- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Organizing your code files
by Johannes Waldmann 10 Aug '21

10 Aug '21

Hécate: > * Type variables are made explicit, and as such I annotate even the > simplest of them (with `:: Type`) This! I am moving towards that style. Especially in teaching (type abstraction, type application) where I want everything to be very much explicit - before discussing abbreviations and omissions (type inference). With current GHC, this is entirely possible but looks somewhat clumsy {-# language ExplicitForall, KindSignatures #-} import Data.Kind (Type) g :: forall (t :: Type) . t -> t ; g x = x {-# language TypeApplications #-} g @N Z yes I could hide these pragmas somewhere but that again feels wrong. But - good thing: after https://github.com/ghc-proposals/ghc-proposals/blob/ghc2021/proposals/0000-… (I understand that GHC2021 is default-enabled in GHC-9.2) we no longer need to write these pragmas. Yay! Sadly, we still need the import. - J. NB: Haskell's implicit declaration of type variables by their starting with lowercase letters always reminds me of Fortran's implicit type specification for variables, going by the first letter (I .. N means integer). Fortran has "implicit none" though, so let's have "t :: Type"...

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Re: [Haskell-cafe] Why not some subclass of Floating to model NaNs as some handleable bottom?
by Olaf Klinke 09 Aug '21

09 Aug '21

> * libraries assume a naive equality works for all types. Holds in a world > of infinte precision and lossless operations, but never holds for > approximations. > > * our propagation of universal error values is incomplete, and usually > missing from complex algorithms. In other words `Either String` Monad does > not work: we want collections of error values just like we have collections > of inputs. > > Personally I will be overjoyed when our community finally gets the better > type class library for approximated types. > > Would You agree to review a teaser if I post it here? Yes, please. I'm curious whether there is a single abstraction that can describe both finite precision with variable errors as well as potentially infinite precision with known errors. Olaf

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Re: [Haskell-cafe] Why not some subclass of Floating to model NaNs as some handleable bottom?
by Olaf Klinke 09 Aug '21

09 Aug '21

> So it should have been another family of `Num` classes, within which, various NaN related semantics can be legal, amongst which I'd think: > > * Silent propagation of NaN in arithmetics, like `Maybe` monad does, seems quite acceptable > * Identity test, namely `NaN` /= `NaN` - this lacks theoretical ground or not? > * Comparison, neither `NaN` > 1 nor `NaN` <= 1 - whether or not there's a theoretical framework for this to hold? Maybe `Boolean` type needs enhancement too to do it? > > No such family of `Num` classes exists to my aware by now, I just can't help wondering why. > > Cheers, > Compl > I like to think of NaN as a glimpse of interval arithmetic. NaN is the interval -infintity to infinity [*]. When ordering intervals by reverse inclusion, NaN is indeed the bottom of the domain. For a general (closed) interval [x,y], how would you answer the questions [x,y] < [1,1]? [x,y] /= [1,1]? There are several possibilities known, extending relations on points to relations on sets. See Smyth-, Hoare- and Egli-Milner lifting of relations. So a more descriptive type of Float-ordering may be (<) :: Float -> Float -> RelationLifting -> Bool For example, NaN /= NaN under all three relation liftings mentioned above, but also NaN == NaN, so a /= b = not (a == b) does not hold anymore. > If we take this into consideration, we notice that most interesting > computations occur on collections of values, and thus yield a > collection of results, not just a single output. Indeed, one route to real arithmetic is via limits of collections of approximants. For example, consider a dense set of rationals, excluding zero, where that all arithmetic operations are well-defined and total on the approximants. Then express a real number as (Dedekind-)cuts and see what cut operations like 0/0 result in. Each non-proper cut corresponds to a special Float value. Incidentally, this is how Conway constructed his surreal numbers that also contain values like infinity and -0. I'm in favour that there be two floating-point types: One IEEE- compliant that behaves just like in other languages, and one more lawful one (thereby with fewer class instances) that leverages the expressive power of Haskell. Ho matter how broken, the former should be the default unless we want to alienate numerically inclined Haskell adopters. Olaf [*] The mathematical function \(x,y) -> x/y attains every real value arbitrarily close to (0,0), whence NaN = 0/0 should be interpreted as the interval encompassing the real line. Likewise log(0) for complex 0.

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Call for Workshops - FLoC 2022
by Victor Perez 06 Aug '21

06 Aug '21

Second Call for Workshops- FLoC 2022 — The 2022 Federated Logic Conference July 31 - August 12, 2022 Haifa, Israel http://www.floc2022.org/ CALL FOR WORKSHOPS The Eighth Federated Logic Conference (FLoC 2022) will host the following ten conferences and affiliated workshops. LICS (37th Annual ACM/IEEE Symposium on Logic in Computer Science) http://lics.rwth-aachen.de/ Workshop chair: Frederic Blanqui Frederic.Blanqui(a)inria.fr FSCD (7th International Conference on Formal Structures for Computation and Deduction) http://fscd-conference.org/ Workshop chair: Nachum Dershowitz nachumd(a)tau.ac.il ITP (13th International Conference on Interactive Theorem Proving) https://itp-conference.github.io/ Workshop chair: Cyril Cohen cyril.cohen(a)inria.fr IJCAR (International Joint Conference on Automated Reasoning) http://www.ijcar.org Workshop chairs: Simon Robillard simon.robillard(a)imt-atlantique.fr Sophie Tourret stourret(a)mpi-inf.mpg.de CSF (35th IEEE Computer Security Foundations Symposium) http://www.ieee-security.org/CSFWweb/ Workshop chair: Musard Balliu musard(a)kth.se CAV (34th International Conference on Computer Aided Verification) http://i-cav.org/ Workshop chair: TBD KR (19th International Conference on Principles of Knowledge Representation and Reasoning) http://www.kr.org/ Workshop chair: Stefan Borgwardt stefan.borgwardt(a)tu-dresden.de ICLP (38th International Conference on Logic Programming) https://www.cs.nmsu.edu/ALP/conferences/ Workshop chair: Daniela Inclezan inclezd(a)miamioh.edu SAT (25th International Conference on Theory and Applications of Satisfiability Testing) http://www.satisfiability.org Workshop chair: Alexander Nadel alexander.nadel(a)intel.com CP (25th International Conference on Principles and Practice of Constraint Programming) http://a4cp.org/events/cp-conference-series Workshop chair: TBD SUBMISSION OF WORKSHOP PROPOSALS Researchers and practitioners are invited to submit proposals for workshops on topics in the field of computer science, related to logic in the broad sense. Each workshop proposal must indicate one affiliated conference of FLoC 2022. It is strongly suggested that prospective workshop organizers contact the relevant conference workshop chair before submitting a proposal. Each proposal should consist of the following two parts. 1) A short scientific justification of the proposed topic, its significance, and the particular benefits of the workshop to the community, as well as a list of previous or related workshops (if relevant). 2) An organisational part including: - contact information for the workshop organizers; - proposed affiliated conference; - estimate of the number of workshop participants (please note that small workshops, i.e., of less than ~13 participants, will likely be cancelled or merged); - proposed format and agenda (e.g. paper presentations, tutorials, demo sessions, etc.); - potential invited speakers (note that expenses of workshop invited speakers are not covered by FLoC); - procedures for selecting papers and participants; - plans for dissemination, if any (e.g. a journal special issue); - duration (which may vary from one day to two days); - preferred period (pre or post FLoC); - virtual/hybrid backup plans (including platform preference). The FLoC Organizing Committee will determine the final list of accepted workshops based on the recommendations from the Workshop Chairs of the hosting conferences and availability of space and facilities. Proposals should be submitted through EasyChair: https://easychair.org/conferences/?conf=floc2022workshops Please see the Workshop Guidelines page: https://floc2022.org/workshops/ for further details and FAQ. IMPORTANT DATES Submission of workshop proposals deadline: September 27, 2021 (note extended deadline) Notification: November 1, 2021 Pre-FLoC workshops: Sunday & Monday, July 31–August 1, 2022 (note corrected dates) Post-FLoC workshops: Thursday & Friday, August 11-12, 2022 CONTACT INFORMATION Questions regarding proposals should be sent to the workshop chairs of the proposed affiliated conference. General questions should be sent to: shaull(a)technion.ac.il GuillermoAlberto.Perez(a)uantwerpen.be FLoC 2022 WORKSHOP CHAIRS Shaull Almagor Guillermo A. Perez

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Call for Lightning Talks: Haskell Implementors' Workshop @ ICFP'21
by Ningning Xie 06 Aug '21

06 Aug '21

Call for Lightning Talks ACM SIGPLAN Haskell Implementors' Workshop https://icfp21.sigplan.org/home/hiw-2021 Virtual, 22 Aug, 2021 Co-located with ICFP 2021 https://icfp21.sigplan.org/ Important dates --------------- Deadline: Thursday, 19 Aug, 2021 (or when slots are full, whichever is sooner) Workshop: Sunday, 22 Aug, 2021 The 13th Haskell Implementors' Workshop is to be held alongside ICFP 2021 this year virtually. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure, to share their work and discuss future directions and collaborations with others. We will have a number of slots for lightning talks. Lightning talks will be ~7 minutes and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Lightning talks are proposed by submitting a title and an abstract. Submissions will not be part of the peer-review process. Notification of acceptance will be continuous until slots are full. Submissions should be made via Google form: https://forms.gle/BmUSyWWTXt1AMTec8 Accepted lightning talks will be posted on the workshop’s website. Scope and target audience ------------------------- The Implementors' Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community encouraged to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are specially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Logistics --------- Due to the on-going COVID-19 situation, ICFP (and, consequently, HIW) will be held remotely this year. However, the organizers are still working hard to provide for a great workshop experience. While we are sad that this year will lack the robust hallway track that is often the highlight of HIW, we believe that this remote workshop presents a unique opportunity to include more of the Haskell community in our discussion and explore new modes of communicating with our colleagues. We hope that you will join us in making this HIW as vibrant as any other. Contact ------- * Ningning Xie <xnningxie(a)gmail.com>

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Call for Participation: ICFP 2021
by Sam Tobin-Hochstadt 06 Aug '21

06 Aug '21

===================================================================== Call for Participation ICFP 2021 26th ACM SIGPLAN International Conference on Functional Programming and affiliated events August 22 - August 27, 2021 Online http://icfp21.sigplan.org/ Early Registration until August 7! ===================================================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. This year, the conference will be a virtual event. All activities will take place online. The main conference will take place from August 23-25, 2021 during two time bands. The first band will be 4PM-11PM Seoul time, and will include both technical and social activities. The second band will repeat (with some variation) the technical program and social activities 12 hours later, 3PM-10PM New York, the following day. We’re excited to announce that ICFP 2021 will feature an invited talk from Ravi Chugh of the University of Chicago. Keynote sessions will take place at 10 PM Seoul/9 AM New York. ICFP has officially accepted 35 exciting papers, and (in its second year) there will also be presentations of 4 papers accepted recently to the Journal of Functional Programming. Co-located symposia and workshops will take place the day before and two days immediately after the main conference. Registration is now open. The early registration deadline is August 7th, 2021. Registration is not free, but is significantly lower than usual, including a $10 discounted registration option available to all. Students who are ACM or SIGPLAN members may register for FREE before the early deadline. https://regmaster.com/2021conf/ICFP21/register.php New this year: Attendees will be able to sign-up for the ICFP Mentoring Program (either to be a mentor, receive mentorship or both). * Overview and affiliated events: http://icfp21.sigplan.org/home * Accepted papers: http://icfp21.sigplan.org/track/icfp-2021-papers#event-overview * JFP Talks: https://icfp21.sigplan.org/track/icfp-2021-jfp-talks#event-overview * Registration is available via: https://regmaster.com/2021conf/ICFP21/register.php Early registration ends 8 August, 2021. * Programming contest: https://icfpcontest2021.github.io/ * Student Research Competition: https://icfp21.sigplan.org/track/icfp-2021-Student-Research-Competition * Follow us on Twitter for the latest news: http://twitter.com/icfp_conference This year, there are 10 events co-located with ICFP: * Erlang Workshop (8/26) * Haskell Implementors' Workshop (8/22) * Haskell Symposium (8/26-8/27) * Higher-Order Programming with Effects (8/22) * miniKanren Workshop (8/26) * ML Family Workshop (8/26) * OCaml Workshop (8/27) * Programming Languages Mentoring Workshop (8/22) * Scheme Workshop (8/27) * Type-Driven Development (8/22) ### ICFP Organizers General Chair: Sukyoung Ryu (KAIST, South Korea) Program Chair: Ron Garcia (UBC, Canada) Artifact Evaluation Co-Chairs: Brent Yorgey (Hendrix College, USA) Gabriel Scherer (INRIA Saclay, France) Industrial Relations Chair: Alan Jeffrey (Roblox, USA) Simon Marlow (Facebook, UK) Programming Contest Organizers: Alex Lang and Jasper Van der Jeugt Publicity and Web Chair: Sam Tobin-Hochstadt (Indiana University, USA) Student Research Competition Chair: Anders Miltner (University of Texas, USA) Workshops Co-Chairs: Zoe Paraskevopoulou (Northeastern University, USA) Leonidas Lampropoulos (University of Maryland, USA) Video Co-Chairs: Leif Andersen (Northeastern University, USA) Ben Chung (Northeastern University, USA) Student Volunteer Co-Chairs: Hanneli Tavante (McGill University, Canada) Jaemin Hong (KAIST, South Korea) Lily Bryant (UBC, Canada) Accessibility Co-Chairs: Lindsey Kuper (UCSC, USA) Kathrin Stark (Princeton, USA)

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[ANN] Cabal-3.6.0.0
by Emily Pillmore 05 Aug '21

05 Aug '21

Hello All, The Cabal team is excited to announce the release of Cabal-3.6.0.0! This is the fourth release of the 3.0 release series, and highlights include support for GHC 9.2, as well as many new code quality improvements + organization work on the repo itself. For future plans, we've announced a State of the Cabal post which describes where we want to take the library and executable over the next year or two here: https://discourse.haskell.org/t/state-of-the-cabal-q1-q2-2021/2548. If you'd like to get involved, feel free to contact anyone from the maintainer team directly, or drop by #hackage on libera.chat ( http://libera.chat/ ) to speak with us. Additionally, as we continue to modernize Cabal, I'd like to highlight and show appreciation for all of the help we've gotten from the community, including the developer hours coming from Well-Typed, Haskell Foundation/Haskell.org ( http://foundation/Haskell.org ) , Obsidian Systems, and the Haskell Language Server folks. I'm glad we could work together! For a full set of release notes, see https://github.com/haskell/cabal/blob/master/release-notes/Cabal-3.6.0.0.md. If you have issues, we'd love to hear about there here: https://github.com/haskell/cabal/issues. Happy hacking! Emily

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IFL'21 Final call for papers
by Pieter Koopman 05 Aug '21

05 Aug '21

================================================================================ IFL 2021 33rd Symposium on Implementation and Application of Functional Languages venue: online 1 - 3 September 2021 https://ifl21.cs.ru.nl <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> ================================================================================ Note: - We do accept extended abstracts for presentation - Submission is open - Registration is open 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 2021 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. Industrial track and topics of interest This year's edition of IFL explicitly solicits original work concerning *applications* of functional programming in industry and academia. These contributions will be reviewed by experts with an industrial background. 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 specialisation * run-time code generation * partial evaluation * (abstract) interpretation * meta-programming * 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 * testing and proofing * virtual/abstract machine architectures * validation, verification of functional programs * tools and programming techniques * applications of functional programming in the industry, including ** functional programming techniques for large applications ** successes of the application functional programming ** challenges for functional programming encountered ** any topic related to the application of functional programming that is interesting for the IFL community Post-symposium peer-review Following IFL tradition, IFL 2021 will use a post-symposium review process to produce the formal proceedings. Before the symposium authors submit draft papers. These draft papers will be screened by the program chairs to make sure that they are within the scope of IFL. The draft papers will be made available to all participants at the symposium. Each draft paper is presented by one of the authors at the symposium. After the symposium every presenter is invited to submit a full paper, incorporating feedback from discussions at the symposium. Work submitted to IFL may not be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy. 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 for the formal proceedings. We plan to publish these proceedings in the International Conference Proceedings Series of the ACM Digital Library, as in previous years. Moreover, the proceedings will also be made publicly available as open access. Important dates Submission deadline of draft papers: 17 August 2021 Notification of acceptance for presentation: 19 August 2021 Registration deadline: 30 August 2021 IFL Symposium: 1-3 September 2021 Submission of papers for proceedings: 6 December 2021 Notification of acceptance: 3 February 2022 Camera-ready version: 15 March 2022 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 <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> . (For LaTeX users, start your document with \documentclass[format=sigconf]{acmart}.) Note that this format has a rather long but limited list of packages that can be used. Please make sure that your document adheres to this list. The submission Web page for IFL21 is https://easychair.org/conferences/?conf=ifl21 <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> . Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured 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. Organisation IFL 2021 Chairs: Pieter Koopman and Peter Achten, Radboud University, The Netherlands IFL Publicity chair: Pieter Koopman, Radboud University, The Netherlands PC: Peter Achten (co-chair) - Radboud University, Netherlands Thomas van Binsbergen - University of Amsterdam, Netherlands Edwin Brady - University of St. Andrews, Scotland Laura Castro - University of A Coruña, Spain Youyou Cong - Tokyo Institute of Technology, Japan Olaf Chitil - University of Kent, England Andy Gill - University of Kansas, USA Clemens Grelck - University of Amsterdam, Netherlands John Hughes - Chalmers University, Sweden Pieter Koopman (co-chair) - Radboud University, Netherlands Cynthia Kop - Radboud University, Netherlands Jay McCarthey - University of Massachussetts Lowell, USA Neil Mitchell - Facebook, England Jan De Muijnck-Hughes - Glasgow University, Scotland Keiko Nakata - SAP Innovation Center Potsdam, Germany Jurriën Stutterheim - Standard Chartered, Singapore Simon Thompson - University of Kent, England Melinda Tóth - Eötvos Loránd University, Hungary Phil Trinder - Glasgow University, Scotland Meng Wang - University of Bristol, England Viktória Zsók - Eötvos Loránd University, Hungary Virtual symposium Because of the Covid-19 pandemic, this year IFL 2021 will be an online event, consisting of paper presentations, discussions and virtual social gatherings. Registered participants can take part from anywhere in the world. Registration Please use the link below to register for IFL 2021: https://docs.google.com/forms/d/e/1FAIpQLSdMFjo-GumKjk4i7szs7n4DhWqKt96t8of… <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> Thanks to the sponsors and the support of the Radboud university registration is free of charge. [image: beacon]

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Re: [Haskell-cafe] Why not some subclass of Floating to model NaNs as some handleable bottom?
by Michal J Gajda 04 Aug '21

04 Aug '21

Dear Yue, Bottom has much weaker semantics than an exception: it means You may never get a result and thus will never handle it! Another reason is convenience: it is frequently the case that giving NaN in a row of numbers is much more informative than crashing a program with an exception and never printing the result anyway. Finally IEEE special values have clear propagation semantics: they are basically Maybe on steroids. The problem with this approach is indeed a silent handling. But in order to fix this, it is better to add preconditions to specific algorithms that do not allow IEEE special value on input (`isFinite` or `isNotNaN`) and then track the origin of the special value with the methods like those described here: https://skillsmatter.com/skillscasts/14905-agile-functional-data-pipeline-i… Never throw an error without telling exactly why it happened and exactly where to fix it :-). Using bottom is last resort; exceptions likewise. -- Cheers Michał

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Re: [Haskell-cafe] Parsing XML
by Michal J Gajda 04 Aug '21

04 Aug '21

Dear John, I recommend Xeno: https://gitlab.com/migamake/xeno It was released on Hackage some time ago by Chris Done, then maintained by Marco Zocca. It was benchmarked against fastest parsers in both Haskell and other languages: * https://arxiv.org/abs/2011.03536 * http://neilmitchell.blogspot.com/2016/12/new-xml-parser-hexml.html It allows you to use SAX and DOM-style processing. It has an awesome memory efficiency that is surpassed only by PugiXML parser (which builds DOM in place, but occasionally crashes). It does not support some XML features (namespaces, entity normalization etc.), but these can be added as postprocessing after the DOM is built. It is maintained. And there is a yet unreleased version that can be used to parse HTML documents and documents that are not well formed. Disclosure: I am current maintainer. -- Cheers Michał J. Gajda

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