- Haskell-Cafe - Haskell.org

[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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GHC 9.x on M1 mac?
by Stuart Hungerford 04 Aug '21

04 Aug '21

Hi Haskellers, Has anyone been able to build a 9.x series GHC installation for the M1 mac with macOS, in native binary form (i.e. not under Rosetta translation)? TIA, Stu

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Why not some subclass of Floating to model NaNs as some handleable bottom?
by YueCompl 03 Aug '21

03 Aug '21

Dear Cafe, I kinda understand the [Floating](https://hackage.haskell.org/package/base/docs/GHC-Float.html#t:Fl… <https://hackage.haskell.org/package/base/docs/GHC-Float.html#t:Floating>) class doesn't care about NaN, as not expecting all floating point implementations to have such semantics. But [IEEE Silent NaN](https://en.wikipedia.org/wiki/NaN#Quiet_NaN <https://en.wikipedia.org/wiki/NaN#Quiet_NaN>) has become a norm today, I think it deserves more than mere [isNaN](https://hackage.haskell.org/package/base/docs/GHC-Float.html#v:isNaN <https://hackage.haskell.org/package/base/docs/GHC-Float.html#v:isNaN>) in the [RealFloat](https://hackage.haskell.org/package/base/docs/GHC-Float.html#t:R… <https://hackage.haskell.org/package/base/docs/GHC-Float.html#t:RealFloat>) class. While [Signaling NaN](https://en.wikipedia.org/wiki/NaN#Signaling_NaN <https://en.wikipedia.org/wiki/NaN#Signaling_NaN>) can be an `Exception` triggering bottom like "divide by zero" is, the silent `NaN` feels like a different kind of bottom, or some thing similar to `Nothing` as in the `Num a => Maybe a` monad? Is Haskell's type system capable of encoding silent NaN as a special kind/type of bottom that handleable? Though I don't think I've gained correct understanding at all, on "bottom"s, I'm interested in what options we have to encode them, especially ergonomics ways to handle them accordingly. Best regards, Compl

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Sets, typeclasses and functional dependencies
by Stuart Hungerford 02 Aug '21

02 Aug '21

Hi Haskellers, After reading: https://stackoverflow.com/questions/34790721/where-is-the-set-type-class https://stackoverflow.com/questions/25191659/why-is-haskell-missing-obvious… https://stackoverflow.com/questions/11508642/haskell-how-can-i-define-a-typ… I can see why Haskell base does not provide typeclasses for sets. I'm wondering now though if I did create a Set typeclass what it would look like. There's several approaches using various language extensions and to me this approach using functional dependencies seems simpler than the other approaches: class Setish set a | set -> a where empty :: set singleton :: a -> set -- and so on. My question is how does the functional dependency in Setish interact with "extra" types needed for richer set operations like finding the powerset or taking a cartesian product? Something like: class Setish set a | set -> a where empty :: set singleton :: a -> set power_set :: set -> ?something product :: set -> ?something -> ?something -- and so on. TIA, Stu

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Explanation of Data.Set, please
by Galaxy Being 02 Aug '21

02 Aug '21

I'm looking at this <https://hackage.haskell.org/package/containers-0.6.5.1/docs/src/Data.Set.In…> code and wondering, first, about the strategy behind the data type Set itself data Set a = Bin {-# UNPACK #-} !Size !a !(Set a) !(Set a) | Tip It says it's a "balanced tree." I found this <http://groups.csail.mit.edu/mac/users/adams/BB/index.html> talking about maybe why that is. Will read. But in the meantime, any explanation in plain English as to why we're doing it as a tree and not some other structure would be helpful. And why are we bringing Size along, and in general, why all the strictness !'s? All this might have something to do with why a balanced tree is better than quick-and-dirty list representation like I see in beginner tutorials? Next, is this ZFC? I've seen treatments that supposedly are ZFC-friendly. Finally, I've taken a preliminary look at Agda, and right from the start there's Set, and no doubt an entirely alternative, category universe approach to the concept of set theory. Any contrast and compare between Haskell and Agda's set notions would be appreciated. Haskell seems to dance in and out of Category Theory, while Agda seems pretty much just CT.... -- ⨽ Lawrence Bottorff Grand Marais, MN, USA borgauf(a)gmail.com

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I want to read documents about haskell.
by Kim Chaegon 01 Aug '21

01 Aug '21

I want read documents about haskell, pure functional language. Rgank you!

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Re: [Haskell-cafe] Help on syntactic sugar for combining lazy & strict monads?
by Olaf Klinke 30 Jul '21

30 Jul '21

On Thu, 29 Jul 2021, Benjamin Redelings wrote: > Hi Olaf, > > I think you need to look at two things: > > 1. The Giry monad, and how it deals with continuous spaces. I believe I understand the Giry monad well, and it is my measuring stick for functional probabilistic programming. Even more well-suited for programming ought to be the valuation monad, because that is a monad on domains, the [*] semantic spaces of the lambda calculus. Unfortunately, to my knowledge until now attempts were unsuccessful to find a cartesian closed category of domains which is also closed under this probabilistic powerdomain construction. [*] There are of course other semantics, domains being one option. > > 2. The paper "Practical Probabilistic Programming with Monads" - > https://doi.org/10.1145/2804302.2804317 Wasn't that what you linked to in your original post? As said above, measure spaces is the wrong target category, in my opinion. There is too much non constructive stuff in there. See the work of Culbertson and Sturtz, which is categorically nice but not very constructive. > > Also, observing 2.0 from a continuous distribution is not nonsensical. > > -BenRI Perhaps I am being too much of a point-free topologist here. Call me pedantic. Or I don't understand sampling at all. To me, a point is an idealised object, only open sets really exist and are observable. If the space is discrete, points are open sets. But on the real line you can not measure with infinite precision, so any observation must contain an interval. That aligns very nicely with functional programming, where only finite parts of infinite lazy structures are ever observable, and these finite parts are the open sets in the domain semantics. So please explain how observing 2.0 from a continuous distribution is not nonsensical. Olaf > > On 7/21/21 11:15 PM, Olaf Klinke wrote: >>> However, a lazy interpreter causes problems when trying to introduce >>> *observation* statements (aka conditioning statements) into the monad >>> [3]. For example, >>> >>> run_lazy $ do >>> x <- normal 0 1 >>> y <- normal x 1 >>> z <- normal y 1 >>> 2.0 `observe_from` normal z 1 >>> return y >>> >>> In the above code fragment, y will be forced because it is returned, and >>> y will force x. However, the "observe_from" statement will never be >>> forced, because it does not produce a result that is demanded. >> >> I'm very confused. If the observe_from statement is never demanded, then >> what semantics should it have? What is the type of observe_from? It seems >> it is >> a -> m a -> m () >> for whatever monad m you are using. But conditioning usually is a function >> Observation a -> Dist a -> Dist a >> so you must use the result of the conditioning somehow. And isn't the >> principle of Monte Carlo to approximate the posterior by sampling from it? >> I tend to agree with your suggestion that observations and sampling can not >> be mixed (in the same do-notation) but the latter have to be collected in a >> prior, then conditioned by an observation. >> >> What is the semantic connection between your sample and obsersvation monad? >> What is the connection between both and the semantic probability >> distributions? I claim that once you have typed everything, it becomes >> clear where the problem is. >> >> Olaf >> >> P.S. It has always bugged me that probabilists use elements and events >> interchangingly, while this can only be done on discrete spaces. So above I >> would rather like to write >> (2.0==) `observe_from` (normal 0 1) >> which still is a non-sensical statement if (normal 0 1) is a continuous >> distribution where each point set has probability zero. >

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