- Haskell-Cafe - Haskell.org

2024 Haskell Ecosystem Workshop, June 6-7, co-located with Zurihac
by Jose Calderon 04 Mar '24

04 Mar '24

Hello, In this two-day event, held on the lakeside campus of OST in lovely Rapperswil, Switzerland, you can learn what you need to know in order to get started working on these tools. We’ve asked the presenters to identify ‘good first issues’ for those wanting to get their feet wet on contributing. Because the workshop is immediately prior to Zurihac 2024, you will have the opportunity to tackle one of these issues while the core developers are easily available! The following speakers have been confirmed, with more to follow: Michael Peyton Jones: Haskell Language Server Julian Ospald: GHCUp Richard Eisenberg: GHC Alan Zimmerman: ghc-exactprint Hécate: Haddock and Documentation There will also be experts on ecosystem-wide issues (e.g. Security), in order to facilitate conversations about how to address cross-cutting issues in our tooling ecosystem. We will update the list of confirmed speakers as we receive confirmation. Registration is via eventbrite: https://www.eventbrite.com/e/2024-haskell-ecosystem-workshop-tickets-851066… More details on the Haskell Foundation website: https://haskell.foundation/events/2024-haskell-ecosystem-workshop.html I hope to see you there! -Jose

1 0

Midlands Graduate School (MGS)
by Graham Hutton 04 Mar '24

04 Mar '24

Dear all, There are just a few days left now to register for this years Midlands Graduate School (MGS) in Leicester. Seven fantastic courses on category theory, proof theory, type theory, session types, and more. 8-12 April 2024, Leicester, UK. Registration closes Friday 8th March. Best wishes, Graham Hutton ========================================================== Midlands Graduate School 2024 8-12 April 2024, Leicester, UK https://www.cs.le.ac.uk/events/mgs2024/ BACKGROUND: The Midlands Graduate School (MGS) in the Foundations of Computing Science provides an intensive course of lectures on the mathematical foundations of computing. The MGS has been running since 1999, and is aimed at PhD students in their first or second year of study, but the school is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES: Seven courses will be given. Participants usually take all the introductory courses and choose additional options from the advanced courses depending on their interests. Guest lecture - Formalisation of Mathematics, Kevin Buzzard Introductory courses - Category Theory, Thorsten Altenkirch - Proof Theory, Abhishek De and Iris van der Giessen - Type Theory with Agda, Todd Ambridge Advanced courses - Session Types, Sonia Marin - Synthetic Homotopy Theory with HoTT/UF, Ulrik Buchholtz - Graph Rewriting, Reiko Heckel - Categorical Realisability, Tom de Jong REGISTRATION: Registration is £295 for students, and £550 for academic, industry and independent participants. The fee includes all lecture courses and example classes, lunch and coffee breaks, and the conference dinner. The registration deadline is ** Friday 8th March **. Spaces are limited, so please register early to secure your place. SPONSORSHIP: We offer a range of sponsorship opportunities for industry (bronze, silver, gold and platinum), each with specific benefits. Please see the website for further details. ========================================================== — Professor Graham Hutton School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~pszgmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

1 0

Re: [Haskell-cafe] Is it possible to type a function to accept only literal values?
by Olaf Klinke 01 Mar '24

01 Mar '24

> Recently I was experimenting with a GCC intrinsic functions for x86 > SMID instructions to write a fast CSV parser Could you please elaborate on what you are planning to vectorize? Profiling shows that for usually number-heavy formats such as CSV or JSON, decoding the data fields outweighs the work necessary to decode the structure of the data format. Thus I assume you would want a streaming parser to decode input into a structure of yet unparsed blobs (cassava does this), then traverse the structure in parallel to finish parsing. I can imagine this poses difficulties to the standard model of parse error reporting, though, which often relies on sequential processing. Pretty much every streaming framework has incorporated cassava, and some streaming frameworks have abstractions for parsing. What is missing? (Not related to the OP:) Is streaming and parallel processing incompatible with formats such as XML or JSON, where well-formedness is typically determined by the very last byte in the input? (The last closing parenthesis or tag.) Olaf

2 1

S-REPLS 14 at Jane Street London on March 8th: Call for participation
by Richard Eisenberg 28 Feb '24

28 Feb '24

============================================================================ S-REPLS 14 South of England Regional Programming Language Seminar series Jane Street London, 2 & A Half Devonshire Square, Premier Place, London EC2M 4UJ Fri 8 March 2024 ============================================================================ S-REPLS is a series of informal meetings for people in the South of England interested in the principles, design and implementation of programming languages. Events take place approximately thrice yearly, organised by members of the community. Attendance at S-REPLS 14 is free and lunch will be provided. Due to security concerns and planning needs all attendees need to register. Please RSVP here: https://docs.google.com/forms/d/e/1FAIpQLSeODsd6ZXNi58hTBBP1oMOLkjgkZK40QdK… <https://docs.google.com/forms/d/e/1FAIpQLSeODsd6ZXNi58hTBBP1oMOLkjgkZK40QdK…> Schedule below. Talk abstracts and further details can be found on the S-REPLS 14 website: https://www.cl.cam.ac.uk/events/s-repls14/ <https://www.cl.cam.ac.uk/events/s-repls14/> 0900 Arrival and breakfast 1000 Keynote: Graded types and Algebraic Effects Dominic Orchard (University of Kent and University of Cambridge) 1100 Break 1130 Automatically Finding Upper and Lower Time Complexity Bounds for Parallel Evaluation Carsten Fuhs (Birkbeck, University of London) 1200 Somewhat Dynamic Build Systems Neil Mitchell (Meta) 1230 Lunch 1330 The Dafny Programming Language and Static Verifier Stefan Zetzsche (Amazon) 1400 Implementing a Dependently Typed Language Modelling Algebraic Equivalences Zhiyi Liu (University of Cambridge) 1430 Programming with First-class Constructor Contexts Anton Lorenzen (University of Edinburgh) 1500 Break 1530 Finding cheaper straightline instruction sequences more cheaply Maria A Schett 1600 Starlark: between configuration and programming language Stiopa Koltsov (Meta) 1630 Ill-Typed programs don’t evaluate Charlie Walpole (University of Bristol)

1 0

Is it possible to type a function to accept only literal values?
by Daneel Yaitskov 27 Feb '24

27 Feb '24

Hi List, Recently I was experimenting with a GCC intrinsic functions for x86 SMID instructions to write a fast CSV parser and noticed that some arguments are required to be literal values (known at compile time), which makes live hard, e.g. bit shift operation expects number of bits to shift in such a way. Nonetheless the intel manual defines function prototypes as normal: __m128i _mm_bsrli_si128 (__m128i a, int imm8) Using a variable as second argument in _mm_bsrli_si128 produces unclear, but compilation error with exact line number. Definitely some magic happens here, because it is not possible to express this constraint type system of C language. Haskell is known as one of the best languages in type acrobatics, but could it beat C here? -- Best regards, Daniil Iaitskov

3 2

[ANNOUNCE] Agda 2.6.4.2
by Andreas Abel 26 Feb '24

26 Feb '24

Dear all, The Agda Team is pleased to announce the release of Agda 2.6.4.2. Agda 2.6.4.2 is a bugfix release over Agda 2.6.4.1: - Fix an inconsistency in Cubical Agda related to catch-all clauses. - Fix some internal errors. - Fix an issue with `opaque`. - Fix building with cabal flag `-f debug-serialisation`. # GHC supported versions Agda 2.6.4.2 has been tested with GHC 9.8.1, GHC 9.6.4, 9.4.8, 9.2.8, 9.0.2, 8.10.7, 8.8.4 and 8.6.5 on Linux, macOS and Windows. # Installation Agda 2.6.4.2 can be installed using cabal-install or stack: 1. Getting the tarball $ cabal update $ cabal get Agda-2.6.4.2 $ cd Agda-2.6.4.2 2. a. Using cabal-install $ cabal install -f +optimise-heavily -f +enable-cluster-counting 2. b. Using stack $ stack --stack-yaml stack-a.b.c.yaml install --flag Agda:optimise-heavily --flag Agda:enable-cluster-counting replacing `a.b.c` with your version of GHC. The flags mean: - optimise-heavily: Turn on extra optimisation for a faster Agda. Takes large resources during compilation of Agda. - enable-cluster-counting: Enable unicode clusters for alignment in the LaTeX backend. Requires the ICU lib to be installed and known to pkg-config. These flags can be dropped from the install if causing trouble. # Standard library You can use standard library v1.7.3, v2.0 or the `master` branch of the standard library with Agda 2.6.4.2. This branch is available at https://github.com/agda/agda-stdlib/ # Fixed issues over Agda 2.6.4.1 https://hackage.haskell.org/package/Agda-2.6.4.2/candidate/changelog Enjoy Agda 2.6.4.2! Andreas, on behalf of the Agda Team -- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel(a)gu.se http://www.cse.chalmers.se/~abela/

1 1

[ANN] Darcs 2.18.1 release
by Ganesh Sittampalam 25 Feb '24

25 Feb '24

Hi, On behalf of the Darcs team, I would like to announce the release of Darcs 2.18.1 [1]. The full release notes [2] are appended below. Regards, Ganesh [1] https://hackage.haskell.org/package/darcs-2.18.1 [2] https://hackage.haskell.org/package/darcs-2.18.1/changelog Darcs 2.18.1, 25 Feb 2024 * Supports GHC 9.8 and the most recent version of other dependencies at the time of release, with the exception of the tls 2.0 package, which has been held back because of problems connecting to hub.darcs.net (see https://bugs.darcs.net/issue2715) * Substantial rewrite of the 'darcs test' command. The most important user visible change is that a test script can now return an exit code of 125 to reflect an untestable/skipped state (as with with "git bisect run"). This in turn means that a group of patches can be found to be responsible for a failure rather than just a single one. By default, Darcs will try to minimise such a group by reordering patches to remove irrelevant ones from the initial group found from the patch ordering in the repository. This behaviour can be disabled with --no-shrink-failure. * Remove support for downloading via curl This is no longer particularly useful as we now use modern, maintained Haskell libraries for native HTTP downloading, and substantially simplifies this area of the code. * Patch index: Significant performance improvement The patch index is used in commands like annotate and log. A couple of performance improvements were made that should speed up using the patch index. * Progress reporting Progress reports are now provided during more long-running operations, including updating the "index" (a cache that speeds up detecting changes in the working directory), and during merge operations. They also behave better on Windows and when outputting long lines. * Other changes/fixes: * Use hardlinks more often to share files between repositories/caches. * Support --leave-test-dir for all commands that support --test * Avoid extraneous "repo:." entries in _darcs/prefs/sources [issue2672] * Add 'darcs clean' command as an alias for 'darcs revert -l' * 'darcs rebase unsuspend': add more patch editing options * Fix stale lock files after Ctrl-C * External merge tools: preserve output, and fail if tool does * Properly reference renamed files in external merge [issue189] * Mark conflicts properly if tag pulled at the same time [issue2682] * Remove the useless optimize pristine subcommand * 'darcs convert': honour the --compress and --diff-algorithm options * Fix contrib/darcs-shell [issue2646] * Fix 'darcs pull --dont-allow-conflicts' with external-merge [issue1819] * Problems with local pristine files now tell user to run 'darcs repair' [issue1981] * Fix various problems with symlinks, including on Windows * Add --no-prefs-templates option when creating a repository * Allow 'darcs rebase unsuspend' when there are non-conflicting unrecorded changes * Handle broken pending patches in 'darcs check' and 'darcs repair' * Improve error reporting when remote _darcs/format doesn't exist * 'darcs optimize reorder': add --deep/--shallow options * 'darcs optimize compress/uncompress': also handle pristine files * 'darcs optimize cache': don't work with lists of darcs repos Instead just the global cache is cleaned by checking hard-link counts * Skip the pager when $DARCS_PAGER / $PAGER are set to the empty string * 'darcs convert export': allow relative paths for --read-marks and --write-marks * Fix 'darcs amend --unrecord' to move unrecorded changes to pending [issue2697] * Don't treat cancelling an operation as failure [issue2074] * Fix cloning of ssh repo when using Ctrl-C to stop getting patches [issue2701] * Don't report invalid regexes as a bug in darcs [issue2702] * Add short option -n for --dry-run * 'darcs diff': support --look-for-moves and --look-for-adds * Fix buffering problem with 'darcs diff' [issue2704] * 'darcs obliterate' and 'darcs rebase': offer to revert any conflicting unrecorded changes * Stop displaying context lines in various interactive scenarios: it didn't work properly and would require a lot of work to fix. * Improve conflict display for Rebase and V3 patches * Increase size limit to 100K for environment variables like DARCS_PATCHES_XML, and warn when it is exceeded * 'darcs rebase unsuspend': improve the display of dropped dependencies * 'darcs amend --ask-deps': also provide a way to remove dependencies * 'darcs push': support --reorder-patches option * Remove the --remote-repo option * Don't display hints about using --set-default * Conflict resolution: unrecorded changes will suppress conflict marking of appropriate changes [issue2708] * Explain what a "clean tag" is in help for tag command * Fix problem with naming patch bundles after patches that contain characters incompatible with the current locale [issue2716]

2 1

Package Takeover: Hexpat
by Pavan Rikhi 25 Feb '24

25 Feb '24

Hi, as per the "Taking over a package" wiki page, I am sending this message as I would like to takeover basic maintenance of the hexpat package: https://hackage.haskell.org/package/hexpat I have attempted to reach the original author from multiple of their publicly available addresses 3 weeks ago & have gotten no response. The last commit to the package was over 7 years ago. I have submit multiple PRs to fix compilations to their repository with no response: https://github.com/the-real-blackh/hexpat/pull/13 https://github.com/the-real-blackh/hexpat/pull/14 The hackage trustees have applied some of these, but co-maintainership by me would mean less work for them, and eventually code changes will be required to keep the package compiling: https://github.com/haskell-infra/hackage-trustees/issues/363 https://github.com/haskell-infra/hackage-trustees/issues/394 Pavan Rikhi

1 0

[ANNOUNCE] GHC 9.8.2 is now available
by Zubin Duggal 23 Feb '24

23 Feb '24

The GHC developers are happy to announce the availability of GHC 9.8.2. Binary distributions, source distributions, and documentation are available on the [release page](https://www.haskell.org/ghc/download_ghc_9_8_2.html). GHC Blog Post: https://www.haskell.org/ghc/blog/20240223-ghc-9.8.2-released.html This release is primarily a bugfix release addressing many issues found in the 9.8 series. These include: * A fix for a bug where certain warnings flags were not recognised (#24071) * Fixes for bugs in the renamer and typechecker (#24084, #24134, #24279, #24083) * Fixes for bugs in the simplifier and code generator (#24160, #24242, #23628, #23659, #24160, #23862, #24295, #24370) * Fixes for some memory leaks in GHCi (#24107, #24118) * Improvements to error messages (#21097, #16996, #11050, #24196, #24275, #23768, #23784, #23778) * A fix for a recompilation checking bug where GHC may miss changes in transitive dependencies when deciding to relink a program (#23724). * And many more fixes A full accounting of changes can be found in the [release notes]. As some of the fixed issues do affect correctness users are encouraged to upgrade promptly. We would like to thank Microsoft Azure, GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, 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. Enjoy! -Zubin [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.8.2/docs/users_guide/9.8.2-notes.html

1 0

what monad is this?
by Johannes Waldmann 21 Feb '24

21 Feb '24

Dear Cafe, I was surprised to see ghc accept this code ghci> do let {x = False}; not x True because I initially thought: there's a `do`, so there must be some monad, but which is it? some implicit Identity monad perhaps? But the type is indeed plain `Bool`, and the explanation is (I think): there is a `do` but there is no monad, since the translation according to ( https://www.haskell.org/onlinereport/haskell2010/haskellch3.html#x8-470003.… ) does never produce `(>>=)`. So, all is fine, nothing to see here. Perhaps keep in mind as an edge case, useful to confuse students. Actually, to motivate them to read the language standard ... - J.W.

5 4