- Haskell-Cafe - Haskell.org

broadcasting stateful computations
by Olaf Klinke 02 Sep '21

02 Sep '21

Dear Café, I have a sequence of state-modifying computations action :: MonadUnliftIO m => StateT s m () where the state s should be visible to other threads. Thus I created a TVar in which I keep track of this state s for other threads to read. The type system tells me it can't be done, which suggests I am using the wrong abstraction. The following type-checks but may be unsafe. import Control.Concurrent.STM import Control.Monad.IO.Unlift updateStateTVar :: MonadUnliftIO m => TVar s -> StateT s m () -> m () updateStateTVar var action = withRunInIO (\inIO -> do s0 <- atomically (readTVar var) s1 <- inIO (execStateT action s0) atomically (writeTVar var s1)) Yet the splitting into readTVar and writeTVar is dangerous if several threads have read/write access to the same TVar. I was hoping to write the above using modifyTVar. However, the action essentially gives me a Kleisli map s -> m s which I somehow have to turn into an m (s -> s) but it is not possible in general. (The reverse works for any functor.) What should I do? * Switch to WriterT (Endo s) m? This is not as powerful as StateT s m. * Do everything in the STM monad? But this disallows arbitrary IO because it would facilitate nested STM transactions. The code above is safe, I believe, if only one thread has read/write access and the others are read-only. Are there type-level abstractions of this kind? (I suppose one could easily make them with some newtypes.) Thanks in advance for any thoughts on this. Olaf

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[conference announcement] Haskell Love Conference 2021
by Ida Bzowska 31 Aug '21

31 Aug '21

Hi Haskellers, Kindly reminder: https://haskell.love is taking place in 10 days. The conference is free to attend, held online, with the best schedule you can imagine (talks by: Simon Peyton-Jones as a keynote, Chris Penner, Dmitrii Kovanikov, Gergő Érdi, Ivan Gromakovskii, Jan Christopher Vogt, Jeremy Gibbons, Marcin Szamotulski, Mikael Tönnberg, Noon van der Silk, Rebecca Skinner, Ryan Orendorff, Stephanie Weirich, Thomas Tuegel, Gershom Bazerman, Joseph Morag, Veronika Romashkina). If you don't have a good excuse to skip the event then grab your ticket! λCheers, Ida Bzowska

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IFL'21 final call for participation
by Pieter Koopman 30 Aug '21

30 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…> *Registration* *Registration is **free of charge, but required for participation!* We will mail the zoom link only to registered participants. Use the below link 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…> *Program* The program is now available at https://ifl21.cs.ru.nl/Program <https://ifl21-publicity-dot-yamm-track.appspot.com/Redirect?ukey=1NdKhGOLpm…> . *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. *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 [image: beacon]

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Take-over request for: blaze-textual
by Andrey Prokopenko 30 Aug '21

30 Aug '21

Hello, - Few months ago I opened PR in `blaze-textual`: https://github.com/bos/blaze-textual/pull/14 <https://github.com/bos/blaze-textual/pull/14> - The package is either direct or transient dependency for `haskell-language-server`, `sqlite-simple` and few more packages. - While forks maintenance is a well-known practice it creates burden on maintainers. I would like to become a maintainer for `blaze-textual` package and keep it up-to-date at least for a next few years. Please consider this message as a step 2 in take-over procedure: https://wiki.haskell.org/Taking_over_a_package <https://wiki.haskell.org/Taking_over_a_package> Best Regards, Andrey Prokopenko

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Remove 'show-build-info' from lib:Cabal
by Fendor 30 Aug '21

30 Aug '21

Hello everyone! The lib:Cabal (Setup.hs) command 'show-build-info' is going to be removed with the next Cabal version (3.8). It is being replaced by the build flag '--enable-build-info' that is added to 'build' directly. If you depend on 'show-build-info' in any way, please give us feedback on [1] or [2]. Details on the purpose and implementation of 'show-build-info' can be found here: [1] Best regards, Fendor [1]: https://github.com/haskell/cabal/issues/7489 [2]: https://github.com/haskell/cabal/pull/7498

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Re: [Haskell-cafe] Contents of Haskell-Cafe digest...
by Kim Chaegon 29 Aug '21

29 Aug '21

Hello! I want read and learn continually haskell for mathematics. Please send me your text about haskell. Thank you!

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[Call for reviewers] Switch `text`'s internal representation to UTF-8
by Hécate 27 Aug '21

27 Aug '21

Hello everyone, After tremendous efforts, the pull request to switch `text`'s internal representation to UTF-8 is here, and unsurprisingly this is a titan's work. It lives here: https://github.com/haskell/text/pull/365 We are sending out a call for reviewers, as this is a cornerstone of our ecosystem. The performance gains from this PR are huge and I would like to ensure we can have a multitude of eyes to take a look. I wish to express my thanks to all of you. This is definitely the kind of advances that will make Haskell a stronger language for the times to come. Cheers, Hécate. -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW: https://glitchbra.in RUN: BSD

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The second day of the 2021 Haskell Symposium is now streaming on YouTube
by Hage, J. (Jurriaan) 27 Aug '21

27 Aug '21

Haskellers, Today is the 2nd day of the 2021 Haskell Symposium and it is being streamed on Youtube. If you want a taste of it join us while it is still public. After the invited talk of Mathieu Boespflug yesterday (we maxed out at about a 100 viewer on Youtube and some 74 people in Airmeet) we will have yet another invited talk on Linear Haskell today by Jean-Philippe Bernardy, and one of the five research talks will be on Linear Haskell as well. On top of that there are four more research talks on your favorite programming language. Here’s the link: https://youtu.be/6pJKIjn95eU Do not miss out, and no need to register for ICFP. Best, Jurriaan Hage Chair

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[Haskell] [ANNOUNCE] GHC 8.10.7 released
by Zubin Duggal 27 Aug '21

27 Aug '21

The GHC team is very pleased to announce the availability of GHC 8.10.7. Source and binary distributions are available at the [usual place](https://downloads.haskell.org/ghc/8.10.7/). Download Page: https://www.haskell.org/ghc/download_ghc_8_10_7.html Blog Post: https://www.haskell.org/ghc/blog/20210827-ghc-8.10.7-released.html This is a small bugfix release, fixing one linking portability issue (#19950) present in GHC 8.10.5 and GHC 8.10.6 on some x86_64 macOS toolchains, which resulted in undefined symbol errors for `___darwin_check_fd_set_overflow`. Issue #19950 is caused by a bug in newer Apple toolchains (specifically XCode 12) where programs compiled with affected versions of XCode are not backwards compatible with configurations running older version of XCode (certain versions of XCode 11). We claimed to have fixed this in GHC 8.10.6, but alas this wasn't the case. The fix was originally tested on the master branch, which uses a different build configuration from the 8.10 branch. We have now tested the fix on the GHC 8.10 branch and finally squashed the bug. We would like to thank Microsoft Research, GitHub, IOHK, the Zw3rk stake pool, Tweag I/O, Serokell, Equinix, SimSpace, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. We would also like to thank the hundreds of open-source contributors whose work makes GHC possible. A complete list of bug fixes and improvements can be found in the [release notes](https://downloads.haskell.org/ghc/8.10.7/docs/html/users_guide/8. 10.7-notes.html). As always, feel free to report any issues you encounter via [gitlab.haskell.org](https://gitlab.haskell.org/ghc/ghc/-/issues/new).

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Magical Haskell book preview: Haskell and type theory in pictures and in a fun and accessible way
by Anton Antich 26 Aug '21

26 Aug '21

Dear all, I started "Magical Haskell" 3 years ago with the goal to fill the void of explaining typed functional programming from the first principles, but in a fun and accessible way. Imperative patterns really mess with learning Haskell, while alternative top-down approaches are usually too technical and math-heavy, so that the beauty and elegance of the concepts involved is lost on many. So I tried to use the latter, but build it up gradually, from intuition and functional thinking, so that a high school student could understand. Now the book is about 50% ready as I came back to writing it after a sabbatical break, now covers the foundations, functional thinking, different types, typeclasses, and specific examples gently building up from Maybe and List through Monoid and up to Functor and Bifunctor. Applicative, Monad and real world programs via Monad Transformer Stacks are coming up. It is available here: https://leanpub.com/magicalhaskell - free to read online. Would very much appreciate your feedback - what is missing, what do you think of such a style, what is maybe too much, etc. Also, if anyone is ready to contribute a public testimonial - will gladly give a free copy of the ebook and all future updates in offline formats! Thank you very much!

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