July 2025 - Haskell-Cafe

Correct parsers for bounded integral values
by Stefan Klinger 07 Aug '25

07 Aug '25

Hello everybody =) I've been bugged by the silent overflowing of integer parsers as provided by `base`, `attoparsec`, and others. I'd go so far as to call it a bug when the user types `298` and the parser says `Right 42`. Unfortunately, all parsing libraries I've looked at get this wrong. A [solution][4] is proposed below. I'm asking for feedback on how to continue from here. Kind regards Stefan The following examples can be reproduced with $ git clone 'https://github.com/s5k6/robust-int.git' $ cd robust-int $ cabal repl robust-int:demo Situation --------- This is the current situation with [read][1] from base: > read "298" :: Word8 42 And with [decimal][2] from attoparsec: > A.parseOnly (A.decimal :: A.Parser Word8) $ pack "298" Right 42 And the solution [usually suggested][5] for Parsec (which relies on `read`): parsecWord8 :: P.Parser Word8 parsecWord8 = read <$> P.many1 P.digit > P.runParser parsecWord8 () "" "298" Right 42 Even worse, the latter would rather exhaust memory than realise its input is way out of bounds: > P.runParser parsecWord8 () "" $ repeat '1' ⊥ Also, some 3rd-party libraries get this wrong, e.g., [parsec3-numbers][6]: > P.runParser (PN.decimal :: P.Parser Word8) () "" "298" Right 42 And [megaparsec][8], which is at least nice enough to warn about this in its documentation: > M.parseMaybe (M.decimal :: M.Parsec () String Word8) "298" Just 42 I find this misses the point of a parser validating its input. Solution -------- It is [possible to implement][7] parsers for bounded integral types which verify the bounds of the parsed value *while* parsing, and even doing this without the use of a “bigger” type. The idea is as follows: As usual, we parse digits left to right, and collect the resulting value in an accumulator `acc`, i.e., for each new digit `d`, the accumulator is updated to base * acc + d Nothing new up to here. However, before we start parsing, calculate (lim, m) = upper_bound `divMod` base and before updating the accumulator with another digit `d`, verify that acc < lim || (acc == lim && d <= m) which exactly guarantees that the accumulator will not overflow. The reason why this works is is easily seen by doing the example for `Word16` in base 10: > (maxBound :: Word16) `divMod` 10 (6553,5) > 10 * fst it + snd it 65535 Complexity: This adds a modulo operation and two comparisons for every literal being parsed, plus one comparison for every digit. In order to limit memory consumption, some comparison has to take place during parsing, at least for limiting the number of digits consumed. In total, this does not look too expensive. I have [implemented][4] this idea for `parsec` and `attoparsec` to demonstrate the idea (only for decimal values). What now? --------- Obviously, this *should not be a another library*, trying to fix some aspect of some other libraries. My code is rather intended for demonstration. I'd prefer to help this idea migrate to the libraries (`base`, `parsec`, `attoparsec`, …), where the correct parsers should be. Unfortunately, I got a bit lost when trying to track down the code of `read` in the `base` package. And I think I may have overengineered my solution for attoparsec to accommodate different stream types. Also, I get the impression that Haskell *library* code seems to be written with a different mindset, a deeper understanding of GHC than mine, i.e., more tailored to what the compiler will *actually do* when using the code, trying not to spoil opportunities for optimisation. And I'm not sure I'm up to that task. So I'm asking for feedback on the proposed algorithm, my implementation, and hints on where and how to get this into established libraries. Build instructions ================== $ cabal build $ cabal run demo $ cabal test $ cabal haddock [1]: https://hackage.haskell.org/package/base-4.21.0.0/docs/Prelude.html#v:read [2]: https://hackage.haskell.org/package/attoparsec-0.14.4/docs/Data-Attoparsec-… [3]: https://hackage.haskell.org/package/parsec-3.1.18.0/docs/Text-Parsec-Token.… [4]: https://github.com/s5k6/robust-int [5]: https://stackoverflow.com/questions/24171005/how-to-parse-an-integer-with-p… [6]: https://hackage.haskell.org/package/parsec3-numbers [7]: https://github.com/s5k6/robust-int/blob/master/src/Data/RobustInt/Parsec.hs… [8]: https://hackage.haskell.org/package/megaparsec-9.7.0/docs/Text-Megaparsec-C… -- Stefan Klinger, Ph.D. -- computer scientist o/X http://stefan-klinger.de /\/ https://github.com/s5k6 \ I prefer receiving plain text messages, not exceeding 32kB.

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-i in OPTIONS_GHC
by amindfv＠mailbox.org 30 Jul '25

30 Jul '25

I'd like to update the search path of a Haskell module, using the OPTIONS_GHC pragma. >From the documentation[0], OPTIONS_GHC allows you to set dynamic flags, which `-i` appears to be.[1] Here's a quick demo of what I believe _should_ work, but doesn't: A.hs: {-# OPTIONS_GHC -isrc #-} import B main = print b src/B.hs: module B where b = "!" `ghc A.hs` fails, but (of course) `ghc -isrc A.hs` succeeds. Is there a way to get this to work? Is the current behavior intended? Is what I want a misfeature? (E.g. there are security implications?) Thanks, Tom [0] https://downloads.haskell.org/ghc/latest/docs/users_guide/using.html#comman… [1] https://downloads.haskell.org/ghc/latest/docs/users_guide/flags.html#findin…

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GHC Users Guide PDF?
by amindfv＠mailbox.org 30 Jul '25

30 Jul '25

I notice that as late as May 2023, PDF versions of the GHC Users Guide have been available, e.g. https://downloads.haskell.org/ghc/9.2.8/docs/ . For more recent versions, I can't find them anywhere. "Documentation" on the GHC homepage now links only to the HTML version. Has the team decided to stop pre-rendering a PDF version? That would be a shame; in some contexts a PDF is much more useful than HTML. (Btw: the GHC man page still links to https://downloads.haskell.org/ghc/latest/docs/users_guide.pdf, which is now a 404 - as is the HTML link) Thanks, Tom

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GHC 9.10.3-rc1 is now available
by Zubin Duggal 28 Jul '25

28 Jul '25

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.10.3. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.10.3 is a bug-fix release fixing over 50 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 11 August 2025. We would like to thank Well-Typed, Tweag I/O, Juspay, QBayLogic, Channable, Serokell, 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. 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-9.10/docs/users_guide/9.10.3-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.10.3-rc1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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IFL 2025 - Call For Draft Papers (deadline extension)
by Mart Lubbers 27 Jul '25

27 Jul '25

Please, find below the call for draft papers for IFL 2025. The submission deadline has been extended to August 31. In this CFP we also include the announcement of our keynote speakers and of tutorials to be held on September 29 and 30, prior to IFL. Please forward this to anyone you think may be interested. ===================================================================== IFL 2025 37th Symposium on Implementation and Application of Functional Languages Montevideo, Uruguay October 1-3, 2025 https://www.fing.edu.uy/inco/congresos/ifl2025 ===================================================================== [NEWS: Extended deadline for draft paper submission, Keynote speakers, Tutorials] ### 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 2025 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 ### Keynote speakers - Roberto Ierusalimschy Departamento de Informática, PUC-Rio, Río de Janeiro, Brazil - Iván Pérez NASA Ames Research Center, California, USA ### Tutorials On September 29 and 30, the two days prior to the symposium, four tutorials will be held: - Gradual typing Éric Tanter, University of Chile, Chile - Type Based Static Analysis Jurriaan Hage, Heriot-Watt University, UK - Development of dApps in the UTxO model TxPipe, Argentina - TBA ### Peer-review process Differently from previous editions of IFL, IFL 2025 solicits two kinds of submissions: * Regular papers (12 pages excluding references) * Draft papers for presentations ('weak' limit between 5 and 15 pages) Regular papers will undergo a rigorous review by the program committee, and will be evaluated according to their correctness, novelty, originality, relevance, significance, and clarity. Regular papers can be: accepted for publication in the formal proceedings, accepted for presentation at the symposium or rejected. Draft papers will be screened to make sure that they are within the scope of IFL, and will be accepted for presentation or rejected accordingly. We require that at least one of the authors present the work at IFL 2025. Authors of accepted presentations will be given the opportunity to incorporate the feedback from discussions at the symposium and will be invited to submit a revised full article for the formal post-proceedings after the symposium. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected. ### Important dates Submission of regular papers: June 23, 2025 (extended) Regular papers notification: August 4, 2025 Submission of draft papers: August 31, 2025 (extended) Draft papers notification: September 4, 2025 Deadline for early registration: September 5, 2025 Submission of pre-proceedings version: September 8, 2025 Pre-symposium tutorials September 29-30, 2025 IFL Symposium: October 1-3, 2025 Submission of papers for post-proceedings: December 15, 2025 Notification of acceptance: February 28, 2026 Camera-ready version: March 30, 2026 Deadlines are end of day Anywhere on Earth (UTC-12) (https://www.timeanddate.com/time/zones/aoe) ### 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 draft paper here: https://easychair.org/conferences/?conf=ifl2025 using the track [IFL 2025 - Draft papers]. 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 may be found on the ACM website, as follows: - Full details of the new ICPS publishing model: https://www.acm.org/publications/icps/faq - Full details of the ACM Open program: https://www.acm.org/publications/openaccess - Please direct all questions about the new model to 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: Alberto Pardo, Universidad de la República, Montevideo, Uruguay Marcos Viera, Universidad de la República, Montevideo, Uruguay Publicity Chair: Mart Lubbers, Radboud University, The Netherlands Local Chairs: Alberto Pardo, Universidad de la República, Montevideo, Uruguay Marcos Viera, Universidad de la República, Montevideo, Uruguay ### Program committee: Matteo Cimini, University of Massachusetts Lowell Facundo Domínguez, Tweag João Paulo Fernandes, Universidade do Porto Jeremy Gibbons, Oxford University Jurriaan Hage, Heriot Watt University Jason Hemann, Seton Hall University Maja Hanne Kirkeby, Roskilde University Mart Lubbers, Radboud University Bruno C. D. S. Oliveira, The University of Hong Kong Rinus Plasmeijer, Radboud University Andre Rauber Du Bois, Universidade Federal de Pelotas Rodrigo Ribeiro, Universidade Federal de Ouro Preto Alejandro Russo, Chalmers University of Technology João Saraiva, University of Minho Wenhao Tang, University of Edinburgh Zhixuan Yang, Imperial College London Brent Yorgey, Hendrix College Beta Ziliani, Manas.Tech Viktória Zsók, Eötvös Loránd University ### Venue IFL 2025 will be held physically in Montevideo, Uruguay. See the website for more information. https://www.fing.edu.uy/inco/congresos/ifl2025 ### 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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how to expand ~ in a filepath
by PICCA Frederic-Emmanuel 24 Jul '25

24 Jul '25

Hello, I am trying to open and read the content of this kind of filepath. ~/debian/changelog So is there a prefered way to expand the ~ into the real $HOME. thanks for your help Frédéric Classification de confidentialité SOLEIL Ce message et ses pièces jointes peuvent contenir des informations soumises à des règles de diffusion : * P (Public) : Diffusion libre y compris à l'extérieur de SOLEIL. * I (Interne) : Diffusion libre au sein de SOLEIL, ne doit pas être communiqué à l’extérieur sauf mention spécifique. * C (Confidentiel) : Diffusion restreinte aux personnes autorisées, internes ou externes. Le partage nécessite l'accord de la hiérarchie. * S (Sensible) : Accès restreint aux seuls destinataires. Partage non autorisé. Les informations contenues dans cet e-mail sont la propriété de SOLEIL. Si vous n'êtes pas le destinataire prévu, merci de nous en notifier et de ne pas utiliser, copier ou distribuer les informations qu'il contient.

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Call for Papers: Tests and Proofs (TAP) (Now a Track at FM 2026)
by Achim D. Brucker 24 Jul '25

24 Jul '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: [Haskell-cafe] Correct parsers for bounded integral values
by Olaf Klinke 20 Jul '25

20 Jul '25

> Both approaches > require one comparison per digit read (the number-counting approach > needs to count the digits and test whether the limit of this counter > has been reached, the “modulo” approach needs to check whether `lim` > has been reached). And both approaches need to accumulate the digits > read so far (digit-counting collects the digits and converts them to > a > value just before reading the final digit, “modulo” accumulates the > final value on the go). Some, but not all, parser combinator libraries have a user-defined state component. Since the parser updates its internal state anyways, the overhead might be smaller than anticipated. If the parser is not a monad transformer, a workaround is to newtype the region containing a number literal, so that the parser state can accomodate the extra accumulator. https://hackage.haskell.org/package/parsec-3.1.18.0/docs/Text-Parsec.html#t… https://hackage.haskell.org/package/attoparsec-0.14.4/docs/Data-Attoparsec-… https://hackage.haskell.org/package/megaparsec-9.7.0/docs/Text-Megaparsec-S… > I don't know where to start, `base` just always > happened to be there already. I.e., could someone please help me to > get a simple setup (my usual modus operandi is the shell, cabal, and > an editor) where the base library is accessible for modification and > testing? base is just a package like others. You can download a copy from hackage, unpack and build it with your build tool of choice, can't you? (Never thried that myself, though.) If parsing speed is a concern: For those parsers that build on a parser type class (megaparsec or the parser-combinators package) one can implement a simple parser that has less book-keeping overhead and embed it into fancier parsers, calling the proper parser on the input only in case something goes wrong. https://hackage.haskell.org/package/faster-megaparsec Olaf

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GHC LTS Releases
by Andreas Klebinger 16 Jul '25

16 Jul '25

I'm pleased to announce LTS plans for GHC Read all the details here: https://www.haskell.org/ghc/blog/20250702-ghc-release-schedules.html There is also a discourse thread if you have feedback: https://discourse.haskell.org/t/ghc-lts-releases-the-glasgow-haskell-compil… Best Wishes Andreas

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Combining RequiredTypeArguments and type class methods?
by Anthony Clayden 14 Jul '25

14 Jul '25

On Sun, Jul 13, 2025 at 11:47:36AM +0100, Tom Ellis wrote: > >* There is, however, a known trick. This works: *> Ah yes. Same solution here https://discourse.haskell.org/t/how-to-use-requiredtypearguments-with-typec… Currently, `RequiredTypeArguments` is documented as " only partially implemented in GHC". Full specification to be found in proposal #281. That proposal doesn't give examples of how to write instances for `sizeOf`, as and when we get Dependent Haskell in full. Will it still need the type equality trick? > >* (But I prefer your [Viktor's] solution: the wrapper.)* *>* Yes. That in effect still uses a term-level proxy for the type, as argument to _sizeOf. For example I could go pattern Bool :: Bool pattern Bool = undefined ... _sizeOf Bool ...

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