ago [0]. The maintainer of streaming and streaming-bytestring has been unreachable, and provided his continued absence, I would like to become a maintainer of these two libraries. I have put up PRs fixing issues [1] and I've offered on the issue tracker to become a comaintainer [2]. I use this library a lot at work, so I have an interest in keeping it in good shape. [0] https://mail.haskell.org/pipermail/libraries/2017-August/028141.html [1] https://github.com/michaelt/streaming-bytestring/pull/11 [2] https://github.com/michaelt/streaming-bytestring/issues/19 -- -Andrew Thaddeus Martin

6 12

How to write a polymorphic serializer?
by Viktor Dukhovni 16 Sep '17

16 Sep '17

I tried to implement a polymorphic serializer that uses a enclosed MVar () to serialize an action in an arbitrary IO monad, without a need for its user to resort to explicit liftIO calls. So, as a first step I create a typeclass that has a natural default implementation, and some instances for the Monads of interest that just use the natural default: type Serially m = (MonadIO m) => forall a. IO a -> m a class (MonadIO m) => Serializable m where serialize :: MVar () -> Serially m serialize lock = liftIO . withMVar lock . const instance Serializable IO instance Serializable (StateT Int IO) ... With this, given: foo :: Serially IO -> ... -> IO () foo serially ... = do ... serially $ ... ... bar :: Serially (StateT Int IO) -> ... -> StateT Int IO () bar serially ... = do ... serially $ ... ... I can write: lock <- newMVar () foo (serialize lock) ... bar (serialize lock) and the type system figures out the correct version of serialize for foo's and bar's actual monad. Is it possible to create a single "serialize lock" closure that works for both "foo" and "bar"? Something that works along the lines of: let x = liftIO . withMVar lock . const :: ??? foo x ... bar x ... If I leave out the "liftIO", then I can of course use: x :: forall a. IO a -> IO a and the "liftIO" can be put explicitly into "foo" and "bar". foo x ... = liftIO $ x $ ... bar x ... = liftIO $ x $ ... but is it possible for "x" to both be polymorphic with respect to its user's monad and at the same time to be a *closure* around some MVar, and thus not directly a method of a type class. Of course needing to add an extra "liftI0" here and there is not onerous, I'm mostly just curious whether I'm missing something that can hide that boilerplate call in the serializer implementation. -- Viktor.

2 2

Executing conduit streams in parallel leads to memory leaks
by Simon Hafner 13 Sep '17

13 Sep '17

When I run my conduit without any additions, it works as expected, with low constant memory usage, as advertised. It's a bit slow, so I tried to speed it up with worker pools (via parallel-io) and staged folding (via stm-conduit). However, then the memory usage indicates all the ByteString from the file readings are being fully allocated and kept in memory, even though they're not being used after a step of conduit. [1] I thought maybe because of the closing IO, the release of the file handle somehow keeps the read string in memory, so I wanted to make absolutely sure that's not the problem. [2] Switch out the `Lib.readFile` with `B.readFile` to undo that specific part. I was not using a worker pool in the beginning, so maybe the `mapConcurrently_` somehow allocated all the threads, but with the pooled solution, that should be solved as well. What else could cause all the ByteStrings to be kept in memory in the parallel version? The example is available on: https://github.com/reactormonk/non-constant-memory [1] https://github.com/reactormonk/non-constant-memory/blob/master/src/Lib.hs#L… [2] https://github.com/reactormonk/non-constant-memory/blob/master/src/Lib.hs#L…

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HPC and coverage report
by Baa 13 Sep '17

13 Sep '17

Hello Everyone. To generate coverage, Haskellers use HPC. HPC has command report [--xml-output] ... which allows to get XML output of coverage. Jenkins CI "understands" Cobertura Coverage XML format, which is shown as code source marked with red/green/etc background lines - uncovered/covered code lines. Also it's possible to mark branches (if/else/etc). It's true for Python, Java, etc. Can HPC (or other Haskell tool) does the same, i.e. generate Cobertura-compatible XML (to be understandable by Jenkins CI) ? What peoples use for coverage reporting under Jenkins CI w/ Haskell ? Is this `hpc report --xml-output` compatible w/ Jenkins CI ? === Best regards, Paul

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Is this a GHC parser error? A test case compiles from one line but not another.
by Jeffrey Brown 10 Sep '17

10 Sep '17

The test suite below[1] does what it's supposed to. The last line of it is a commented-out test case: -- assertBool "broken" $ True If I uncomment that, it fails to compile: > :reload [13 of 13] Compiling TParse ( test/TParse.hs, interpreted ) test/TParse.hs:67:3: error: parse error on input ‘assertBool’ | 67 | assertBool "broken" $ True | ^^^^^^^^^^ Failed, 12 modules loaded. > However, if I move it to somewhere earlier in the code, it works. [1] https://github.com/JeffreyBenjaminBrown/digraphs-with-text/blob/e5afd39b950… -- Jeff Brown | Jeffrey Benjamin Brown Website <https://msu.edu/~brown202/> | Facebook <https://www.facebook.com/mejeff.younotjeff> | LinkedIn <https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss messages here) | Github <https://github.com/jeffreybenjaminbrown>

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Re: [Haskell-cafe] Haskell Numerics / Data Science at ICFP
by Doug McIlroy 08 Sep '17

08 Sep '17

I won't be at ICFP, but would like to put in a reminder about the shabbiness of GHC floating-point output conversion. When I raised this issue once before, I got the surprising reaction that speed was more important than accuracy. Doug McIlroy

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floating point conversion
by Carter Schonwald 07 Sep '17

07 Sep '17

On Wed, Sep 6, 2017 at 5:22 PM, Doug McIlroy <doug(a)cs.dartmouth.edu> wrote: > I won't be at ICFP, but would like to put in a reminder about > the shabbiness of GHC floating-point output conversion. When I > raised this issue once before, I got the surprising reaction > that speed was more important than accuracy. > @doug: could you point me to the issue ? i'm actually allocating some of my time over the next year to improving floating point matters in ghc and the standard, and specific issues you can point me to that you've previously articulated would be super helpful :) > > Doug McIlroy > _______________________________________________ > 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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optparse-applicative in stack LTS <= 9.3
by Viktor Dukhovni 06 Sep '17

06 Sep '17

FYI, the version of optparse-applicative (0.13.2.0) in Stack LTS-9.3 and earlier does not appear to handle the "noIntersperse" info modifier correctly. Instead of stopping parsing flags after the first non-option argument, it instead simply never parses any options. This is fixed in 0.14.0.0, which is in "Stackage Nightly". Perhaps someone else will run into the same issue. And it would of course be nice to see 0.14.0.0 appear in an upcoming LTS version (say 9.4). -- Viktor. Demo program, this fails to even process "--help" with the outdated optparse-applicative, which just reports all arguments as positional: module Main (main) where import Options.Applicative import Data.Monoid ((<>)) data Opts = Opts { bl :: Bool , fl :: Bool , st :: Maybe String , pos :: String , args :: [String] } deriving (Show) main :: IO () main = do let parse = Opts <$> switch ( long "bool" <> short 'b' ) <*> switch ( long "flag" <> short 'f' ) <*> optional ( strOption ( long "string" <> short 's' ) ) <*> strArgument ( metavar "FILE" ) <*> many ( strArgument ( metavar "ARGS..." ) ) i = info (helper <*> parse) $ fullDesc <> noIntersperse <> header "Option parser" <> progDesc "- test POSIX-style options" execParser i >>= print -- Viktor.

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