- Haskell-Cafe - Haskell.org

data type familly and makeLenses
by PICCA Frederic-Emmanuel 04 Mar '22

04 Mar '22

Hello, I defined a typeclass like this with a data familly class HasConfig a where data BinocularsConfig a :: * new :: (MonadIO m, MonadLogger m, MonadThrow m) => Maybe FilePath -> m (BinocularsConfig a) getConfig :: Maybe FilePath -> IO (Either String (BinocularsConfig a)) combineWithCmdLineArgs :: BinocularsConfig a -> Maybe ConfigRange -> Maybe (Path Abs Dir) -> BinocularsConfig a update :: (MonadIO m, MonadLogger m, MonadThrow m) => FilePath -> m (BinocularsConfig a) the instance is for now instance HasConfig PreConfig where data BinocularsConfig PreConfig = BinocularsPreConfig { _binocularsPreConfigProjectionType :: ProjectionType } deriving (Eq, Show) [...] Since I use Ini to serialize/un-serialize the configuration, I need lens for this type My question is how can I generate the like easily makeLenses ''(BinocularsConfig PreConfig) does not work thanks for considering Frederic

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order of assertEqual arguments is counterintuitive
by Daneel Yaitskov 02 Mar '22

02 Mar '22

Hi List, I noticed, that I pay more attention than I should, when working with assertions, because I am not sure about argument order i.e. whether the expected value goes first or vice-versa. Does anybody have similar thought? Such subtle detail should be easy to grasp with regular practice, but I observe difficulties and I suspect that there is a logical reason for that. Unit tests appeared long time ago in Java and spread over all languages. HUnit library inherited de facto standard assert function name and signature. I don't know reasoning behind original signature. I spell "assertEqual" expression as: "Assert that x equals to y" "y" sounds like a model value (i.e. expected value). In assignments "x <- y" y is the model value, because it defines "x". You get "x" - value on the left not on the right. Similar issue with test fixing - I always have to check first, that an expected value is actually one. There is no type safety preventing mixing arguments. I had to open and comprehend a source file with test, because test log is not 100% safe. -- Best regards, Daniil Iaitskov

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generic way to construct and deconstruct a newtype
by PICCA Frederic-Emmanuel 01 Mar '22

01 Mar '22

Hello, I try to write some code use to parse an ini file for one of my softwares, using config-ini[1]. In this config file I have scientific values with units, meter, angstrom, degrees, etc... So I created a bunch of newtype in order to deal with this part of the config file newtype Meter = Meter (Length Double) deriving (Eq, Show) newType Angstrom = Angstrom (Length Double) [...] Then I created a typeclasse in order to have a generic way to extract the fileds values using the BiDir api [2] class HasFieldValue a where fieldvalue :: FieldValue a instance HasFieldValue Meter where fieldvalue = FieldValue { fvParse = mapRight (Meter . (*~ meter)) . fvParse auto , fvEmit = \(Meter m) -> pack . show . (/~ meter) $ m } instance HasFieldValue Angstrom where fieldvalue = FieldValue { fvParse = mapRight (Meter . (*~ angstrom)) . fvParse auto , fvEmit = \(Angstrom m) -> pack . show . (/~ angstrom) $ m } I would like to factorize via a method which should take at least an unit, in order to avoid repetition. I started with this sort of funtion, but I do not know how to write something generic for <???> numberUnit :: (Num a, Fractional a, Read a, Show a, Typeable a) => Unit m d a -> FieldValue (Quantity d a) numberUnit u = FieldValue { fvParse = mapRight (<???> . (*~ u)) . fvParse number' , fvEmit = \(<???> v) -> pack . show . (/~ u) $ v } thanks for your help [1] https://hackage.haskell.org/package/config-ini-0.2.4.0 [2] https://hackage.haskell.org/package/config-ini-0.2.4.0/docs/Data-Ini-Config…

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Initiating package takeover: size-based and testing-feat
by Brent Yorgey 28 Feb '22

28 Feb '22

Hi everyone, Wen Kokke (cc'd) and I intend to take over maintainership of the size-based and testing-feat packages. I have tried to contact the current maintainer, Jonas Duregård (also cc'd), multiple times over the past year via both GitHub and email. I have both requested new releases incorporating existing PRs, and also offered to help with maintenance, but I have not received any response. I don't intend to do do anything fancy with the packages or make major changes, but they are nice packages and I would like to see them able to build on newer GHCs. Happy to hear any comments or feedback (especially from Jonas), but in any case, this email serves as official notice of our intention. If I still haven't heard from Jonas after a while I will proceed with contacting the Hackage admins to request a transfer of maintainership. -Brent

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2nd Call for Participation: Virtual BOB 2022 (March 11)
by Stefan Wehr 23 Feb '22

23 Feb '22

========================================================================= BOB 2022 Conference “What happens if we simply use what’s best?” March 11, 2022, online 0100+UTC https://bobkonf.de/2022/ Program: https://bobkonf.de/2022/program.html Registration: https://bobkonf.de/2022/program.html ========================================================================= BOB conference is a place for developers, architects, and decision-makers to explore technologies beyond the mainstream in software development and to find the best tools available to software developers today. Our goal is for all participants of BOB to return home with new insights that enable them to improve their own software development experience. The program features 14 talks and 8 tutorials on current topics: https://bobkonf.de/2022/program.html The subject range includes functional programming, effects, distributed programming, formal methods, generative art, event-driven systems, the human brain, Haskell, Python, Scala, Lua, Clojure, Erlang, Nix, and others. Derek Dreyer will give the keynote talk. Due to COVID-related risks, BOB will take place online, entirely within a Gather Town virtual world. We've placed special emphasis on enabling social, casual interaction, in addition to our stellar program. Registration is open - student tickets are €10, regular tickets are €30. As always, grants are available for members of groups underrepresented in tech: https://bobkonf.de/2022/program.html

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Explicit type signatures and wrappers / impedance-matching
by Benjamin Redelings 22 Feb '22

22 Feb '22

Hi, I am trying to understand (and implement) how Haskell handles explicit type signatures. Specifically, I'm trying to understand how explicit type signatures interact with wrappers. 1. Is there any paper or documentation that explains wrappers and/or explicit type signatures in detail? There are some non-obvious details regarding wrappers, such as using eliminating type arguments by supplying the Any type as an argument... 2. Do explicit type signatures impose any unification constraints, or can they be thought of entirely in terms of wrappers? For example, if we have g :: Int -> Int (f,g) = (\x ->x, f) then the signature for g is added to the environment when typing the right-hand-side. One way that this could be handled is: (i) typecheck rhs -> rhs_type (ii) generate type of lhs with fresh variables for every binder -> lhs_type = (a,b) (iii) unify(lhs_type, rhs_type) (iv) do one-way unification: match(inferred-type-of-g, explicit-type-for-g) Is this correct? Step (iv), the way that I have written it, would impose unification constraints. Without considering the type signature, we would have { f_mono :: a -> a, g_mono :: a -> a} If we just use wrappers to impose the explict type, it seems like we would get something like let tup = /\a.let {(f:a,g:a) = (\x:a -> x:a, f::a->a) f = /\a.case tup a of (f,g) -> f g = case tup @Int of (f,g) -> g where f :: forall a.a ->a and g :: Int -> Int. THIH seems to imply that type signatures are merely checked: no unification constraints are imposed (I think). However, ghc reports f :: Int -> Int. I apologize if this is a dumb question. I have found the definition of HsWrapper in ghc/compiler/GHC/Tc/Types/Evidence.hs, but I am still struggling a bit. thanks! -BenRI

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[TFP'22] final call for papers: Trends in Functional Programming 2022 (deadline March 7 2022)
by Peter Achten 21 Feb '22

21 Feb '22

================ TFP 2022 ================= == Final Call For Papers == == registration opened == =========================================== 23rd Symposium on Trends in Functional Programming 17-18 March, 2022 Online event https://trendsfp.github.io/index.html Due the pandemic, we have had to make TFP virtual this year. As a result, we've decided to push back the deadlines and conference date by a few weeks. In particular, the pre-symposium deadline for submitting the first version of your paper is now just after the ICFP deadline. == Important Dates == Submission deadline for draft papers Monday 7th March, 2022 Notification for draft submissions Friday 11th March, 2022 Symposium dates Thursday 17th - Friday 18th March, 2022 Submission deadline for post-symposium reviewing Wednesday 6th April, 2022 Notification for post-symposium submissions Friday 27th May, 2022 The Symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions. == Scope == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: * Research Articles: Leading-edge, previously unpublished research work * Position Articles: On what new trends should or should not be * Project Articles: Descriptions of recently started new projects * Evaluation Articles: What lessons can be drawn from a finished project * Overview Articles: Summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: * Functional programming and multicore/manycore computing * Functional programming in the cloud * High performance functional computing * Extra-functional (behavioural) properties of functional programs * Dependently typed functional programming * Validation and verification of functional programs * Debugging and profiling for functional languages * Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. * Interoperability with imperative programming languages * Novel memory management techniques * Program analysis and transformation techniques * Empirical performance studies * Abstract/virtual machines and compilers for functional languages * (Embedded) domain specific languages * New implementation strategies * Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2022 program chairs, Wouter Swierstra and Nicolas Wu. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Instructions to Author == Papers must be submitted at: https://easychair.org/conferences/?conf=tfp22 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Post-symposium formal review process == Draft papers will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback received at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == Draft papers and papers submitted for formal review are submitted as extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which all authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site. == Program Committee == Guillaume Allais University of St Andrews José Manuel Calderón Trilla Galois, Inc. Stephen Chang University of Massachusetts Boston Matthew Flatt University of Utah Jeremy Gibbons University of Oxford Zhenjiang Hu Peking University Mauro Jaskelioff CIFASIS / Universidad Nacional de Rosario Moa Johansson Chalmers University of Technology Shin-ya Katsumata National Institute of Informatics Oleg Kiselyov Tohoku University Bas Lijnse Netherlands Defence Academy / Radboud University Nijmegen Kazutaka Matsuda Tohoku University Nico Naus Virginia Tech Christine Rizkallah University of New South Wales Alejandro Serrano 47 Degrees Amir Shaikhha Ecole Polytechnique Fédérale de Lausanne Aaron Stump University of Iowa Wouter Swierstra (Co-chair) Utrecht University Baltasar Trancón Y Widemann Semantics GmbH Nicolas Wu (Co-chair) Imperial College London Ningning Xie University of Hong Kong

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Re: [Haskell-cafe] recommend book for self-study group
by Johannes Waldmann 20 Feb '22

20 Feb '22

> https://www.seas.upenn.edu/~cis194/spring13/lectures.html I agree strongly. See also https://haskell.markmail.org/search/?q=CIS194 Then, you want to quickly move to https://thinkingwithtypes.com/ (the second half of CIS194 already shows the way) ... because that's what makes present-day Haskell useful and unique (and not "thinking with lists (and Ints)", as some (LISP-era) introductory texts want you to believe) > ... I just don't have time to prepare and deliver a class. then hire a (remote) consultant? Buy a few copies of Maguire's book. - J.W.

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recommend book for self-study group
by Amy de Buitléir 20 Feb '22

20 Feb '22

I want to encourage more people at my company to learn Haskell, but I just don't have time to prepare and deliver a class. But then it occurred to me I could lead a self-study group, where people learn on their own but would have a forum to discuss what they're learning and ask questions. I would encourage people to answer each other's questions, but I would answer the more difficult questions. What book(s) do you think would be best suited for self-study? The participants would all be experienced programmers, but would likely have no knowledge of functional programming?

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Munich Virtual Haskell Meeting, 2022-02-22 @ 19:30
by Leah Neukirchen 18 Feb '22

18 Feb '22

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, February 22 on Jitsi at 19:30 CEST. **Due to the pandemic, this meeting will take place online!** For details see here: https://muenchen.haskell.bayern/dates.html A Jitsi link to join the room is provided on the page. Everybody is welcome, especially the Haskellers from Bavaria that do not usually come to our Munich meetings due to travel distance! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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