- Haskell-Cafe - Haskell.org

cradle: a simpler process library
by Julian Arni 15 May '24

15 May '24

Hi all, We just released cradle, a library aimed at a being simpler and more intuitive subprocess library. More details in: - The announcement: https://garnix.io/blog/announcing-cradle - The hackage page: https://hackage.haskell.org/package/cradle-0.0.0.0/docs/Cradle.html Feedback welcome! Cheers, Julian

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[ANN] Copilot 3.19.1
by Frank Dedden 14 May '24

14 May '24

Hi everyone! We are very excited to announce Copilot 3.19.1 [1,2]. Copilot is a stream-based EDSL in Haskell for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms. Copilot marked as NASA Class D open-source software, and is being used at NASA in drone test flights. Through the NASA tool Ogma [3] (also written in Haskell), Copilot also serves as a runtime monitoring backend for NASA's Core Flight System, Robot Operating System (ROS2), and FPrime (the software framework used in the Mars Helicopter). This release does not contain any API breaking changes, but consists of some improvements to the copilot-theorem package. Thanks to Ryan Scott (Galois Inc.) a problem related to the interface with the Kind 2 model checker is fixed. Additionally, improvements have been made to the documentation. As always, we're releasing exactly 2 months since the last release. Our next release is scheduled for July 7th, 2024. Current emphasis is on improving the codebase in terms of stability and test coverage, removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our new coding standards. Additionally, as an ongoing process, work is being done on making Copilot more accessible to people less familiar with Haskell. Users are encouraged to participate by opening issues and asking questions via our github repo [4]. Happy Haskelling! Frank Dedden [1] https://github.com/Copilot-Language/copilot/releases/tag/v3.19.1 [2] https://hackage.haskell.org/package/copilot [3] https://github.com/nasa/ogma [4] https://github.com/Copilot-Language/copilot

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Preferred syntax for append
by Mark McConnell 14 May '24

14 May '24

We know that lists have map. Sometimes we want to take the higher perspective of Functor, replacing map with fmap, then replacing fmap with <$> . This post asks the corresponding question about append. The notation for append within List itself is ++ . Often we think of lists as Monads. Applicative generalizes Monad, and Alternative specializes Applicative. Alternative has <|> which behaves as ++ on List. I have been using <|> for this purpose. Recently, I have begun to read and enjoy "Effective Haskell". In Chapter 1, this book uses <> for append. Clearly they are thinking of List as a Semigroup. I'm curious about your thoughts on ++ versus <|> versus <> .

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Re: [Haskell-cafe] Preferred syntax for append
by Olaf Klinke 13 May '24

13 May '24

> Concatenation with (<>) is more meaningful and holds better semantics > than (<|>), described as just "An associative binary operation". (<>) is also "just an associative binary operation", no more guarantees than (<|>). That said, for append (<>) should be preferred over (<|>) because one can then switch to more efficient append implementations just by changing the type signature, e.g. when switching from String to Text: The former is an Alternative, the latter ist not. (<|>) for list models non-deterministic choice, which can be useful in combinatorial problems. Olaf

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GHC 9.10.1 is now available
by Ben Gamari 10 May '24

10 May '24

The GHC developers are very pleased to announce the release of GHC 9.10.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org] and shortly via [GHCup]. GHC 9.10 brings a number of new features and improvements, including: * The introduction of the `GHC2024` language edition, building upon `GHC2021` with the addition of a number of widely-used extensions. * Partial implementation of the [GHC Proposal #281], allowing visible quantification to be used in the types of terms. * [Extension] of LinearTypes to allow linear `let` and `where` bindings * The implementation of the [exception backtrace proposal], allowing the annotation of exceptions with backtraces, as well as other user-defined context * Further improvements in the info table provenance mechanism, reducing code size to allow IPE information to be enabled more widely * Javascript FFI support in the WebAssembly backend * Improvements in the fragmentation characteristics of the low-latency non-moving garbage collector. * ... and many more A full accounting of changes can be found in the [release notes]. As always, GHC's release status, including planned future releases, can be found on the [GHC Wiki]. We would like to thank GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket] if you see anything amiss. [release notes]: https://downloads.haskell.org/ghc/9.10.1/docs/users_guide/9.10.1-notes.html [GHC Wiki]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [exception backtrace]: https://github.com/ghc-proposals/ghc-proposals/pull/330 [GHC Proposal #281]: https://github.com/ghc-proposals/ghc-proposals/pull/281 [linear let]: https://github.com/ghc-proposals/ghc-proposals/pull/624 [downloads.haskell.org] https://downloads.haskell.org/ghc/9.10.1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [GHCup]: https://www.haskell.org/ghcup/

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System.IO but not with Data.String?
by Hilco Wijbenga 10 May '24

10 May '24

Hi all, We have Text and ByteString as alternatives to String but as soon as you want to do anything IO related (read a file, get a directory's content, et cetera) it seems your only option is to use String. For an occasional IO action, this is obviously irrelevant but for a compiler, a build system, or anything else that does a lot of IO this seems like it would be(come) an issue. So I was wondering what would be involved in adding (portable) support for System.IO with an alternative to String (this alternative does not necessarily need to be Text or ByteString). I did a little bit of research into how GHC handles this and there appear to be several other String types in the GHC tree, including ByteString(?). How feasible is an alternative System.IO API? How tied to GHC would such an alternative need to be? To be clear, I am not looking to _replace_ System.IO but to _add_ an alternative API (and not a wrapper that maps to/from String). Please do not assume I necessarily know what I am talking about! Especially, when it comes to the "portable" part. :-) Cheers, Hilco

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[ANN] Jacinda 3.0.1.0, a functional AWK standin
by Vanessa McHale 10 May '24

10 May '24

Hello all, I recently rewrote the backend to Jacinda, a functional riff on AWK: https://hackage.haskell.org/package/jacinda See the github https://github.com/vmchale/jacinda/?tab=readme-ov-file#installation and also the guide https://vmchale.github.io/jacinda/ Cheers, Vanessa McHale

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[ANN] Cabal 3.12 released
by Francesco Ariis 08 May '24

08 May '24

Dear cafe, Cabal team is happy to announce the release of `Cabal` the library version `3.12.0.0` and the companion pre-release of `cabal-install` (the commandline tool; scroll down for more information). ## What is new? There are a number of new features in this release (`Cabal`) and pre-release (`cabal-install`), such as: - Add support for `asm`, `cmm`, and `js` sources in executable components. - Add `--haddock-output-dir` flag to `cabal haddock`. - Add `--semaphore` option to `./Setup build` interface. - Add `--promised-dependency` flag to `./Setup configure` interface. - Add the ability to `--ignore` specific checks to `cabal check`. - Add support for `GHC2024` language edition. - Add support for loading multiple components into one repl session (especially important for HLS users). - Add `cabal path` command. - Add support for authentication tokens for uploading to Hackage. - Allow more flags in the init section of config file. - Add `--semaphore` flag to enable interaction with GHC Job Server protocol. - Adds functionality for the `--offline` flag with the `build` command. - Improve solver rejections in brevity and accuracy. There is much more: for a detailed list of enhancements, changes, and bugfixes, please check the Cabal-3.12.0.0 changelog [1] (and the cabal-install 3.12.0.0-prerelease changelog [2]. [1] https://github.com/haskell/cabal/blob/master/release-notes/Cabal-3.12.0.0.md [2] https://github.com/haskell/cabal/blob/master/release-notes/WIP-cabal-instal… ## Authors and contributors Cabal is a collaborative effort; these people contributed with code to this release: aleeusgr Adam Gundry Andrea Bedini Andreas Abel Andreas Klebinger Arjun Kathuria Artem Pelenitsyn BasLaa Bas Laarakker Ben Gamari Bodigrim Brandon Chinn Brandon S. Allbery Bryan Richter Colton Clemmer Csaba Hruska cydparser Daniel Trstenjak David Binder David Christiansen Edwin Marshall Elodie Lander Erik de Castro Lopo Felix Yan Fendor Finley Francesco Ariis Francesco Gazzetta Fraser Tweedale Gershom Bazerman Hamish Mackenzie Hécate Moonlight Ikko Eltociear Ashimine Jana Chadt Javier Sagredo Jean-Paul Calderone Jens Petersen Jessica Hamilton John Paul Adrian Glaubitz Josh Meredith Julia Longtin Julian Ospald Kazuki Okamoto Kleidukos Kristen Kozak Krzysztof Gogolewski liamzee Liisi Kerik Lin Runze malteneuss Malte Neuss Marcin Szamotulski Matthew Pickering Mel Zuser Michael Peyton Jones Mike Pilgrem Mikolaj Konarski mixphix Oleg Grenrus Ondřej Šebek Patrick Augusto Patrick Dougherty Phil de Joux Pierre Le Marre Rebecca Turner Rodrigo Mesquita Ryan Scott Samuel Thibault Sander Sebastian Tee Sergey Vinokurov Shae Erisson sheaf Simon Hengel Siyuan Chen Sören Tempel Suganya Raju Sylvain Henry Taylor Fausak Teo Camarasu Tom Ellis Tom Smeding Torsten Schmits Tristan Cacqueray Troels Henriksen Wismill Yvan Sraka The release could not be done without the help of the manual QA team and devops people, we thank them both. Thanks also to the many users who provided bug reports and suggestions for improvements. A special mention to Hécate, who recently stepped down from Cabal release coordination and left the process in a better, more organised shape than what was before. ## How to get the `cabal-install` pre-release This release is a Cabal-the-library release, but if you want to test the new features of `cabal-install`, you can download the pre-release of the commandline tool via GHCup. Use one of the following commands, depending on your OS: ghcup --no-cache install cabal -u 'https://gitlab.haskell.org/haskell/cabal/-/jobs/1848320/artifacts/raw/out/c…' 3.12.0.0-prerelease ghcup --no-cache install cabal -u 'https://gitlab.haskell.org/haskell/cabal/-/jobs/1848326/artifacts/raw/out/c…' 3.12.0.0-prerelease ghcup --no-cache install cabal -u 'https://gitlab.haskell.org/haskell/cabal/-/jobs/1848327/artifacts/raw/out/c…' 3.12.0.0-prerelease or an analogous command for any other of the artifacts produced by the [pre-release pipeline](https://gitlab.haskell.org/haskell/cabal/-/pipelines/93759). ## How to help? Cabal is a complex piece of software running on many different machine. Two easy ways to help the development team producing quality releases are: - Join the manual QA team - Test nightly binary `cabal-install` snapshots and pre-releases (such as the 3.12.0.0 pre-release mentioned above) and report any problem you find. [3] https://discourse.haskell.org/t/manual-qa-for-cabal-install/6225

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[Haskell] [ANNOUNCE] Haskell Language Server 2.8.0.0 released
by Zubin Duggal 08 May '24

08 May '24

The HLS team is pleased to announce the release of Haskell Language Server [2.8.0.0](https://github.com/haskell/haskell-language-server/releases/tag/2.…. Binaries for this release are available at [Index of /~hls/haskell-language-server-2.8.0.0/](https://downloads.haskell.org/~hls/haskell-language-server-2.8.0.0/). All of these tarballs have associated GPG signatures. The signature should be from `Zubin Duggal <zubin(a)well-typed.com>` (key ID [588764FBE22D19C4](https://keys.openpgp.org/search?q=588764FBE22D19C4)) The prebuilt binaries in this release support the following GHC versions: - 9.2.8 - 9.4.8 - 9.6.5 - 9.8.2 # Changelog - Bindists for GHC 9.6.5 - New hls-notes plugin (#4126, @jvanbruegge) - Floskell, hlint and stylish-haskell plugins enabled for GHC 9.8 - Improvements for hls-graph increasing robustness (#4087, @soulomoon) - Improvements to multi-component support (#4096, #4109, #4179, @wz1000, @fendor) Happy editing! - Zubin

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Help with GHC.Generics -- How to get field selector name into value level?
by Compl Yue 07 May '24

07 May '24

Greetings! I’m stuck: ```hs -- | a named (with a selector) field instance (KnownSymbol sel, DbaStorable' f, f ~ K1 R c, DbaField c ft, Typeable c) => DbaStorable' (M1 S ('MetaSel ('Just sel) su ss ds) f) where -- _loadDbaField store bsp fno cno vin = M1 <$> _loadDbaField store fsp fno cno vin where fieldName = symbolVal (Proxy @sel) fieldPath = fieldName ++ "::" ++ dbaBasePath @c fsp = case bsp of "" -> fieldPath -- a field of a top level record _ -> bsp ++ "/" ++ fieldPath -- a field of a nested record _storeDbaField store bsp fno cno m@(M1 xr) = _storeDbaField store fsp fno cno xr where fieldName = selName m fieldPath = fieldName ++ "::" ++ dbaBasePath @c fsp = case bsp of "" -> fieldPath -- a field of a top level record _ -> bsp ++ "/" ++ fieldPath -- a field of a nested record ``` With the `selName` approach as in the `_storeDbaField ` above, it’s rejected as: ```log • Could not deduce (GHC.Generics.SingI su) arising from a use of ‘selName’ from the context: (KnownSymbol sel, DbaStorable' f, f ~ K1 R c, DbaField c ft, Typeable c) bound by the instance declaration at src/Frp/DbaStore/Internal.hs:(646,3)-(647,55) • In the expression: selName m In an equation for ‘fieldName’: fieldName = selName m In an equation for ‘_storeDbaField’: ``` But can I really evident `SingI` instance from my side? Which is unexpected from GHC.Generics... Otherwise with the `symbolVal` approach as in the `_loadDbaField ` above, there’s the complain against the ultimate use site: ```log • No instance for (GHC.TypeLits.KnownSymbol sel0) arising from a use of ‘storeDba’ • In a stmt of a 'do' block: storeDba rootDir series'data In the expression: do forM_ series'data print storeDba rootDir series'data sd <- loadDba @(Envelope2D Double) rootDir forM_ sd print ``` But I failed to prove `KnownSymbol sel` with all methods I can think of. Help please! With best regards, Compl

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