- Haskell-Cafe - Haskell.org

Why does [1.0, 3 ..4] contain 5?
by Bence Kodaj 19 Oct '16

19 Oct '16

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tokenize parser combinators and free applicatives
by Ruben Astudillo 18 Oct '16

18 Oct '16

Hi all on [1] it is said the following "Dealing with whitespace and comments is awkward in the parser; you need to wrap everything in a token combinator. (If you decide to do that, at least use a free applicative functor to ensure that you don’t forget to consume that whitespace)." Reading on `free` the def of Ap, frankly I don't see how can the free applicative be used for this. Anybody could drop a hint? I would appreciate it. [1]: https://ro-che.info/articles/2015-01-02-lexical-analysis -- Ruben

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1TB vsize for all haskell processes?
by Michael Alan Dorman 18 Oct '16

18 Oct '16

Hey, haskell-cafe, I realize that this should not be a problem, but it is very strange to me that *every* haskell process on my system has a 1TB VSIZE. If I sort my `ps auwx` output on vsize, the top of the list looks like: mdorman 1208 0.0 0.1 1074011536 12500 ? S Oct14 0:04 /home/mdorman/.xmonad/xmonad-x86_64-linux mdorman 21900 0.0 0.2 1074111408 19712 pts/1 Sl+ 09:06 0:00 cabal run melpa2nix -- --output melpa-generated.nix --melpa /home/mdorman/src/melpa --work /home/mdorman/src/emacs2nix/.workdir mdorman 1363 0.0 0.1 1074383784 13052 ? Sl Oct14 1:14 /home/mdorman/.cache/taffybar/taffybar-linux-x86_64 +RTS -I0 -V0 --RTS --dyre-master-binary=/nix/store/6skvglp84w5xzqx8dxxydazk1zj8h2ih-taffybar-0.4.6/bin/taffybar mdorman 21981 8.6 0.5 1076223012 42308 pts/1 Sl+ 09:06 0:19 /home/mdorman/src/emacs2nix/dist/build/melpa2nix/melpa2nix --output melpa-generated.nix --melpa /home/mdorman/src/melpa --work /home/mdorman/src/emacs2nix/.workdir Each of those haskell processes has a vsize 5 orders of magnitude more than their resident set size, whether it's the two I always have running (xmonad and taffybar), or in this case, cabal itself, as well as the compiled executable it's running. I've spent a reasonable amount of time attempting to google this, to no avail. Is this perhaps a peculiarity of how GHC was built? I'm running on nixos-unstable, using ghc-8.0.1---is there some compilation that we should or shouldn't be setting? Thanks for any guidance, Mike.

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Easy cross platform CI testing of Haskell packages
by Harendra Kumar 18 Oct '16

18 Oct '16

Hi, If as a package maintainer, you want to: * test your package with cabal & stack both * test your package on Linux, Mac, Windows * test your package on travis, appveyor or local machine in the same way * make sure that the _source dist_ that you are going to upload is tested * upload coverage report to coveralls.io * customize the build your way But you do not want the drudgery and the pain of writing elaborate shell scripts inside travis or appveyor yaml config and then debug them, then this script is for you. You just have to declare some environment variables in your build matrix and finally call this script and you are done. It works consistently the same way for all build types so you don't worry about whether all platforms are testing the same way or not. * Script: https://github.com/harendra-kumar/package-test * Travis Example: https://github.com/harendra-kumar/xls/blob/master/.travis.yml * Appveyor Example: https://github.com/harendra-kumar/xls/blob/master/appveyor.yml Feedback and suggestions are welcome! -harendra

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An use case of the Free-Monad: logging
by Damian Nadales 18 Oct '16

18 Oct '16

Hi, I'm trying to figure out how would you incorporate logging when using the free monad. I've made the following question to StackOverflow: http://stackoverflow.com/questions/40105759/logging-using-the-free-monad Maybe somebody have any ideas. Thanks, Damian.

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conference rating for Haskell Symposium
by Kazu Yamamoto 18 Oct '16

18 Oct '16

Hello, I would like to know a reasonable conference rating for Haskell Symposium. Many rating pages have only Haskell Workshop. For instance, it is categorized as Rank C: http://lipn.univ-paris13.fr/~bennani/CSRank.html Should we ask such pages to register Haskell Symposium? --Kazu

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code.haskell.org down
by Henning Thielemann 17 Oct '16

17 Oct '16

Currently, both HTTP and SSH to code.haskell.org fail with a timeout. :-(

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Arrows and Computation exercises?
by David Banas 17 Oct '16

17 Oct '16

Hi all, I’m wondering if anyone else happens to be working their way through the exercises in Ross Paterson’s *Arrows and Computation*, and would like to compare notes and/or discuss solutions to his exercises. Here are mine, so far: https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/… <https://htmlpreview.github.io/?https://github.com/capn-freako/Haskell_Misc/…> Thanks, -db

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[ANN] xls-0.1.0 Parse MS Excel spreadsheets
by Harendra Kumar 17 Oct '16

17 Oct '16

I have uploaded the xls package [1] on Hackage [2]. It works pretty well for the basic use case of parsing all sheets in a single stream of rows composed of cells. The cell values are presented as plain strings i.e. no data type based interpretation. Such stuff can be added if required, it is supported by the underlying C library (libxls). One thing that I would like to have added to the API is a way to list all sheets and select sheets to parse in a workbook. It should be pretty easy to do if anyone wants to do it. 1. https://github.com/harendra-kumar/xls 2. https://hackage.haskell.org/package/xls -harendra

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MTL vs Free-monads, what are your experiences
by Oleg 16 Oct '16

16 Oct '16

Matt wrote: > The mtl technique subsumes the free monad technique. if you have a term: > getCurrentTime :: MonadClock m => m UTCTime The relationship between MTL and Free(r) monad approaches is filled with confusion, as you message has just demonstrated. There is nothing specific to MTL in writing the constraints like MonadClock. There is absolutely nothing that prevents you from defining instance Member ClockEffect r => MonadClock (Eff r) or similar with Free monads, instance MonadClock (Free CurrentTimeF) (which are less efficient, compose less well and require the boilerplate of writing functor instances). In short, defining constraints like MonadClock, MonadState etc. is not specific to any approach to effects. The difference between the monad transformer and Free monad is how you build types that satisfy the MonadClock etc. constraint. In MTL, you build by applying monad transformer to a suitable base monad. In Free monad, you define functors like CurrentTimeF and then build the Free monad. In Freer monad approach, your example getCurrentTime will look like getCurrentTime :: Member ClockEffect r => Eff r UTCTime which looks quite like getCurrentTime :: MonadClock m => m UTCTime in your example. Therefore, there is usually no need to define a separate MonadClock class. But nothing stops you from doing that.

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[ANN] HackerNews 1.0
by David Johnson 14 Oct '16

14 Oct '16

Released new API bindings to the HackerNews API ( https://github.com/HackerNews/API) *Changes/Updates:* - Matching GHCJS implementation, all AJAX calls are tested thanks to phantomjs w/ hspec. - All aeson instances derived generically - Nix-based CI w/ travis ensures successful building on the following platforms: - *nixpkgs-16.09* - ghcjs-7103 - ghc-801 - *Stackage LTS * - LTS 7.3 *Release links*: - http://hackage.haskell.org/package/hackernews - https://github.com/dmjio/hackernews More platforms to be added for testing. - David

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Type alias in constraints
by Sylvain Henry 14 Oct '16

14 Oct '16

Hi, I have been using constraints of the form: xxx :: forall x xs ys zs m. ( Monad m , zs ~ Union (Filter x xs) ys , Catchable x xs , Liftable (Filter x xs) zs , Liftable ys zs ) => Variant xs -> (x -> Flow m ys) -> Flow m zs Where "zs" is used as a type alias. Now with GHC8 and -Wredundant-constraints, GHC complaints that "zs" is redundant (indeed it is). Is there a way to do this properly? If not, could we introduce a new syntax to make this kind of local declaration? We could borrow the syntax of local declarations into list-comprehensions: "let zs ~ ..." Thanks, Sylvain

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Req. transfer of maintainership of network-multicast
by Marco Zocca 14 Oct '16

14 Oct '16

To the Hackage trustees, following a communication with Audrey Tang, I would like to become new maintainer of `network-multicast` . My Hackage account name is `ocramz`. Thank you, Marco

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Help wanted for the architecture backing perf-service.haskell.org
by Sebastian Graf 12 Oct '16

12 Oct '16

Hi all, I'm about to wrap up my work for the Haskell committee (think half a summer of code): feed-gipeda <https://github.com/sgraf812/feed-gipeda> It's basically a daemon which will spawn benchmarking jobs for every commit of registered repositories. Much like Travis CI, but for benchmarks. You can see a simple web server, hosting the gipeda <https://github.com/nomeata/gipeda/>-generated sites, at http://perf-service.haskell.org/ghc/#all. While the Haskell part is working smoothly enough for now, I'd really like some help setting up proper sandboxing environments for the benchmark slaves, in such a way that security isn't as much a concern as it currently is. We can go over the details on a less publicly shared medium, but I doubt the current solution (invoking shell scripts from a non-root user) is safe. So, some concrete points I need help with: 1. Administrative expertise: Which part of the architecture runs has which rights, setting up proper sandboxing environments for benchmark slaves 2. Ops stuff: Creating master and slave containers for a low barrier to entry and reproducible environments 3. Distributed protocols: Someone with experience in stuff like SSH-tunneling/CloudHaskell/other useful things I should make the communication protocol of feed-gipeda aware of 4. Some Haskellers which want to take a look at my code and contribute criticism or even code to it :) Thanks in advance! So long, Sebastian Graf

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Announcing binary-parsers
by 韩冬(基础平台部) 12 Oct '16

12 Oct '16

Hi all, I am happy to announce binary-parsers. A ByteString parsing library built on binary. I borrowed lots of design/tests/document from attoparsec so that i can build its shape very quickly, thank you bos! And thanks to binary's excellent design, the codebase is very small(<500 loc). From my benchmark, it’s insanely fast, it outperforms attoparsec by 10%~30% in aeson benchmark. it’s also slightly faster than scanner(a non-backtracking parser designed for speed) in http request benchmark. I’d like to ask you to give it a shot if you need super fast ByteString parsing. These parsers are just binary's Get monads, so you can seamlessly combine them with combinators from binary package. You can now write more complex Binary instances using comprehensive combinators, with serialisation packages like blaze-texual. all these goodies come for free! Happy hacking! Github: https://github.com/winterland1989/binary-parsers Hackage: http://hackage.haskell.org/package/binary-parsers Winterland

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Galois is hiring!
by Iavor Diatchki 12 Oct '16

12 Oct '16

Hello, Galois is hiring again! We're looking for researchers, principal investigators, software engineers, and project leads, including those with expertise in functional programming, formal methods, machine learning, embedded systems, computer security, or networking. For the exact available positions, please have a look at our web-site: http://galois.com/careers We have two offices: one in Portland, OR, and one in Arlington, VA. There are positions available at both locations. Generally, we are looking for people to work on site, not remotely. Mostly, we are looking for candidates who are already allowed to work in the US, but in exceptional situations we can work with the candidate to obtain the necessary documentation. If you are interested, please send us your resume through the web site. Cheers, -Iavor

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 10 Oct '16

10 Oct '16

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, deadline 31st October 2016. Many thanks, Graham ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 31st October 2016 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 2016. 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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Call for Contributions - Haskell Communities and Activities Report, November 2016 edition (31th edition)
by Mihai Maruseac 09 Oct '16

09 Oct '16

Dear all, We would like to collect contributions for the 31th edition of the ============================================================ Haskell Communities & Activities Report http://www.haskell.org/haskellwiki/Haskell_Communities_and_Activities_Report Submission deadline: 30 October 2016 (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/11-2016/template.tex There is also a LaTeX style file at http://haskell.org/communities/11-2016/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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[ANN] wrecker - An HTTP Benchmarker
by Jonathan Fischoff 07 Oct '16

07 Oct '16

I am happy to announce the release of 'wrecker-0.1.3.2', a library for HTTP benchmarks. 'wrecker' makes it easy to benchmark complex API interactions, by providing a 'wreq' like interface for creating suites of HTTP benchmarks. For more detailed information, tutorials, and examples checkout the README.md https://github.com/skedgeme/wrecker/blob/master/README.md Additionally there is documentation on Hackage: https://hackage.haskell.org/package/wrecker. Cheers, Jonathan Fischoff

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Cross-compiling network package
by Arie Peterson 06 Oct '16

06 Oct '16

Can the network package be cross-compiled? I'm running into problems because the preprocessor cannot handle some of the directives that network uses when it's working in cross-compilation mode. Specifically, this part gives trouble: <https://github.com/haskell/network/blob/master/Network/Socket/Types.hsc#L10…> > #if __GLASGOW_HASKELL__ < 800 > #let alignment t = "%lu", (unsigned long)offsetof(struct {char x__; t (y__); }, y__) > #endif > > instance Storable In6Addr where > > sizeOf _ = #const sizeof(struct in6_addr) > > alignment _ = #alignment struct in6_addr In my first attempt, with ghc-7.10, this failed because the "let" directive is not supported when cross-compiling. Looking at the above code I thought I'd try ghc-8.0, but as it turns out the "alignment" directive is also not supported when cross-compiling... Any ideas? I'm compiling from x86_64 to arm-linux-gnueabihf BTW, to run my haskell program on the raspberry pi (3).

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Recursive attoparsec
by Lian Hung Hon 06 Oct '16

06 Oct '16

Dear cafe, Given data Expression = ExpToken String | ExpAnd Expression Expression How to write an attoparsec parser that parses this example: "a" and "b" and "c" into ExpAnd (ExpToken "a") (ExpAnd (ExpToken "b") (ExpToken "c"))? Regards, Hon

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Reminder: Workshop on Coalgebra, Horn Clause Logic, and Types
by František Farka 06 Oct '16

06 Oct '16

Reminder: Call for Papers, Presentations and Participation Workshop on Coalgebra, Horn Clause Logic Programming and Types 28-29 November 2016, Edinburgh, UK https://ff32.host.cs.st-andrews.ac.uk/coalpty16/ Abstract submission: 15 October, 2016 Registration deadline: 1 November, 2016 ==================================================== Objectives and scope ------------------- The workshop marks the end of the EPSRC Grant Coalgebraic Logic Programming for Type Inference, by K. Komendantskaya and J. Power and will consist of two parts: Part 1 - Semantics: Lawvere theories and Coalgebra in Logic and Functional Programming Part 2 - Programming languages: Horn Clause Logic for Type Inference in Functional Languages and Beyond We invite all colleagues working in related areas to present and share their results. We envisage a friendly meeting with many stimulating discussions, and therefore welcome presentations of already published research as well as novel results. Authors of original contributions will be invited to submit their papers to EPTCS post-proceedings. We especially encourage early career researchers to present and participate. Venue ----- The workshop will be held at the International Center for Mathematical Sciences, in Edinburgh city center, just 2 minutes walk from the Informatics Forum. Invited speakers and tutorials ------------------------------ Theory: * Logic programming: laxness and saturation John Power, University of Bath, UK * Comodels and interaction Tarmo Uustalu, Tallinn University of Technology, Estonia. * Refinement Types and Higher-Order Constrained Horn Clauses Steven Ramsay and Luke Ong, University of Oxford, UK Applications and Implementations: * Abstract compilation for type analysis of OO languages Davide Ancona, University of Genoa, Italy * Classes for the masses Claudio Russo, Microsoft Research Cambridge, UK * Relational specification of type systems using Logic Programming Ki Yung Ahn, Nanyang Technological University, Singapore Proceedings publication ----------------------- Presentations: We invite submission of 2-page extended abstracts via Easychair, by the 15th October 2016. These will be subject to light review process. Preliminary proceedings will be made available at the conference in electronic form. Post-proceedings: Authors presenting original work will be invited to submit full papers to the post-proceedings of the workshop. The post-proceedings volume will be published in Electronic Proceedings in Theoretical Computer Science and peer-reviewed according to EPTCS standards by the PC members. Important dates --------------- Extended Abstract Submission: 15 October, 2016 Author notification: 25 October, 2016 Workshop registration: 1 November, 2016 Workshop: 28–29 November, 2016 EPTCS proceedings invitations: 15 December, 2016 EPTCS final version submission: 30 January, 2017 Programme committee ------------------- Ki Yung Ahn, Nanyang Technological University, Singapore Davide Ancona, University of Genoa, Italy Filippo Bonchi, CNRS, ENS de Lyon, France Iavor Diatchki, Galois, Inc, USA Peng Fu, Heriot-Watt University, Edinburgh, UK Neil Ghani, University of Strathclyde, UK Patricia Johann, Appalachian State University, USA Ekaterina Komendantskaya, Heriot-Watt University, Edinburgh, UK Clemens Kupke, University of Strathclyde, UK J. Garrett Morris, University of Edinburgh, UK Fredrik Nordvall Forsberg, University of Strathclyde, UK John Power, University of Bath, UK Claudio Russo, Microsoft Research Cambridge, UK Martin Schmidt, DHBW Stuttgart and Osnabrück University , Germany Stephan Schulz, DHBW Stuttgart, Germany Aaron Stump, The University of Iowa, USA Niki Vazou, University of California, San Diego, USA Joe Wells, Heriot-Watt University, Edinburgh, UK Fabio Zanasi, Radboud University of Nijmegen, The Netherlands Workshop chairs -------- Ekaterina Komendantskaya, Heriot-Watt University, UK John Power, University of Bath, UK Publicity chair --------------- František Farka, University of Dundee, UK and University of St Andrews, UK -- František Farka

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Contribute to Stack in Llubjana 14th October
by Luke Murphy 06 Oct '16

06 Oct '16

Hi all, I am co-organizing a Haskell event in Llubjana and trying to get the word out. We'd like to come together and work on contributing to Stack together. We'll specifically tackle the issues labeled `newcomer`. It's on the 14th of October 2016, in Llubjana, Slovenia. You can find details over at Github or Meetup: - https://github.com/haskellpeople/stack - https://www.meetup.com/Ljubljana-Lambdas/events/234646552/ This may be last minute (it is), but if anyone is close, please feel free to join us. Best, Luke

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History of Ajhc Haskell compiler
by Kiwamu Okabe 06 Oct '16

06 Oct '16

Hi all, Ajhc Haskell compiler [0] project is shutdown. However we would like to show the knowledge. Please read Metasepi Foundation report in Japanese [1], that includes detail of technical information around Ajhc's runtime and GC. However you may hardly read it, because written by Japanese language. If you would like to automatically translate it by Google translate, this source code of the document [2] may be useful. We are welcome that you contribute us to translate it into English. But this document is a technical report as fiction novel style. This document has many "tentacles" words, because the novel part is parody of Squid Girl [3]. Please relax to read it like reading some fiction novel. Best regards, [0] http://ajhc.metasepi.org/ [1] http://metasepi.org/doc/c84-metasepi-foundation-ja.pdf [2] https://gist.github.com/master-q/733dfa2cf008261a3849564c38a7933b [3] https://en.wikipedia.org/wiki/Squid_Girl -- Kiwamu Okabe at METASEPI DESIGN

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Why did the number of LOC in GHC nearly triple in 2014!?
by Dimitri DeFigueiredo 05 Oct '16

05 Oct '16

Hello folks, I was looking at this: https://www.openhub.net/p/ghc/analyses/latest/languages_summary And was really surprised by the graph. Is this correct!? Did the complexity of GHC's codebase significantly increase in 2014? Can anybody shed a light on why that is? Cheers, Dimitri -- 2E45 D376 A744 C671 5100 A261 210B 8461 0FB0 CA1F

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Re: [Haskell-cafe] Representing Hierarchies with Typeclasses
by Dimitri DeFigueiredo 05 Oct '16

05 Oct '16

I have looked at how to embedded object oriented systems into haskell for practical reasons. By far the best resource I found was Oleg Kiselyov and Ralph Lämmel's work: https://arxiv.org/pdf/cs/0509027.pdf It shows the multiple possibilities. I have used the idea of having a super class be a polymorphic type with a tail. data Point s = Pt { x :: Int, y:: Int, tail :: s} And then specializing the parameter s into your derived class type Radius = Int type Circle = Point Radius many times. But *be warned*, I try to avoid object hierarchies like the plague! They lead to code that is not reusable. You may want to consider other simpler possibilities. Here is one of my earlier experiments that may be useful to you (I no longer have the views expressed there). https://github.com/dimitri-xyz/inheritance-in-haskell Cheers, Dimitri -- 2E45 D376 A744 C671 5100 A261 210B 8461 0FB0 CA1F

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Representing Hierarchies with Typeclasses
by Rahul Muttineni 05 Oct '16

05 Oct '16

Hi cafe, I want to embed Java class hierarchies in Haskell, but I am unable to find a clean way to do it. Assume the class hierarchy C derives from B derives from A. Partial Solution: --- type family Super (a :: *) :: * class Extends a b where supercast :: a -> b instance {-# INCOHERENT #-} (Class a, Class c, Super a ~ b, Super b ~ c) => Extends a c where data A data B data C type instance Super C = B type instance Super B = A instance Extends C B instance Extends B A -- This is fine and is successfully able to infer Extends C A, but it's redundant and cannot infer that Extends D A if we let Super D = C. Is there a way to only specify the parent-child relationship once and get GHC to infer the entire hierarchy without the use of UndecidableInstances? Other solutions I've tried which avoid redundancy cause an infinite loop in the context reduction step of GHC. Thanks, Rahul Muttineni

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Speakers for a kickoff meetup on functional programming.
by Damian Nadales 05 Oct '16

05 Oct '16

Hi, I'm planning on organizing a Meetup group about Functional Programming in Eindhoven, for next year. Currently there is very few people doing that in this area (according to the few jobs available here), and I would like to promote it. Next to that I would like to advertise Haskell, but I wanted to start with a more broader scope. My current employer is willing to sponsor this, and hence I was looking which speakers could be possible to bring for the big opening event. My first question is which speakers you know in the FP world that can clearly convey the ideas on "why functional programming matter for your company". The idea is to try to spark the interest of the different stakeholders in this city (and region). Second, I've seen some material here and there on FP propaganda, but I would like to know which ones are you favorites. Thanks a lot in advance, Damian.

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Re: [Haskell-cafe] Batteries included (Was: GHC is a monopoly compiler)
by Olaf Klinke 03 Oct '16

03 Oct '16

I did not intend to start a Python-bashing thread. Most people on this list will agree on which language is superior. I did not intend to suggest that Haskell is still mainly a research language, nor that it should remain to be. I'd love to see more problems to be tackled with lenses, FRP or GADTs, just to show that it can be done this way. Maybe one day an idiom will prove superior to its competitors and take its place in whatever is the equivalent of base then. I am happy to have packages coexist that use either of String, Text, ByteString.Lazy or ByteString.Strict. I am a fan of the Unix philosophy: Do one thing, and do it well. There are modules in base that are very good examples of this: Data.Map provides just one data structure with a very easy interface, no newtypes, no typeclasses. The user needs no knowledge of how it is implemented, but the internals can be exposed if necessary. Control.DeepSeq provides one single typeclass to provide one single functionality. In Unix the glue between programs are streams of bytes. I feel that the glue between Haskell libraries should be lambda calculus and algebraic datatypes. So when you write a library that processes HTTP traffic as conduits: Provide a wrapper function whose type does not mention the conduit classes. When you write another efficient text library, provide fromString and toString functions, even if they are inefficient. As to what kind of batteries should be included: * I feel that Haskell already has an excellent set of containers for all sorts of tasks. * It has excellent parsers. * The web stuff seems less uniform, and my complaints about idioms apply. * To compete with other recent teaching languages, a really simple GUI library to use within ghci would be fine. (diagrams and GTK?) Quick Basic included "line" and "circle" commands to play with, even though the rest of the language did not prepare me for more advanced languages. * I know too little about the state of Haskell's number crunching libraries, but it seems that Vector is reasonably efficient nowadays. But what should I use to solve A*x = b? This is a problem so basic that is should be solved by a basic library. I like Peter's suggestion of an official wiki highlighting the state-of-the-art packages for common tasks. As to the versioning and backward compatibility issues of a standard library: In my eyes the whole concept of version numbers is broken. Dependencies should be stated in terms of type signatures. Olaf

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Re: [Haskell-cafe] Batteries included (Was: GHC is a monopoly compiler)
by Olaf Klinke 03 Oct '16

03 Oct '16

Can someone please define what exactly a "batteries included" standard library is? IMHO that Python-Haskell comparison is unfair. Although both claim to be general-purpose languages, the focus in Haskell certainly has been on language research for most of its life. I recently hacked together a web client in python, my first project in that language. Documentation is excellent. Yet I am still horrified I had to use a language that provides so few static guarantees to control megawatt machines. What puts me off Haskell nowadays is the direct result of Haskell's roots in language research: Often when I come across a package that does what I need, it uses the conduit, lens or another idiom, which are like a language in a language to learn. In milder ways Python seems to suffer the same problem. So please, developers: Write more batteries, but make them expose a neat lambda calculus interface if possible that can be combined freely with other batteries. Regards, Olaf

16 29

simple search for new contributors
by Takenobu Tani 02 Oct '16

02 Oct '16

Hi cafe, In relation to these [1][2], I pushed simple search in multiple wiki sites for new contributors. Haskell wiki search for multiple wiki sites https://takenobu-hs.github.io/haskell-wiki-search I'm glad if it would be useful. [1]: https://mail.haskell.org/pipermail/ghc-devs/2016-September/012830.html [2]: https://github.com/ghc-proposals/ghc-proposals/pull/10 Regards, Takenobu

1 0

nbody benchmark please
by Branimir Maksimovic 02 Oct '16

02 Oct '16

can someone put bang pattern with parameters in nbody benchmark program of mine as it is on my machine significantly faster just because of that: run :: Int -> Ptr Planet -> IO () run 0 _ = return () run !i !p = do advance p run (i-1) p PS I lost my account and if someone has it please do this for me ;) http://benchmarksgame.alioth.debian.org/u64q/program.php?test=nbody&lang=gh… Also author of site removed my knucleotide benchmark which was among fastest because I didn't use data.hashtable (which is slow), rather used my own (which is few lines of code)

1 0

Re: [Haskell-cafe] Proposal: add Monoid1 and Semigroup1 classes
by Mario Blažević 01 Oct '16

01 Oct '16

CC-ing the Café on class naming... On 2016-10-01 04:07 AM, Edward Kmett wrote: > I'm somewhat weakly against these, simply because they haven't seen > broad adoption in the wild in any of the attempts to introduce them > elsewhere, and they don't quite fit the naming convention of the other > Foo1 classes in Data.Functor.Classes > > Eq1 f says more or less that Eq a => Eq (f a). > > Semigroup1 in your proposal makes a stronger claim. Semgiroup1 f is > saying forall a. (f a) is a semigroup parametrically. Both of these > constructions could be useful, but they ARE different constructions. The standard fully parametric classes like Functor and Monad have no suffix at all. It makes sense to reserve the suffix "1" for non-parametric lifting classes. Can you suggest a different naming scheme for parametric classes of a higher order? I'm also guilty of abusing the suffix "1", at least provisionally, but these are different beasts yet again: -- | Equivalent of 'Functor' for rank 2 data types class Functor1 g where fmap1 :: (forall a. p a -> q a) -> g p -> g q https://github.com/blamario/grampa/blob/master/Text/Grampa/Classes.hs What would be a proper suffix here? I guess Functor2 would make sense, for a rank-2 type? > > If folks had actually been using, say, the Plus and Alt classes from > semigroupoids or the like more or less at all pretty much anywhere, I > could maybe argue towards bringing them up towards base, but I've seen > almost zero adoption of the ideas over multiple years -- and these > represent yet _another_ point in the design space where we talk about > semigroupal and monoidal structures where f is a Functor instead. =/ > > Many points in the design space, and little demonstrated will for > adoption seems to steers me to think that the community isn't ready to > pick one and enshrine it some place central yet. > > Overall, -1. > > -Edward > > On Fri, Sep 30, 2016 at 7:25 PM, David Feuer <david.feuer(a)gmail.com > <mailto:david.feuer@gmail.com>> wrote: > > I've been playing around with the idea of writing Haskell 2010 > type classes for finite sequences and non-empty sequences, > somewhat similar to Michael Snoyman's Sequence class in > mono-traversable. These are naturally based on Monoid1 and > Semigroup1, which I think belong in base. > > class Semigroup1 f where > (<<>>) :: f a -> f a -> f a > class Semigroup1 f => Monoid1 f where > mempty1 :: f a > > Then I can write > > class (Monoid1 t, Traversable t) => Sequence t where > singleton :: a -> t a > -- and other less-critical methods > > class (Semigroup1 t, Traversable1 t) => NESequence where > singleton1 :: a -> t a > -- etc. > > I can, of course, just write my own, but I don't think I'm the > only one using such. > > > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org <mailto:Libraries@haskell.org> > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries > <http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries> > > > > > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

5 4

Fwd: Alternative: you can fool many people some time, and some people many time, but...
by Corentin Dupont 01 Oct '16

01 Oct '16

Hi guys, I'm playing with the mysterious "some" and "many" from Control.Applicative. If I try: many $ Just 1 It just loops, I understand why: http://stackoverflow.com/questions/18108608/what-are-alterna tives-some-and-many-useful-for It seems that some and many are normally used in a context where something is consumed, and can be depleted, so the loop ends. But why doesn't this terminates? take 3 $ many $ Just 1 It's a recursive call, but the construction of the result should be lazy... -- ===================================== Corentin Dupont CREATE-NET OpenIoT Research Area - Senior Researcher Via alla Cascata 56/D - 38123 Povo, Trento - Italy e-mail: corentin.dupont(a)create-net.org Skype: corentin.dupont1 www.create-net.org ====================================== -- ===================================== Corentin Dupont CREATE-NET OpenIoT Research Area - Senior Researcher Via alla Cascata 56/D - 38123 Povo, Trento - Italy e-mail: corentin.dupont(a)create-net.org Skype: corentin.dupont1 www.create-net.org ======================================

2 2

Re: [Haskell-cafe] [Haskell] Branch Streaming (was GHC is a monopoly compiler)
by Tony Day 30 Sep '16

30 Sep '16

I've actually looked down that particular rabbit hole. Here's a link to a monoid for pipes that represents a branch: https://github.com/tonyday567/pipes-extended/blob/master/src/Pipes/Monoid.h… For flavour, the computation involves hoisting and lifting back and forth over several layers, as the various meta-physical wires cross. That was years ago, but I haven't seen anything since. It looks like Pipes is the wrong abstraction point to stream with branching. I wonder what is? On Wed, Sep 28, 2016 at 9:59 PM, Carter Schonwald < carter.schonwald(a)gmail.com> wrote: > Nope :) > > And I think we are still learning how to do stream. Have have streaming > in a line down pat, but streaming with a DAG or general graphs wendontnhave > yet ;) > > > On Wednesday, September 28, 2016, Tom Ellis <tom-lists-haskell-cafe-2013@ > jaguarpaw.co.uk> wrote: > >> On Mon, Sep 26, 2016 at 08:56:55PM -0500, Christopher Allen wrote: >> > Streaming is a good example here. It's not "obvious" how to do many >> > things in Haskell that are "obvious" in other languages. Partly >> > because industry hasn't used languages like Haskell much, partly >> > because the canvas we work with permits more structure. >> >> Is it obvious how to do streaming in other languages? >> _______________________________________________ >> 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. > > > _______________________________________________ > 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 3

Question regarding Candidate Package builds
by Guru Devanla 30 Sep '16

30 Sep '16

Is there any information on what kinds of checks happen on candidate packages that are uploaded. There was a cabal error on a published build. So, I have fixed that and have uploaded a candidate package. I was hoping the same build/checks happen on the candidate package, but I have not seen that happen. This link on the HOME page is very old and does not give any definitive information on what is currently working: https://github.com/haskell/hackage-server/issues/41#issuecomment-25005344 Thanks Guru

1 0

Library pretty print values in Tabular format
by Gurudev Devanla 30 Sep '16

30 Sep '16

Hello All, I am happy to publish a new library on Hackage that lets one print values contained in lists, maps, vectors in a tabular format. This is motivated from the output I am used to seeing while using the Pandas library in Python. This is my first Haskell library and I look forward to feedback and suggestions on improving the library. https://hackage.haskell.org/package/pptable https://github.com/gdevanla/pptable#readme One thing, which I right away do not like about the library is the constraints where the values will have to derive from both Data.Data and GHC.Generic.Generics. Thank you and I look forward to some feedback. Regards Guru P.S: I spent a lot of time trying to make Hackage produce the haddock links. Any pointers to that would be helpful. And "stack sdist" does not package the documentation automatically.

4 3

Re: [Haskell-cafe] Library pretty print values in Tabular format
by Ivan Lazar Miljenovic 30 Sep '16

30 Sep '16

Actually sending this to the list (no idea where the googlegroups bit came from). On 30 September 2016 at 23:49, Ivan Lazar Miljenovic <ivan.miljenovic(a)gmail.com> wrote: > On 30 September 2016 at 22:06, Gurudev Devanla > <gurudev.devanla(a)gmail.com> wrote: >> Hello All, >> >> I am happy to publish a new library on Hackage that lets one print values >> contained in lists, maps, vectors in a tabular format. This is motivated >> from the output I am used to seeing while using the Pandas library in >> Python. This is my first Haskell library and I look forward to feedback and >> suggestions on improving the library. >> >> https://hackage.haskell.org/package/pptable >> https://github.com/gdevanla/pptable#readme >> >> One thing, which I right away do not like about the library is the >> constraints where the values will have to derive from both Data.Data and >> GHC.Generic.Generics. > > You could provide a type-class for values as well; this would also > help avoid the usage of get_type == "Bool" that you have. > >> Thank you and I look forward to some feedback. >> >> Regards >> Guru >> >> P.S: I spent a lot of time trying to make Hackage produce the haddock >> links. Any pointers to that would be helpful. And "stack sdist" does not >> package the documentation automatically. > > Hackage should automatically generate the documentation after a period > of time; they are generated server-side not client-side (hence why > "stack sdist" didn't generate them). > >> >> >> _______________________________________________ >> 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. > > > > -- > Ivan Lazar Miljenovic > Ivan.Miljenovic(a)gmail.com > http://IvanMiljenovic.wordpress.com -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

1 0

Alternative: you can fool many people some time, and some people many time, but...
by Corentin Dupont 30 Sep '16

30 Sep '16

Hi guys, I'm playing with the mysterious "some" and "many" from Control.Applicative. If I try: many $ Just 1 It just loops, I understand why: http://stackoverflow.com/questions/18108608/what-are-alterna tives-some-and-many-useful-for It seems that some and many are usually used in a context where something is consumed, and can be depleted, so the loop ends. But why doesn't this terminates? take 3 $ many $ Just 1 It's a recursive call, but the construction of the result should be lazy...

4 4

PLDI 2017 - Call for Workshops and Tutorials
by Tobias Grosser 30 Sep '16

30 Sep '16

*Call for Workshops and Tutorials* ============================= 2017 ACM Conference on Programming Language Design and Implementation (PLDI) June 19-23, 2017 in Barcelona, Spain http://conf.researchr.org/home/pldi-2017 PLDI 2017 will host co-located workshops and tutorials for which it calls for proposals. This year, PLDI is a part of a large cluster of co-located conferences including ECOOP, Curry On, LCTES, ISMM, DEBS and others. Take your chance in addressing the diverse audience of the premier forum in programming language design and implementation by proposing your event. PLDI welcomes prominent events focusing on programming language design theory and practice, for which it can provide guidance in ublishing results in the ACM Digital Library. * Submission guidelines * ===================== http://conf.researchr.org/track/pldi-2017/pldi-2017-workshops-and-tutorials Please submit proposals in plain text to Workshops and Tutorials Chair Aaron Smith <aaron.smith(a)microsoft.com>. A proposal should provide: * Name of the workshop/tutorial. * Duration of the workshop/tutorial. * Organizers: names, affiliation, contact information, brief (100 words) biography. * A short description (150-200 words) of the topic. * Event format: workshop/tutorial; type of submissions if any; review process; results dissemination; references to previous events. * Expected attendance and target audience within PLDI community. * Important dates * ================ Published Workshops proposals due 28 Nov 2016 Acceptance Notification 9 Dec 2016 Unpublished Workshops and Tutorials proposals due 30 Jan 2017 Workshop and Tutorials held (tentatively) 18, 22, 23 Jun 2017 *Organizing Committee* ==================== http://conf.researchr.org/committee/pldi-2017/pldi-2017-organizing-committee General Chair: Albert Cohen, INRIA, France Program Chair: Martin Vechev, ETH Zurich, Switzerland Workshops & Tutorials Chair: Aaron Smith, University of Edinburgh Organizing Chair: Fernando Orejas, Universitat Politècnica de Catalunya, Spain Publicity Chairs: Adrian Sampson, Cornell, USA Tobias Grosser, ETH Zurich, Switzerland Web Chair: Oleksandr Zinenko, INRIA, France Financial Chair: Louis-Noël Pouchet, Ohio State University, USA Student Travel Chair: Ronald Mak, San Jose State University, USA

1 0

Writing insertionSort using foldr and a helper function
by jorgemal1960＠gmail.com 30 Sep '16

30 Sep '16

I am posting the same question again because I had not subscribed to the list and I received a message saying it was automatically rejected. I have the following function that takes an element and a list and inserts the element into the list at the first position where it is less than or equal to the next element. So, if the list is sorted, then the list will remain sorted. myInsert :: Ord a => a -> [a] -> [a] myInsert x [] = [x] myInsert x (y:ys) = if x < y then x:y:ys else y:myInsert x ys Now, I have to use the above function myInsert and foldr to implement another function called insertionSort. I have been able to do it without using foldr as follows and it works just fine: insertionSort :: Ord a => [a] -> [a] insertionSort [] = [] insertionSort [x] = [x] insertionSort (x:xs) = myInsert x (insertionSort xs) I have worked for 2 days to use foldr without success, for example: insertionSort :: Ord a => [a] -> [a] insertionSort [] = [] insertionSort [x] = [x] insertionSort (x:xs) = foldr (myInsert) x (insertionSort xs) But it does not even compile, I get the following error which refers to last instruction at position "x" in "foldr (myInsert) x (insertionSort xs)": Couldn't match expected type ‘[a]’ with actual type ‘a’ I will very much appreciate your feedback in order to solve my issue. Best regards.

5 4

Take over word24 package on hackage
by 韩冬(基础平台部) 29 Sep '16

29 Sep '16

Dear hackage administrators: I'd like to take over the maintenance of word24 package on hackage, here is the conversation between me and current maintainer. My hackage account is winterland, currently my package mysql-haskell rely on word24. If there's anything you need to know, please contact me. Thanks! Winterland SEP 29/ 2016 ________________________________ From: 韩冬(基础平台部) Sent: Tuesday, August 30, 2016 5:10 PM To: John Lato Subject: Re: Query about word24 package on package How is the stackage thing going? I hesitate to add it myself because i’m not the maintainer. my hackage account is winterland, If you decide to leave the maintaince to me just drop me a message, thanks! Winter On Aug 27, 2016, at 03:57, John Lato <jwlato(a)gmail.com<mailto:jwlato@gmail.com>> wrote: Hi sorry for the delay, for some reason I've had really inconsistent messages from GitHub. If you want to do maintenance that's awesome I'll see if I can get it set up today. On Thu, Aug 25, 2016, 10:46 PM 韩冬(基础平台部) <handongwinter(a)didichuxing.com<mailto:handongwinter@didichuxing.com>> wrote: Hi, John Really really sorry to bother you by email, recently i’m writing a mysql driver in haskell, i use your word24 package to get a proper Word24 type, so i’d like to ask you to add it to stackage, i open a github issue here: https://github.com/JohnLato/word24/issues/1 , but since you didn’t reply, so i drop this email, hope you can reply ASAP. If you permit, i can do the version bump and package upload maintaince in future. Thanks for your code and time! Winter

2 2

Haskell opportunity at MemCachier
by Amit Levy 29 Sep '16

29 Sep '16

Hi friends! David and I are looking for a software engineer to join MemCachier and help work with us on our automation, analytics monitoring and dashboard, server management and core infrastructure. The work is mostly in Haskell, with the core infrastructure in Go as well as bits in pieces in whatever else is needed. There's lots of opportunity for open source contributions too! I've included the job description below (also at https://www.memcachier.com/job) If you're interested, send a resume and cover letter to jobs(a)memcachier.com or contact David or me. ============================================= MemCachier is the largest provider of memcache-as-service to PaaS applications. Our home-grown, fully distributed and multi-tenant implementation of memcache serves billions of requests each day, powering a range of applications from scrappy startups to fortune 500 companies. As the newest addition to our team, you’ll be working on improving fail over automation, analytics, monitoring, making MemCachier faster and more reliable, and well as contributing to the ecosystem of open source memcache clients in all languages. You’ll also share in on-call duties. Our design is failure resilient, so incidents are rare, but we do share in carrying around a pager. We use tools and languages we genuinely like, with a high skew towards type-safe languages. Our memcache implementation is built in Go and most of the rest of our infrastructure in Haskell. We value well designed software and compile-time guarantees. We are a small team and, like our service, we are distributed—residing on two coasts of the United States and in Europe (or elsewhere, depending on the season). While we are collaborative, this means the job requires being comfortable with a high-degree of independence. In return, you’ll be able to work wherever you are and won’t be bound to a particular schedule most of the time. We encourage functional programmers of all stripes, but we particularly encourage people from groups that are underrepresented in software. Finally, the qualifications below are not strict requirements, but rather guidelines for the kinds of skills we’re looking for. ## Qualifications * B.S. in Computer Science or equivalent experience. Advanced degrees encouraged (the current team either has, or is working on, PhDs), but we know there are plenty of other ways to come by the same knowledge. * Proficiency with distributed systems concepts. * Proficiency in either Go or Haskell, or a closely related language like ML, Rust or a desire and ability to learn. * Good English written communication skills—you don’t to be a native speaker, but you must be proficient. * Experience with web technologies (HTTP, web frameworks, etc). * Experience working independently or in remote teams. ## Responsibilities * Share in on-call duties. Our design is failure resilient, so incidents are rare, but we do share in carrying around a pager. * Contribute throughout the full stack, from provisioning services and core infrastructure, to the analytics dashboard and customer portal. * Participate in discussions about software and product design. ## Benefits * Self-Direction: You'll have a high-degree of autonomy to work on what you think is most interesting and valuable. * Open Source: We try to contribute as much of our work as possible to the open source ecosystem. * Full-Stack: We write software in many languages (Haskell, Go, Ruby, JavaScript) across the stack (front-end, middleware, distributed backends, monitoring). * Hard Problems: We have plenty of unsolved distributed systems problems and lots of data. * Flexible Hours: Work where and when is best for you. To apply, e-mail jobs(a)memcachier.com with a resume, cover letter and other supporting materials.

1 0

Re: [Haskell-cafe] Batteries included (Was: GHC is a monopoly compiler)
by Alex Belanger 28 Sep '16

28 Sep '16

Just a reminder, I think Haskell (the language) is being conflated by `base` (the library). `base` has exactly the minimum required for GHC to bootstrap and compile itself. If you guys are interested in an `other-base`, then do it and list that as a dependency in your cabal file. You choose your dependencies by relevance, but it doesn't affect what Haskell is or capable of. The whole point of having even `base` be a library (and extensions) is what allow Haskell to be such a good research language. No need to discuss morals on a non-existant problem. Go ahead and make a different base. Companies do this all the time. Alex. On Sep 28, 2016 3:22 AM, "Peter" <voldermort(a)hotmail.com> wrote: What are the advantages of batteries included? 1) It's easier for newcomers to find the appropriate library for common tasks. 2) Consistency between different programs, as they will mostly use the same standard libraries for common tasks. Do these require the batteries to be installed with the compiler? Do they require the batteries to be installed as a monolithic unit at all? An "official" wiki page pointing to the recommended packages for common tasks would seem to achieve the purpose almost as well, but without the accompanying problems. As for sets of specific library versions that are known to work well together, Stackage has already solved that. -- View this message in context: http://haskell.1045720.n5. nabble.com/Re-Batteries-included-Was-GHC-is-a-monopoly-compiler- tp5843366p5843416.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. _______________________________________________ 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.

2 1

HGamer3D - website refresh - space invaders clone
by Peter Althainz 28 Sep '16

28 Sep '16

Dear All, the http://www.hgamer3d.org website now comes with some updates: slides from Haskell Leipzig 2016 link, more explanations, aio tool explained, space invaders game. regards Peter

2 1

A question on dependent types in Haskell
by Todd Wilson 28 Sep '16

28 Sep '16

I haven't yet had the pleasure of exploring the subtleties of dependently-typed programming in Haskell, but I'm finding myself in need of a little bit of it in advance of that exploration and was hoping for some suggestions. I have a type of regular expressions: data RegExp = Empty | Letter Char | Plus RegExp RegExp | Cat RegExp RegExp | Star RegExp and a type of (deterministic) finite state machines that is polymorphic in the state type: data FSM a = FSM { states :: [a], start :: a, finals :: [a], delta :: [(a,Char,a)] } I've fixed an alphabet sigma :: [Char], and I want to write the function that converts a regular expression to its associated FSM. The machines associated with Empty and Letter are given by data EmptyFSM = Etrap emptyFSM :: FSM EmptyFSM emptyFSM = FSM { states = [Etrap], start = Etrap, finals = [], delta = [(Etrap, c, Etrap) | c <- sigma] } data LetterFSM = Lstart | Lfinal | Ltrap letterFSM :: Char -> FSM LetterFSM letterFSM c = FSM { states = [Lstart, Lfinal, Ltrap], start = Lstart, finals = [Lfinal], delta = [(Lstart, c', if c' == c then Lfinal else Ltrap) | c' <- sigma] ++ [(q, c', Ltrap) | q <- [Lfinal, Ltrap], c' <- sigma] } Suppose I can code the constructions of the union machine, concatenation machine, and star machine so that they have the types unionFSM :: FSM a -> FSM b -> FSM (a,b) catFSM :: FSM a -> FSM b -> FSM (a,[b]) starFSM :: FSM a -> FSM [a] Now what I want to do is to put all of this together into a function that takes a regular expression and returns the associated FSM. In effect, my function should have a dependent type like reg2fsm :: {r : RegExp} -> FSM (f r) where f is the function f :: RegExp -> * f Empty = EmptyFSM f (Letter a) = LetterFSM f (Plus r1 r2) = (f r1, f r2) f (Cat r1 r2) = (f r1, [f r2]) f (Star r) = [f r] and be given by reg2fsm Empty = emptyFSM reg2fsm (Letter c) = letterFSM c reg2fsm (Plus r1 r2) = unionFSM (reg2fsm r1) (reg2fsm r2) reg2fsm (Cat r1 r2) = catFSM (reg2fsm r1) (reg2fsm r2) reg2fsm (Star r) = starFSM (reg2fsm r) What is the suggested approach to achieving this in Haskell? -- Todd Wilson A smile is not an individual Computer Science Department product; it is a co-product. California State University, Fresno -- Thich Nhat Hanh

4 6

Type of divMod
by Todd Wilson 28 Sep '16

28 Sep '16

Why is the type of divMod not (Integral a, Integral b) => a -> b -> (a,b)? It would seem to make sense that if b is a size-limited Integral type (like Int), then since the remainder of a division is always smaller than the divisor, it could be given the same size-limited type. I found myself wanting such instances of divMod when writing a function to convert an Integer to a list of digits in some base that is an Int: toBase :: Integer -> Int -> [Int] I can work around not having the appropriate instance of divMod by using fromIntegral to convert from an Integer to an Int, but this seems wrong. Todd Wilson A smile is not an individual Computer Science Department product; it is a co-product. California State University, Fresno -- Thich Nhat Hanh

2 1

Re: [Haskell-cafe] Unable to register on hackage
by Erik Hesselink 28 Sep '16

28 Sep '16

For future reference, the right address here is admin(a)hackage.haskell.org, which I admit seems to be hard to find on hackage (although it's there on the homepage and Guru found it eventually). I'm looking into this. Erik > On 28 September 2016 at 14:18, Gurudev Devanla <gurudev.devanla(a)gmail.com> > wrote: > >> Hello, >> >> This may be the wrong mailing list for this question, but I appreciate >> any pointers on whom to contact. I have been unable to register as a new >> user on https://hackage.haskell.org to upload a package. I have tried >> number of times, but have not received the activation email. >> >> I have also not found any "Contact" links on that page. Therefore, any >> pointers would be of great help. >> >> Regards >> Guru >> >> >> >> >> _______________________________________________ >> 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. >> > >

1 0

seq and lambda with patterns
by Denis Moskvin 28 Sep '16

28 Sep '16

There is some subtle, but reasonable difference between \pat1 pat2 -> expr and \pat1 -> \pat2 -> expr: > seq ((\True y -> "DEFINED") undefined) 42 42 > seq ((\True -> \y -> "DEFINED") undefined) 42 *** Exception: Prelude.undefined The reason is the translation from Haskell Report 2010 (3.3) \ p1 . . . pn -> e = \ x1 . . . xn -> case (x1 , . . . , xn ) of (p1 , . . . , pn ) -> e Today I found (GHC 8.0.1) that > seq ((\True -> \y -> undefined) undefined) 42 42 Is the last result correct? -- Denis Moskvin

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Unable to register on hackage
by Gurudev Devanla 28 Sep '16

28 Sep '16

Hello, This may be the wrong mailing list for this question, but I appreciate any pointers on whom to contact. I have been unable to register as a new user on https://hackage.haskell.org to upload a package. I have tried number of times, but have not received the activation email. I have also not found any "Contact" links on that page. Therefore, any pointers would be of great help. Regards Guru

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