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Midlands Graduate School, Nottingham, UK, 13-17 April 2026
by Graham Hutton (staff) 01 Dec '25

01 Dec '25

Dear all, I'm delighted to announce that the next Midlands Graduate School (MGS) in the Foundations of Computing Science will be held in Nottingham, UK, from 13-17 April 2026. Please share in your communities! Best wishes, Graham Hutton ========================================================== 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: - To be announced Introductory courses: - Category Theory for the Lazy Functional Programmer Thorsten Altenkirch (Nottingham) - Introduction to HoTT/UF with Agda Martin Escardó (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) 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> ========================================================== 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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Jonathan Bowen to give the Peter Landin Semantics Seminar: 4 December 2025, BCS London office and on Zoom
by Andrei Popescu 26 Nov '25

26 Nov '25

Dear Colleagues, Please see below details about the event, which will be preceded by the BCS-FACS Annual General Meeting. The event can be attended either online or in person. Best wishes, Andrei https://www.bcs.org/events-calendar/2025/december/hybrid-facs-agm-and-peter… (free registration online) Hybrid event: *BCS-FACS AGM & Peter Landin Semantics Seminar* *Formal Methods: Whence and Whither* BCS London office (near Moorgate underground station) and on Zoom, 4 December 2025 Speaker: *J <https://sites.google.com/site/jpbowen/>**onathan Bowen <https://sites.google.com/site/jpbowen/>* (Chair of FACS)Agenda 3:30pm - Networking for attendees (refreshments and biscuits) *4:00pm* - 5:00pm *FACS AGM* (optional!) 5:15pm - Networking for physical/online attendees. Includes refreshments and biscuits for those in person. *6:00pm* - *Peter **Landin Semantics Seminar Talk* 7:00pm - Questions and answers 7:15pm - Networking for physical attendees (light refreshments) 8:00pm - Event ends for online attendees *8:30pm* - Event ends for in-person attendees Synopsis Alan Turing arguably wrote the first paper on formal methods over 75 years ago. Since then, there have been claims and counterclaims about formal methods. Tool development has been slow but aided by Moore’s Law, with the increasing power of computers. Although formal methods are not widespread in practical usage at a heavyweight level, their influence has crept into software engineering practice to the extent that they are no longer necessarily called formal methods in their use. In addition, in areas where safety and security are important, with the increasing use of computers in such applications, formal methods are a viable way to improve the reliability of such software-based systems. Their use in hardware, where a mistake can be very costly, is also important. This talk explores the journey of formal methods to the present day and speculates on future directions, including the use of Artificial Intelligence. About the speaker *Jonathan Bowen*, FBCS FRSA, is Chairman of Museophile Limited (founded in 2002), an Emeritus Professor at London South Bank University, where he was Professor of Computing, establishing and heading the Centre for Applied Formal Methods from 2000. From 2017, he has been an Adjunct Professor at Southwest University, Chongqing, China. Between 2013–15, he was Professor of Computer Science at Birmingham City University. During 2006–07, he was a visiting academic at University College London. Between 2007–09, he was a Visiting Professor at King's College, London, and during 2008–09, he was an Associate at Praxis High Integrity Systems (now Altran). From 2010, he was a Visiting Professor at the University of Westminster. During 2010, he was a Visiting Professor at Waikato University in New Zealand, and in 2012, he was a Visiting Professor at the Pratt Institute in New York. He is the current Chair of the BCS-FACS Specialist Group. ------------------------ Our events are for adults aged 16 years and over. BCS is a membership organisation. If you enjoy this event, please consider joining BCS. You’ll be very welcome. You’ll receive access to many exclusive career development tools, an introduction to a thriving professional community and also help us Make IT Good For Society. Join BCS today <https://www.bcs.org/membership/events> Please note: if you have any accessibility needs, please let us know via groups(a)bcs.uk and we’ll work with you to make suitable arrangements. If you are attending in person, please familiarise yourself with the Visitor Instructions <https://www.bcs.org/media/ww4jlkud/visitor-instructions.docx> for the BCS London Office. For overseas delegates who wish to attend the event, please note that BCS does not issue invitation letters. Photo by Markus Spiske This event is brought to you by: FACS (Formal Aspects of Computing Science) group <https://www.bcs.org/membership-and-registrations/member-communities/facs-fo…>

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CfP: SLE 2026 - 19th ACM SIGPLAN International Conference on Software Language Engineering
by Andrei Chis 20 Nov '25

20 Nov '25

19th ACM SIGPLAN International Conference on Software Language Engineering (SLE 2026) 2 - 3 July 2026 Rennes, France https://conf.researchr.org/home/sle-2026 https://www.sleconf.org/2026/ ------------------------------------------------------------------------ We are pleased to invite you to submit papers to the 19th ACM SIGPLAN International Conference on Software Language Engineering (SLE) which is devoted to the principles of software languages: their design, their implementation, and their evolution. The SLE 2026 conference will be co-located with STAF 2026 and hosted in Rennes, France, on 2 - 3 July 2026. --------------------------- Important Dates --------------------------- * Abstract submission (all tracks): Friday 27 February 2026 * Paper submission (all tracks): Friday 6 March 2026 * Paper notification (all tracks): Monday 20 April 2026 * Conference: Thursday 2 - Friday 3 July 2026 (co-located with STAF) All dates are Anywhere on Earth. --------------------------- Topics of Interest --------------------------- SLE covers software language engineering in general, rather than engineering a specific software language. Topics of interest include, but are not limited to: *Software Language Design and Implementation - Approaches to and methods for language design - Static semantics (e.g., design rules, well-formedness constraints) - Techniques for specifying behavioral/executable semantics - Generative approaches (incl. code synthesis, compilation) - Meta-languages, meta-tools, language workbenches - AI-assisted language design and optimisation * Software Language Quality - Verification and formal methods for languages - Testing techniques for languages - Simulation techniques for languages - Model-based testing - AI-assisted validation * Software Language Integration and Composition - Coordination of heterogeneous languages and tools - Mappings between languages (incl. transformation languages) - Traceability between languages - Deployment of languages to different platforms - (AI-assisted) Language refactorings * Software Language Maintenance - Software language reuse - Language evolution - Language families and variability, language and software product lines * Domain-specific approaches for any aspects of SLE (design, implementation, validation, maintenance) * Empirical evaluation and experience reports of language engineering tools - User studies evaluating usability - Performance benchmarks - Industrial applications * Synergies between Language Engineering and emerging/promising research areas - Generative AI in language engineering (e.g., AI-based language modelling, AI-driven code generation tools) - Language engineering for AI. AI and ML language engineering (e.g., ML compiler testing, code classification, DSLs for AI processes and tasks…) - Quantum language engineering (e.g., language design for quantum machines) - Language engineering for physical systems (e.g., CPS, IoT, digital twins) - Socio-technical systems and language engineering (e.g., language evolution to adapt to social requirements) --------------------------- Types of Submissions --------------------------- SLE accepts the following types of papers: * Research papers: These are “traditional” papers detailing research contributions to SLE. Papers may range from 6 to 12 pages in length and may optionally include 2 further pages of bibliography/appendices. Papers will be reviewed with an understanding that some results do not need 12 full pages and may be fully described in fewer pages. * New ideas/vision papers: These papers may describe new, unconventional software language engineering research positions or approaches that depart from standard practice. They can describe well-defined research ideas that are at an early stage of investigation. They could also provide new evidence to challenge common wisdom, present new unifying theories about existing SLE research that provides novel insight or that can lead to the development of new technologies or approaches, or apply SLE technology to radically new application areas. New ideas/vision papers must not exceed 5 pages and may optionally include 1 further page of bibliography/appendices. * SLE Body of Knowledge: The SLE Body of Knowledge (SLEBoK) is a community-wide effort to provide a unique and comprehensive description of the concepts, best practices, tools, and methods developed by the SLE community. In this respect, the SLE conference will accept surveys, essays, open challenges, empirical observations, and case study papers on the SLE topics. These can focus on, but are not limited to, methods, techniques, best practices, and teaching approaches. Papers in this category can have up to 20 pages, including bibliography/appendices. * Tool papers: These papers focus on the tooling aspects often forgotten or neglected in research papers. A good tool paper focuses on practical insights that will likely be useful to other implementers or users in the future. Any of the SLE topics of interest are appropriate areas for tool papers. Submissions must not exceed 5 pages and may optionally include 1 further page of bibliography/appendices. They may optionally include an appendix with a demo outline/screenshots and/or a short video/screencast illustrating the tool. **Workshops**: Workshops will be organised by STAF. Please inform us and contact STAF 2026 organisers if you would like to organise a workshop of interest to the SLE audience. Information on how to submit workshops can be found on the STAF 2026 Website. --------------------------- Submission --------------------------- SLE 2026 has a single submission round for papers, including a mandatory abstract registration. Authors of accepted research papers will be invited to submit artefacts. --------------------------- Format --------------------------- Submissions have to use the ACM SIGPLAN Conference Format “acmart” ( https://sigplan.org/Resources/Author/#acmart-format) please make sure that you always use the latest ACM SIGPLAN acmart LaTeX template, and that the document class definition is \documentclass[sigplan,anonymous,review]{acmart}. Do not make any changes to this format! Ensure that your submission is legible when printed on a black and white printer. In particular, please check that colours remain distinct and font sizes in figures and tables are legible. To increase fairness in reviewing, a double-blind review process has become standard across SIGPLAN conferences. Accordingly, SLE will follow the double-blind process. Author names and institutions must be omitted from submitted papers, and references to the authors’ own related work should be in the third person. No other changes are necessary, and authors will not be penalized if reviewers are able to infer their identities in implicit ways. All submissions must be in PDF format. You can access the submission site from the conference website: https://conf.researchr.org/home/sle-2026 --------------------------- Concurrent Submissions --------------------------- Papers must describe unpublished work that is not currently submitted for publication elsewhere as described by SIGPLAN’s Republication Policy ( https://www.sigplan.org/Resources/Policies/Republication/) Submitters should also be aware of ACM’s Policy and Procedures on Plagiarism ( https://www.acm.org/publications/policies/plagiarism-overview) Submissions that violate these policies will be desk-rejected. --------------------------- Policy on Human Participant and Subject Research --------------------------- Authors conducting research involving human participants and subjects must ensure that their research complies with their local governing laws and regulations and the ACM’s general principles, as stated in the ACM’s Publications Policy on Research Involving Human Participants and Subjects ( https://www.acm.org/publications/policies/research-involving-human-particip…) If submissions are found to be violating this policy, they will be rejected. --------------------------- Reviewing Process --------------------------- All submitted papers will be reviewed by at least three members of the program committee. Research papers and tool papers will be evaluated concerning soundness, relevance, novelty, presentation, validation, and replicability. New ideas/vision papers will be evaluated primarily concerning soundness, relevance, novelty, and presentation. Tool papers will be evaluated concerning relevance, presentation, and replicability. For fairness reasons, all submitted papers must conform to the above instructions. Submissions that violate these instructions may be rejected without review at the discretion of the PC chairs. --------------------------- Artefact Evaluation --------------------------- SLE will use an evaluation process to assess the quality of artefacts on which papers are based to foster the culture of experimental reproducibility. Authors of accepted research papers are invited to submit artefacts. --------------------------- Awards --------------------------- * Distinguished paper: Award for the most notable paper, as determined by the PC chairs based on the recommendations of the program committee. * Distinguished artefact: Award for the artefact most significantly exceeding expectations, as determined by the AEC chairs based on the recommendations of the artefact evaluation committee. * Distinguished reviewer: Award for the programme committee member that produced the most useful reviews as assessed by paper authors. * Most Influential Paper: Award for the SLE 2016 paper with the greatest impact, as judged by the SLE Steering Committee. --------------------------- Publication --------------------------- All accepted papers will be published in the ACM Digital Library. **AUTHORS TAKE NOTE**: The official publication date is the date the proceedings 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. --------------------------- Organisation --------------------------- * General chair: Arnaud Blouin, Univ Rennes, INSA Rennes, Inria, CNRS, IRISA * PC co-chair: Jordi Cabot, Luxembourg Institute of Science and Technology * PC co-chair: Shigeru Chiba, University of Tokyo, Japan --------------------------- Contact --------------------------- For additional information, clarification, or answers to any questions, please get in touch with the program co-chairs (jordi.cabot(a)list.lu and chiba(a)g.ecc.u-tokyo.ac.jp)

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Haskell.org Committee: Call for Nominations
by Rebecca Skinner 20 Nov '25

20 Nov '25

Dear Haskellers, We are pleased to announce that nominations are now open for the Haskell.org committee. You can nominate yourself or a friend for a three-year term (2026-2028) by sending an email to [committee at haskell.org] by December 05, 2025. There are three seats open for election this year. The committee will elect members in December 2025 for the term beginning in January 2026. Self-nominations and re-nominations are also welcome. Please include any relevant information about yourself or your nominee that you think will help us make our decision. Committee members do not have to be technical experts in Haskell. We are looking for people who are enthusiastic about improving the Haskell community and come from a variety of backgrounds, such as academia, industry, open-source development, and community building. Our goal is to represent the various facets of the Haskell world, including gender, race, location, and industry or research. The committee’s responsibilities include setting policies, providing guidance for Haskell.org infrastructure, planning for the long term, and being fiscally responsible with Haskell.org funds and donations. Being a committee member does not require a significant amount of time, but members should be responsive during discussions and should be able to attend monthly calls and participate in the Haskell.org Slack and mailing lists. Candidates for the committee should possess strong leadership, communication, and judgment skills. They must be able to set aside personal or business-related biases and make decisions with the good of the open-source Haskell community in mind. For more information about the committee’s roles and responsibilities, please visit Haskell.org Committee If you have any questions about the nomination process, please feel free to email us at [committee at haskell.org] or contact one of us individually.

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Final Call for Papers: Tests and Proofs (TAP) -- Now a Track at FM 2026
by Achim D. Brucker 18 Nov '25

18 Nov '25

**CALL FOR PAPERS** **Special Track on Tests and Proofs (TAP 2026)** *at the* **27th International Symposium on Formal Methods (FM 2026)** **May 18-22, 2026 --- Tokyo, Japan** **Website:** <https://conf.researchr.org/track/fm-2026/> **Abstract Submission**: Tuesday, 25 November 2025 **Full Paper Submission:** Tuesday, 2 December 2025 ### **New TAP Track at FM 2026: A Premier Venue for Tests and Proofs** Since 2007, the [Test and Proof (TAP) conference](https://tapconference.github.io/2024/) has long been a leading venue for research on the intersection of software testing and formal verification. Now, TAP is joining the 27th International Symposium on Formal Methods (FM 2026) as a new special track. This integration places the ground-breaking work of the Test and Proofs community at the heart of the world's premier conference on formal methods. This new track provides a dedicated forum for researchers, practitioners, and tool developers to present and discuss the latest advances in the synergistic combination of traditionally distinct areas of dynamic analysis, e.g., testing, and static analysis, e.g., proving. By joining FM, the TAP track offers authors a wider, more diverse audience and the prestige of publication in the main, open-access FM 2026 proceedings, published by Springer in the LNCS series. We invite you to be part of this exciting new chapter for the tests and proofs community! **Track Highlight: FM 2026 Keynote by Professor Cristian Cadar** We are thrilled to announce that TAP Track at FM 2026 will feature a keynote address by **Professor Cristian Cadar** of Imperial College London. Professor Cadar is a world-renowned authority on software reliability, security, and verification, and is particularly celebrated for his pioneering contributions to symbolic and dynamic execution (e.g., KLEE). His selection as a main symposium keynote speaker is a powerful testament to the increasing importance of the core topics of the TAP track to the broader computer science community. ### **Scope and Topics of Interest** The TAP track solicits high-quality, original research on the interplay between dynamic techniques such as testing, runtime verification etc.testing and formal verification such as proving, model checking, abstract interpretation, etc. . The track aims to foster new collaborations and advance the state of the art in creating reliable and secure software and systems. Topics of interest include, but are not limited to, the following areas: **Foundations for Combining Testing and Verification** - Formalisms and theories that unify testing and proof\ - Semantic foundations for combined static and dynamic analysis\ - Proof theory for test-case generation and specification conformance\ - Type systems with a testing and proving focus\ - Formal models of test-based and proof-based development **Synergistic Techniques and Tools** - Combination of model checking, theorem proving, and runtime verification - Synergies between symbolic execution, fuzzing, and formal analysis - Test-case generation from formal specifications (e.g., using B, Z, TLA+, VDM) - Using test execution results to guide or automate proof discovery - Static analysis for test-suite reduction, prioritization, and optimization - Verification-based and property-based testing - Formal methods for testing AI/ML-based systems - AI/ML techniques for enhancing formal verification and testing - Derivation of specifications and contracts from tests - Combination of static and dynamic analysis for security vulnerability detection **Applications and Empirical Evaluation** - Case studies and experience reports applying combined test-and-proof techniques to industrial systems (e.g., in security, cyber-physical systems, autonomous systems, blockchain, or IoT) - Empirical comparisons of different verification, testing, and combined techniques - Tool demonstration papers for new and innovative tools that support tests and proofs - Application of TAP techniques to challenge problems and benchmarks ### **Submission Categories and Guidelines** The TAP track papers can be submitted in all paper categories supported by the FM 2026 Research Track and submissions to the TAP track will be reviewed following the policies and quality criteria of the FM Research Track. The TAP track solicits papers in the following categories: - **Regular Papers (max 15 pages, excluding references and appendices):** For mature, original research contributions. - **Long Tool Papers (max 15 pages, excluding references and appendices):** For presenting mature tools, their theoretical foundations, and empirical evaluations. - **Case Study Papers (max 15 pages, excluding references and appendices):** For in-depth reports on the application of TAP techniques to significant, real-world problems. - **Short Papers (max 6 pages, excluding references and appendices):** For presenting novel but not yet fully mature ideas, or for tool demonstration papers that focus on a tool's features and usage. Papers should be original work, not published or submitted elsewhere, in Springer [LNCS format](https://www.springer.com/gp/computer-science/lncs/conference-procee…, and written in English. Submit your papers at https://easychair.org/conferences/?conf=fm2026 Reviewing is single-blind. Each paper will be evaluated by at least three members of the Program Committee. Papers will be accepted or rejected in the category in which they were submitted and will not be moved between categories Authors of accepted papers are strongly encouraged to submit their supporting artifacts to the FM 2026 Artifact Evaluation track. ### **Important Dates** All deadlines are **Anywhere on Earth (AoE, UTC-12h)**. The deadlines for the TAP track are aligned with the FM 2026 Research Track. Milestone Date --------------------------- ------------------------------- **Abstract Submission** **Tuesday, 25 November 2025** **Full Paper Submission** **Tuesday, 2 December 2025** **Author Notification** **Friday, 6 February 2026** **Camera-Ready Version** **Monday, 2 March 2026** **FM 2026 Conference** **May 18-22, 2026** ### **Publication** All accepted papers for the TAP track will be published as part of the main FM 2026 conference proceedings. The proceedings will be published by Springer in their **open-access Lecture Notes in Computer Science (LNCS)** series. At least one author of an accepted paper must register for the conference and present the work. ### **Track Organization** **Track Chairs:** - Marie-Christine Jakobs, Ludwig-Maximilan University, Munich, Germany - Achim D. Brucker, University of Exeter, UK For inquiries, please contact the track chairs. -- 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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Re: lost polymorphism in Typed Tagless Final Interpreters
by Olaf Klinke 12 Nov '25

12 Nov '25

> So change lit <$> safeRead n to (\x -> > lit x) <$> safeRead n, for example. Does anyone else find this highly non-obvious? SPJ gives an example https://github.com/ghc-proposals/ghc-proposals/pull/287#issuecomment-543683… of a context that can indeed distinguish, semantically, a function and its eta expansion. But the fact that, for the benefit of soundness, there must exist contexts where one can be a well-typed program while the other is not, is still mysterious to me. Can a type system with polymorphism really not do better than this? The discussion thread has some more interesting posts, e.g. https://github.com/ghc-proposals/ghc-proposals/pull/287#issuecomment-544377… https://github.com/ghc-proposals/ghc-proposals/pull/287#issuecomment-112046… At least, thanks to Jaro, the error index now explains when you should eta-expand. https://errors.haskell.org/messages/GHC-83865/ Olaf

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lost polymorphism in Typed Tagless Final Interpreters
by Anthony Carrico 12 Nov '25

12 Nov '25

In his tutorial lecture "Typed Tagless Final Interpreters" https://www.okmij.org/ftp/tagless-final/course/lecture.pdf Oleg Kiselyov deals with the issue of losing polymorphism, tf1'_both :: IO() tf1'_both = case tf1' of Left e -> putStrLn ("Error: " ++ e) Right (x) -> do print (eval x) print (view x) "We have lost polymorphism. The problem is subtle: the function fromTree is indeed polymorphic over repr, as its inferred type shows. However, to extract the de-serialized term, we have to do pattern-matching; the variable x is bound in the case pattern and hence, like a lambda-pattern–bound variable, gets a monomorphic, non-generalizable type. Therefore, we cannot interpret x with several arbitrary interpreters; the extensibility is lost." He shows how to use a newtype wrapper to work around the issue, but also says in a foot note: "With the impredicative polymorphism GHC extension, we do not have to fake first-class polymorphism and do not need Wrapped." Two questions: 1. Is this true? I still get the error. 2. Can anyone summarize the current state of this issue today? It can be hard follow the issue through the history of Haskell/GHC. Thanks to Oleg for publishing this lecture, it is possible to learn quite a bit from it, and thanks to whoever would like to give an update! I've smashed together my source code from the F module and the Serialization module together below. You can see the "defered type error" at the very bottom. $ ghc --version The Glorious Glasgow Haskell Compilation System, version 9.8.4 {-# LANGUAGE NoMonomorphismRestriction #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE ImpredicativeTypes #-} module F where class ExpSYM repr where lit :: Int -> repr neg :: repr -> repr add :: repr -> repr -> repr instance ExpSYM Int where lit n = n neg e = -e add e0 e1 = e0 + e1 eval :: Int -> Int eval = id instance ExpSYM String where lit n = show n neg e = "(-" ++ e ++ ")" add e0 e1 = "(" ++ e0 ++ " + " ++ e1 ++ ")" view :: String -> String view = id data Tree = Leaf String | Node String [Tree] deriving (Eq, Read, Show) instance ExpSYM Tree where lit n = Node "Lit" [Leaf (show n)] neg e = Node "Neg" [e] add e0 e1 = Node "Add" [e0, e1] toTree :: Tree -> Tree toTree = id type ErrMsg = String safeRead :: Read a => String -> Either ErrMsg a safeRead s = case reads s of [(x, "")] -> Right x _ -> Left $ "Read error: " ++ s fromTree :: (ExpSYM repr) => Tree -> Either ErrMsg repr fromTree (Node "Lit" [Leaf n]) = lit <$> (safeRead n) fromTree (Node "Neg" [e]) = neg <$> (fromTree e) fromTree (Node "Add" [e0, e1]) = add <$> (fromTree e0) <*> (fromTree e1) fromTree e = Left ("Invalid tree: " ++ show e) tf1 :: ExpSYM repr => repr tf1 = add (lit 8) (neg (add (lit 1) (lit 2))) tf1_tree :: Tree tf1_tree = toTree F.tf1 tf1' :: ExpSYM repr => Either ErrMsg repr tf1' = fromTree tf1_tree tf1'_eval :: IO() tf1'_eval = case tf1' of Left e -> putStrLn ("Error: " ++ e) Right x -> print (eval x) -- >>> tf1'_eval -- 5 tf1'_view :: IO() tf1'_view = case tf1' of Left e -> putStrLn ("Error: " ++ e) Right x -> print (view x) -- >>> tf1'_view -- "(8 + (-(1 + 2)))" tf1'_both :: IO() tf1'_both = case tf1' of Left e -> putStrLn ("Error: " ++ e) Right (x) -> do print (eval x) print (view x) -- >>> tf1'_both -- *** Exception: /tmp/danteIpH3fg.hs:90:19: error: [GHC-83865] -- • Couldn't match type ‘Int’ with ‘[Char]’ -- Expected: String -- Actual: Int -- • In the first argument of ‘view’, namely ‘x’ -- In the first argument of ‘print’, namely ‘(view x)’ -- In a stmt of a 'do' block: print (view x) -- (deferred type error) -- Anthony Carrico

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GHC 9.12.3-rc2 is now available
by Zubin Duggal 12 Nov '25

12 Nov '25

The GHC developers are very pleased to announce the availability of the second release candidate for GHC 9.12.3. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.3 is a bug-fix release fixing several issues of a variety of severities and scopes. A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 24 November 2025. The changes from the first release candidate are * Fix a regression resulting in a panic with empty cases (#26442, #25960). * Fix for a potential segfault in the bytecode interpreter (#23210). * Fix for a regression with tabs not being allowed in string gaps (#26415). * Fix for a crash with the non-moving GC (#26204). * A rework of how internal symbols used by the code-generator are handled to adapt to changes in the Apple toolchain, enabling this release to bootstrap on macOS 26 Tahoe (#26166). GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to that these sponsors and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket][] if you see anything amiss. [release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.3-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.3-rc2 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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[ANN] Copilot 4.6
by Ivan Perez 11 Nov '25

11 Nov '25

Hi café! We are really excited to announce Copilot 4.6 [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), 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 major release improves the Bluespec backend, producing more suitable Verilog code. Prior implementations required modifying the resulting Verilog to help connect it to external systems (e.g., sensors, actuators), while the new Bluespec backend produces code that can be used without modification. The new implementation is compatible with versions of GHC from 8.6 to 9.12. This release has been made possible thanks to Sukhman Kahlon (NASA), who carried out a thorough evaluation of our FPGA backend, and to Ryan Scott (Galois), who implemented the updated solution. This work has also greatly benefited from discussions with the Bluespec team on the code generated by Copilot and possible improvements. 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 Jan 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 [2] https://hackage.haskell.org/package/copilot [3] https://github.com/nasa/ogma [4] https://github.com/Copilot-Language/copilot

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ICFP 2026: Call for Papers
by ICFP Publicity 11 Nov '25

11 Nov '25

ICFP 2026 Call for Papers Accepted papers to be invited for presentation at: *The 31st ACM SIGPLAN International Conference on Functional Programming*August 23-29, 2026 Indianapolis, Indiana, USA https://icfp26.sigplan.org ------------------------------ Submission Information - *Submission web site*: https://icfp26.hotcrp.com - *Submission Deadline*: 19 Feb 2026 (AoE) Double-blind review - Reviews: 20 Apr 2026 (AoE) - Author Response: 20 Apr 2026 - 23 Apr 2026 (AoE) - Notification of Conditional Acceptance: 14 May 2026 (AoE) - Revision: 3 Jun 2026 (AoE) - Final Notification: 10 Jun 2026 (AoE) - Camera Ready: 1 Jul 2026 (AoE) ------------------------------ PACMPL issue ICFP 2026 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Topics of interest include (but are not limited to): - Language Design: concurrency, parallelism, and distribution; modularity; components and composition; meta-programming; macros; pattern matching; type systems; type inference; dependent types; effect types; gradual types; refinement types; session types; interoperability; domain-specific languages; imperative programming; object-oriented programming; logic programming; probabilistic programming; reactive programming; generic programming; bidirectional programming; secure programming. - Implementation: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimisation; garbage collection and memory management; runtime systems; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources. - Software-Development Techniques: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling; build systems; program synthesis. - Analysis and Transformation: control flow; data flow; abstract interpretation; partial evaluation; program calculation. - Foundations: formal semantics; lambda calculus; program equivalence; rewriting; type theory; logic; category theory; computational effects; continuations; control; state; names and binding; program verification. - Applications: symbolic computing; formal-methods tools; systems programming; distributed systems and web programming; hardware design; databases; scientific and numerical computing; graphical user interfaces; graphics and multimedia; GPU programming; scripting; system administration; security. - Education: teaching introductory programming; mathematical proof; algebra. Submissions will be evaluated according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. PACMPL issue ICFP 2026 also welcomes submissions in two separate categories — Functional Pearls and Experience Reports — that must be marked as such when submitted and that *need not* report original research results. Detailed guidelines on both categories are given at the end of this call. In an effort to achieve a balanced, diverse program, each author may be listed as a (co)author on a maximum of four submissions. Authors who require financial support to attend the conference can apply for PAC funding (http://www.sigplan.org/PAC/) The General Chair and PC Chair may not submit papers. PC members (other than the PC Chair) may submit papers. Please contact the Program Chair if you have questions or are concerned about the appropriateness of a topic. Double-blind Submissions <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#double-bind-submissi…> ICFP 2026 will use a full double-blind reviewing process. 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. The use of full double-blind reviewing has several consequences for authors. - Submissions: Authors must omit their names and institutions from their paper submissions. In addition, references to authors’ own prior work should be in the third person (e.g., not “We build on our previous work …” but rather “We build on the work of …”). - Supplementary material: Authors must fully anonymize any supplementary material (see below). Links to supplementary material on external websites are not permitted. - Author response: In responding to reviews, authors should not say anything that reveals their identity, since author identities will not be revealed to reviewers at that stage of the reviewing process. - Dissemination of work under submission: Authors are welcome to disseminate their ideas and post draft versions of their paper(s) on their personal website, institutional repository, or arXiv (reviewers will be asked to turn off arXiv notifications during the review period). But authors should not take steps that would almost certainly reveal their identities to members of the Program Committee, e.g., directly contacting PC members or publicizing the work on widely-visible social media or major mailing lists used by the community. The purpose of the above restrictions is to help the Program Committee come to a judgment about the paper without bias, not to make it impossible for them to discover the authors’ identities if they were to try. In particular, nothing should be done in the name of anonymity that weakens the quality of the submission. However, there are occasionally cases where adhering to the above restrictions is truly difficult or impossible for one reason or another. In such cases, the authors should contact the Program Chair to discuss the situation and how to handle it. The FAQ on Double-Blind Reviewing ( https://popl24.sigplan.org/track/POPL-2024-popl-research-papers#FAQ-on-Doub…) addresses many common scenarios and answers many common questions about this topic. But there remain many grey areas and trade-offs. If you have any doubts about how to interpret the double-blind rules or you encounter a complex case that is not clearly covered by the FAQ, please contact the Program Chair for guidance. Preparation of submissions <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#preparation-of-submi…> The deadline for submissions is: *** Thursay, 19 Feb 2026 AoE *** ( https://www.timeanddate.com/time/zones/aoe) This deadline will be strictly enforced. - 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. Please download the latest version of the ACM style from https://www.acm.org/publications/authors/submissions, since the citation format has recently been changed. See also PACMPL’s Information and Guidelines for Authors at https://pacmpl.acm.org/authors.cfm. There is a limit of *25 pages* for a full paper or Functional Pearl and *12 pages* for an Experience Report; in either case, the bibliography and an optional clearly marked appendix will not be counted against these limits. Submissions that exceed the page limits or, for other reasons, do not meet the requirements for formatting, will be desk rejected. - Submission: Submissions will be accepted at https://icfp26.hotcrp.com Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. - Author Response Period: Authors will have a 96-hour period, starting at 00:00 (midnight) AoE on Monday, 20 April, 2026, to read reviews and respond to them. - Appendix and Supplementary Material: Authors have the option to include a clearly marked appendix and/or to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at such an appendix or supplementary material. Supplementary material may be uploaded as a separate PDF document or tarball. Any supplementary material must be uploaded at submission time, not by providing a URL in the paper that points to an external repository. All supplementary material must be anonymised. - Authorship Policies: All submissions are expected to comply with the ACM Policies for Authorship that are detailed at https://www.acm.org/publications/authors/information-for-authors. - Republication Policies: Each submission must adhere to SIGPLAN’s republication policy, as explained on the web at http://www.sigplan.org/Resources/Policies/Republication. Review Process <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#review-process> This section outlines the two-stage process with double-blind reviewing that will be used to select papers for PACMPL issue ICFP 2026. Like last year, ICFP 2026 will adapt a full double-blind reviewing process. More information see below. ICFP 2026 will have two Associate Chairs who will help the PC Chair monitor reviews, solicit external expert reviews for submissions when there is not enough expertise on the committee, and facilitate reviewer discussions. ICFP 2026 will employ a two-stage review process. The first stage in the review process will assess submitted papers using the criteria stated above and will allow for feedback and input on initial reviews through the author response period mentioned previously. As a result of the review process, a set of papers will be conditionally accepted and all other papers will be rejected. Authors will be notified of these decisions on 14 May, 2026. Authors of conditionally accepted papers will be provided with committee reviews along with a set of optional or mandatory revisions. By 3 June, 2026, the authors should provide a revised submission. The second and final reviewing phase assesses whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. The intent and expectation is that the mandatory revisions can feasibly be addressed within a couple of weeks. The second submission should clearly identify how the mandatory revisions were addressed. To that end, the second submission *must be accompanied by a cover letter* mapping each mandatory revision request to specific parts of the paper. The cover letter will facilitate a quick second review, allowing for confirmation of final acceptance within two weeks. Conversely, the absence of a cover letter will be grounds for the paper’s rejection. Information for Authors of Accepted Papers <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#information-for-auth…> As a condition of acceptance, final versions of all papers must adhere to the ACM Small format. The page limit for the final versions of papers will be *increased by two pages* to help authors respond to reviewer comments and mandatory revisions: 27 pages plus bibliography for a regular paper or Functional Pearl, 14 pages plus bibliography for an Experience Report. Authors of accepted submissions will be required to agree to one of the three ACM licensing options, one of which is Creative Commons CC-BY publication; this is the option recommended by the PACMPL editorial board. A reasoned argument in favour of this option can be found in the article Why CC-BY? published by OASPA, the Open Access Scholarly Publishers Association. The other options are copyright transfer to ACM or retaining copyright but granting ACM exclusive publication rights. PACMPL is a Gold Open Access journal, and authors are encouraged to publish their work under a CC-BY license. Gold Open Access guarantees permanent free online access to the definitive version in the ACM Digital Library, and the recommended CC-BY option also allows anyone to copy and distribute the work with attribution. Gold Open Access has been made possible by generous funding through ACM SIGPLAN, which will cover all open access costs in the event authors cannot. Authors who can cover the costs may do so by paying an Article Processing Charge (APC). PACMPL, SIGPLAN, and ACM Headquarters are committed to exploring routes to making Gold Open Access publication both affordable and sustainable. ACM Author-Izer is a unique service that enables ACM authors to generate and post links on either their home page or institutional repository for visitors to download the definitive version of their articles from the ACM Digital Library at no charge. Downloads through Author-Izer links are captured in official ACM statistics, improving the accuracy of usage and impact measurements. Consistently linking to the definitive version of an ACM article should reduce user confusion over article versioning. After an article has been published and assigned to the appropriate ACM Author Profile pages, authors should visit http://www.acm.org/publications/acm-author-izer-service to learn how to create links for free downloads from the ACM DL. The official publication date is the date the journal is made available in the ACM Digital Library. The journal issue and associated papers will be published no earlier than 1 August, 2026. The official publication date affects the deadline for any patent filings related to published work. Authors of each accepted submission are invited to attend and be available for the presentation of that paper at the conference. The schedule for presentations will be determined and shared with authors after the full program has been selected. ORCID: ORCID provides a persistent digital identifier (an ORCID iD) that you own and control, and that distinguishes you from every other researcher: https://orcid.org/. ACM now require an ORCID iD for every author of a paper, not just the corresponding author. So, the author who is filling out the permission form should make sure they have the ORCID iDs for all of their coauthors before filling out the form. Any authors who do not yet have an ORCID iD can go to https://orcid.org/register to have one assigned. By submitting your article to an ACM Publication, you are hereby acknowledging that you and your co-authors are subject to all ACM Publications Policies, including ACM’s new Publications Policy on Research Involving Human Participants and Subjects. Alleged violations of this policy or any ACM Publications Policy will be investigated by ACM and may result in a full retraction of your paper, in addition to other potential penalties, as per ACM Publications Policy. Artifact Evaluation <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#artifact-evaluation> Authors of papers that are conditionally accepted in the first phase of the review process will be encouraged (but not required) to submit supporting materials for Artifact Evaluation. These items will then be reviewed by an Artifact Evaluation Committee, separate from the paper Review Committee, whose task is to assess how the artifacts support the work described in the associated paper. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Authors of accepted papers will be encouraged to make the supporting materials publicly available upon publication of the papers, for example, by including them as “source materials” in the ACM Digital Library. An additional seal will mark papers whose artifacts are made available, as outlined in the ACM guidelines for artifact badging. Participation in Artifact Evaluation is voluntary and *will not influence* the final decision regarding paper acceptance. Special categories of papers <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#special-categories-o…> In addition to research papers, PACMPL issue ICFP solicits two kinds of papers that do not require original research contributions: Functional Pearls, which are full papers, and Experience Reports, which are limited to half the length of a full paper. Authors submitting such papers should consider the following guidelines. Functional Pearls <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#functional-pearls> A Functional Pearl is an elegant essay about something related to functional programming. Examples include, but are not limited to: - a new and thought-provoking way of looking at an old idea; - an instructive example of program calculation or proof; - a nifty presentation of an old or new data structure; - an interesting application of functional programming techniques; - a novel use or exposition of functional programming in the classroom. While pearls often demonstrate an idea through the development of a short program, there is no requirement or expectation that they do so. Thus, they encompass the notions of theoretical and educational pearls. Functional Pearls are valued as highly and judged as rigorously as ordinary papers, but using somewhat different criteria. In particular, a pearl is not required to report original research, but, it should be concise, instructive, and entertaining. A pearl is likely to be rejected if its readers get bored, if the material gets too complicated, if too much-specialised knowledge is needed, or if the writing is inelegant. The key to writing a good pearl is polishing. A submission that is intended to be treated as a pearl must be marked as such on the submission web page and should contain the words “Functional Pearl” somewhere in its title or subtitle. These steps will alert reviewers to use the appropriate evaluation criteria. Pearls will be combined with ordinary papers for the purpose of computing the conference’s acceptance rate. Experience Reports <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#experience-reports> The purpose of an Experience Report is to describe the experience of using functional programming in practice, whether in industrial application, tool development, programming education, or any other area. Possible topics for an Experience Report include, but are not limited to: - insights gained from real-world projects using functional programming; - comparison of functional programming with conventional programming in the context of an industrial project or a university curriculum project-management, business, or legal issues encountered when using functional programming in a real-world project; - curricular issues encountered when using functional programming in education; - real-world constraints that created special challenges for an implementation of a functional language or for functional programming in general. An Experience Report is distinguished from a normal PACMPL issue ICFP paper by its title, by its length, and by the criteria used to evaluate it. Both in the papers and in any citations, the title of each accepted Experience Report must end with the words “(Experience Report)” in parentheses. The acceptance rate for Experience Reports will be computed and reported separately from the rate for ordinary papers. Experience Report submissions can be at most 12 pages long, excluding bibliography. Each accepted Experience Report will be presented at the conference, but depending on the number of Experience Reports and regular papers accepted, authors of Experience Reports may be asked to give shorter talks. Because the purpose of Experience Reports is to enable our community to understand the application of functional programming, an acceptable Experience Report need not add to the body of knowledge of the functional-programming community by presenting novel results or conclusions. It is sufficient if the report describes an illuminating experience with functional programming, or provides evidence for a clear thesis about the use of functional programming. The experience or thesis must be relevant to ICFP, but it need not be novel. The review committee will accept or reject Experience Reports based on whether they judge the paper to illuminate some aspect of the use of functional programming. Anecdotal evidence will be acceptable provided it is well-argued and the author explains what efforts were made to gather as much evidence as possible. Typically, papers that show how functional programming was used are more convincing than papers that say only that functional programming was used. It can be especially effective to present comparisons of the situations before and after the experience described in the paper, but other kinds of evidence would also make sense, depending on context. Experience drawn from a single person’s experience may be sufficient, but more weight will be given to evidence drawn from the experience of groups of people. An Experience Report should be short and to the point. For an industrial project, it should make a claim about how well functional programming worked and why; for a pedagogy paper, it might make a claim about the suitability of a particular teaching style or educational exercise. Either way, it should produce evidence to substantiate the claim. If functional programming worked in this case in the same ways it has worked for others, the paper need only summarise the results — the main part of the paper should discuss how well it worked and in what context. Most readers will not want to know all the details of the experience and its implementation, but the paper should characterise it and its context well enough so that readers can judge to what degree this experience is relevant to their own circumstances. The paper should take care to highlight any unusual aspects; specifics about the experience are more valuable than generalities about functional programming. If the paper not only describes experience but also presents new technical results, or if the experience refutes cherished beliefs of the functional-programming community, it may be better to submit it as a full paper, which will be judged by the usual criteria of novelty, originality, and relevance. The Program Chair will be happy to advise on any concerns about which category to submit to. About PACMPL <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#about-pacmpl> Proceedings of the ACM on Programming Languages (PACMPL https://pacmpl.acm.org/) is a Gold Open Access journal publishing research on all aspects of programming languages, from design to implementation and from mathematical formalisms to empirical studies. Each issue of the journal is devoted to a particular subject area within programming languages and will be announced through publicised Calls for Papers, like this one. Important update on ACM’s new open access publishing model for 2026 ACM Conferences: <https://icfp26.sigplan.org/track/icfp-2026-icfp-papers#important-update-on-…> Starting January 1, 2026, ACM will fully transition 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). With over 1,800 institutions already part of ACM Open, the majority of ACM-sponsored conference papers will not require APCs from authors or conferences (currently, around 70–75%). Authors from institutions not participating in ACM Open will need to pay an APC to publish their papers, unless they qualify for a geographic or discretionary 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…> . To support a smooth transition and encourage broader ACM Open participation, ACM has introduced a temporary subsidy on APC pricing for 2026, funded directly by ACM. This pricing applies to all articles published in ACM and SIG sponsored conferences taking place in 2026. The subsidized conference pricing for 2026 is as follows: Authors No ACM or SIG members At least 1 ACM or SIG member ACM and SIG Sponsored Conference Article $350 $250 From a lower-middle-income country <https://www.acm.org/publications/policies/lower-middle-income-countries> $175 $125 This represents a 65% discount <https://www.acm.org/publications/openaccess>, funded directly by ACM. Authors are encouraged to help advocate for their institutions to join ACM Open during this transition period.

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