- Haskell-Cafe - Haskell.org

Some questions on Atkey-style indexed monads
by Nicolas Trangez 05 Dec '22

05 Dec '22

All, For some project, I'm considering (again) to use an indexed state monad, which are now somewhat ergonomic to use with QualifiedDo. When looking into existing packages exposing relevant types/classes, I had some questions: 1. These packages provide something like ``` class IxFunctor f where imap :: (a -> b) -> f i j a -> f i j b class IxFunctor f => IxApplicative f where ... ``` Is this `IxFunctor` actually required/useful? It seems to me the implementation of `imap` for some `IxFunctor f` would be equal to `fmap` in the `Functor` implementation for `forall i j. f i j`. Hence, can `IxFunctor` be dropped in lieu of ``` class (forall i j. Functor (f i j)) => IxApplicative f where ... ``` 2. Existing packages predate MonadFail and QualifiedDo. The latter requires (in some cases) an implementation of `fail` and `mfix` to be provided by the module also providing `>>=` etc. I was wondering whether or not there need to be (or can be) `IxMonadFail` and `IxMonadFix` classes like ``` class IxMonad m => IxMonadFail m where ifail :: String -> m i j a class IxMonad m => IxMonadFix m where ifix :: (a -> m i j a) -> m i j a ``` I'm not sure it "makes sense" to have an `ifail` which returns an `m i j a` vs. having only a `MonadFail` (and hence `fail`) implementation for `m i i` only, taking into account the requirement for `fail f >>= k` to be equal to `fail f`, hence `ifail f >>=: k` to be equal to `ifail f`. I think the above question boils down to: is there any use in having `ifail :: String -> m i j a` next to `fail :: String -> m i i a`, or should (i)fail always be state-type-preserving? Similar doubts about `IxMonadFix m` vs. `MonadFix (m i i)`. Thanks for any insights, Nicolas

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TFPIE 2023 call for submissions (deadline Dec 27th)
by Elena Machkasova 04 Dec '22

04 Dec '22

Trends in Functional Programming in Education (TFPIE) 2023 Call for papers https://wiki.tfpie.science.ru.nl/TFPIE2023 (January 12th 2023, Boston, MA, USA, co-located with TFP 2023 and followed by POPL 2023) TFPIE 2023 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: FP and beginning CS students FP and Computational Thinking FP and Artificial Intelligence FP in Robotics FP and Music Advanced FP for undergraduates FP in graduate education Engaging students in research using FP FP in Programming Languages FP in the high school curriculum FP as a stepping stone to other CS topics FP and Philosophy The pedagogy of teaching FP FP and e-learning: MOOCs, automated assessment etc. Best Lectures - more details below In addition to papers, we are requesting best lecture presentations. What's your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. The length of the presentation should be comparable to that of a paper. In addition, the speaker can provide commentary on effectiveness or student feedback. Submissions Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 20 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website. Papers and abstracts can be submitted via easychair at the following link: https://easychair.org/conferences/?conf=tfpie2023 After the workshop, presenters are invited to submit (a revised version of) their article for the formal review. The PC will select the best articles for publication in the Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. Important Dates Submission deadline: December 27th 2022, Anywhere on Earth. Notification: December 30th 2022 (Note: earlier submissions will receive earlier response) TFPIE Registration Deadline: see https://trendsfp.github.io/register.html Workshop: January 12th 2023 Submission for formal review: April 19th 2023, Anywhere on Earth. Notification of full article: May 24th 2023 Camera ready: July 1st 2023 Program Committee Christopher Anand - McMaster University, Canada Attila Egri-Nagy - Akita International University, Japan Jason Hemann - Seton Hall University, USA Kevin Kappelmann - Technical University of Munich, Germany Elena Machkasova (Chair) - University of Minnesota Morris, USA Kristina Sojakova - INRIA, France Jørgen Villadsen - Technical University of Denmark, Denmark Invited Speaker: Shriram Krishnamurthi, Brown University Registration information: See https://wiki.tfpie.science.ru.nl/TFPIE2023 for updated information. Registration and attendance are mandatory for at least one author of every paper that is presented at the workshop. Only papers that have been presented at TFPIE may be submitted to the post-reviewing process. -- Dr. Elena Machkasova Associate Professor of Computer Science Division of Science and Mathematics University of Minnesota, Morris Office: Sci 2325 (320) 589-6308 http://cda.morris.umn.edu/~elenam/ Pronouns: she/her/hers or any other

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How to create a list of each constructor value
by PICCA Frederic-Emmanuel 04 Dec '22

04 Dec '22

Hello, I have a type like this data InputType = CristalK6C | MarsFlyscan | MarsSbs | SixsFlyMedH | SixsFlyMedV | SixsFlyMedVEiger | SixsFlyMedVS70 | SixsFlyScanUhv | SixsFlyScanUhv2 | SixsFlyScanUhvTest | SixsFlyScanUhvUfxc | SixsSbsFixedDetector | SixsSbsMedH | SixsSbsMedV | SixsSbsMedVFixDetector deriving (Eq, Show) I want to create a list of each values in order to create meaningfull error message for the user and simplify my Arbitrary instances. I do not want to type two time the values. instance Arbitrary InputType where arbitrary = oneof (map pure [ CristalK6C , MarsFlyscan , MarsSbs , SixsFlyMedH , SixsFlyMedV , SixsFlyMedVEiger , SixsFlyMedVS70 , SixsFlyScanUhv , SixsFlyScanUhv2 , SixsFlyScanUhvTest , SixsFlyScanUhvUfxc , SixsSbsFixedDetector , SixsSbsMedH , SixsSbsMedV , SixsSbsMedVFixDetector ] ) Thanks for your help Frederic

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Debugging a test suite freeze
by David Feuer 02 Dec '22

02 Dec '22

The logict-sequence test suite consistently freezes up on the last test when compiled with GHC 9.4.3. logict-sequence and its test suite don't do anything special with that GHC/base version as far as I can see, or anything particularly strange in general, so I'm pretty confident the problem lies elsewhere. My best guesses are hedgehog, tasty, and tasty-hedgehog. Has anyone else run into weird issues with any/all of these on GHC 9.4.3? David

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ANN: hledger 1.28
by Simon Michael 02 Dec '22

02 Dec '22

I'm pleased to announce hledger 1.28 ! https://github.com/simonmichael/hledger/releases/1.28 https://hledger.org/install https://hledger.org/release-notes.html#hledger-1-28 Nothing earth-shaking for users in this release, but internal changes and the usual incremental improvements. Highlights: new hledger-ui screens and default screen; new hledger-move, watchaccounts scripts. Thank you to release contributors Felix Yan, Patrick Fiaux. What is hledger ? - Fast, reliable, free, multicurrency, double-entry, plain text accounting[1] software that runs on unix, mac, windows, and the web - Built around human-readable, version-controllable plain text files - Inspired by and largely compatible with Ledger CLI[2]; convertible to and from Beancount[3] - Written in Haskell for correctness and longevity. 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 welcome! Aloha, -Simon [1] https://plaintextaccounting.org [2] https://ledger-cli.org [3] https://beancount.github.io

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FOSDEM Haskell devroom: we need proposals!
by Fraser Tweedale 30 Nov '22

30 Nov '22

Previously: https://mail.haskell.org/pipermail/haskell-cafe/2022-November/135674.html **We need more proposals! We need your help!** FOSDEM 2023 will be held on 4 & 5 February 2023, in Brussels. For more information see the [official site](https://fosdem.org/2023/). The Haskell devroom (specialist track) will take place on Sunday 5 February, from 13:10 to 17:00 UTC+1. This is an amazing opportunity to promote Haskell, and functional programming generally, to a legion of free software developers and enthusiasts. But right now, we are not even close to filling our schedule. If we don't fill our ~4 hour schedule, the Haskell devroom will not happen. Therefore we are extending our Call for Proposals until Saturday 2022-12-10. We are also now welcoming proposals for tutorials/workshops and longer presentations (up to 45 minutes). Shorter presentations are still welcome, of course. So if you want to propose an introductory workshop, install fest, hack session, or something similar, have at it. You can also help by sharing our CFP far and wide, and encourage specific people you think might have something interesting to present, to submit a proposal. Thanks, Fraser Tweedale

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Call for Haskell.org Committee Nominations
by Ida Bzowska 30 Nov '22

30 Nov '22

Dear Haskellers, The Haskell.org Committee is happy to announce that we are opening the call for nominations for new members. Details can be found [here <https://discourse.haskell.org/t/call-for-haskell-org-committee-nominations-…> ]. You can nominate yourself or your friend! If you have any questions, don't hesitate to ask. λCheers Ida Bzowska

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Writing and testing a Storable instance for a record wrapping ForeignPtrs
by Hécate 29 Nov '22

29 Nov '22

Hi everyone, In a fit of madness I have found myself writing Haskell code where I need to implement a Storable instance. However, by virtue of not being a C programmer, I'm fairly lost on some of the details, especially the value of the sizeOf and alignment methods. My Haskell-level record is the following: data SignedMessage = SignedMessage { messageLength :: CSize , messageForeignPtr :: ForeignPtr CUChar , signatureForeignPtr :: ForeignPtr CUChar } Here is the code of the Storable instance: https://gist.github.com/Kleidukos/31346d067f309f2a86cbd97a85c0f1e8#file-sig… And so I used `hedgehog-classes` to test the Storable instance. However, all the tests fail with the same reason: Prelude.undefined: https://gist.github.com/Kleidukos/31346d067f309f2a86cbd97a85c0f1e8#file-und… The main problem (and that's certainly a red herring for me) is that the `undefined` call comes frombase:Foreign.Marshal.Array. Which shouldn't be a problem, as it is not supposed to be evaluated! Yet apparently it is. If you're interested to see the full code, it's located here: https://github.com/haskell-cryptography/libsodium-bindings/blob/add-sel-pac… I'm not sure how to proceed from here. What would be a good angle to approach this? Cheers, Hécate -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW: https://glitchbra.in RUN: BSD

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PhD and post-doc positions in Mainz, Germany
by Erdweg, Sebastian 26 Nov '22

26 Nov '22

We have multiple open positions for PhD students and post-docs in the PL Group of the University of Mainz in Germany. The available positions include a gross monthly salary of ~4000 Euro. Our team meets and socializes in Mainz; remote work is an option. The PL Group at the University of Mainz was founded in 2019. Our goal is to support developers in creating and maintaining software systems that are easier to write, more secure, run faster, and consume less energy. Our current research topics include: -- Incremental computing: How can a computation react to a change of its input efficiently? We have observed up to 10,000x speedups in prior work, can incrementality help us save as much energy? Can we build a new foundation for incremental computing to support a wider range of computations? -- WebAssembly: How can we discover and prevent security vulnerabilities in WebAssembly? We have built a data-flow analysis platform for WebAssembly to identify properties of WebAssembly programs at compile time. Can this platform be used to protect WebAssembly users while also optimizing the code for performance? -- Datalog: How can the power of Datalog best be exploited in modern software development? How can we abstract over and hide the technicalities of Datalog, for example, by compiling DSLs to Datalog. And how can we optimize Datalog code to provide truly declarative performance, without exposing users to details of the underlying database technology? -- Language engineering: How can we build programming-language tools with modest effort and without duplicating the language's semantics? For example, can we derive type checkers, debuggers, and other editor services from the language’s semantics? And does this require a language workbench or can we support rich services for embedded languages as well? Mainz is part of the Frankfurt Metropolitan Area and only a short train ride away from Frankfurt's international community and culture. Mainz itself lies at the confluence of the Rhine and Main rivers, surrounded by plenty of nature. https://mainz.de/en/worth-seeing/reasons-to-love-mainz.php I'm excited to hear from interested candidates via email. If you know potential candidates, please forward this message to them. Sebastian Erdweg https://www.pl.informatik.uni-mainz.de/erdweg

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Munich Haskell Meeting, 2022-11-30 @ 19:30
by Leah Neukirchen 26 Nov '22

26 Nov '22

Dear all, Next week, our last* monthly Munich Haskell Meeting of the year 2022 will take place again on Wednesday, November 30 at Cafe Puck at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this nuudel so we can reserve enough seats! It is OK to add yourself to the nuudel anonymously or pseudonymously. https://nuudel.digitalcourage.de/haskell-munich-nov-2022 Everybody is welcome! *) There will be no meeting in late December due to festivities, but perhaps again in the first week of January, as is tradition. cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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