- Haskell-Cafe - Haskell.org

Memory leak in infinite recursion
by Никита Фуфаев 20 Jun '18

20 Jun '18

Hello everyone In C you can't implement main loop with recursion like void mainLoop() { doSomething(); mainLoop(); } because without optimisations stack will overflow. In haskell it's common to write mainLoop = doSomething >> mainLoop, and it doesn't leak memory because of haskell's evaluation model. Does memory leak or argument stack overflow happen in this case? mainLoop = doSomething >> mainLoop >> exit ExitSuccess What about this case? mainLoopModeA = do doSomething when condition mainLoopModeB mainLoopModeA mainLoopModeB = do doSomethingElse when anotherCondition mainLoopModeA mainLoopModeB or this case? mainLoopModeA = do doSomething if condition then mainLoopModeB else mainLoopModeA mainLoopModeB = do doSomethingElse if anotherCondition then mainLoopModeA else mainLoopModeB -- Nikita Fufaev

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Anybody interested in Dart? Maintainer needed.
by Mario Blažević 18 Jun '18

18 Jun '18

There is package named language-dart on Hackage by Kwang Yul Seo. The package includes the Dart AST and pretty-printer, but no parser. It hasn't been updated in 2 years. I have implemented a parser in a pull request (https://github.com/kseo/language-dart/pull/1) but the original author says he doesn't have time to maintain this package at the moment and is willing to transfer its maintainance. As for myself, I'd be happy to help as a co-maintainer but I feel that a proper feeding and care of the package requires somebody with interest in Google Dart per se. Does anybody here fit this description?

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ghc_ticker not checking return code?
by Jon Fairbairn 18 Jun '18

18 Jun '18

I’ve just been rebuilding something I wrote ages ago, using stack with lts-11.6 (so that I can use a recent Conduit). Part (not a part I was modifying) of the code runs as a CGI script, and I was horrified to find that when run by httpd it soaked up CPU like nobody’s business without producing any output. Running it at the command line worked fine, so I traced the problem via audit: type=AVC msg=audit(1529223103.790:1705516): avc: denied { read } for pid=36764 comm="ghc_ticker" path="[timerfd]" dev=anon_inodefs ino=4597 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:object_r:anon_inodefs_t:s0 tclass=file type=AVC msg=audit(1529223103.790:1705517): avc: denied { read } for pid=36764 comm="ghc_ticker" path="[timerfd]" dev=anon_inodefs ino=4597 scontext=system_u:system_r:httpd_sys_script_t:s0 tcontext=system_u:object_r:anon_inodefs_t:s0 tclass=file The solution is to add an audit rule to allow that, but surely ghc_ticker shouldn’t be trying again so fast when whatever it is trying to do isn’t permitted? I don’t know what component ghc_ticker belongs to, so where should I report the problem? -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk

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Announcement: MPC 2019, Porto, Portugal
by Graham Hutton 18 Jun '18

18 Jun '18

Dear all, I'm delighted to announce that the next Mathematics of Program Construction (MPC) conference will be held in the historic city of Porto, Portugal in October 2019, co-located with Formal Methods (FM). Please share, and submit your best papers! Best wishes, Graham ====================================================================== 13th International Conference on Mathematics of Program Construction 7-9 October 2019, Porto, Portugal Co-located with FM 2019 https://tinyurl.com/MPC-Porto ====================================================================== BACKGROUND: The International Conference on Mathematics of Program Construction (MPC) aims to promote the development of mathematical principles and techniques that are demonstrably practical and effective in the process of constructing computer programs. MPC 2019 will be held in Porto, Portugal from 7-9 October 2019, and is co-located with the International Symposium on Formal Methods, FM 2019. Previous conferences were held in Königswinter, Germany (2015); Madrid, Spain (2012); Québec City, Canada (2010); Marseille, France (2008); Kuressaare, Estonia (2006); Stirling, UK (2004); Dagstuhl, Germany (2002); Ponte de Lima, Portugal (2000); Marstrand, Sweden (1998); Kloster Irsee, Germany (1995); Oxford, UK (1992); Twente, The Netherlands (1989). SCOPE: MPC seeks original papers on mathematical methods and tools put to use in program construction. Topics of interest range from algorithmics to support for program construction in programming languages and systems. Typical areas include type systems, program analysis and transformation, programming language semantics, security, and program logics. The notion of a 'program' is interpreted broadly, ranging from algorithms to hardware. Theoretical contributions are welcome, provided that their relevance to program construction is clear. Reports on applications are welcome, provided that their mathematical basis is evident. We also encourage the submission of 'programming pearls' that present elegant and instructive examples of the mathematics of program construction. IMPORTANT DATES: Abstract submission 26th April 2019 Paper submission 3rd May 2019 Author notification 14th June 2019 Camera ready copy 12th July 2019 Conference 7-9 October 2019 SUBMISSION: Submission is in two stages. Abstracts (plain text, maximum 250 words) must be submitted by 26th April 2019. Full papers (pdf, formatted using the llncs.sty style file for LaTex) must be submitted by 3rd May 2019. There is no prescribed page limit, but authors should strive for brevity. Both abstracts and papers will be submitted using EasyChair. Papers must present previously unpublished work, and not be submitted concurrently to any other publication venue. Submissions will be evaluated by the program committee according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. Accepted papers must be presented in person at the conference by one of the authors. The proceedings of MPC 2019 will be published in the Lecture Notes in Computer Science (LNCS) series, as with all previous instances of the conference. Authors of accepted papers will be expected to transfer copyright to Springer for this purpose. After the conference, authors of the best papers from MPC 2019 and MPC 2015 will be invited to submit revised versions to a special issue of Science of Computer Programming (SCP). For any queries about submission please contact the program chair, Graham Hutton <graham.hutton(a)nottingham.ac.uk>. PROGRAM COMMITTEE: Graham Hutton University of Nottingham, UK (chair) The full committee will be announced as soon as it is available. VENUE: The conference will be held at the Alfândega Porto Congress Centre, a 150 year old former custom's house located in the historic centre of Porto on the bank of the river Duoro. The venue was renovated by a Pritzer prize winning architect and has received many awards. LOCAL ORGANISERS José Nuno Oliveira University of Minho, Portugal For any queries about local issues please contact the local organiser, José Nuno Oliveira <jno(a)di.uminho.pt>. ====================================================================== 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 contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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DataHaskell Newsletter #1, June 2018
by Marco Zocca 17 Jun '18

17 Jun '18

Hi all, I'd like to share with you a few of the things that happened during the past months on and around DataHaskell (DH), and a summary of the current state of things. Time permitting, this will become a regular newsletter, with the idea to keep up to date those who don't usually hang out on our Gitter chatroom [1]. ---------------------------------------------------------------------------------------------------------------- * Outreach activities and related meetings ICFP 2017 : Early September 2017 we had an hour-long lunch mini-workshop at ICFP during which a few people presented how they use Haskell in their numerical and data-crunching work. Mostly positive opinions, as well as a "contrarian" viewpoint (from an expert practitioner) who lamented the low-performance of native Haskell numerical code (e.g. the large memory footprint of boxed data). Michal Gajda presented how he uses IHaskell for interactive data exploration (btw, it's a thing and you can try it today!), Trevor McDonell introduced Accelerate (the high-performance array library that can target CUDA GPUs), Adam Scibior presented `monad-bayes` and Praveen Narayan presented `hakaru` (two probabilistic progamming laguages embedded in Haskell). ZuriHac 2018 : community bonding mostly (read: no hacking was done). Received more feedback of the usual sort "how do I do X in Haskell?" "I was expecting a more advanced state of machine learning capabilities in Haskell", etc. There may or may not be a set of Haskell bindings for Apache Arrow in the works, stay tuned! ICFP 2018 : There will be two very interesting workshops (FHPC, functional programming in high-performance computing and NPFL, numerical programming in functional languages), for those who will be attending the conference. One of the workshop chairs of NPFL is Dominic Steinitz of Tweag, author of the excellent idontgetoutmuch.wordpress.com blog. ---------------------------------------------------------------------------------------------------------------- * DH survey On April 5 I've published a survey [2], that tried to gauge the community interest and pain points related to doing "data science" in our beloved language. The survey is still open but I won't be collecting data anymore (70 people have taken the questionnaire and 62 have completed it), and I've scraped and formatted the dataset (you can find it at https://github.com/DataHaskell/surveys) Some of the free text answers are particularly interesting. I don't have much time currently to create the plots and publish a blog post about it, but it would be a Good Thing to have, if anyone wants to step up. The project backbone is ready for new contributors! ---------------------------------------------------------------------------------------------------------------- * Contributors wanted : External projects At regular intervals, new exciting projects appear and it's becoming quite hard to keep track of everything that's happening in this area. I'd like to highlight here a few that are seeing significant activity as of late and have large impact potential. ** General-purpose (e.g. numerics-related) `numhask` [3] is an experiment at replacing the numerical typeclasses of `base`, in particular those related to `Num`, in favor of a finer-grained and more principled hierarchy. It is already available and receiving quite a bit of attention recently, but there still are a number of areas that could use some help, for example property checking, test coverage, the `accelerate` bindings, etc. ** Data science `boke-hs` [4] : a native Haskell interface to generate Bokeh plots. The project was mostly developed during the ZuriHac weekend; currently it's functional and you can create line plots with it, but helping out with the domain mapping would be a very valuable contribution. In particular, the library emits JSON blobs that are interpreted in the browser by BokehJS ; "domain mapping" means creating the Haskell data that will serialize into JSON appropriately. A currently-unnamed library for linking databases and Haskell dataframes. This is Gagandeep Bhatia's ongoing Summer of Haskell project, and you can find a writeup and links to his current work (which uses `beam` as a database binding library and `Frames` as type-safe in-memory representation) here: https://www.gagandeepbhatia.com/blog/ . `haskell.do` [5] : a native Haskell notebook/interactive editor/IDE for the browser. The project started well, has a website and a few initial releases, but currently needs some love to achieve its full potential. Interactive development with visual feedback is a crucial part of data science work, and contributions to this project will be very valuable. ** Machine learning `hasktorch` [6] is in developer beta ! This is a set of Haskell bindings for `torch` (the deep learning C library), and comes wrapped in a typed interface that provide statically-checked vector dimensions, and the like. ** Probabilistic programming languages `deanie` [7] is a probabilistic EDSL. Currently it's lacking code for its general-purpose inference engine (see https://github.com/jtobin/deanie/blob/master/lib/Deanie/Inference/Comonadic…) The implementation technique is related to "Co-Free for interpreters" as shown in [8]. ---------------------------------------------------------------------------------------------------------------- * Contributors wanted : DataHaskell internal projects We do have a few projects set up that could use some collaborators. If you are willing to contribute to any of these, please open a ticket on the project issue tracker and the maintainers will be in touch shortly. * `type-providers` : a unified code generation library for accessing structured data in a type-safe way : https://github.com/DataHaskell/type-providers . Michal Gajda is willing to mentor a student who wants to translate his own `json-autotype` to a new library that can generate type-safe code for XML, and can be queried in-memory via Frames. Contributing to this library will likely require some knowledge of Template Haskell. * A fork of the venerable `statistics` library, that separates the dense linear algebra library as a standalone library : https://github.com/DataHaskell/statistics . There is currently a PR to the upstream library (https://github.com/bos/statistics/pull/143) longer-term plans include giving it a typeclass-based interface, for example based on `numhask`. * `numhask-linear-algebra` : this is a longer shot at unifying native linear algebra libraries under a single typeclass representation, as provided by `numhask` (project at https://github.com/DataHaskell/numhask-linear-algebra ). This is something that's currently unavailable in the Haskell ecosystem and will be a highly relevant contribution to many. ---------------------------------------------------------------------------------------------------------------- * DataHaskell internal administration In addition to helping out with the survey blogpost, some help in the following areas would be much appreciated ** Knowledge base : testers wanted ! The knowledge base ( http://www.datahaskell.org/docs/community/current-environment.html ) is a growing curated collection of libraries for doing data science-related tasks; anything from manipulating storable data to statistical inference. It's pretty useful as it is, but I think the entries should be annotated with additional information, such as the degree of completeness and developer- and user-friendliness. For this, some help in testing out the libraries and reporting back would be very useful. Ultimately, it would be very useful to contribute such an assessment back to the "state of the ecosystem" document [9], which is highly visible but not so much up to date on the data-science related things. ** Maintainers wanted ! Currently, Nikita and I are the only owners of the github organization. It would be great if additional people stepped up for "tending the garden", e.g. keeping track of issue tickets, filling out the documentation, lending a hand on the gitter channel to address newcomers' issues, etc. Historically, data science and numerical computing have been underserved niches of the Haskell ecosystem, and while things are steadily improving, together we can bring about this change soon ! ---------------------------------------------------------------------------------------------------------------- That's it for now, I hope you enjoyed this Newsletter; don't hesitate to share your thoughts either here or on our Gitter chatroom! [1] Marco github.com/ocramz ---------------------------------------------------------------------------------------------------------------- References : [1] DH Gitter chatroom : https://gitter.im/dataHaskell/Lobby [2] DH user survey April 2018: https://www.surveymonkey.com/r/3FBBJWR [3] numhask : github.com/tonyday567/numhask [4] boke-hs , native Haskell bindings for Bokeh : https://github.com/ahaym/boke-hs [5] HaskellDO, the interactive Haskell editor: http://haskell.do/ , https://github.com/theam/haskell-do [6] hasktorch, the Haskell bindings to Torch : https://github.com/hasktorch/hasktorch [7] deanie , probabilistic programming language : https://github.com/jtobin/deanie [8] "Free for DSLs, co-free for interpreters" http://dlaing.org/cofun/posts/free_and_cofree.html [9] State of the Haskell ecosystem : https://github.com/Gabriel439/post-rfc/blob/master/sotu.md

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the purpose of QuickCheck's size parameter
by Petr Pudlák 17 Jun '18

17 Jun '18

Hi everyone, I'd like to better understand the principles behind the 'size' parameter. Looking at quickCheckWithResult [1], its computation seems to be somewhat non-trivial, or even arbitrary. As far as I understand it, the size is varied throughout tests, increasing from small to larger values. I see two main purposes: - Test on smaller as well as larger values. But with generators having proper distribution of values, this should happen anyway, just as if we had a constant, larger 'size' parameter. - Starting with smaller sizes allows to find smaller count-examples first. But with shrinking, it doesn't matter that much, big counter-examples are shrunk to smaller ones anyway in most cases. So is this parameter actually necessary? Would anything change considerably if it was dropped? Thanks, Petr [1] http://hackage.haskell.org/package/QuickCheck-2.11.3/docs/src/Test-QuickChe…

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Lattice and calculation of Least Upper Bounds
by Aaron Gray 16 Jun '18

16 Jun '18

Hi, I am trying to work out how to use the Algebra.Lattice family of Lattice data structures. Firstly how do I construct a lattice ? What I am wanting to do is to be able to construct a lattice to represent a multiple inheritance hierarchy. Then I to be able to find the Least Upper Bound of a set of classes/types. This is in order to find the type of a multiple case expression. I am not sure if the Haskell classes are actually applicable ? but if they are how do I apply them to the following problem please ? -- Aaron Gray Independent Open Source Software Engineer, Computer Language Researcher, Information Theorist, and amateur computer scientist.

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Hedgehog - Integrated shrinking, shrinks obey invariants by construction.
by Petr Pudlák 15 Jun '18

15 Jun '18

Hi everyone, I found the above interesting sentence in Hedgehog's [1] documentation. What does this mean? Is construction there somewhat tied to shrinking, perhaps something like going in the reverse direction? Thanks, Petr [1] https://github.com/hedgehogqa/haskell-hedgehog#features

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Re: [Haskell-cafe] LIA bindings?
by ARJANEN Loïc Jean David 15 Jun '18

15 Jun '18

Hello, It was purely curiosity which made me ask that question given that the report mentions this standard but as you said, if no one maintains it there’s little point in making bindings for it. Regards, ARJANEN Loïc Le 2018-06-13 à 22:48, Richard O'Keefe a écrit : > A couple of years ago I inquired about adding a new module to > the LIA standards to describe binary and decimal fixed point > arithmetic, having run into a standard which deferred the > semantics of its fixed point arithmetic to LIA. That was a > bit odd, because LIA explicitly refused to say anything about > the matter. The result was the implementations not agreeing, > in quite fundamental ways, with each other. I offered a > draft executable specification in Haskell, checked with > QuickCheck. I basically got the answer "nice work, but nobody > in the industry cares about LIA any more, which is why LIA-1 > was revised but LIA-2 and LIA-3 never were and never will be." > > So the question has to be asked: what exactly would be the > benefit in building library code to support a standard that > nobody wants to maintain any more? > > On 13 June 2018 at 20:44, ARJANEN Loïc Jean David > <arjanen.loic(a)gmail.com <mailto:arjanen.loic@gmail.com>> wrote: > > Dear Café, > > I saw in the report that the standard libraries’ operations don’t > conform to LIA and that such operations should be done in an > external library. Does such a library exist? > > Regards, > ARJANEN Loïc > > _______________________________________________ > Haskell-Cafe mailing list > To (un)subscribe, modify options or view archives go to: > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > <http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe> > Only members subscribed via the mailman list are allowed to post. >

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Call for draft papers for presentation at IFL 2018 (Implementation and Application of Functional Languages)
by Jurriaan Hage 15 Jun '18

15 Jun '18

Hello, Please, find below the fourth call for papers for IFL 2018. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL --- Call for Draft papers for presentations ================================================================================ IFL 2018 30th Symposium on Implementation and Application of Functional Languages University of Massachusetts Lowell, MA, USA September 5th-7th, 2018 http://iflconference.org ================================================================================ ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2018 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialization - run-time code generation - partial evaluation - (abstract) interpretation - metaprogramming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Keynote Speakers * Adam Chlipala, Massachusetts Institute of Technology CSAIL * Arjun Guha, University of Massachusetts Amherst ### Submissions and peer-review Differently from previous editions of IFL, IFL 2018 solicits two kinds of submissions: * Regular papers (12 pages including references) * Draft papers for presentations ('weak' limit between 8 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. A set of regular papers will be conditionally accepted for publication. Authors of conditionally accepted papers will be provided with committee reviews along with a set of mandatory revisions. Regular papers not accepted for publication will be considered as draft papers, at the request of the author. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. Prior to the symposium: Authors of conditionally accepted papers and accepted presentations will submit a pre-proceedings version of their work that will appear in the draft proceedings distributed at the symposium. The draft proceedings does not constitute a formal publication. We require that at least one of the authors present the work at IFL 2018. After the symposium: Authors of conditionally accepted papers will submit a revised versions of their paper for the formal post-proceedings. The program committee will assess whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. Our interest is to ultimately accept all conditionally accepted papers. If you are an author of a conditionally accepted paper, please make sure that you address all the concerns of the reviewers. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected. ### Publication The formal proceedings will appear in the International Conference Proceedings Series of the ACM Digital Library. At no time may work submitted to IFL be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy: http://www.sigplan.org/Resources/Policies/Republication ### Important dates Submission of regular papers: May 25, 2018 [PASSED!] Submission of draft papers: July 17, 2018 [UPCOMING!] Regular and draft papers notification: July 20, 2018 Deadline for early registration: August 8, 2018 Submission of pre-proceedings version: August 29, 2018 IFL Symposium: September 5-7, 2018 Submission of papers for post-proceedings: November 7, 2018 Notification of acceptance: December 22, 2018 Camera-ready version: February 10, 2019 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template Authors submit through EasyChair: https://easychair.org/conferences/?conf=ifl2018 ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honored article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organization and Program committee Chairs: Jay McCarthy & Matteo Cimini, University of Massachusetts Lowell, USA Program Committee: * Arthur Chargueraud, Inria, FR * Ben Delaware, Purdue University, USA * Christos Dimoulas, Northwestern University, USA * David Darais, University of Vermont, USA * Dominic Orchard, University of Kent, UK * Ekaterina Komendantskaya, Heriot-Watt University, UK * Garrett Morris, University of Kansas, USA * Heather Miller, EPFL & Northeastern University, CH & USA * Jeremy Yallop, University of Cambridge, UK * Keiko Nakata, SAP Innovation Center Potsdam, DE * Laura Castro, University of A Coruna, ESP * Magnus Myreen, Chalmers University of Technology, SWE * Natalia Chechina, Bournemouth University, UK * Peter Achten, Radboud Universiteit Nijmegen, NL * Peter-Michael Osera, Grinnell College, USA * Richard Eisenberg, Bryn Mawr College, USA * Trevor McDonell, University of New South Wales, AUS * Yukiyoshi Kameyama, University of Tsukuba, JAP ### Venue The 30th IFL is organized by the University of Massachusetts Lowell. The City of Lowell is located at the heart of the Merrimack Valley just 30 miles northwest of Boston. Lowell can be easily reached by train or taxi. See the website for more information on the venue. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organizers for their work, which is reused here. A part of IFL 2018 format and CFP language that describes conditionally accepted papers has been adapted from call-for-papers of OOPSLA conferences.

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