- Haskell-Cafe - Haskell.org

pipes Producer combination
by PICCA Frederic-Emmanuel 14 Jun '22

14 Jun '22

Hello, I would like to combine Producers in order to create a Producer of another type whcih combine these values I want a Producer of the 'A' type data A :: A a b by I have a Producer of 'a' values and another on of 'b' values. what is the best way to create from thoses two producers a Producer of 'A' ? Is ther a Generic way to automatically generate these combine Producers. In my programmes, I will have plenty of these combine Producers. thanks for considering. Cheers Frederic

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Phase correction?
by Mario Lang 09 Jun '22

09 Jun '22

Hi. This is more a math question then a Haskell specific thing. However, Haskell fits nicely to write down the problem as executable "pseudo" code, so here I am, knowing that you all can read this and actually grasp the problem at hand (which I obviously dont). I stumbled across this while naively playing with C++ infinite ranges, starting with std::ranges::views::iota. So there I was, happily playing with signal generation, until I went stuck here: Modulating oscillation frequency while trying to stay stateless. But code says more then a foreign language, so: #!/usr/bin/env stack -- stack --resolver lts-19.8 runghc import Data.Ratio n = [0 ..] d = 10 -- EXAMPLE, usually 48000 t = (% d) <$> n sine f = (\x -> sin $ 2*pi * fromRational x * f x) <$> t sine1 = sine $ const 1 -- OK -- Lets devise a method to specify a value changing over time data I = No | Lin | Exp erp No a _ _ = a erp Lin a b mu = (1 - mu) * a + mu * b erp Exp a b mu = a * ((b / a) ** mu) data Curve a = Curve a [(I, Double, a)] at (Curve p1 []) _ = p1 at (Curve p1 ((i, d, p2):xs)) t = go 0 d p1 p2 i d xs where go t1 t2 p1 p2 i d xs | t < t2 = erp i p1 p2 $ (t - t1) / d | null xs = p1 | (i', d', p2') <- head xs = go t2 (t2 + d') p2 p2' i' d' $ tail xs -- Frequency modulation? c = Curve 1 [(Exp, 1.0, 2), (Exp, 1.0, 1)] sine2 = sine $ at c . fromRational -- WRONG!🙅 -- Whenever a change occurs, phase is incorrect -- because current step doesn't know about the past main = do print $ take 10 $ sine1 print $ at c 0.5 == at c 1.5 print $ take 10 $ sine2 -- The naive question of an experimenting non-math coder person is: -- Can a version of `at` be written which compensates for the phase -- differences which runs in O(n) where n is the number of curve points? -- Intuitively this should be possible given `d` (denominator). at' :: Curve a -> Ratio b -> a at' c t = undefined -- CYa, ⡍⠁⠗⠊⠕

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Dashboard
by Anton Pichugin 08 Jun '22

08 Jun '22

Hello everyone in the Haskell cafe! Such a nice place! My name is Anton. A month ago I started learning Haskell. I want to make a dashboard about the language. What data should I analyze and add to it? I see this project as a page where you can see charts and diagrams that change in real time. As of now I only have Google Trends (search Interest over time) + number of commits on GitHub. What else can I visualize? Which one could be helpful to the community? Kind regards, Anton Pichugin

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[ANN] Yampa 0.13.5
by Ivan Perez 08 Jun '22

08 Jun '22

Dear all, I'm happy to announce the release of Yampa 0.13.5! Yampa is a fast, elegant FRP library that enforces a separation between effects (e.g., user input, rendering) and FRP signal function specifications.Yampa prides itself in being a long-standing community project. It's now been around for almost 20 years!!! In all this time, it has enjoyed abundant use in research, in open source, and in industry. * Summary of changes - Tests in the yampa-test library have now been reorganized to follow the same structure of Yampa. This change will make it easier to identify what tests are missing. A summary has been produced as part of an issue [1]. - A less-known feature of Yampa is that applicative style is also supported, and renders programs reminiscent of classic FRP. To make Yampa more inviting to users who prefer such style, the descriptions in the package, README and main module have been adapted so that they do not suggest that arrows syntax or the arrow-based interface is the only available or even preferred style. - Tabs will now produce a compilation error. - Multiple maintenance fixes (fix broken links in documentation, remove unnecessary imports, style fixes, etc.). As always, Yampa and yampa-test are released in sync. The CHANGELOGs are available at: https://github.com/ivanperez-keera/Yampa/blob/develop/yampa/CHANGELOG https://github.com/ivanperez-keera/Yampa/blob/develop/yampa-test/CHANGELOG * Releases You can explore the current versions at: https://hackage.haskell.org/package/Yampa https://hackage.haskell.org/package/yampa-test * Code The github repo is located at: https://github.com/ivanperez-keera/Yampa * Upcoming changes We are discussing an upcoming change that may affect users. We are interested in knowing if/how this would affect you (if at all). - Addition of new constraint to integral/derivative: The VectorSpace implementation we are using imposes the Eq and Floating constraints on vector spaces, but they have turned out not to be necessary. An alternative implementation is being proposed [2], which removes those constraints, and gives default implementations for some functions that meet some type constraints. This change would require adapting the code of integral, derivative and some related functions to impose an additional type constraint. We expect most user code to be compatible, but the change is, technically, API-breaking. This topic is open to discussion, we invite interested users to come forward. * Other notes: We have a plan for the upcoming releases. Check out the project issues or message me if you are interested in participating. https://github.com/ivanperez-keera/Yampa/issues All the best, Ivan [1] https://github.com/ivanperez-keera/Yampa/issues/217 [2] https://github.com/ivanperez-keera/simple-affine-space/tree/develop-no-cons…

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Deadline Extended: 26th Brazilian Symposium on Programming Languages (SBLP 2022)
by Cristiano D. Vasconcellos 07 Jun '22

07 Jun '22

SBLP 2022 is the 26th edition of the Brazilian Symposium on Programming Languages<https://cbsoft2022.facom.ufu.br/sblp.php>. It is promoted by the Brazilian Computer Society (SBC) and constitutes a forum for researchers, students, and professionals to present and discuss ideas and innovations in the design, definition, analysis, implementation, and practical use of programming languages. SBLP's first edition was in 1996. Since 2010, it has been part of CBSoft, the Brazilian Conference on Software: Theory and Practice. The Conference is planned to be held on October 3-7, 2022, fully online. Submission Guidelines Papers can be written in Portuguese or English. Submissions in English are encouraged considering that only accepted papers written in English will appear in the proceedings, usually indexed in the ACM Digital Library (to be confirmed). The acceptance of a paper implies the registration of at least one author in the symposium to present it. Papers must be original and not simultaneously submitted to another journal or conference. No-show of scheduled papers will result in excluding them from the proceedings. SBLP 2022 will use a lightweight double-blind review process. The manuscripts should be submitted for review anonymously (i.e., without listing the author’s names on the paper) and references to own work should be made in the third person. Papers must be submitted electronically (in PDF format) via the EasyChair System.<https://easychair.org/conferences/?conf=sblp2022> The following paper categories are welcome (page limits include figures, references, and appendices): • Full papers: up to 8 pages long in ACM 2-column conference format.<http://www.acm.org/publications/proceedings-template> Full papers can be further specialized, at submission time, as student papers (i.e., as papers describing research conducted mainly by a student at any level). student papers will be subject to the exact same reviewing process and criteria but may be entitled for an award (see below). • Short papers: up to 3 pages in the same format. Short papers can discuss new ideas which are at an early stage of development or can report partial results of on-going dissertations or theses. Each paper can have a maximum of one extra page for references. Active graduate and undergraduate students seeking feedback are invited to submit short papers of their original unpublished and in-progress research work. A set of selected papers, which did not get accepted as full papers, may be accepted as short papers. Awards: Two best paper awards will be attributed, distinguishing full paper submissions of the best: • student paper; • non-student paper. List of Topics (related but not limited to the following): • Programming paradigms and styles, scripting and domain-specific languages and support for real-time, service-oriented, multi-threaded, parallel, distributed, and quantum programming; • Program generation and transformation; • Formal semantics and theoretical foundations: denotational, operational, algebraic, and categorical; • Program analysis and verification, type systems, static analysis, and abstract interpretation; • Programming language design and implementation, programming, language environments, compilation, and interpretation techniques; • Programming languages for the blockchain technology: design and implementation of Smart Contract languages, implementation of consensus protocols, language-based security, and cryptographic primitives. A selection of the best papers appearing in the last editions of SBLP have been invited to be extended and considered for publication in a special issue of the Journal of Computer Languages (COLA), by Elsevier. We will approach COLA for a similar special issue regarding the 2022 edition of SBLP. Important dates: • Abstract submission: 20 June, 2022. • Paper submission: 20 June, 2022. • Author notification: 16 Aug, 2022. • Camera ready deadline: 29 Aug, 2022. Program Committee Program Committee Chair: Cristiano Vasconcellos, UDESC Program Committee Alberto Pardo, Universidad de la República Alcides Fonseca, Universidade de Lisboa Alejandro Díaz-Caro, Universidad Nacional de Quilmes & Universidad de Buenos Aires Alex Kavvos, University of Bristol Anderson Faustino, UEM Andrei Paskevich, Université Paris-Sud, LRI Andre Maidl, Elastic Dalvan Griebler, PUCRS/SETREM Emmanuel Chailloux, University Pierre and Marie Curie Fernando Castor, UFPE & Utrecht University Fernando Pereira, UFMG Francisco Sant'anna, UERJ Karina Roggia, UDESC Leonardo dos Santos, UFJF Liam O'Connor, University of Edinburgh Marcos Viera, Universidad de la República Mário Pereira, Universidade NOVA de Lisboa Mariza Bigonha, UFMG Nuno Macedo, INESC TEC & University of Porto Paul Leger, Universidad Católica del Norte Roberto Bigonha, UFMG Roberto Ierusalimschy PUC-Rio Rodrigo Ribeiro, UFOP Samuel Feitosa, UFFS Sérgio Medeiros, UFRN Simão Sousa, Universidade da Beira Interior Stefania Dumbrava, ENSIIE Paris-Evry Contact: All questions about submissions should be emailed to cristiano.vasconcellos(a)udesc.br

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Re: [Haskell-cafe] Should there be a haskell template for inclusion polymorphism in Haskell?
by Olaf Klinke 06 Jun '22

06 Jun '22

> So my central questions for discussions are: > > - Is inclusion polymorphism something we should use at all in Haskell? > - These boiler plate code maybe better be generated using Haskell template > instead, is there one already, or should > there be one? Maybe one of the authors of a sub-typing library can share a more informed opinion on this. My view as a mathematician: A type being a subtype of another is a relation between types. Relations between types is what multi-parameter type classes is about. Hence it seems that this is how subtypes in Haskell ought to be done. For example, in the attenuation and records-sop package, the latter of which is based on genercis-sop, which depends on Template Haskell. So without having used any of the mentioned packages, I believe your second question can be answered with "yes". Regarding the first question, we should probably ask ourselves how much type-safety we're sacrificing for the convenience we gain. The Num example you gave shows one possible danger: While a subtype relation may hold mathematically, the implementiation details may cause this relation to fail in reality. Example: All floating point numbers are rationals, aren't they? So there should be a subtype relation. But how to convert NaN, -infinity or -0 of type Double to a pair of Integers? Olaf

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cabal 3.8 pre-released!
by Mikolaj Konarski 06 Jun '22

06 Jun '22

Hello! The first 3.8 series cabal release candidate is available. Install via ghcup config add-release-channel \ https://raw.githubusercontent.com/haskell/ghcup-metadata/master/ghcup-prere…; ghcup install cabal 3.8.0.20220526 or manually from https://downloads.haskell.org/cabal/cabal-install-3.8.1.0-rc1/. We, the cabal team, are completely dependent on our invaluable contributors and collaborators, thanks to whom this pre-release is possible. Therefore, please test extensively and if anything critical is missing or broken that you'd like to see fixed in 3.8.1.0-final, let us know on the bug tracker. There is still a narrow window to change things and the cabal team will try to guide you along and help you implement them. The dynamic list of known grave bugs that could plausibly be solved for 3.8 is at https://github.com/haskell/cabal/issues?q=is%3Aopen+is%3Aissue+label%3A%22p… At the time of writing none of the bugs on the list is blocking the final 3.8 release. Changelogs are at https://github.com/haskell/cabal/blob/Cabal-v3.8.1.0-rc1/release-notes/Caba… https://github.com/haskell/cabal/blob/cabal-install-v3.8.1.0-rc1/release-no… The list of all authors of cabal is the git commit log. You are great. Happy hacking, Mikolaj

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ANN: hledger-1.26
by Simon Michael 05 Jun '22

05 Jun '22

Aloha! I am pleased to announce hledger 1.26: https://github.com/simonmichael/hledger/releases/1.26 https://hledger.org/install https://hledger.org/release-notes.html#hledger-1-26 1.26 is a modest maintenance release; highlights include faster register reports and clearer error messages. Thank you to core contributor Stephen Morgan. What is hledger ? - free, high quality Plain Text Accounting[1] software: - a fast and robust multicurrency double-entry accounting system - built around human-readable, version-controllable plain text files - inspired by and partly compatible with Ledger CLI[2] - convertible to and from Beancount[3] - written in Haskell for correctness and longevity - easy to install on unix, mac and windows. For help getting started, or more info, see https://hledger.org, and join our chat via Matrix or IRC: https://hledger.org/support. Newcomers, experts, contributors, sponsors, feedback are always welcome! Best wishes, -Simon [1] https://plaintextaccounting.org [2] https://ledger-cli.org [3] https://beancount.github.io

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Re: [Haskell-cafe] Hiding type variables from the signature?
by Olaf Klinke 03 Jun '22

03 Jun '22

> λ f = deasilsB . deasilsA > > <interactive>:2:1: error: > • Could not deduce: Dress seed0 peels0 ~ Dress seed peels > ``` > > What is going on? How can I have my `deasils`? > > I tried attaching all kinds of type annotations, but nothing works so far. I do > not even understand the problem. How is it that an expression can be typed, but > cannot be assigned to a name? > > You can see the complete code at the gist [1]. > > [1]: https://gist.github.com/kindaro/6056f753bcf356ced96b817fee72533c/2823ec2792… The given type annotation for desilsA uses forall, which suggests you want to use ScopedTypeVariables here. But for that feature to kick in, you need to actually mention the scoped type variables in the function body, which you don't. :t deasil . first squeeze deasil . first squeeze :: (ForAll peels Functor, Squeezy' left a peels (Strip left a == '[])) => (a, right) -> Squeezed peels (left, right) You must use ScopedTypeVariables to constrain the type variable `a' to the intended (Dress seed peels). Olaf

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Hiding type variables from the signature?
by Ignat Insarov 02 Jun '22

02 Jun '22

Hello café, hope you all doing well! I have this code [1]. Its purpose is to provide an `fmap` that works at any depth. Here is the gist of the gist: ```Haskell fmapz ∷ forall seed fruit seed' fruit' peels recursive. Squeezish seed seed' fruit fruit' peels recursive ⇒ (seed → seed') → fruit → fruit' fmapz function = stretch . fmap @(Squeezed (Strip seed fruit)) function . squeeze ``` As the examples show, it works, and even has some type inference. However, the type signature is unwieldy. It seems like it should have only 4 variables, but I have to also do some type level book-keeping for which the other 2 variables are needed. These book-keeping type variables are determined by type families from the other 4, so surely I can hide them inside a type synonym or something like that? I tried giving a quantified constraint, like so: ```Haskell type Squeezish ∷ ★ → ★ → ★ → ★ → Constraint type Squeezish seed seed' fruit fruit' = forall peels recursive. Squeezish' seed seed' fruit fruit' peels recursive class Squeezish' seed seed' fruit fruit' (peels ∷ [★ → ★]) (recursive ∷ Bool) instance ( peels ~ Strip seed fruit , ForAll peels Functor , Squeezy seed' fruit' peels recursive , Squeezy seed fruit peels recursive ) ⇒ Squeezish' seed seed' fruit fruit' peels recursive ``` — But then the constraints from the context of `Squeezish'` fail to make it to the use site and numerous errors arise. What can I do to solve this problem? Or is it theoretically impossible? [1]: https://gist.github.com/kindaro/6056f753bcf356ced96b817fee72533c

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