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Re: [Haskell-cafe] traversal with an arrow
by Olaf Klinke 19 Jun '22

19 Jun '22

> On Fri, Jun 17, 2022 at 05:01:55PM +0200, Olaf Klinke wrote: > > Is there prior art to the following generalisation? > > > traverseArrow :: Traversable t => a x y -> a (t x) (t y) > > Perhaps you are looking for this: > > https://github.com/tomjaguarpaw/Arrows2/issues/3#issuecomment-561973678 > Thanks Tom, can you explain what's behind this implementation, for those unfamiliar with arrow syntax? I guess [*] that the Traversal type used is a manifestation of the fact that one can transform any traversable structure (t a) into ([a],t ()) and sort the contents of the linked list back into their original places? This way, arbitrary traversals can be reduced to traversals over linked lists. Then the ArrowChoice is needed to pattern match on the list constructors? E. Kmett's profunctor implementation wanderA, linked to from the end of the discussion, seems to be missing from the current Data.Profunctor.Traversing module. Olaf [*] Structurally, Traversal a r b ~ Free (Const a :*: ((->) r)) b and also their Applicative instances seem to match on first glance. In particular, Traversal a () b ~ ([a],b) whence traversal :: Traversable t => t a -> Traversal a b (t b) can be specialized to traversal :: Traversable t => t a -> ([a],t ())

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traversal with an arrow
by Olaf Klinke 18 Jun '22

18 Jun '22

Dear Café, Is there prior art to the following generalisation? A Hoogle search for the type signatures did not turn up anything. import Control.Arrow import Control.Monad (foldM) -- | Categories which every Traversable is a functor in. -- For Traversable t, the instance should satisfy -- -- @ -- foldMapArrow f = foldMapArrow id . traverseArrow f -- @ class Arrow a => ArrowTraverse a where traverseArrow :: Traversable t => a x y -> a (t x) (t y) foldArrow :: Foldable t => a (y,x) y -> a (y,t x) y instance ArrowTraverse (->) where traverseArrow = fmap foldArrow f = uncurry ((foldl.curry) f) instance Monad m => ArrowTraverse (Kleisli m) where traverseArrow (Kleisli k) = Kleisli (mapM k) foldArrow (Kleisli k) = (Kleisli . uncurry) (foldM (curry k)) -- | Generalizes foldMap. -- For Kleisli m, this function is also known as foldMapM. foldMapArrow :: (ArrowTraverse a, Foldable f, Monoid y) => a x y -> a (f x) y foldMapArrow f = (arr (const mempty) &&& id) >>> foldArrow ((id *** f) >>> arr (uncurry mappend)) The thing is that there are more instances for this class, for example by using Ross Paterson's arrow transformers [1]. I found myself implementing an arrow that is a Kleisli arrow with a reader context. Neither the standard arrow machinery nor the arrows package seem to grant me the power to write a traverseArrow for it. Either it can't be done, or my arrow-fu is not strong enough. Olaf [1] https://hackage.haskell.org/package/arrows

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邀请： Deadline Extended: 26th Brazilian Symposiu... @ 2022年6月17日 (周五) 下午6:30 - 下午7:30 (CST) (haskell-cafe@haskell.org)
by rippletc＠gmail.com 17 Jun '22

17 Jun '22

[Haskell-cafe] Deadline Extended: 26th Brazilian Symposium on Programming Languages (SBLP 2022) 2022年6月17日 (星期五) ⋅ 下午6:30 – 下午7:30 台北标准时间通过 Google Meet 加入视频会议 https://meet.google.com/wvx-gvgo-mmj?hs=224 SBLP 2022 is the 26th edition of the Brazilian Symposium on Programming Languages. 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 lea... 组织者 rippletc(a)gmail.com rippletc(a)gmail.com 邀请对象 rippletc@gmail.com- 组织者 cdvasconcellos(a)hotmail.com haskell-cafe(a)haskell.org 查看所有邀请对象信息 https://calendar.google.com/calendar/event?action=VIEW&eid=M3RxajQ0a2pkamF2… 回复 haskell-cafe(a)haskell.org 的邀请并查看更多详细信息 https://calendar.google.com/calendar/event?action=VIEW&eid=M3RxajQ0a2pkamF2… 您可以选择是否参加。 ~~//~~ 来自 Google 日历的邀请：https://calendar.google.com/calendar/ 您之所以收到这封电子邮件，是因为您是活动的参加者。如要停止接收有关此活动的后续更新，请拒绝此活动。转发此邀请后，任何收件人都可以向组织者发送回复，也可以被添加到邀请对象列表；无论其邀请状态为何，他们都可以邀请其他人；他们还可以修改您的回复。了解详情https://support.google.com/calendar/answer/37135#forwarding

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Post Doc Vacancy at St Andrews
by Christopher Brown 17 Jun '22

17 Jun '22

The Programming Languages Group at the University of St Andrews seeks a post-doctoral research fellow for a fixed 12-month position. Details of the position can be found here: https://www.vacancies.st-andrews.ac.uk/Vacancies/W/4238/0/352367/889/resear… Vacancy Description School of Computer Science Salary: £34,304 per annum Start date: 1 October 2022 or as soon as possible thereafter Fixed-term: 12 months Applications are sought for a committed Post-doctoral Research Fellow to work with Dr Chris Brown conducting research for a EPSRC funded project entitled Energise: Refactorings and Skeletons for Energy-Aware Applications on High-Performance Embedded Systems. The primary duties will be to implementing refactorings for target languages such as C; proving general soundness of the refactorings using e.g. dependent types; developing new programming abstractions (skeletons) for abstracting common energy-reducing programming patterns; running experiments; writing proofs of correctness. The successful applicant will have (or be near to completion of) a PhD in Programming Languages with expertise in formal semantics of programming languages, compilers, program transformation, lightweight formal methods (including, e.g. dependent types) and/or knowledge of parallelism and non-functional properties, including energy. The post is available on a fixed-term basis for 12 months starting 1st October or as soon as possible thereafter. Further details of the project can be found by contacting Dr Christopher Brown (cmb21(a)st-andrews.ac.uk<mailto:cmb21@st-andrews.ac.uk>). Applications are particularly welcome from women, people from the Black, Asian and Minority Ethnic (BAME) community, and other protected characteristics who are under-represented in research posts at the University. Equality, diversity and inclusion are at the heart of the St Andrews experience. We strive to create a fair and inclusive culture demonstrated through our commitment to diversity awards (Athena Swan, Carer Positive, LGBT Charter, Race Charters and Stonewall). We celebrate diversity by promoting profiles of BAME, LGBTIQ+ staff and supporting networks including the Staff BAME Network; Staff with Disabilities Network; Staff LGBTIQ+ Network; and the Staff Parents & Carers Network. Full details available online: https://www.st-andrews.ac.uk/hr/edi/ Closing Date: 29 July 2022 Interview Date: 23 August 2022 Please quote ref:AR2699GB School of Computer Science Salary: £34,304 per annum Start date: 1 October 2022 or as soon as possible thereafter Fixed-term: 12 months

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How to override binary package
by ☂Josh Chia (謝任中) 15 Jun '22

15 Jun '22

Hi, Given that binary is one of the packages that comes with GHC, it seems that it can't be overridden with my own version using the standard ways (e.g. extra-deps in stack.yaml), at least not easily. On GHC 9.2.3, using stack, I would like to use my own version from my github repo. I've tried extra-deps referencing the github repo commit and it did not work; judging by the behavior of some functions, I was still getting the standard binary package instead of my own version. Is there a way to override? Josh

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State Monad Tutorial
by danon 14 Jun '22

14 Jun '22

Saw the discussion on the https://wiki.haskell.org/Talk:State_Monad I don´t have an account on the wiki. If anyone is interested in a small practical example of how to State Monad. I may have 1 or 2. Kind Regards dhj

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CALL FOR PAPERS - IFL22 - The 34th Symposium on Implementation and Application of Functional Languages
by Pieter Koopman 14 Jun '22

14 Jun '22

*CALL FOR PAPERS - The 34th Symposium on Implementation and Application of Functional Languages* *Important dates* Draft paper submission: 7th of August 2022 Draft paper notification: 9th of August 2022 Registration deadline: 12th of August 2022 Symposium: 31th of August to 2nd of September *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 2022 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 *Submissions and peer-review* Following IFL tradition, IFL 2022 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 chair 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, a formal review process will take place, conducted by the program committee. Reviewing is single blind. There will be at least 3 reviews per paper. The reviewers have 6 weeks to write their reviews. For the camera-ready version the authors can make minor revisions which are accepted without further reviewing. *Where* IFL 2022 will be held physically in Copenhagen, Denmark, arranged by DIKU at the University of Copenhagen. See the IFL 2022 website at https://ifl22.github.io/ for more information. [image: beacon]

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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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