- Haskell-Cafe - Haskell.org

restore type from existential
by zoran.bosnjak＠via.si 10 Jan '24

10 Jan '24

Dear haskellers, if for example I have the following (simplified) situation: import GHC.TypeLits type MyTypes = '[ () -- index 0 , Char -- index 1 , Int -- index 2 ] data SNat (n :: Nat) where SZ :: SNat 0 SS :: SNat n -> SNat (n+1) data Wrap where WrapUnsafe :: SNat n -> t -> Wrap t1 = WrapUnsafe SZ () :: Wrap t2 = WrapUnsafe (SS SZ) 'x' :: Wrap t3 = WrapUnsafe (SS (SS SZ)) (1::Int) :: Wrap Is it possible to have an 'unwrap' function? That is: to combine MyType types table and the type index... to get the exact type back. Something in the form: unwrapUnsafe :: Wrap -> t unwrapUnsafe (WrapUnsafe (ix::SNat n) (val::t)) = undefined x1 = unwrapUnsafe t1 x2 = unwrapUnsafe t2 x3 = unwrapUnsafe t3 GHC didn't like any of my attempt. Is it even possible? regards, Zoran

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[ANNOUNCE] GHC 9.6.4 is now available
by Zubin Duggal 09 Jan '24

09 Jan '24

The GHC developers are happy to announce the availability of GHC 9.6.4. Binary distributions, source distributions, and documentation are available on the [release page](https://www.haskell.org/ghc/download_ghc_9_6_4.html). This release is primarily a bugfix release addressing a few issues found in the 9.6 series. These include: * A fix for a bug where certain warnings flags were not recognised (#24071) * Fixes for a number of simplifier bugs (#23952, #23862). * Fixes for compiler panics with certain package databases involving unusable units and module reexports (#21097, #16996, #11050). * A fix for a typechecker crash (#24083). * A fix for a code generator bug on AArch64 platforms resulting in invalid conditional jumps (#23746). * Fixes for some memory leaks in GHCi (#24107, #24118) * And a few other fixes A full accounting of changes can be found in the [release notes]. As some of the fixed issues do affect correctness users are encouraged to upgrade promptly. We would like to thank Microsoft Azure, GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, 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. Happy hacking! -Zubin [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.6.4/docs/users_guide/9.6.4-notes.html

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Technical Working Group: Call for Volunteers
by Jose Calderon 03 Jan '24

03 Jan '24

Hello, The Haskell Foundation Technical Working Group (TWG) <https://github.com/haskellfoundation/tech-proposals/blob/main/proposals/PRO…> serves as an advisory organization for both the HF management and the Haskell community as a whole, by evaluating specific proposals for projects that can have broad, ecosystem-wide effects. These proposals can be: - Community RFCs that seek the community’s input on a project - Community projects that will be executed primarily by the proposer, but seek administrative or financial support from the HF - HF projects that a community member would like us to execute - Other topics of relevance to the community Volunteers wanted! We presently have three openings on the working group, and we’re seeking volunteers. Members are expected to attend a monthly meeting, to participate in and moderate discussion threads regarding specific proposals, and to evaluate proposals for their technical merits. From time to time, committee members may also be asked to help a community member revise their proposal. The ability to communicate well and respectfully is important for any potential member. These discussions have a real impact on the Haskell ecosystem, so this is an opportunity to give back in a meaningful way. If you are interested, or if you know someone who might be, please get in touch with me at director(a)haskell.foundation! You don’t have to be a long-term Haskeller, or someone who is deeply embedded in Haskell development - we have members with this background already. If you are unsure as to whether you would fit in, please get in touch, and we can have a chat about it. We would like to have members with diverse backgrounds, professional experiences, and knowledge. All self-nominations must be submitted by the end of the day on Jan 12th 2024. Best wishes, Jose

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[TFP (and TFPiE) 2024] Call For Participation (January 9-12, Seton Hall University, NJ, USA)
by Peter Achten 22 Dec '23

22 Dec '23

# TFP 2024 -- Call For Participation (trendsfp.github.io) ## Venue TFPiE and TFP will take place in-person at Seton Hall University, New Jersey in the United States. ## Dates TFPiE Workshop: Tuesday 9th January, 2024 TFP Symposium: Wednesday 10th - Friday 12th January, 2024 The Symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions. ## Keynote speakers We are happy to have the following keynotes in the programme: * Jeremy Gibbons, Oxford University * Benjamin Pierce, University of Pennsylvania * John Reppy, University of Chicago ## Programme The programme schedule can be found here: trendsfp.github.io/schedule.html ## Excursion and banquet After lunch on Thursday there is a private guided tour of the Thomas Edison National Historical Park and Museum. Thursday evening we have the TFP banquet at Forno's of Spain. During dinner the winners of the best paper awards of last year's TFP will be announced.

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RFC: Changes to the Haskell Symposium
by J. Garrett Morris 20 Dec '23

20 Dec '23

Dear Haskellers, In recent years, submissions to the Haskell Symposium have dropped precipitously: from 37 in 2017 to just 15 in 2023. This has made it increasingly challenging for the program committee to put together a program that is vibrant and intellectually rigorous. The Haskell Symposium steering committee has developed two proposals to reinvigorate the Symposium. The first is to invite a new category of presentations of work-in-progress results; the second is to submit accepted papers to the Journal of Functional Programming for publication rather than continuing the Symposium's proceedings. A full description of the proposed changes can be found on the Haskell Foundation's GitHub: https://github.com/haskellfoundation/tech-proposals/pull/62. We invite feedback from the community, particularly on how these changes would effect your participation (either as authors or attendees) in the future. Yours, /g J. Garrett Morris PC Co-chair, 2024 Haskell Symposium For the Haskell Symposium Steering Committee

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Call for Participation: BOB 2024 (Berlin, March 15)
by Stefan Wehr 15 Dec '23

15 Dec '23

========================================================================= BOB 2024 Conference “What happens if we simply use what’s best?” March 15, 2024, Berlin https://bobkonf.de/2024/ Program: https://bobkonf.de/2024/program.html Registration: https://bobkonf.de/2024/registration.html ========================================================================= BOB conference is a place for developers, architects, and decision-makers to explore technologies beyond the mainstream in software development and to find the best tools available to software developers today. Our goal is for all participants of BOB to return home with new insights that enable them to improve their own software development experience. The program features 14 talks and 8 tutorials on current topics: https://bobkonf.de/2024/program.html Talk subjects includes functional programming, property-based testing, service API design, programming for spacecraft, accessibility, hypermedia, business processes, software analytics, event-based communication and zero-knowledge proofs. BOB will feature tutorials on F#, Haskell, Lean, SwiftUI, Copilot, the K Framework, functional domain modelling, and Liberating Structures. Andreas Rossberg will give the keynote talk. Registration is open - online tickets are all under 200€, and many discount options are available, as are grants for members of groups underrepresented in tech: https://bobkonf.de/2024/registration.html

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Package takeover request for socks
by Markus Läll 14 Dec '23

14 Dec '23

Hi I would like to take over maintainership of the socks package (as in the SOCKS network proxy protocol). Vincent announced archiving the package in September[1] (I'm also cc'ing him here). The github repository is here[2]. Unless there are objections, my plan is to simply maintain it under my own github account, because when I took over rapid, I created a new github organization for it. But until there are other people interested in contributing, then having an org for each library is not worth it IMO. [1] https://twitter.com/vincenthz/status/1704395906374889934 [2] https://github.com/vincenthz/hs-socks -- Markus Läll

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ICFP 2024: Call for Workshops and Co-Located Events
by ICFP Publicity 12 Dec '23

12 Dec '23

CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS ICFP 2024 29th ACM SIGPLAN International Conference on Functional Programming September 2 - 7, 2024 Milan, Italy https://icfp24.sigplan.org/ The 29th ACM SIGPLAN International Conference on Functional Programming will be held in Milan, Italy on September 2 - 7, 2024, with the option of virtual participation. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as symposiums) to be affiliated with ICFP 2024 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on September 2nd (the day before ICFP) and September 6-7th (the two days after ICFP). A separate call for Call for Tutorial, Panel, and Discussion Proposals is going to be circulated later. ---------------------------------------------------------------------- Submission details Deadline for submission: January 11, 2024 Notification of acceptance: January 19, 2024 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2024 workshop co-chairs (Chandrakana Nandi and Yannick Forster) via email to chandra(a)certora.com yannick.forster(a)inria.fr by January 11, 2024. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified whether their event proposal is accepted by January 19, 2024, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2024-files/icfp24-workshops-form.txt.docx PC Template: http://www.icfpconference.org/icfp2024-files/pc-template.xlsx Further information about SIGPLAN sponsorship is available at: http://www.sigplan.org/Resources/Proposals/Sponsored/ ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2024 organizing committee, together with the members of the SIGPLAN executive committee. Workshop Co-Chair: Chandrakana Nandi (Certora) Workshop Co-Chair: Yannick Forster (Inria) General Chair: Marco Gaboardi (Boston University) Program Chair: Brigitte Pientka (McGill University) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Chandrakana Nandi and Yannick Forster), via email to chandra(a)certora.com end yannick.forster(a)inria.fr

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Issues with static linking of a C ".a" library with cabal
by Hécate 11 Dec '23

11 Dec '23

Hi everyone, I'm hitting a number of roadblocks while trying to embed a ".a" file (and its headers) in Haskell code. The setup is the following: I have a bindings library that handles all of the cAPI FFI declarations, and a consumer that does not directly depend on the underlying C library. As such, I use a combination of extra-bundled-libraries, include-dirs and install-includes stanzas in my cabal file: elifflag(bundled-libsodium) extra-bundled-libraries: Csodium include-dirs: include install-includes: include/sodium.h include/sodium/core.h include/sodium/crypto_aead_aes256gcm.h […] (full file here: https://github.com/haskell-cryptography/libsodium-bindings/blob/37-libsodiu…) It all seemed to work on my day-to-day system, but further tests on a system that did not have libsodium installed system-wide showed that there's still a missing part: |/usr/bin/ld.gold:error:cannotfind-lsodium collect2:error:ldreturned1exitstatus `gcc'failedinphase`Linker'.(Exitcode:1)| At this point I am simply baffled, because I thought that I had the right invocation for all of this to work. What else can I do? Am I missing something obvious? I have opened a ticket here with a bit more details: https://github.com/haskell/cabal/issues/9509 Cheers, Hécate -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW:https://glitchbra.in RUN: BSD

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OverloadedStrings, but with compile-time invariants
by Max Ulidtko 11 Dec '23

11 Dec '23

Greetings @cafe, Transparent wrapping of string literals into custom types, driven automatically by type inference, is of course very useful. I'm getting huge mileage off GHC's OverloadedStrings when working with e.g. the Text type: class IsString a where fromString :: String -> a instance IsString Text {- ... -} greeting :: Text greeting = "Hello" But I hope there's possibly room for improvement. I've got a bag of several use-cases; perhaps the simplest is the following. Consider a type called NonEmptyText which is a (wrapper around) Text, but with an added invariant that the contained text is never the empty string "". Depending on codebase, such a type can be very useful too, allowing to offload the burden of keeping track of the invariant onto machine; the typechecker will show me all the spots to handle, current or future ones. IOW, this type enables writing a non-boolean-blind null check, toNonEmptyText :: ToText str => str -> Maybe NonEmptyText — which makes not only the programmer, but also the compiler, aware of the null-check result. I'm focusing the example on Text to somewhat maintain generality of the idea. NonEmpty Char can be an alternative formulation of "non-empty String"; length-indexed vectors could possibly handle this too. But there're all sorts of invariants besides non-emptiness one may wish to express. I'll omit other examples; but to summarize, I've got plenty of practical motivation to get "smart literals". And to the point: IsString as it stands, forces us to write much unsatisfactory instances: instance IsString NonEmptyText where fromString (c:cs) = NonEmptyText.new c cs fromString [] = error "unavoidable runtime panic" -- argh ... despite fromString being invoked, presumably with OverloadedStrings, on a string literal — which is statically known at compile-time. I'd imagine upgrading the interface with GHC's own TypeLits: class KnownSymbol lit => IsString' str lit where fromString' :: proxy lit -> str This 2-parameter formulation of IsString enables pretty straightforward user code, along the lines of: type family MyInvariant (s :: Symbol) :: Constraint where MyInvariant "" = TypeError ('Text "Empty string literal") MyInvariant _s = () instance (MyInvariant lit, KnownSymbol lit) => IsString' NonEmptyText lit where fromString' = nothingImpossible . NeT.fromText . toText . symbolVal where nothingImpossible (Just x) = x nothingImpossible Nothing = error "typelevel invariant violated" text1, text2 :: NonEmptyText text1 = fromString' $ Proxy @"hello, types" text2 = fromString' $ Proxy @"" -- compile error here, as expected! With the primes, this is possible to write today. With AllowAmbiguousTypes, the unwieldy syntax can be abbreviated somewhat, e.g. smartLiteral @"overloaded string literal with compiler-checked invariant" — but is still rather awkward... in the same way that ubiquitous T.pack is annoying enough to want to enable OverloadedStrings and stop seeing it all over the place. The question is, could this IsString' somehow become the IsString that OverloadedStrings is friends with? I guess, not soon, with compatibility in mind... But in principle? Is it even worth trying to pursue the GHC Proposal path? Perhaps a new extension OverloadedTypelevelStrings? Relatedly... Can a GHC Plugin do this? And overall, to zoom out of "XY Problem" pitfalls: am I missing a neater way to have "partial" IsString instances, those that can reject some literals at compile-time? Having this code work is the goal: text1, text2 :: NonEmptyText text1 = "hello, types" text2 = "" -- compile error Best regards, Max

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