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bug in ghci module loading post 9.12.4?
by Evan Laforge 03 Jul '26

03 Jul '26

I recently upgraded from ghc 9.2 to 9.6 (I know, I'm slow), and one of the things I was looking forward to was better recompilation avoidance, that wouldn't be fooled by spurious mtime changes that are common with with e.g. git branch switches. Unfortunately, it seems to have gotten buggy at the same time! I upgraded again to 9.12.4 and it looks like it's still buggy. Either that or I'm doing things wrong somehow. Here's a repro, it requires 3 modules: % cat >BugA.hs module BugA where x :: Int x = 13 % cat >BugB.hs module BugB where import qualified BugA f :: IO () f = print BugA.x % cat >BugC.hs module BugC where import qualified BugB bug :: IO () bug = BugB.f % ghci -fobject-code # compile so we can load .o GHCi, version 9.12.4: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /Users/elaforge/qlib/dotfiles/.ghci Prelude> :load BugC [1 of 3] Compiling BugA ( BugA.hs, BugA.o ) [2 of 3] Compiling BugB ( BugB.hs, BugB.o ) [3 of 3] Compiling BugC ( BugC.hs, BugC.o ) Ok, three modules loaded. Leaving GHCi. % ghci Prelude> :load BugC Ok, three modules loaded. Prelude BugC> bug 13 As expected! Now go edit BugA.hs, and change 13 to say 14, and save. Now reload: Prelude BugC> :r [1 of 3] Compiling BugA ( BugA.hs, interpreted ) [Source file changed] Ok, three modules reloaded. Prelude BugC> bug 13 So that's not right! This will also cause linking errors if something was removed, though it's easier to reproduce the stale values. For my interpretation of what's going on, I believe previously it would have also reloaded BugB. While it has noticed that BugA must be reloaded (and switched to bytecode), it hasn't noticed that BugB is in the dependency path and should also be reloaded, and possibly winds up using stale values inlined into BugB.o. Is it a bug?

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monomorphism restriction vs unused
by Evan Laforge 23 Jun '26

23 Jun '26

I have a little DSL I use from ghci and I finally tracked down a minor annoyance, which is when I comment out some lines in a definition, sometimes certain now-unused `where` definitions now become ambiguity errors. Here's a minimized repro: ``` {-# LANGUAGE OverloadedStrings #-} -- {-# LANGUAGE NoMonomorphismRestriction #-} import Data.String (IsString(..)) data Thing a = Thing -- 1. IsString instance on concrete type. instance IsString (Thing ()) where fromString _ = Thing -- 2. trans is polymorphic trans :: Thing a -> Thing a trans = id -- 3. ambig is a simple binding under the Monomorphism Restriction, and is -- unused. ex :: () ex = () where unused = trans "k" -- Ambiguous type variable 'a0' ``` In place of `ex` imagine a large expression with many things in `where`, and part of the expression was temporarily commented out which just happened to contain the uses of `unused`. As the comment implies, this is ultimately a monomorphism restriction thing. My understanding is that `trans` keeps defaulting from happening and the restriction then forbids leaving `unused` polymorphic. It was confusing to me given that unused is unused, but I'm guessing the type checking runs before dead code elimination. So I think this is all working as intended, or rather, an unexpected interaction between defaulting being a "best effort" heuristic, and monomorphism restriction doing its thing, and the type checking -> dead code order, but all 3 things exist for good reasons which are unlikely to change. The way around is to turn on NoMonomorphismRestriction, which unfortunately counts as a flag change and hence causes ghci to not be able to load .o files... or compile the .o files with that too, but that of course may lead to unexpected redundant evaluation. https://www.haskell.org/onlinereport/decls.html#sect4.5.5 talks about "no way to enforce monomorphic use of an exported binding", but is this still relevant when it's usual to require type signatures for all top-level bindings? Are there still non-toplevel let/where-bound things which could result in redundant work?

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Haskell IDE
by Andrew Goh 18 Jun '26

18 Jun '26

Hi Haskell Cafe, Is anyone thinking of building a new functioning Haskell IDE based on GHC and GHCi. I am using a legacy Haskell plug-in for Eclipse IDE and the Haskell extension on VS Code, Miss Leksah much, and I simply wish that somebody will bring it back or develop a new IDE or a plug-in for the Eclipse IDE and maybe VS too. Warm Wishes, - Andrew

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ICFP 2026 Tutorials: Proposal Deadline on June 21!
by ICFP Publicity 18 Jun '26

18 Jun '26

ICFP 2026: Last Call for Tutorials *** Deadline: June 21, AoE ****Submission Portal*: https://icfp26events.hotcrp.com/ The 31st ACM SIGPLAN International Conference on Functional Programming (ICFP) is calling for tutorials! ICFP will be held in Indianapolis, IN, United States from *Monday, August 24 to Saturday, August 29, 2026*. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementation, principles, and uses of functional programming. *Tutorials* (or panels, discussions, etc.) should last approximately 3 hours each, and will be presented during ICFP and its co-located workshops and other events. Tutorials may focus either on a concrete technology or on a theoretical or mathematical tool. Tutorials may be intended primarily for researchers or for practitioners. Ideally, tutorials will have a concrete result, such as “Learn to do X with Y” rather than “Learn language Y”. The workshops, tutorials, etc. may occur on August 24th (the day before ICFP) and August 28-29th (the two days after ICFP). *All co-located events* must submit a proposal — workshops, tutorials, symposiums, or side meetings. Submission Details <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#submission-details> - Deadline for Tutorial Proposal Submission: June 21, 2026 - Notification of Acceptance: June 28, 2026 Prospective organizers of tutorials, panels, or discussions should submit proposals by the Tutorial deadline. Proposals should outline the objectives, intended audience, and planned activities. See the Submission Portal for details. *Submission Portal*: https://icfp26events.hotcrp.com/Selection Committee <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#selection-committ…> Event proposals will be evaluated by a committee comprising members from the ICFP 2026 organizing committee, in collaboration with the SIGPLAN executive committee. Contact Information <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#contact-informati…> For inquiries, please contact: Ben Greenman: blg(a)cs.utah.edu Jiasi Shen: sjs(a)cse.ust.hk We look forward to your proposals and to creating a vibrant and engaging program at ICFP 2026!

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call for talks, tutorials, performances: LeFUNK 2026 Leipzig (Germany) September 29/30
by Johannes Waldmann 16 Jun '26

16 Jun '26

LeFUNK 2026 Leipzig Workshop on Functional Programming September 29/30, Leipzig, Germany https://www.imn.htwk-leipzig.de/LFUNK2026/ abstract submission: by July 12 bringing together functional programming developers, researchers, enthusiasts and beginners to listen to talks, take part in tutorials, and join in interesting conversations; continuing the tradition of "Haskell in Leipzig" (started in 2006) Topics: in general: functional programming in applications, teaching, research. in particular: we welcome contributions in these areas expressive types interactive programming and proving functional programming for music and arts a contribution can be: a talk (30 min), a tutorial (90 min), a performance. Program Committee (under construction) Joachim Breitner, Lean FRO Andres Löh, Well Typed Henning Thielemann Johannes Waldmann, HTWK Leipzig Best regards, and see you - Johannes. NB: in order to add some actual Haskell content, here's a puzzle: explain the difference in numbers of test cases: ghci> import Test.LeanCheck ghci> check $ \ x y -> x || y == y || x +++ OK, passed 2 tests (exhausted). ghci> check $ \ x y -> (x || y) == (y || x) +++ OK, passed 4 tests (exhausted). you're welcome to bring puzzles to the workshop as well!

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POPL 2027 Call for Workshops
by Ningning Xie 10 Jun '26

10 Jun '26

POPL 2027 Call for Workshops Sun 10 - Sat 16 January 2027 Mexico City, Mexico https://popl27.sigplan.org/ ============================= Submission details Deadline for submission: 24 July 2026 Notification of acceptance: 4 August 2026 A workshop proposal should provide the following information: - Name of the workshop. - A short description (150-200 words) of the workshop. - Call for submissions. - Duration of the workshop. - Whether the workshop will be Conference-approved or SIGPLAN-approved (see below). - Organizers: names, affiliation, contact information, brief (100 words) biography. - Event format: workshop; type of submissions if any; review process; results dissemination. - Expected attendance and target audience. - Potential PC members - please do not contact them before the workshop is approved. - History of the workshop. - Plans for remote participation. Please submit your proposals at https://popl27.sigplan.org/track/POPL-2027-workshops-and-co-located-events --------------------------------------------------------------------- SIGPLAN Sponsorship POPL co-located events are sponsored by SIGPLAN (http://sigplan.org/) There are two kinds of co-located events: Conference-approved (no proceedings) and SIGPLAN-approved (proceedings in the ACM Digital Library). See http://www.sigplan.org/Resources/Guidelines/Workshops/ for more information, including a full listing of prescriptions for Conference-approved and SIGPLAN-approved workshops. SIGPLAN-approved workshops must respect the SIGPLAN Diversity Policy. Proposals for SIGPLAN-approved workshops must additionally include the gender, country of affiliation, and professional status of potential PC members. See https://www.sigplan.org/Resources/Policies/Diversity/ for more details. --------------------------------------------------------------------- Selection committee All submissions will be evaluated by a committee comprising the workshops co-chairs, the general chair, and the program chair. --------------------------------------------------------------------- Further information Any questions regarding POPL 2027 co-located event proposals should be addressed to the workshops chairs, Aws Albarghouthi (aws(a)cs.wisc.edu) and Alan Schmitt (alan.schmitt(a)inria.fr)

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POPL 2027 Call for Papers
by Ningning Xie 10 Jun '26

10 Jun '26

POPL 2027 Call for Papers Sun 10 - Sat 16 January 2027 Mexico City, Mexico https://popl27.sigplan.org/ ============================= PACMPL Issue POPL 2027 seeks contributions on all aspects of programming languages and programming systems, both theoretical and practical. Authors of papers published in PACMPL Issue POPL 2027 will be invited – but not required – to present their work in the POPL conference in January 2027, which is sponsored by ACM SIGPLAN, in cooperation with ACM SIGACT and ACM SIGLOG. **NEW FOR 2027** - Clarification about expectations concerning mechanized proofs; see Submission Guidelines: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers#submission-… - At least one author of each paper submission must be registered as a Reserve Reviewer as per the Reserve Reviewer Policy: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers#reserve-rev… See details: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers ## Important Dates - Paper submission deadline: Thursday July 9, 2026 - Author response period: Mon 7 - Thu 10 Sep, 2026 - Author notification: Mon 5 Oct, 2026 - Revision deadline: Mon 26 Oct, 2026 - Final acceptance notification: Mon 9 Nov, 2026 - Camera ready deadline: Fri 20 Nov, 2026 ## Submission Site Information The submission site is https://popl27.hotcrp.com. Papers may be resubmitted to the submission site multiple times up until the deadline, but only the last version submitted before the deadline will be reviewed. There is no abstract deadline. The submission site requires entering author names and affiliations, relevant topics, and potential conflicts. Addition or removal of authors after the submission deadline will need to be approved by the Program Chair (as this kind of change potentially undermines the goal of eliminating conflicts during paper assignment). The submission deadline is 11:59PM July 9, 2026 anywhere on earth: https://en.wikipedia.org/wiki/Anywhere_on_Earth ## Scope Principles of Programming Languages (POPL) is a forum for the discussion of all aspects of programming languages and programming systems. Both theoretical and experimental papers are welcome, on topics ranging from formal frameworks to experience reports. We seek submissions that make principled, enduring contributions to the theory, design, understanding, implementation, or application of programming languages. ## Evaluation Criteria The Review Committee (aka Program Committee, PC) will evaluate the technical contribution of each submission as well as its accessibility to both experts and the general POPL audience. All papers will be judged on significance, originality, relevance, correctness, and clarity. Each paper must explain its scientific contribution in both general and technical terms, identifying what has been accomplished, explaining why it is significant and comparing it with previous work. Advice on writing technical papers can be found on the SIGPLAN author information page (https://www.sigplan.org/Resources/Author/) ## Double-Blind Reviewing POPL 2027 will use a full double-blind reviewing process (similar to the one used in recent years (POPL 2023 - 2026) but different from the lightweight double-blind process used before then). This means that identities of authors will not be made visible to reviewers until after conditional-acceptance decisions have been made, and then only for the conditionally-accepted papers. ## Important update on ACM’s new open access publishing model for ACM Conferences Starting January 1, 2026, ACM has fully transitioned to Open Access. All ACM publications, including those from ACM-sponsored conferences, will be 100% Open Access. Authors will have two primary options for publishing Open Access articles with ACM: the ACM Open institutional model or by paying Article Processing Charges (APCs). For a paper to be covered by ACM Open, the corresponding author must be affiliated with a participating institution. APC pricing for 2027 conferences is currently under review and will be finalized in June. With over 2,600 institutions already part of ACM Open, the majority of ACM-sponsored conference papers will not require APCs from authors or conferences. Authors from institutions not participating in ACM Open will need to pay an APC to publish their papers, unless they qualify for a waiver. To find out whether an APC applies to your article, please consult the list of participating institutions (https://libraries.acm.org/acmopen/open-participants) in ACM Open and review the APC Waivers and Discounts Policy ( https://www.acm.org/publications/policies/policy-on-open-access-apc-waivers… ).

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Richard Bird Distinguished Dissertation Award - Call for Nominations
by Graham Hutton (staff) 01 Jun '26

01 Jun '26

Dear all, I'm pleased to announce that JFP is establishing the Richard Bird Distinguished Dissertation Award, to recognise an outstanding PhD dissertation in functional programming. Please share! Best wishes, Graham Hutton ================================================================= CALL FOR NOMINATIONS Richard Bird Distinguished Dissertation Award 2025 Deadline: 31st August 2026 http://tinyurl.com/jfp-bird-award ================================================================= OVERVIEW The Journal of Functional Programming is pleased to establish the Richard Bird Distinguished Dissertation Award, to recognise an outstanding PhD dissertation in functional programming. Richard Bird (1943-2022) was one of the leading figures in functional programming. He was a Professor in Oxford, where he founded the Algebra of Programming group, and served as Director of the Computing Laboratory. Richard is renowned for his many books and pearls on functional programming, which set a lasting standard for clear and elegant writing. It seems fitting that an award be established in his name to further encourage these values in the field. The award includes a prize of £1,000. Funding for the prize is supported by a generous donation from Richard himself to further the cause of functional programming. CRITERIA Eligible dissertations must have been completed in 2025. Depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise. The award is open to all topics within the remit of JFP, with a particular emphasis on dissertations that reflect Richard's own values of clarity, simplicity and elegance. For a dissertation to be considered for the award it should: - Reach a high standard of exposition; - Make a noteworthy contribution to the subject; - Place the results in the wider context of computer science. NOMINATIONS Please submit the following information to the award chair, <graham.hutton(a)nottingham.ac.uk>, by 31st August 2026: - Two letters of support, explaining why the dissertation should be considered for the award. One letter should be from the advisor/supervisor, and one from an independent source with no conflict of interest with the candidate, such as an external examiner or other expert in the field. - A copy of the dissertation itself. AWARD COMMITTEE Graham Hutton (chair), University of Nottingham Matthew Flatt, University of Utah Jeremy Gibbons, University of Oxford François Pottier, INRIA Wouter Swierstra, University of Utrecht Ningning Xie, University of Toronto The JFP editors-in-chief serve as observers of the committee. ================================================================= 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.

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PLMW @ ICFP 2026: Funding Call
by conrad.watt＠ntu.edu.sg 29 May '26

29 May '26

APPLICATION FOR PLMW TRAVEL FUNDING Applications for travel funding to PLMW @ ICFP are now open - we will begin awarding funding starting from June 1 AOE until all funding is committed. So long as funding remains, we will continue to consider applications submitted before June 30th AOE. We advise all interested to apply as soon as possible, especially if a visa is required. https://icfp26.sigplan.org/home/PLMW-ICFP-2026#Call-for-Participation The application can be accessed directly at the following URL: https://forms.gle/adtuWjLAbBtGTcCNA PLMW is a workshop co-located with ICFP 2026 (the International Conference on Functional Programming) in Indanapolis, US, from August 24-29. The purpose of this mentoring workshop is to encourage graduate students and senior undergraduate students to pursue careers in programming language research. This workshop will bring together world leaders in programming languages research and teaching from academia and industry to help students imagine how they might contribute to our research community. Topics will range from the abstract (e.g., what is PL research and how does one become involved in it) to the concrete (e.g., how to navigate an academic conference, how to pick a research area) as well as technical talks on cutting-edge topics. See the link below for more details: https://icfp26.sigplan.org/home/PLMW-ICFP-2026

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[ANN] Copilot 4.7.1
by Ivan Perez 28 May '26

28 May '26

Hi café! We are really excited to announce Copilot 4.7.1 [1]. Copilot is a stream-based EDSL in Haskell for writing and monitoring embedded systems, 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. Compilation to Bluespec, to target FPGAs, is also supported. Copilot is NASA Class D open-source software, and is being used at NASA in drone test flights and with rovers. Through the NASA tool Ogma [2] (also written in Haskell), Copilot also serves as a programming language and runtime framework for NASA's Core Flight System, Robot Operating System (ROS 2) and FPrime (the software framework used in the Mars Helicopter). Ogma now supports producing flight and robotics applications directly in Copilot, not just for monitoring, but for implementing the logic of the applications themselves. This release introduces several improvements to Copilot: - Fix corner cases in the treatment of special floating point numbers in the Bluespec backend and `copilot-theorem`. - Fix errors in examples in `copilot-theorem` that use Z3. - Add to `copilot-libraries` a module to perform sanity checks of Copilot specifications. - Add to `copilot-libraries` a module to facilitate implementing state machines. Copilot is compatible with versions of GHC from 8.6 to 9.10. Packages are published on Hackage [3], as well as several Linux distributions (e.g., Debian, Fedora). This release has been possible thanks to submissions from Ryan Scott (Galois) and Chris Hathhorn (Galois). We are grateful to them for their contributions, and for making Copilot better every day. For details on this release, see: https://github.com/Copilot-Language/copilot/releases/tag/v4.7.1. As always, we're releasing exactly 2 months since the last release. Our next release is scheduled for Jul 7th, 2026. We want to remind the community that Copilot is now accepting code contributions from external participants again. Please see the discussions and the issues in our Github repo [4] to learn how to participate. Current emphasis is on using Copilot for full data processing applications (e.g, system control, arduinos, rovers, drones), improving usability, performance, and stability, increasing test coverage, removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our coding standards. Users are encouraged to participate by opening issues, asking questions, extending the implementation, and sending bug fixes. Happy Haskelling! Ivan -- [1] https://github.com/Copilot-Language/copilot/releases/tag/v4.7.1 [2] https://github.com/nasa/ogma [3] https://hackage.haskell.org/package/copilot [4] https://github.com/Copilot-Language/copilot

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The Leksah (Haskell) IDE for Windows, Linux & macOS
by Andrew Goh 27 May '26

27 May '26

Dear Haskell Cafe, There was the Leksah (Haskell) IDE about 10 to 12 years ago. I wonder if you chaps can bring it back for the Windows, Linux and maybe macOS platform. I have the GHCup toolchain installed after a few mistries, and set up VS Code for Haskell programming, but I still would really prefer the Leksah IDE (this time in native mode) instead. As for the macOS platform, there is a Haskell Mac for IDE that can be brought for under US$10. Lastly, why don't you allow Haskell users to subscribe to all Haskell mailing lists rather than go individaully to each one to do that. - Andrew

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Can't use my hackage account, and "upgrade page" fails too
by Mario Lang 26 May '26

26 May '26

Hi. I just tried to upload a new version of my package chessIO. Apparently, my hackage account (mlang) does no longer work. Last upload was about 2 years ago maybe? Found the upgrade page on Hackage, but that gives me an "authoisation scheme" error, with Firefox and Chrome. Maybe that page is broken? Maybe there is something else wrong with my account? What do I need to do to get it working again? Creating a new one doesn't really solve the problem, as I would still need someone to intervene to get access rights for my package. -- CYa, ⡍⠁⠗⠊⠕

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IFL 2026 First call for papers
by Mart Lubbers 20 May '26

20 May '26

======================================================================= IFL 2026 38th Symposium on Implementation and Application of Functional Languages venue: Aspenäs Herrgård, Gothenburg, Sweden October 28 - 30 2026 https://ifl26.cse.chalmers.se/ ======================================================================= ### 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 2026 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. ### Topics of interest Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialisation - run-time code generation - partial evaluation - (abstract) interpretation - meta-programming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques ### Peer-review process Following IFL tradition, IFL 2026 will use a post-symposium review process for the formal proceedings. Authors are invited to submit draft papers before the symposium. The program chairs will screen submissions for relevance to IFL, and accepted drafts will be shared with all participants. Each accepted paper must be presented at the symposium by at least one author. If submissions exceed capacity, selection will be based on quality, maturity, and relevance. Authors of accepted presentations will have the opportunity to revise their work in response to symposium feedback and submit a full paper to the post-proceedings. These submissions will be reviewed by the program committee for correctness, novelty, originality, relevance, significance, and clarity. The post-symposium review process is single-blind, with at least three reviews per paper. Camera-ready versions may include minor revisions without further review. ### Important dates Submission of draft papers September 4, 2026 Draft papers notification September 11, 2026 Deadline for early registration September 18, 2026 Deadline for late registration September 25, 2026 IFL symposium October 28-30, 2026 Submission of papers for proceedings November 25, 2026 Notification of acceptance February 12, 2027 Camera-ready version March 12, 2027 Deadlines are end of day Anywhere on Earth (UTC-12). ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template Submit your paper here: https://easychair.org/conferences/?conf=ifl26 Important note to authors about the new ACM open access publishing model: ACM has introduced a new open access publishing model for the International Conference Proceedings Series (ICPS). Authors based at institutions that are not yet part of the ACM Open program and do not qualify for a waiver will be required to pay an article processing charge (APC) to publish their ICPS article in the ACM Digital Library. To determine whether or not an APC will be applicable to your article, please follow the detailed guidance here: https://www.acm.org/publications/icps/author-guidance Further information: ICPS publishing model FAQ: https://www.acm.org/publications/icps/faq ACM Open program details: https://www.acm.org/publications/openaccess Questions: icps-info(a)acm.org ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organisation PC Chairs: - Alex Gerdes, Chalmers and University of Gothenburg, Sweden - Koen Claessen, Chalmers and University of Gothenburg, Sweden Publicity Chair: - Mart Lubbers, Radboud University, The Netherlands Local Chairs: - Alex Gerdes, Chalmers and University of Gothenburg, Sweden - Koen Claessen, Chalmers and University of Gothenburg, Sweden Please direct any questions you may have towards alexg(a)chalmers.se. ### Program committee - Abhiroop Sarkar, ETH Zurich - Andres Löh, Well-Typed LLP - Daan Leijen, Microsoft - Dominic Orchard, University of Kent - Fritz Henglein, DIKU - Graham Hutton, University of Nottingham - Guillaume Allais, University of Strathclyde - Jesper Cockx, Delft University of Technology - Mart Lubbers, Radboud University - Nachiappan Valliappan, University of Edinburgh - Nicolas Wu, Imperial College London - Niki Vazou, IMDEA Software Institute The program committee is still being finalized and may be updated. ### Venue IFL 2026 will be held at Aspenäs Herrgård, just outside Gothenburg, Sweden. Aspenäs Herrgård will host the symposium venue and provide a scenic setting for the conference. We will add more information about the venue, accommodation, and travel options soon. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organisers for their work, which is reused here.

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Conduit missing closing file handles
by Henning Thielemann 14 May '26

14 May '26

I have a pretty simple program for converting ZIP to TAR archives using the 'zip' and 'tar-conduit' packages, both using Conduit for streaming data. In principle the program works, but if the ZIP archive contains a non-trivial number of files, the program breaks because of exceeded limit of open file handles: $ zip2tar /usr/share/libreoffice/share/config/images_colibre.zip >/tmp/images_colibre.tar zip2tar: Uncaught exception ghc-internal:GHC.Internal.IO.Exception.IOException: /usr/share/libreoffice/share/config/images_colibre.zip: openFile: resource exhausted (Too many open files) While handling /usr/share/libreoffice/share/config/images_colibre.zip: openFile: resource exhausted (Too many open files) HasCallStack backtrace: throwIO, called at ./Control/Monad/Trans/Resource.hs:195:13 in resourcet-1.3.0-8b355f9483371034fb75ff40adb2e07157502721c941fbf8a6f607df6dd81546:Control.Monad.Trans.Resource The main function is essentially this one: [1] convertZipToTar :: (Zip.EntrySelector -> Zip.EntryDescription -> CTar.FileInfo) -> Sort -> FilePath -> IO () convertZipToTar fileInfoFromZipEntry_ sortMode zipPath = Zip.withArchive zipPath $ do entries <- Map.toList <$> Zip.getEntries files <- for entries $ \(selector, descr) -> flip fmap (Zip.getEntrySource selector) $ \src -> src .| (C.yield (Left $ fileInfoFromZipEntry_ selector descr) >> C.mapC Right) C.liftIO $ runConduitRes $ sequence_ files .| void CTar.tar .| C.stdoutC 'Zip.getEntrySource selector' generates a conduit for reading a file from the ZIP archive. It opens the archive anew for every accessed file, but it calls Conduit.Binary.sourceIOHandle, which promises to close a file promptly after reading. [2] It seems that files are not immediately closed after reading, but I cannot spot the cause. I suspected that "sequence_ files" might concatenate the Conduits while accumulating open file handles, but I think it should not and I did not find a matching alternative to sequence_. [1] https://hackage-content.haskell.org/package/zip2tar-0.0/src/src/Main.hs [2] https://hackage-content.haskell.org/package/zip-2.2.1/docs/src/Codec.Archiv…

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Subscription management
by Joachim Durchholz 14 May '26

14 May '26

Hi all, I accidentally subscribed two of my mail addresses to Haskell-cafe; here are the pertinent envelope address lines from the incoming mails: Envelope-to: joachim(a)durchholz.org Envelope-to: jo(a)durchholz.org I tried to unsubscribe (both, actually), but https://mailman.haskell.org/accounts/password/reset/ claims to have no knowledge of any of these two addresses. What should I do next? Regards, Jo P.S.: Something is wrong in the appended footer. The HTML version may be fine, but the text version I'm seeing obviously misses a link in the second-to-last line: > _______________________________________________ > Haskell-Cafe mailing list -- haskell-cafe(a)haskell.org > To (un)subscribe, modify options or view archives go to: > Only members subscribed via the mailman list are allowed to post. Sorry for going to the list itself, but I don't know the list administrator's mail address.

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Uploading packages from CLI
by Ivan Perez 09 May '26

09 May '26

Hi, Cabal is getting stuck when I try to upload a package from CLI. My user and password are correct. It this a known problem? Thanks, Ivan

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton (staff) 05 May '26

05 May '26

Dear all, If you or one of your students recently completed a PhD (or Habilitation) in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, open access, 200+ published to date, deadline 30st May 2026. Please share! Best wishes, Graham Hutton ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 31st May 2026 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, twice per year the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the student and the advisor/supervisor although we encourage them to coordinate. Habilitation dissertations are also eligible for inclusion. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 31st May 2026 o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 350 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting; if your original abstract exceeds the word limit, please submit an abridged version within the limit) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ 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.

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Questions about my findings about versioning, dependencies and breakages on Hackage
by Jon Kristensen 04 May '26

04 May '26

Hi! I’m currently wrapping up my master’s thesis, which is about dependencies and breakages on Hackage. In short, I’m analyzing all packages released onto Hackage during a certain window (currently the first quarter of 2025). I’m using the Hackage package index and the Hackage API to collect metadata. I’m using print-api[1] to attempt to detect breaking API changes between these releases and their predecessors. I’m using HIE DB[2] to identify which symbols are actually being used by reverse dependencies. My goal is to investigate versioning and dependency constraint practices, as well as package breakages. I’m now at a point where I would like to evaluate my findings with experts in the Haskell community (such as experienced developers and package maintainers). If you could spare a bit of time I would love to hear your thoughts on my work. I’m thinking the questions could be sent via email, but if you prefer a call we could do that as well. You will be anonymous when any data is presented. Thank you for whatever you can do! All the best, Jon [1]: https://github.com/Kleidukos/print-api [2]: https://github.com/haskell/HieDb

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Two Haskell Talks from Bellroy at Melbourne Compose Group May Meetup
by theghostjw＠gmail.com 02 May '26

02 May '26

We're thrilled to have two Bellroy Haskellers presenting a double-feature at Melbourne Compose Group. Michael Webb (CTO) will share how Bellroy built and scaled a $120M+ brand with a tiny Haskell team. Jack Kelly (Staff Engineer) will walk through deploying Haskell in the cloud with an opinionated guide to Haskell on AWS Lambda. Whether you're using Haskell in production, curious about serverless, or just want to see how a small team moves fast without fear, come along! The Talks Michael Webb - CTO Maximum Agency, Minimum Footguns Lessons from scaling a $120M+ carry brand with a tiny engineering team At Bellroy, we've built a small engineering team that moves fast, ships confidently, and hands real power to the people closest to the work - content editors, ops staff, marketers - without lying awake worrying about what they might break. The secret isn't process, approval chains, or change management theatre. It's that we've encoded the constraints that actually matter directly into our tools - many of them built in Haskell - and trusted our people with everything else. This talk is about the philosophy behind that approach: what it means to design for agency rather than safety, what cultural practices make such an approach practical and why a type system is the most underrated management tool in a company's arsenal. Jack Kelly - Staff Engineer Lambda on Lambda: Running Serverless Haskell Functions on AWS [AWS Lambda]([https://aws.amazon.com/lambda/](https://aws.amazon.com/lambda/)) is AWS's "function-as-a-service" offering, where your code runs in an isolated "microVM" on AWS-managed infrastructure and you pay only for the resources used while your code runs. Fitting your binaries into this model means making your code talk to some internal AWS APIs, and luckily the Haskell ecosystem has some good tools for doing this. In this talk, I'll explain at a high level what AWS Lambda is, how it executes your code, and then provide an opinionated guide and demo for getting your Haskell functions into the cloud. When and Where Format: Strictly IRL When: Thursday 21 May 2026, 6:00pm – 8:00pm Where: Kathleen Syme Centre, Activity Room 2, Carlton (Melbourne Victoria, Australia) RSVP: [luma](https://luma.com/uhdgct1v) About Melbourne Compose Group Melbourne Compose Group is the monthly in-person meetup for functional programmers in Melbourne, every 3rd Thursday of the month in Carlton. As always, newcomers welcome.

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Third CfP: Festschrift and Workshop in Honor of David Basin (Deadline extended to 11 June 2026)
by Achim D. Brucker 27 Apr '26

27 Apr '26

Dear Fellow Researchers! Our dear colleague and friend David Basin is turning 65 in December 2026 and this has to be celebrated! We therefore organize a Festschrift and a Fest to celebrate his birthday and his extensive research contributions! The Fest/celebration itself will be held as a one-day event on the 15th of January 2027 at ETH Zürich. We have already checked that David is available. You do not have to keep it a secret - on the contrary, it is great if you share this message with anybody who might like to contribute! We hereby cordially invite you to contribute an article to the Festschrift and present it at the Fest. We welcome contributions in all areas close to David's research and interests, including but not limited to security, privacy, formal methods, logic, automated reasoning, model checking, theorem proving, software engineering, bridge, juggling, biking and more. The articles will be lightly reviewed by the Festschrift committee, and the proceedings will be **published by Springer Heidelberg in the LNCS series**. David will of course love to receive a research article from you, but also short personal articles that celebrate the history and friendship with David will be very much appreciated. We would like to set a deadline for submissions at the 21st of May 2026 via our submission site <https://easychair.org/conferences/?conf=feschi2027>. Articles should be formatted in Springer’s LNCS style and not exceed 5 pages for personal articles and 16 pages for scientific articles. If you have a work that you would like to contribute that does not fit into this page limit, it might be possible, but please reach out to us first. There will be no participation fee for the Fest and coffee breaks, lunch, and dinner will be included. Travel and accommodation costs are at the expense of the participants. We are happy to provide hotel suggestions for Zürich. Submission Information: * Format: 16 pages in LNCS format, templates available at: <https://www.springer.com/gp/computer-science/lncs/conference-proceedings-gu…> * Submission: <https://easychair.org/conferences/?conf=feschi2027> * Website (under construction) with updates and further information: <https://feschi2027.github.io/> * Timeline: * Submission: 11 June 2026 (extended) * Notification: end of June 2026 (to be confirmed) * Camera Ready Copy: early September 2026 (to be confirmed) Please let us know if you have any questions! Best wishes Achim D. Brucker (University of Exeter) Sebastian Mödersheim (Danmarks Tekniske Universitet) Christoph Sprenger (ETH Zürich) Luca Viganò (King’s College London) -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Storing a Haskellwiki-page fails
by X Y 24 Apr '26

24 Apr '26

L.S., After editing a page at wiki.haskell.org, I tried to store the page and got the following error message: Database error A database query error has occurred. This may indicate a bug in the software. [274dd5bf9e736eea1c9a5c34] 2026-04-23 13:41:25: Fatal exception of type "Wikimedia\Rdbms\DBQueryError" Can someone solve this please? Regards, ಹೆಂಕ್-ಜಾನ್ ವ್ಯಾನ್ ಟುಯ್ಲ್ Henk-Jan van Tuyl

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Wiki account creation
by Vanessa McHale 06 Apr '26

06 Apr '26

Would it be possible for me to get a Wiki account? I sent something to wiki-account-request(a)haskell.org but that has been quiet. Preferred username would be vem or vmchale Cheers, Vanessa McHale

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Aeson
by Ivan Perez 03 Apr '26

03 Apr '26

Hi Café The aeson (https://github.com/haskell/aeson) package hasn't seen updates in a while. The last one I see is from Oct 2025. It's getting out of date wrt new versions of dependencies available on Hackage, such as QuickCheck. It's also heavily depended on. What's the best course of action here? What can be done to get this updated? Thanks, Ivan

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Enriching errors in the "network" library
by Kazu Yamamoto 02 Apr '26

02 Apr '26

Hi all, For many years, users of the "network" library have been suffered from poor error handling. For example, the "bind" function displays an error message like the following, but it doesn't tell you which port you were trying to bind to. Network.Socket.bind: resource busy (Address already in use) I am working to improve this situation. The error message becomes as follows: Network.Socket.bind: resource busy (Address already in use [EADDRINUSE] <socket: 13> [::1]:53) If you're interested, please join the discussion: https://github.com/haskell/network/pull/610 P.S. In my opinion, Show IOException should display errno. Why doesn't it display? instance Show IOException where showsPrec p (IOError hdl iot loc s _errno fn) = (case fn of Nothing -> case hdl of Nothing -> id Just h -> showsPrec p h . showString ": " Just name -> showString name . showString ": ") . (case loc of "" -> id _ -> showString loc . showString ": ") . showsPrec p iot . (case s of "" -> id _ -> showString " (" . showString s . showString ")") --Kazu

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tls v2.3.1
by Kazu Yamamoto 31 Mar '26

31 Mar '26

Hi all, I have just released the "tls" library version 2.3.1. As I said before, this version uses ML-KEM (Post-Quantum Cryptography) by default. Since no changes to the existing code are necessary, I released this as a minor version. However, ClientHello and ServerHello become larger by more than 1000 bytes. If the world breaks down, I will deprecate v2.3.1 and re-release a major version. I've written an explanatory article in Japanese. If you're interested, please read it using machine translation. https://eng-blog.iij.ad.jp/archives/35451 --Kazu

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Re: HasCallStack constraint for maximum in Prelude?
by Olaf Klinke 27 Mar '26

27 Mar '26

> Mind you there's a conflict between the suggested `foldMap'` > implementation for Bounded elements and efficient implementations > with ordered Foldable collections (Map, IntMap, Set, ...). > > The latter, just return quickly return the least or greatest element > without paying a linear cost to perform the proposed fold. ... which is why functions like sum, product, maximum and minimum have become Foldable class methods, to be overridden whenever it is more efficient. I fail to see how your boundedMinimum reduces time complexity. It is still a general fold in the non-empty case. I wonder, though, how sustainable it is to bloat the Foldable interface with special cases of foldMap that can be overridden. What special monoid structures do exist that warrant a specialized fold implementation? We have (1) commutative monoids, such as Sum and Product, (2) semilattices, where (x<>) is idempotent for every x, (3) Short-circuiting monoids such as First and Last, where either (x<>) or (<>x) is constant for x /= mempty. Evidently, for cases (2) and (3) there are examples where the short- circuiting behavior of the monoid itself can be leveraged to short- circuit foldMap. Does anyone know of a real-world example where sum and product are overridden? All instances Hoogle turns up are O(n). I can't cast that into a type signature right now, but I feel all of null, sum, product, maximum, minimum can be unified given a suitable sub-class that relates the particular Foldable f to the contraint (Ord, Num etc.) present in the head of the function. Olaf

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GHC 9.12.4 is now available
by Zubin Duggal 27 Mar '26

27 Mar '26

The GHC developers are very pleased to announce the release of GHC 9.12.4. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.4 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fixed a critical code generation regression where sub-word division produced incorrect results (#26711, #26668), similar to the bug fixed in 9.12.2 * Numerous fixes for register allocation bugs, preventing data corruption when spilling and reloading registers (#26411, #26526, #26537, #26542, #26550) * Fixes for several compiler crashes, including issues with CSE (#25468), and the simplifier(#26681), implicit parameters (#26451), and the type-class specialiser (#26682) * Fixed cast worker/wrapper incorrectly firing on INLINE functions (#26903) * Fixed LLVM backend miscompilation of bit manipulation operations (#20645, #26065, #26109) * Fixed associated type family and data family instance changes not triggering recompilation (#26183, #26705) * Fixed negative type literals causing the compiler to hang (#26861) * Improvements to determinism of compiler output (#26846, #26858) * Fixes for eventlog shutdown deadlocks (#26573) and lost wakeups in the RTS (#26324) * Fixed split sections support on Windows (#26696, #26494) and the LLVM backend (#26770) * Fixes for the bytecode compiler, PPC native code generator, and Wasm backend * The runtime linker now supports COMMON symbols (#6107) * Improved backtrace support: backtraces for `error` exceptions are now evaluated at throw time * `NamedDefaults` now correctly requires the class to be standard or have an in-scope default declaration, and handles poly-kinded classes (#25775, #25778, #25882) * ... 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://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.4-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.4 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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Call for Submissions: ICFP 2026 Student Research Competition
by Kimball Germane 27 Mar '26

27 Mar '26

ICFP 2026 Student Research Competition Call for Submissions ICFP 2026 invites students to participate in the Student Research Competition in order to present their research and get feedback from prominent members of the programming language research community. The SRC consists of three rounds: * Submission of an extended abstract * Poster session at ICFP 2026 * Finalists' presentations at ICFP 2026 During the first round students submit an extended abstract detailing their research to be reviewed by the program committee. Those students whose abstracts get accepted advance to the poster session round which will take place during ICFP 2026. Winners of the poster session advance to the next round, where they will give a 5-minute presentation about their work on the ICFP main stage in front of a live audience. IMPORTANT DATES AND TIMES * Submission Deadline: 11 May 2026 (Monday) * Author Notification: 1 June 2026 (Monday) * ICFP 2026 Conference in Indiana, USA: 24 August 2026 (Monday) - 26 August 2026 (Wednesday) SUBMISSION OF EXTENDED ABSTRACTS * Submission Website: https://icfp26src.hotcrp.com Each submission (referred to as "abstract" below) should include the student author's name and email address; institutional affiliation; research advisor's name; ACM student member number; category (undergraduate or graduate); research title; and an extended abstract addressing the following: * Problem and Motivation: Clearly state the problem being addressed and explain the reasons for seeking a solution to this problem. * Background and Related Work: Describe the specialized (but pertinent) background necessary to appreciate the work in the context of ICFP areas of interest. Include references to the literature where appropriate, and briefly explain where your work departs from that done by others. * Approach and Uniqueness: Describe your approach in addressing the problem and clearly state how your approach is novel. * Results and Contributions: Clearly show how the results of your work contribute to programming language design and implementation in particular and to computer science in general; explain the significance of those results. * Submissions must be original research that is not already published at ICFP or another conference or journal. One of the goals of the SRC is to give students feedback on ongoing, unpublished work. Furthermore, the abstract must be authored solely by the student. If the work is collaborative with others and/or part of a larger group project, the abstract should make clear what the student's role was and should focus on that portion of the work. * Formatting: Submissions must be in PDF format, printable in black and white on US Letter sized paper, and interpretable by common PDF tools. All submissions must adhere to the "ACM Small" template that is available (in both LaTeX and Word formats) from https://www.acm.org/publications/authors/submissions. For authors using LaTeX, a lighter-weight package, including only the essential files, is available from http://sigplan.org/Resources/Author/#acmart-format. The submission must not exceed 3 pages in PDF format. Reference lists do not count towards the 3-page limit. Further information is available at the ICFP SRC website: https://icfp26.sigplan.org/track/icfp-2026-src

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Re: HasCallStack constraint for maximum in Prelude?
by Olaf Klinke 26 Mar '26

26 Mar '26

> Adding that warning won't affect performance, but it would guide > people > to never use them (Especially Foldable variant; its type is wrong - > it > would make some sense with Bounded - if Bounded were related to Ord). > For (Bounded a, Ord a) one should replace maximum by an ordinary fold, given a suitable newtype wrapper with a Monoid instance, e.g. (Ord a, Bounded a) => Monoid (Data.Semigroup.Max a) In the past I've also used custom newtypes if e.g. I knew all values were non-negative and the least value I cared about was zero. -- Olaf

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Re: HasCallStack constraint for maximum in Prelude?
by Olaf Klinke 25 Mar '26

25 Mar '26

Mathematically, the least amount of structure needed for maximum and minimum is a bounded semilattice, which in contrast to the Bounded class requires only one bound to exist. Such structures are defined for example in the semilattices [1] and lattices [2] packages. The semilattices package provides the instances (Lower a, Join a) => Monoid (Joining a) (Upper a, Meet a) => Monoid (Meeting a) whereas the lattices package provides the BoundedJoinSemilattice and BoundedMeetSemilattice classes and the functions joins :: (BoundedJoinSemiLattice a, Foldable f) => f a -> a meets :: (BoundedMeetSemiLattice a, Foldable f) => f a -> a joins1 :: (Lattice a, Foldable1 f) => f a -> a meets1 :: (Lattice a, Foldable1 f) => f a -> a as well as the wrappers Meet and Join with appropriate Monoid instances to recover the joins and meets functions via foldMap. Olaf [1] https://hackage.haskell.org/package/semilattices [2] https://hackage.haskell.org/package/lattices

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Midlands Graduate School, 13-17 April 2026, Nottingham UK
by Graham Hutton (staff) 25 Mar '26

25 Mar '26

Dear all, *** Registration extended until Sunday 29th March *** There are just a few days left now to register for this years Midlands Graduate School (MGS) in Nottingham. Eight fantastic courses on type theory, category theory, lambda calculus and more. 13-17 April 2026, Nottingham, UK. Best wishes, Graham ========================================================== MIDLANDS GRADUATE SCHOOL 2026 13-17 April 2026, Nottingham, UK https://tinyurl.com/MGS-2026 ========================================================== BACKGROUND The Midlands Graduate School (MGS) in the Foundations of Computing Science provides a yearly programme of courses on the mathematical foundations of computing, and recently celebrated its 25th year. The MGS is primarily aimed at PhD students in their first or second year, but is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES Eight courses will be given. Participants usually take around four courses, depending on their interests. Invited course: - Implement your POPL paper (using Haskell) Stephanie Weirich (Pennsylvania) Introductory courses: - Type Theory using Agda Thorsten Altenkirch (Nottingham) - Category Theory Sergey Goncharov (Birmingham) - Lambda Calculus and Combinatory Algebra Sam Speight (Birmingham) Advanced courses: - Effects and Call-By-Push-Value Paul Blain Levy (Birmingham) - Synthetic Homotopy Theory Axel Ljungström (Nottingham) - Categorical Algebra and Logic Sean Moss (Birmingham) - Inductive and Coinductive Reasoning with Isabelle/HOL Andrei Popescu (Sheffield) REGISTRATION Student participants: £350 (or £600 with accommodation) Industry participants: £800 (or £1050 with accommodation) The registration fee includes all lecture courses and example classes, lunch and coffee breaks, and the conference dinner. The 'with accommodation' options include five nights at Rutland Hall with shared bathroom facilities. Registration closes Sunday 29th 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. LOCAL ORGANISERS For any queries, please contact the local organisers: Ulrik Buchholtz <ulrik.buchholtz(a)nottingham.ac.uk> Dan Marsden <dan.marsden(a)nottingham.ac.uk> ========================================================== -- Professor Graham Hutton School of Computer Science University of Nottingham, UK http://people.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.

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HasCallStack constraint for maximum in Prelude?
by Todd Wilson 24 Mar '26

24 Mar '26

Should maximum and minimum have HasCallStack constraints like head and tail do? ghci> :type head head :: GHC.Stack.Types.HasCallStack => [a] -> a ghci> head [] *** Exception: Prelude.head: empty list CallStack (from HasCallStack): error, called at libraries/base/GHC/List.hs:1646:3 in base:GHC.List errorEmptyList, called at libraries/base/GHC/List.hs:85:11 in base:GHC.List badHead, called at libraries/base/GHC/List.hs:81:28 in base:GHC.List head, called at <interactive>:8:1 in interactive:Ghci1 ghci> :type maximum maximum :: (Foldable t, Ord a) => t a -> a ghci> maximum [] *** Exception: Prelude.maximum: empty list CallStack (from HasCallStack): error, called at libraries/base/GHC/List.hs:1646:3 in base:GHC.List errorEmptyList, called at libraries/base/GHC/List.hs:717:28 in base:GHC.List maximum, called at libraries/base/Data/Foldable.hs:745:15 in base:Data.Foldable Todd Wilson

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Functional design question
by Joachim Durchholz 24 Mar '26

24 Mar '26

Hi all, I have some design questions - not for Haskell but for the Java+Vavr combo, but I am about to dip my toes into actual work in a functional manner, as far as that is possible, and I thought I might as well go for the community that's best subscribed to a purely functional style. Bird's eye view: Java everybody knows (I don't like it either, no worries), Vavr is a - to my eyes - pretty nice functional library, https://docs.vavr.io/ for details if you're actually interested. I want to leverage Vavr to get a Java program to be as Haskell-ish as is reasonable; that's not going to be much by a Haskeller's standards, but... baby steps. Application is a simple command-line thing: Read configuration from command line and configuration file, emit diagnostics about any errors in the config, then process. I want the configuration processing to be as functional as reasonable, given the constraints. However, I'm undecides about many things, no doubt because I simply don't know the best design patterns, and it's frustrating to see multiple options and not knowing which ones will paint me into a corner and which ones will not. Things I'm undecided about: a) Data type variations During the configuration phase, I need to carry information about where some configuration item came from (its ("context", usually file, line number, column number). In the processing phase, configuration is considered final and error-free, so context is not needed (that's a done design decision). I could carry context information into the processing phase, but it's going to be awkward: Say, we have the following types (forgive the most un-Haskellish pseudo syntax but I don't dare to use Haskell style because I'd almost certainly get that wrong and provoke misunderstandings) DirectoryConfig { ConfigData<Path> path ConfigData<String> title ... } data ConfigData<a> { String fileName int lineNumber int columnNumber a value } but in the processing phase I don't want my config objects polluted with context, so I want DirectoryConfig { Path path String title ... } No idea how to deal with that. I'd use code generation in Java I guess, but that's horribly inelegant and complicated to set up (no, I don't particularly like Java, it's just what I'm currently using). So... how would one do such a thing in a functional language? Not necessarily Haskell, I guess some language extensions exist for that kind of stuff, but I'm more-or-less tied to Java + functional libraries, so I'll have to stick with the more basic approaches most likely. Besides, even if I did Haskell, I'd want to avoid the advanced stuff until I get confident in the basics. TL;DR: I have a deeply nested configuration data structure where each field has a "context", i.e. the place it came from; how to I make it so that the context is available during configuration evaluation but is unavailable in the later processing phase? I hope this is understandable; it's really hard to do that when you don't even know enough to ask the questions precisely enough. Regards, Jo

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AI for Math Summer Fellowship -- Copilots for Isabelle (Sheffield / Copenhagen / London): application deadline April 10
by Andrei Popescu 21 Mar '26

21 Mar '26

Dear Colleagues, We are pleased to advertise an AI for Math Summer Fellowship opportunity on the project "Copilots for Isabelle: Learning Logical Structure for a Better Proving Experience". The general call and application details (including an application link) can be found here: https://docs.google.com/document/d/1tXlT2A2NyLi_N-Fn1Q5zwG6J0b8Cwhzj/edit Please note that the application deadline is April 10, and the internship will run for 10 weeks, from June 15 to August 21, 2026. In this project, the selected fellow will work with researchers at the University of Sheffield, University of Copenhagen, and King’s College London on developing AI-based copilots for the Isabelle proof assistant. The aim is to leverage the rich structure of interactive proofs to build intelligent tools that assist with proof development, documentation, and automation. The fellowship offers the opportunity to work on topics such as: -- generating polished proofs from informal or partial drafts, -- automatically producing documentation for Isabelle/ML code, -- adapting and tuning LLMs for proof tasks. The position is open to undergraduate, master’s and PhD students, and can be carried out in Sheffield, Copenhagen, or London (with support for travel if needed). Please see the attached project description for further details. Best wishes, Andrei, Dmitriy and Mohammad

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GHC 9.12.4-rc1 is now available
by Zubin Duggal 18 Mar '26

18 Mar '26

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.12.4. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.4 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fixed a critical code generation regression where sub-word division produced incorrect results (#26711, #26668), similar to the bug fixed in 9.12.2 * Numerous fixes for register allocation bugs, preventing data corruption when spilling and reloading registers (#26411, #26526, #26537, #26542, #26550) * Fixes for several compiler crashes, including issues with CSE (#25468), SetLevels (#26681), implicit parameters (#26451), and the type-class specialiser (#26682) * Fixed cast worker/wrapper incorrectly firing on INLINE functions (#26903) * Fixed LLVM backend miscompilation of bit manipulation operations (#20645, #26065, #26109) * Fixed associated type family and data family instance changes not triggering recompilation (#26183, #26705) * Fixed negative type literals causing the compiler to hang (#26861) * Improvements to determinism of compiler output (#26846, #26858) * Fixes for eventlog shutdown deadlocks (#26573) and lost wakeups in the RTS (#26324) * Fixed split sections support on Windows (#26696, #26494) and the LLVM backend (#26770) * Fixes for the bytecode compiler, PPC native code generator, and Wasm backend * The runtime linker now supports COMMON symbols (#6107) * Improved backtrace support: backtraces for `error` exceptions are now evaluated at throw time * `NamedDefaults` now correctly requires the class to be standard or have an in-scope default declaration, and handles poly-kinded classes (#25775, #25778, #25882) * ... 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][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 26 March 2026. 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://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.4-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.4-rc1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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Midlands Graduate School, 13-17 April 2026, Nottingham
by Graham Hutton (staff) 17 Mar '26

17 Mar '26

Dear all, There are just a few days left now to register for this years Midlands Graduate School (MGS) in Nottingham. Eight fantastic courses on type theory, category theory, lambda calculus and more. 13-17 April 2026, Nottingham, UK. Registration closes Sunday 22nd March. Best wishes, Graham ========================================================== MIDLANDS GRADUATE SCHOOL 2026 13-17 April 2026, Nottingham, UK https://tinyurl.com/MGS-2026 ========================================================== BACKGROUND The Midlands Graduate School (MGS) in the Foundations of Computing Science provides a yearly programme of courses on the mathematical foundations of computing, and recently celebrated its 25th year. The MGS is primarily aimed at PhD students in their first or second year, but is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES Eight courses will be given. Participants usually take around four courses, depending on their interests. Invited course: - Implement your POPL paper (using Haskell) Stephanie Weirich (Pennsylvania) Introductory courses: - Type Theory using Agda Thorsten Altenkirch (Nottingham) - Category Theory Sergey Goncharov (Birmingham) - Lambda Calculus and Combinatory Algebra Sam Speight (Birmingham) Advanced courses: - Effects and Call-By-Push-Value Paul Blain Levy (Birmingham) - Synthetic Homotopy Theory Axel Ljungström (Nottingham) - Categorical Algebra and Logic Sean Moss (Birmingham) - Inductive and Coinductive Reasoning with Isabelle/HOL Andrei Popescu (Sheffield) REGISTRATION Student participants: £350 (or £600 with accommodation) Industry participants: £800 (or £1050 with accommodation) The registration fee includes all lecture courses and example classes, lunch and coffee breaks, and the conference dinner. The 'with accommodation' options include five nights at Rutland Hall with shared bathroom facilities. Registration closes Sunday 22nd 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. LOCAL ORGANISERS For any queries, please contact the local organisers: Ulrik Buchholtz <ulrik.buchholtz(a)nottingham.ac.uk> Dan Marsden <dan.marsden(a)nottingham.ac.uk> ========================================================== -- Professor Graham Hutton School of Computer Science University of Nottingham, UK http://people.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.

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Hackage down?
by Ivan Perez 13 Mar '26

13 Mar '26

Hi cafe, I just received this when trying to access hackage: Error 503 Backend unavailable, connection timeout Backend unavailable, connection timeout Error 54113 Details: cache-pao-kpao1770051-PAO 1773366957 2060396358 ------------------------------ Varnish cache server Is this known? Thanks, Ivan

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Second CfP: Festschrift and Workshop in Honor of David Basin (Deadline: 21st May 2026)
by Achim D. Brucker 10 Mar '26

10 Mar '26

Dear Fellow Researchers! Our dear colleague and friend David Basin is turning 65 in December 2026 and this has to be celebrated! We therefore organize a Festschrift and a Fest to celebrate his birthday and his extensive research contributions! The Fest/celebration itself will be held as a one-day event on the 15th of January 2027 at ETH Zürich. We have already checked that David is available. You do not have to keep it a secret - on the contrary, it is great if you share this message with anybody who might like to contribute! We hereby cordially invite you to contribute an article to the Festschrift and present it at the Fest. We welcome contributions in all areas close to David's research and interests, including but not limited to security, privacy, formal methods, logic, automated reasoning, model checking, theorem proving, software engineering, bridge, juggling, biking and more. The articles will be lightly reviewed by the Festschrift committee, and the proceedings will be **published by Springer Heidelberg in the LNCS series**. David will of course love to receive a research article from you, but also short personal articles that celebrate the history and friendship with David will be very much appreciated. We would like to set a deadline for submissions at the 21st of May 2026 via our submission site <https://easychair.org/conferences/?conf=feschi2027>. Articles should be formatted in Springer’s LNCS style and not exceed 5 pages for personal articles and 16 pages for scientific articles. If you have a work that you would like to contribute that does not fit into this page limit, it might be possible, but please reach out to us first. There will be no participation fee for the Fest and coffee breaks, lunch, and dinner will be included. Travel and accommodation costs are at the expense of the participants. We are happy to provide hotel suggestions for Zürich. Submission Information: * Format: 16 pages in LNCS format, templates available at: <https://www.springer.com/gp/computer-science/lncs/conference-proceedings-gu…> * Submission: <https://easychair.org/conferences/?conf=feschi2027> * Website (under construction) with updates and further information: <https://feschi2027.github.io/> * Timeline: * Submission: 21 May 2026 * Notification: end of June 2026 (to be confirmed) * Camera Ready Copy: early September 2026 (to be confirmed) Please let us know if you have any questions! Best wishes Achim D. Brucker (University of Exeter) Sebastian Mödersheim (Danmarks Tekniske Universitet) Christoph Sprenger (ETH Zürich) Luca Viganò (King’s College London) -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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PhD Position in Bridging the Gap Between Mathematical Numbers and Software Systems (Deadline: 2026-03-22)
by Achim D. Brucker 10 Mar '26

10 Mar '26

We are seeking an enthusiastic PhD candidate with a strong background in computer science, software engineering, mathematics, or closely related fields. Expertise in formal methods such as program reasoning, programming language semantics, model checking, theorem proving, or computational logic is essential. Mathematical models, e.g., describing physical systems or cryptographic algorithms, rely on ideal numbers. For instance, mathematical integers are infinite and mathematical reals continuous and infinite. Computers work with finite approximations that are bounded (i.e., there is a smallest and largest number) and discrete. This "digital gap" between mathematical models and actual systems is a challenge when implementing safety-critical or security-critical systems: for example, autonomous aircraft or self-driving cars require high-precision representations of their position to avoid collisions. Hence, not considering the approximation of the approximative representation of numbers in computers can result in crashes that can endanger the life of humans. Moreover, many security-critical systems, not limited to cryptographic algorithms, rely on the correct handling of over- and underflows in integer computations. Actually, underflow- and overflow bugs are a root cause for a large number vulnerabilities exploited by cyber security criminal, e.g., for stealing digital currencies worth several billion of dollars. While this is not a new problem (e.g., already in 1982, an float conversion error in a trading systems at the Vancouver Stock Exchange resulted in a loss of several millions of US dollars), an integrated development method preventing such bugs is still not available. This PhD project will address this challenge by developing a rigour approach for developing systems relying on precise representations of numbers, using the interactive theorem prover Isabelle/HOL. The PhD project can focus on 1) the formalisation of concrete representations of machine numbers (e.g., IEEE754, POSIT, Decimal Floating Point, Fixed Point Arithmetic), their (algebraic) properties, and relationship to abstract mathematical numbers; 2) the formalisation and verification of numerical or cryptographic algorithms, establishing a reusable verified library, or 3) the development of an end-to-end refinement approach from mathematical models to machine representations. The PhD will be jointly supervised by Prof. Dr. Achim Brucker (<a.brucker(a)exeter.ac.uk>) and Prof. Dr. Burkhart Wolff (<burkhart.wolff(a)universite-paris-saclay.fr>), leading to a joint degree from the University of Exeter and the University of Paris-Saclay. Information about the programme can be found at * <https://www.exeter.ac.uk/study/pg-research/funding/phdfunding/paris-saclay/> * <https://adum.fr/as/ed/voirproposition.pl?langue=en&matricule_prop=71068&sit…> All applications have to be made via the ADUM system: <https://adum.fr/as/ed/voirproposition.pl?langue=en&matricule_prop=71068&sit…>, latest on the 22nd of March 2026. Best, Achim (and Bukrhart) -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Call for Participation: Workshop on AI and Theorem Provers in Mathematics (AITPM)
by Achim D. Brucker 10 Mar '26

10 Mar '26

The Workshop on AI and Theorem Provers in Mathematics (AITPM) will explore with leading experts some of the recent developments related to the use of AI and theorem provers in mathematics as well as the perspectives for such future use. - Workshop website: https://aitpm.github.io/ - Venue: Online - Attendance is free. - Registration: https://forms.office.com/e/c7gth3Rb6Q - Date: 8. - 10. April 2026 ## Speakers - Kevin Buzzard (Imperial College) - Minhyong Kim (International Centre for Mathematical Sciences, Edinburgh) - Yang-Hui He (London Institute for Mathematical Sciences) - Paola Iannone (University of Edinburgh) - Shinichi Mochizuki (Research Institute for Mathematical Sciences Kyoto) - Leonardo De Moura (Amazon Web Services) - Lawrence Paulson (University Cambridge) - Chelsea Edmonds (University of Western Australia) - Patrick Massot (University Paris Saclay) ## Programme Schedule (to be confirmed) The preliminary schedule of the workshop is: * April 8th 2026 * 08:00-09:00 Kevin Buzzard * 09:15-10:15 Paola Iannone * 10:45-11:45 Lawrence Paulson * 12:00-13:00 Discussion/panel session * April 9th 2026 * 08:00-09:00 Chelsea Edmond * 09:15-10:15 Yang Hui Heen * 10:45-11:45 Shinichi Mochizuki * 12:00-13:00 Discussion session * April 10th 2026 * 15:00-16:00 Patrick Massot * 16:15-17:15 Leonardo De Moura * 17:45-18:45 Natarajan Shankar (tbc) * 19:00-20:00 Discussion/panel session and closure All times are BST (i.e., London, observing daylight saving time). ## Organisers - Mohamed Saidi (Department of Mathematics and Statistics, University of Exeter) - Barrie Cooper (Department of Mathematics and Statistics, University of Exeter) - Gihan Marasingha (Department of Mathematics and Statistics, University of Exeter) - Achim D. Brucker (Department of Computer Science, University of Exeter) - Diego Marmsoler (Department of Computer Science, University of Exeter) -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Cabal transitive constraint puzzle
by Viktor Dukhovni 06 Mar '26

06 Mar '26

Dear Cafe and GHC-devs, I am happy to see that Yamamoto-san (cc:d) (the maintainer of the `tls` package) is extending it to include support for MLKEM key agreement. This in turn depends on the `mlkem` library by Olivier Chéron (also many thanks!). Now it turns out that for maximum portability, `mlkem` in turn has a build flag `use_crypton` that selects either `crypton`, or (current default) the older `cryptonite` library as its dependency. So the dependen graph is: tls <- mlkem <- if (use_crypton): crypton else: cryptonite But, at this, point `tls` is crypton-only, and no longer builds with the older cryptonite equivalents. Therefore `tls` adds constraints: mlkem +use_crypton to its `cabal.project` file, which solves the problem for `tls`, but sadly not for any projects that in turn depend on `tls`. To them the constraints in the `cabal.project` file of `tls` are effectively invisible. Since the default flag value in `mlkem` is for now `use_crypton: false`, each project that wants to use the (work-in-progress) `tls` appears to need to explictly know that `tls` requires a non-default build of `mlkem`, and must add the same constraints to its `cabal.project`. That transitive explicit configuration requirement is not something one can reasonably ask projects that depend on `tls to have to add. And of course, more generally, any other such indirect flag-dependent conflict must not become a burden on all consumers of library B that is only compatible with a specific variant of library C. How is this situation supposed to be handled? Is there something in cabal that can automatically convince the solver to select a setting of the `mlkem` flag that is compatible with `tls`? Must `mlkem` be forked instead to be two libraries, one dependent on `cryptonite` and another dependent on `crypton`? I've been unable to find a satisfactory workaround. Any help appreciated. -- Viktor.

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How to unsubscribe?
by Tom Ellis 05 Mar '26

05 Mar '26

Does the footer appear like this to everyone else? _______________________________________________ Haskell-Cafe mailing list -- haskell-cafe(a)haskell.org To (un)subscribe, modify options or view archives go to: Only members subscribed via the mailman list are allowed to post. "go to" where? Does anyone know how to unsubscribe? Thanks, Tom

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Hackage treatment of source code
by Olaf Klinke 02 Mar '26

02 Mar '26

In the past I had no problem with copy & paste from the colorized html that is produced by haddock. Perhaps some browsers/window managers attempt to copy html as html and not plain text, which may obfuscate this experience. As Brandon said, download & unpack the tar.gz linked from a package's main page to obtain the raw source. No need to reach for cabal. Olaf

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Hackage treatment of source code
by Douglas McIlroy 01 Mar '26

01 Mar '26

Hackage allows one to retrieve "source". However, the so-called source code can't be used, because it is a colorized .html file, not .hs. Even if one wants to use only a snippet of what's on the screen, one must turn to the heavy artillery of Cabal to get it. Can there not be an option to retrieve plain text from Hackage without interposing the colorizer? Doug McIlroy

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Appreciation
by Volker Wysk 01 Mar '26

01 Mar '26

Hi! I've set up my Haskell environment with GHCup and Cabal and compiled a program of mine. It has worked really really well. The developers have my thanks and appreciation. Cheers, Volker

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finding out ghc version from closed issue
by Zoran Bošnjak 28 Feb '26

28 Feb '26

Dear members, I am facing this problem with ghc-9.10.3: https://gitlab.haskell.org/ghc/ghc/-/issues/25477 It looks like the problem is already fixed at some later version. My question is... how do I find out the ghc version from the issue or from the git commit? Zoran

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tls: Hybrid key exchange of ECC and Post-Quantum
by Kazu Yamamoto 27 Feb '26

27 Feb '26

Hello, TLS client of OpenSSL version 3.5 or later specifies hybrid key exchange of ECC and Post-Quantum (such as X25519MLKEM768) and an ECC key exchange (such as X25519) in TLS ClientHello. I have implemented both the hybrid algorithms and the OpenSSL specifying-method in the Haskell "tls" library. Interop with OpenSSL is quite good. I would like to discuss how to specify algorithms in ClientHello before releasing. If you are interested, I would like to invite you to this issue: https://github.com/haskell-tls/hs-tls/issues/516 I thank Olivier Chéron for implementing excellent "mlkem" library. --Kazu

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Midlands Graduate School, 13-17 April 2026, Nottingham, UK
by Graham Hutton (staff) 26 Feb '26

26 Feb '26

Dear all, Registration is now open for the Midlands Graduate School (MGS) in Nottingham! Eight fantastic courses on type theory, category theory, lambda calculus, and more. 13-17 April 2026, Nottingham, UK. Registration closes Sunday 22nd March. Best wishes, Graham ========================================================== MIDLANDS GRADUATE SCHOOL 2026 13-17 April 2026, Nottingham, UK https://tinyurl.com/MGS-2026 ========================================================== BACKGROUND The Midlands Graduate School (MGS) in the Foundations of Computing Science provides a yearly programme of courses on the mathematical foundations of computing, and recently celebrated its 25th year. The MGS is primarily aimed at PhD students in their first or second year, but is open to everyone, and has increasingly seen participation from industry. We welcome participants from all over the world! COURSES Eight courses will be given. Participants usually take around four courses, depending on their interests. Invited course: - Implement your POPL paper (using Haskell) Stephanie Weirich (Pennsylvania) Introductory courses: - Type Theory using Agda Thorsten Altenkirch (Nottingham) - Category Theory Sergey Goncharov (Birmingham) - Lambda Calculus and Combinatory Algebra Sam Speight (Birmingham) Advanced courses: - Effects and Call-By-Push-Value Paul Blain Levy (Birmingham) - Synthetic Homotopy Theory Axel Ljungström (Nottingham) - Categorical Algebra and Logic Sean Moss (Birmingham) - Inductive and Coinductive Reasoning with Isabelle/HOL Andrei Popescu (Sheffield) REGISTRATION Student participants: £350 (or £600 with accommodation) Industry participants: £800 (or £1050 with accommodation) The registration fee includes all lecture courses and example classes, lunch and coffee breaks, and the conference dinner. The 'with accommodation' options include five nights at Rutland Hall with shared bathroom facilities. Registration closes Sunday 22nd 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. LOCAL ORGANISERS For any queries, please contact the local organisers: Ulrik Buchholtz <ulrik.buchholtz(a)nottingham.ac.uk> Dan Marsden <dan.marsden(a)nottingham.ac.uk> ========================================================== -- Professor Graham Hutton School of Computer Science University of Nottingham, UK http://people.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.

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Call for Talks: Haskell Implementors' Workshop 2026
by Christiaan Baaij 19 Feb '26

19 Feb '26

Haskell Implementors' Workshop 2026 https://haskell.foundation/events/2026-haskell-implementors-workshop.html June 5, 2026 Organized by the Haskell Community Co-located with ZuriHac 2026 and Haskell Ecosystem Workshop 2026 Hosted by the Haskell Foundation at Eastern Switzerland University of Applied Sciences (OST) https://www.ost.ch/en/university-of-applied-sciences/campus/rapperswil-jona… Important dates --------------- Deadline: April 10, 2026 (AoE) Notification: May 8, 2026 Workshop: June 5, 2026 The 18th Haskell Implementors' Workshop is to be held alongside ZuriHac 2026 this year near Zurich. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure to share their work and to discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos, and short lightning talks. Scope and target audience ------------------------- The Implementors' Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community are encouraged to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are especially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Talks ----- We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words. Submissions can be made via this form https://forms.gle/S8fpAgFaFEvqoMqH6 until April 10 (anywhere on earth). We will also have a lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks should be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Program Committee ----------------- * Andrew Lelechenko * Avi Press * Christiaan Baaij (chair) * Gergo Erdi * Jeffrey Young Contact ------- * Christiaan Baaij <chrisitaan.baaij at gmail.com>

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[ANN] Copilot 4.6.1
by Ivan Perez 12 Feb '26

12 Feb '26

Hi café! We are really excited to announce Copilot 4.6.1 [1, 2]. Copilot is a stream-based EDSL in Haskell for writing and monitoring embedded systems, 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. Compilation to Bluespec, to target FPGAs, is also supported. Copilot is 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 programming language and runtime framework for NASA's Core Flight System, Robot Operating System (ROS 2) and FPrime (the software framework used in the Mars Helicopter). Ogma now supports producing flight and robotics applications directly in Copilot, not just for monitoring, but for implementing the logic of the applications themselves. This release improves the Bluespec backend, fixing corner cases related to the generation of Bluespec (and thus Verilog). The release also introduces some general maintenance improvements. Copilot is compatible with versions of GHC from 8.6 to 9.12. This release has been made possible thanks to Chris Hathhorn (Galois) and Trevor Kann (Galois). The team also benefited from discussions with Ryan Scott (Galois). We are grateful to all of them for their contributions, and for making Copilot better every day. For details on this release, see [1]. As always, we're releasing exactly 2 months since the last release. Our next release is scheduled for Mar 7th, 2026. We want to remind the community that Copilot is now accepting code contributions from external participants again. Please see the discussions and the issues in our Github repo [4] to learn how to participate. Current emphasis is on using Copilot for full data processing applications (e.g, system control, arduinos, rovers, drones), improving usability, performance, and stability, increasing test coverage, removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our coding standards. Users are encouraged to participate by opening issues, asking questions, extending the implementation, and sending bug fixes. Happy Haskelling! Ivan -- [1] https://github.com/Copilot-Language/copilot/releases/tag/v4.6.1 [2] https://hackage.haskell.org/package/copilot [3] https://github.com/nasa/ogma [4] https://github.com/Copilot-Language/copilot

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