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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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