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Critical code generation bug with GHC 9.12.3
by Zubin Duggal 08 Jan '26

08 Jan '26

Hello all, Unfortunately we discovered a major code generation regression in GHC 9.12.3 that results in incorrect runtime results for certain operations involving sub-word divisions. We recommend avoiding upgrading to this minor release at this time. See https://gitlab.haskell.org/ghc/ghc/-/issues/26711 for more details. This is the same bug that affected GHC 9.12.1. A patch re-introducing this bug was accidently backported onto the 9.12.3 branch and went unnoticed throughout the testing period. We are taking steps to ensure similar situations are less likely to occur again, including looking at ways to improve our testing procedure for minor GHC release, potentially using the Stackage infrastructure to run the testsuites of a broad range of packages to detect such issues. We are also starting to prepare GHC 9.12.4 with a fix, which we hope to release soon. However, a significant amount of time has passed since the initial set of backports to GHC 9.12.3 were completed, which means that a number of merge requests addressing issues of various severities has been marked for backporting to the GHC 9.12 branch. We are in the process of triaging this list and preparing a robust and reliable GHC 9.12.4 release. Thanks, Zubin.

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GHC 9.14.1 is now available
by Zubin Duggal 27 Dec '25

27 Dec '25

The GHC developers are very pleased to announce the release of GHC 9.14.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. GHC 9.14 brings a number of new features and improvements, including: * Significant improvements in specialisation: * The `SPECIALISE` pragma now allows use of type application syntax * The `SPECIALISE` pragma can be used to specialise for expression arguments as well as type arguments. * Specialisation is now considerably more reliable in the presence of `newtype`s * Significant GHCi improvements including: * Correctness and performance improvements in the bytecode interpreter * Features in the GHCi debugger * Support for multiple home units in GHCi * Implementation of the [Explicit Level Imports proposal][levels] * `RequiredTypeArguments` can now be used in more contexts * Greatly improved [SSE/AVX2 support][sse] in the x86 native code generator backend * Initial native code generator support for LoongArch * The WebAssembly backend now supports [evaluation via the interpreter][wasm-ghci], allowing GHCi and TemplateHaskell evaluation, including `foreign import javascript` usage from within the browser * A new primop [`annotateStack#`][annotate-stack] for pushing arbitrary data onto the call stack for later extraction when decoding stack traces * [`-Wincomplete-record-selectors`][incomplete-selectors] is now part of `-Wall`. Libraries compiled with `-Werror` may need adjustment. * A major update of the Windows toolchain * Improved compatibility with [macOS Tahoe][macos] * ... and many more A full accounting of changes can be found in the [release notes][]. See the [migration guide][] for guidance on migrating programs to this release. Note that while this release makes many improvements in the specialisation optimisation, polymorphic specialisation remains disabled by default in the release due to concern over regressions of the sort identified in [#26329][T26329]. Users needing more aggressive specialisation can explicitly enable this feature with the `-fpolymorphic-specialisation` flag. Depending upon our experience with 9.14.1, we may enable this feature by default in a later minor release. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to thank these sponsors 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 comprises this release. As always, do give this release a try and open a [ticket][] if you see anything amiss. [downloads.haskell.org] https://downloads.haskell.org/ghc/9.14.1 [release notes]: https://downloads.haskell.org/ghc/9.14.1/docs/users_guide/9.14.1-notes.html [ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new [macos]: https://gitlab.haskell.org/ghc/ghc/-/issues/26166 [T26329]: https://gitlab.haskell.org/ghc/ghc/-/issues/26329 [levels]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0682-e… [wasm-ghci]: https://www.tweag.io/blog/2025-04-17-wasm-ghci-browser/ [incomplete-selectors]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0516-i… [annotate-stack]: https://gitlab.haskell.org/ghc/ghc/-/issues/26218 [migration guide]: https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.14 [sse]: https://gitlab.haskell.org/ghc/ghc/-/issues/25030

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GHC 9.12.3 is now available
by Zubin Duggal 27 Dec '25

27 Dec '25

The GHC developers are very pleased to announce the release of GHC 9.12.3. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. GHC 9.12.3 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fix a number of crashes and miscompilations in the compiler frontend (#25004, #25960, #26256) * Improvements to efficiency of the runtime linker (#26009) * Fixes for several bugs in bytecode generation and the bytecode interpreter (#23210, #25975, #25750) * Fixes for bugs in the handling of WHITEHOLEs in the RTS (#26204, #26205) * Fix incorrect code generation for SSE vector operations (#25859) * Fix a use-after-free in the Windows runtime linker (#26613) * Support for synchronous JSFFI exports for the wasm backend * And many more! A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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/9.12.3/docs/users_guide/9.12.3-notes.html [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.3 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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[TFP 2026] 1st Call for Participation for the 27th International Symposium on Trends in Functional Programming, Odense, Denmark, January 27-29 2026 - TFPiE Jan 26
by Peter Achten 24 Dec '25

24 Dec '25

TFP 2026 -- Call For Participation (trendsfp.github.io [1]) Venue TFPiE and TFP will take place in-person in Odense, Denmark, at the University of Southern Denmark. Dates Early registration: 31 December, 2025 Late registration: 20 January , 2026 TFPiE Workshop: Monday 26 January, 2026 TFP Symposium: Tuesday 27 - Thursday 29 January, 2026 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. Keynote speakers We are happy to have the following keynotes in the programme: Alex Gerdes (TFPiE), Gothenburg University and Chalmers: "Generating Feedback from Rewrite Strategies for Interactive Exercises" Joachim Breitner, Lean Focused Research Organization: "Lean Highlights" Ohad Kammar, University of Edinburgh: "Synthetic Convolution" András Kovács, Gothenburg University and Chalmers: TBA Programme We have 13 paper presentations, as well as invited talks. A preliminary programme schedule can be found here: trendsfp.github.io/schedule.html [2] Excursion and banquet In the afternoon and evening of Wednesday January 28th we have an excursion to H.C. Andersen Museum, followed by a break before heading to Madklubben for the conference banquet. Travel Scholarship Thanks to the generous support from the Carlsberg Foundation, we are able to offer travel scholarships (DKK 3000 ~ USD 470 ~ EUR 400) to young researchers traveling to attend TFP 2026 in Odense, Denmark. Information on how to apply can be found here: https://trendsfp.github.io/scholarship.html Links: ------ [1] https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ftrendsfp.g… [2] https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Ftrendsfp.g…

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Call for Participation: BOB 2026 (Berlin, Mar 13)
by Stefan Wehr 19 Dec '25

19 Dec '25

there's quite a bit of Haskell material at BOB 2026. Come along! ========================================================================= BOB 2026 Conference “What happens if we simply use what’s best?” March 13, 2026, Berlin https://bobkonf.de/2026/ Program: https://bobkonf.de/2026/program.html Registration: https://bobkonf.de/2026/registration.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 16 talks and 8 tutorials on current topics: https://bobkonf.de/2026/program.html Talk subjects includes functional programming, software architecture, formal methods, accessibility, UI programming, reactive systems, and domain-driven design. BOB tutorial include sessions on TypeScript, OCaml, Haskell, Agda, accessibility, and reactive systems. Stefan Kaufmann will give the keynote talk on digital sovereignty. Registration is open - many discount options - including limited early-bird discounts - are available, as are grants for members of groups underrepresented in tech. https://bobkonf.de/2026/registration.html

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Call for Participation: BOB 2026 (Berlin, Mar 13)
by Michael Sperber 15 Dec '25

15 Dec '25

BOB 2026 has lots of exciting content on functional programming, type systems and formal methods! ========================================================================= BOB 2026 Conference “What happens if we simply use what’s best?” March 13, 2026, Berlin https://bobkonf.de/2026/ Program: https://bobkonf.de/2026/program.html Registration: https://bobkonf.de/2026/registration.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 16 talks and 8 tutorials on current topics: https://bobkonf.de/2026/program.html Talk subjects includes functional programming, software architecture, formal methods, accessibility, UI programming, reactive systems, and domain-driven design. BOB tutorial include sessions on TypeScript, OCaml, Haskell, Agda, accessibility, and reactive systems. Stefan Kaufmann will give the keynote talk on digital sovereignty. Registration is open - many discount options - including limited early-bird discounts - are available, as are grants for members of groups underrepresented in tech. https://bobkonf.de/2026/registration.html

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TFPiE 2026, Call for Submissions
by Mart Lubbers 15 Dec '25

15 Dec '25

TFPIE 2026 Call for papers https://wiki.tfpie.science.ru.nl/TFPIE2026 (January 26th 2026, Odense, Denmark, co-located with TFP 2026 at University of Southern Denmark) TFPIE 2026 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/my/conference?conf=tfpie26 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 26th 2025, Anywhere on Earth Notification: by December 30th 2025 (Note: submissions will be evaluated on a rolling basis, so earlier submissions will receive an earlier response) TFPIE Registration Deadline: TBA Workshop: January 26th 2026 Submission for formal review: April 22nd 2026, Anywhere on Earth Notification of full article: May 27th 2026 Camera ready: June 24th 2026 ## Program Committee Mart Lubbers, Radboud University, Nijmegen, Netherlands (PC Chair) Tim Steenvoorden, Open Universiteit, Heerlen, Netherlands Marco T. Morazán, Seton Hall University, South Orange, NJ, USA Guannan Wei, Tufts University, Medford, MA, USA Marcos Viera, Universidad de la República, Montevideo, Uruguay Johannes Åman Pohjola, Chalmers University of Technology, Gothenburg, Sweden ## Registration information See https://wiki.tfpie.science.ru.nl/TFPIE2026 for updated information and see https://trendsfp.github.io/ for info on registration 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.

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Soundness of forall mixed with Coercible
by Tom Ellis 12 Dec '25

12 Dec '25

Is it sound to define forallCoercible :: forall f g. (forall a. Coercible (f a) (g a)) => Coercion (Forall f) (Forall g) forallCoercible = unsafeCoerce (Coercion @(f Any) @(g Any)) I'm having trouble coming up with a reason why it is not, but my intuition for these things is not very good. Thanks, Tom

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Re: State of Haskell 2025
by Olaf Klinke 12 Dec '25

12 Dec '25

> Because I haven't tried to upgrade: the risk of breaking something > exceeds any 'benefit' from new 'features', none of which do I want to > use. If you did not try to upgrade, how did you find out that upgrading would break your code? Indeed, only offering "yes" and "no" as options is not enough for this question. "Bottom" would be the appropriate answer in your case, and I'd have chosen that, too. Olaf

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GHC 9.12.3-rc3 is now available
by Zubin Duggal 11 Dec '25

11 Dec '25

The GHC developers are very pleased to announce the availability of the third release candidate for GHC 9.12.3. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.3 is a bug-fix release fixing several issues of a variety of severities and scopes. A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 22 December 2025. The changes from the first release candidate are - Fix use after free on windows due to a linker optimisation introduced in an earlier RC (#26613) - A fix for a bug in the configure script which result in the LLVM toolchain not being detected in certain situations (#26564) - Fixes for the WASM backend GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to that these sponsors 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://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.3-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.3-rc3 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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