March 2025 - Haskell-Cafe

Best way to implement "scoped exceptions"?
by Tom Ellis 28 May '25

28 May '25

I'd like to implement "scoped exceptions"[1], that is, a combinator of type withScopedException :: ((forall a. e -> IO a) -> IO r) -> IO (Either e r) so I can use exceptions in a convenient way, without having to set up fragile "action at a distance" based on the type of the thing I'm throwing and catching, for example: scopedExceptionExample :: IO (Either String (Either Int Void)) scopedExceptionExample = do withScopedException $ \throw1 -> withScopedException $ \throw2 -> if (1 :: Int) < 0 then throw1 "Hello" else throw2 1234 -- ghci> scopedExceptionExample -- Right (Left 1234) Here's a hacky way of doing it, based on tagging each exception with a unique value, and then filtering when handling: data MyException where MyException :: e -> Data.Unique.Unique -> MyException instance Show MyException where show _ = "<MyException>" instance Exception MyException withScopedException :: ((forall a. e -> IO a) -> IO r) -> IO (Either e r) wiathScopedException f = do fresh <- Data.Unique.newUnique flip tryJust (f (\e -> throwIO (MyException e fresh))) $ \case MyException e tag -> -- unsafeCoerce is very unpleasant if tag == fresh then Just (unsafeCoerce e) else Nothing This is the approach taken by the effectful library[2]. But is there a better way? Can I persuade GHC's RTS to work like this directly? Tom [1] I don't know if these already have a name [2] https://hackage.haskell.org/package/effectful-core-2.2.1.0/docs/src/Effectf…

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dumping ByteArray#
by Kazu Yamamoto 29 Mar '25

29 Mar '25

Hello, For debugging, I need to dump the inside of `ByteArray#`. Are there any utility functions for this purpose? --Kazu

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implementing a class using superclasses?
by Mark McConnell 29 Mar '25

29 Mar '25

Here is a simplified, self-contained version of some code I'm working on. I have a Ord type Foo that I want to be ordered primarily by comp1, and, in case of ties, secondarily by comp2. It is important to my users to know that the primary sorting will always be by comp1. Therefore, I am trying to use to the type system to articulate that Foo must be ordered in a two-fold lexicographic way. My code is module Lex2Test where class Ord a => Primary a where comp1 :: a -> a -> Ordering comp1 = compare class Ord a => Secondary a where comp2 :: a -> a -> Ordering comp2 = compare class (Primary a, Secondary a) => Lex2 a instance Lex2 a => Ord a where compare x y = comp1 x y <> comp2 x y However, when I load the code into ghci, I get Lex2Test.hs:13:10: error: • The constraint ‘Lex2 a’ is no smaller than the instance head ‘Ord a’ (Use UndecidableInstances to permit this) • In the instance declaration for ‘Ord a’ |13 | instance Lex2 a => Ord a where | ^^^^^^^^^^^^^^^ I feel I must be missing something. UndecidableInstances seems too extreme for what I am trying to do. (I have never said that I want to go backwards in class inference from Ord to Lex2.) If this were C++, I would be just trying to implement some virtual functions in terms of other virtual functions. Any comments would be appreciated.

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Call for Nominations: SLE 2025 - Artifact Evaluation Committee, Nominations Wanted
by Andrei Chis 28 Mar '25

28 Mar '25

18th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2025) 12-13 June 2025 Koblenz, Germany https://conf.researchr.org/home/sle-2025 https://www.sleconf.org/2025/ https://x.com/sleconf ------------------------------------------------------------------------ The SLE 2025 Artifact Evaluation Committee (AEC) is looking for nominations and self-nominations for committee members. If you are a PhD student, postdoctoral researcher, associate, or professor working in software language engineering, we encourage you to apply. Serving on the AEC is an excellent opportunity to contribute to the community and gain valuable experience in artifact evaluation. -------------------------------------- Important Dates (All deadlines are AoE) -------------------------------------- Artifact submission deadline: April 23, 2025 Artifact bidding: April 24–26, 2025 Camera-ready deadline for SLE papers: May 1, 2025 Kick-the-tires review deadline & rebuttal phase: May 2, 2025 Final review deadline: May 24, 2025 Artifact discussion: May 25–31, 2025 Artifact notification: June 1, 2025 ------------------------------------------------------------------------ To nominate yourself or someone else, please complete the following form by April 6, 2025 Form: https://docs.google.com/forms/d/15Q-9i1tCwHzrtdtRqfJbWqZs4hV7DnJfwBSZuop75b… For any questions, please do not hesitate to contact us. SLE 2025 Artifact Evaluation Co-Chairs, Idriss Riouak and Jeff Smits Idriss Riouak: idriss.riouak(a)cs.lth.se Jeff Smits: j.smits-1(a)tudelft.nl

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Haskell Symposium 2025 First Call for Papers
by Ningning Xie 28 Mar '25

28 Mar '25

======================================================================== Haskell Symposium 2025 Call for Papers Thu 16 - Fri 17 Oct 2025, Singapore https://conf.researchr.org/home/icfp-splash-2025/haskellsymp-2025 ======================================================================== The ACM SIGPLAN Haskell Symposium 2025 will be co-located with the 2025 International Conference on Functional Programming (ICFP) and the 2025 International Conference on Systems, Programming, Languages and Applications: Software for Humanity (SPLASH). The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative programming. Submission deadline: 9 June 2025 (Mon) Notification: 17 July 2025 (Thu) Deadlines are valid anywhere on Earth. Papers should be submitted through HotCRP at: https://haskell25.hotcrp.com/ Topics of interest include: * Language design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts; * Tutorials, to document how to use a particular language feature, programming technique, tool or library within the Haskell ecosystem; * System Demonstrations, based on running software rather than novel research results. Program Committee ================= Andreas Abel Gothenburg University Patrick Bahr IT University of Copenhagen Matthew Fluet Rochester Institute of Technology Adam Gundry Well-Typed LLP Xuejing Huang IRIF Hideya Iwasaki Meiji University Patricia Johann Appalachian State University Hsiang-Shang 'Josh' Ko Institute of Information Science, Academia Sinica András Kovács University of Gothenburg and Chalmers University of Technology Andres Löh Well-Typed LLP J. Garrett Morris (co-chair) University of Iowa Liam O'Connor Australian National University Maciej Piróg University of Wrocław Arnaud Spiwack Tweag Meng Wang University of Bristol Li-yao Xia Inria Ningning Xie (co-chair) University of Toronto Gergő Érdi Standard Chartered Bank If you have questions, please contact the chairs at: ningningxie(a)cs.toronto.edu and garrett-morris(a)uiowa.edu.

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CFP - Haskell Implementors' Workshop 2025
by Andreas Herrmann 27 Mar '25

27 Mar '25

Call for proposals for the Haskell Implementors' Workshop https://haskell.foundation/events/2025-haskell-implementors-workshop.html June 6, 2025 Organized by the Haskell Community Co-located with ZuriHac 2025 and Haskell Ecosystem Workshop 2025 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… ## Overview * Deadline: April 4, 2025 * Notification: May 5, 2025 * Workshop: June 6, 2025 The 17th Haskell Implementors' Workshop is to be held alongside ZuriHac 2025 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 lightning talks. In the past the Haskell Implementors’ Workshop was co-located with ICFP (International Conference on Functional Programming). However, in recent years it has become more and more challenging to attract a large enough audience and sufficiently many speakers for an appealing program. ZuriHac and the Haskell Ecosystem Workshop have become an important annual gathering of a large part of the Haskell community. This year the Haskell Implementors’ Workshop will be co-located with these events to be accessible to a broader audience. ## Scope and Target Audience The Haskell 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, optimization 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. Submissions can be made via the form linked below until April 4, 2025 (anywhere on earth). https://docs.google.com/forms/d/e/1FAIpQLSdczGbxJYGc4eusvPrxwBbZl561PnKeYno… We will also have a lightning talks session. 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 * Luite Stegeman * Jaro Reinders * Emily Pillmore * Rodrigo Mesquita * Ian-Woo Kim * Andreas Herrmann (chair) ## Contact * Andreas Herrmann

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Call for Papers, Functional Software Architecture (Deadline June 16)
by Michael Sperber 26 Mar '25

26 Mar '25

====================================================================== *** FUNARCH 2025 -- CALL FOR PAPERS *** Third ACM SIGPLAN Workshop on Functional Software Architecture - FP in the Large 17th October 2025, Singapore Co-located with ICFP 2025 https://functional-architecture.org/events/funarch-2025/ ====================================================================== TIMELINE: Paper submission 16th June 2025 Author notification 21st July 2025 Camera ready copy 25th August 2025 Workshop 17th October 2025 BACKGROUND: "Functional Software Architecture" refers to methods of construction and structure of large and long-lived software projects that are implemented in functional languages and released to real users, typically in industry. The goals for the workshop are: - To assemble a community interested in software architecture techniques and technologies specific to functional programming; - To identify, categorize, and document topics relevant to the field of functional software architecture; - To connect the functional programming community to the software architecture community to cross-pollinate between the two. The workshop follows on from the Functional Software Architecture open space that was held at ICFP 2022 in Slovenia. SCOPE: The workshop seeks submissions in a range of categories: - You're a member of the FP community and have thought about how to support programming in the large, for example by framing functional ideas in architectural terms or vice verse, comparing different languages in terms of their architectural capabilities, clarifying architectural roles played by formal methods, proof assistants and DSLs, or observing how functional concepts are used in other language and architecture communities. Great, submit a research paper! - You're a member of the architecture community, and have thought about how your discipline might help functional programmers, for example by applying domain-driven design, implementing hexagonal architecture, or designing self-contained systems. Excellent, submit a research paper! - You've worked on a large project using functional programming, and it's worked out well, or terribly, or a mix of both; bonus points for deriving architectural principles from your experience. Wonderful, submit an experience report! - You know a neat architectural idiom or pattern that may be useful to others developing large functional software systems. Fabulous, submit an architectural pearl! - You have something that doesn't fit the above categories, but that still relates to functional software architecture, such as something that can be written up, or that could be part of the workshop format like a panel debate or a fishbowl. Superb, submit to the open category! Research papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. Experience reports and architectural pearls need not necessarily report original research results. The key criterion for such papers is that they make a contribution from which others can benefit. It is not enough simply to describe a large software system, or to present ideas that are specific to a particular system. Open category submissions that are not intended for publication are not required to follow the formatting guidelines, and can submit in PDF, word or plain text format as preferred. Not knowing what kinds of submissions we will receive, we cannot be specific as to how they will be evaluated. However, submissions that seem likely to stimulate discussion around practices in functional architecture are encouraged. If you are unsure whether your contribution is suitable, or if you need any kind of help with your submission, please email the program chairs (Jeff (jmy6342(a)gmail.com) and Christine (christine.rizkallah(a)unimelb.edu.au)) Papers must be submitted by 16th June 2025 using the hotcrp submission page (https://funarch25.hotcrp.com/) Formatting: submissions intended for publication must be in PDF format and follow the ACM SIGPLAN style guidelines, using the acmart format and the sigplan sub-format. Please use the review option when submitting, as this enables line numbers for easy reference in reviews. For further details, see SIGPLAN's author information: http://www.sigplan.org/Resources/Author/#acmart-format If your submission is not a research paper, please mark this using a subtitle (Experience Report, Architectural Pearl, Open Category). Length: submissions must adhere to the limits specified below. However, there is no requirement or expectation that all pages are used, and authors are encouraged to strive for brevity. Research papers 5 to 12+ pages Architectural pearls 5 to 12 pages Experience reports 3 to 6 pages Open category 1 to 6 pages Publication: The proceedings of FUNARCH 2024 will be published in the ACM Digital Library, and authors of accepted papers are required to agree to one of the standard ACM licensing options. Accepted papers must be presented at the workshop by one of the authors, but in special cases we may consider remote presentation. The official publication date is the date the papers are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. PROGRAM CHAIRS: Jeffrey Young (Unaffiliated) Cristine Rizkallah (University of Melbourne) PROGRAM COMMITTEE: Isabella Stilkerich (Schaeffler Technologies) Ryan Scott (Galois) Facundo Dominguez (Tweag) J. Garrett Morris (University of Iowa) Nada Amin (Harvard University) Tom Ellis (Groq) KC Sivaramakrishnan (IIT Madras and Tarides) Hidehiko Masuhara (Institute of Science Tokyo) WORKSHOP VENUE: Room to be determined. The workshop will be co-located with the ICFP 2025 conference at the Marina Bay Sands Convention Centre, Singapore.

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Call for Participation, Functional Software Architecture (Oct. 17th, Singapore)
by Michael Sperber 26 Mar '25

26 Mar '25

====================================================================== *** FUNARCH 2025 -- CALL FOR PARTICIPATION *** The Third ACM SIGPLAN Workshop on Functional Software Architecture - FP in the Large 17th October 2025, Singapore Co-located with ICFP 2025 https://www.functional-architecture.org/events/funarch-2025/ ====================================================================== BACKGROUND: The ACM SIGPLAN Workshop on Functional Software Architecture - FP in the Large aims to disseminate and enable the use of functional programming in the large and long-lived software projects. We specifically want: - To assemble a community interested in software architecture techniques and technologies specific to functional programming; - To identify, categorize, and document topics relevant to the field of functional software architecture; - To connect the functional programming community to the software architecture community to cross-pollinate between the two. We'd love for you to be part of this effort. Whatever your background, you're welcome at FUNARCH - to listen to talks, report on your experience, and interact with others that share our goals. See you at FUNARCH! REGISTRATION: You can register for the workshop via the registration page for the ICFP conference, but there's no need to also register for the conference. KEYNOTE: TBD ACCEPTED SUBMISSIONS: TBD PROGRAM CHAIRS: Jeffrey Young (Active Group, Germany) Christina Rizkallah (University of Edinburgh, UK) PROGRAM COMMITTEE: Isabella Stilkerich (Schaeffler Technologies) Ryan Scott (Galois) Facundo Dominguez (Tweag) J. Garrett Morris (University of Iowa) Nada Amin (Harvard University) Tom Ellis (Groq) KC Sivaramakrishnan (IIT Madras and Tarides) Hidehiko Masuhara (Institute of Science Tokyo) WORKSHOP VENUE: The workshop will be co-located with the ICFP 2025 conference at the Marina Bay Sands Convention Centre, Singapore. ======================================================================

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GHC 9.6.7 is now available
by Luite Stegeman 24 Mar '25

24 Mar '25

The GHC developers are very pleased to announce the availability of GHC 9.6.7. Binary distributions, source distributions, and documentation are available at https://downloads.haskell.org/ghc/9.6.7 We hope to have this release available via ghcup shortly. GHC 9.6.7 brings number of fixes, including: - GHC’s internal Unique type has been widened to 64-bits on 32-bit architectures, avoiding potential miscompilations on large projects. - Fix a runtime crash when using the compacting GC, caused by black holes in large objects. - Added new flags -fspec-eval and -fspec-eval-dictfun to allow switching off speculative evaluation. The following libraries have been updated since GHC 9.6.6: - base-4.18.3.0 - filepath-1.4.301.0 - unix-2.8.6.0 - bytestring-0.11.5.4 - array-0.5.8.0 A more detailed description can be found in the [release notes] and a full list of changes in [GHC!13841] and [GHC!13891] Note about Haskell Language Server and building GHC 9.8+: The change of Unique to 64 bit [GHC#22010] adds the exported symbol ghc_unique_counter64 to the RTS. Unfortunately it's impossible to avoid this without breaking other things. If you encounter a linker error related to ghc_unique_counter64 when building GHC (or building a GHC-derived package like ghc-lib-parser) with GHC 9.6.7, you probably have to add this [fix] to the program you're building. We would like to thank GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. Please give this release a try and open a [ticket] if you see anything amiss. ~ Luite [release notes]: https://downloads.haskell.org/ghc/9.6.7/docs/users_guide/9.6.7-notes.html [GHC!13841]: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13841 [GHC!13891]: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13891 [GHC#22010]: https://gitlab.haskell.org/ghc/ghc/-/issues/22010 [fix] https://gitlab.haskell.org/ghc/ghc/-/merge_requests/13743 [ticket] https://gitlab.haskell.org/ghc/ghc/-/issues/new

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Thesis-Job: Find the best specification method
by lists0＠freea2a.de 22 Mar '25

22 Mar '25

Dear haskell-list, at Siemens Mobility I would like to improve our specifications. For that, I have the opportunity to teach the properties of our product to a student, and ask him/her to specify the product with more or less of the full power of current specification techniques. The goal for me is, to evaluate existing methods and find the best method. We work intensively with specifications, thus a big level of mathematical formalism can count, as long as the technical team likes to learn and use it. The job offering for a final thesis is at the end of the post. Beside that: What does the list think are methods that are fruitful in a commercial high-quality setting ? The implementation shall not or almost not be changed, we just want a system for test generation and analysis of the required (and hopefully correctly implemented) system. Thank you for your answers! #### Job-offering (German): https://jobs.siemens.com/careers?query=440671&pid=563156121392428&organizat… As part of your work, you can do the following tasks: Search and justify a selection of an existing textual specification method (Domain Specific Language or Framework in a proven programming language). Specify parts of our existing system with the selection and apply the specification, e.g. for test case generation or for the detection of system properties. Examine the practicality of the specification method for daily use. What do you bring? You are studying computer science or a similar field. You already have knowledge of syntax and semantics / specification methods. Ideally, you have knowledge of several imperative languages and knowledge of functional programming (e.g. Haskell, OCaml, ...). Knowledge of machine proving is an advantage. You have good German and English language skills. You can write the work in German, English or bilingual. If you would like to complete a mandatory internship in advance, this is also possible after consultation. -- Mein PGP-Schlüssel-Fingerabdruck: B3CD 2CB8 EC08 B6BD D82C 9BE1 F702 BF50 C4AF 179D oder 88E6 D1E7 9276 BC56 849C CF02 9F96 BE18 43FA 2CC0

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