October 2017 - Haskell-Cafe

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 05 Oct '17

05 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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