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heterogeneous container smart constructor question
by Zoran Bošnjak 05 Sep '23

05 Sep '23

Dear haskellers, I am trying to add some type safety to the program in the following situation: There are some distinct 'Item t' types which come in groups. That is: 'EList' container can contain either: - items 0,1 - items 0,1,2,3 - items 0,1,2,3,4,5,6 All other combinations (like items 0,1,2) are invalid and shall be rejected by compiler. The 'EList' implementation (see below) seems to have this property. In addition, I would like to define a smart constructor (mkEList), to simplify EList construction from some linear (no groups) IList type. In other words, mkEList shall slice IList to proper groups. I am aware that I need to use a type class / type families for this. I have tried several approaches, but ghc was not happy with any. What is the correct implementation of mkEList? Here is a sample code and the intended usage: -- (sample build-test.hs) import GHC.TypeLits data Item (t :: Nat) = Item -- List/group of items data IList (ts :: [Nat]) where INil :: IList '[] ICons :: Item t -> IList ts -> IList (t ': ts) nil :: IList '[] nil = INil infixr 5 &: (&:) :: Item t -> IList ts -> IList (t : ts) (&:) = ICons -- Extended list of groups data EList (ts :: [Nat]) (tss :: [[Nat]]) where EList :: IList ts1 -> Maybe (EList ts2 tss) -> EList ts1 (ts2 ': tss) instance Eq (EList ts tss) -- Manual test type T1 = '[0, 1] type T2 = '[ '[2, 3], '[4, 5, 6], '[] ] test1 :: EList T1 T2 test1 = EList (Item @0 &: Item @1 &: nil) Nothing test2 :: EList T1 T2 test2 = EList (Item @0 &: Item @1 &: nil) (Just (EList (Item @2 &: Item @3 &: nil) Nothing)) test3 :: EList T1 T2 test3 = EList (Item @0 &: Item @1 &: nil) (Just (EList (Item @2 &: Item @3 &: nil) (Just (EList (Item @4 &: Item @5 &: Item @6 &: nil) Nothing)))) -- Intended usage -- | Helper function or class method :: IList ? -> EList ? ? mkEList :: a mkEList = undefined el1 :: EList T1 T2 el1 = mkEList ( Item @0 &: Item @1 &: nil) el2 :: EList T1 T2 el2 = mkEList ( Item @0 &: Item @1 &: Item @2 &: Item @3 &: nil) el3 :: EList T1 T2 el3 = mkEList ( Item @0 &: Item @1 &: Item @2 &: Item @3 &: Item @4 &: Item @5 &: Item @6 &: nil) check :: Bool -- expecting True check = and [el1 == test1, el2 == test2, el3 == test3] -- (end of sample) regards, Zoran

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The Haskell Foundation is seeking a new Executive Director
by David Christiansen 05 Sep '23

05 Sep '23

Dear Cafe, I just realized that we didn't yet post this here - apologies! I'll be stopping as ED of the Haskell Foundation at the end of the month, because I got an offer to go back to software development and work on a combination of technologies that I personally find extremely interesting (dependent types, procedural hygienic macros, language embedding, software verification, documentation and tools). It wasn't an easy decision to make, but I won't be disappearing from the world of pure functional programming. This means we need a new ED! You can see details here: https://haskell.foundation/careers/executive-director.html Every application received by the 29th will receive full consideration, but the board will continue taking applications until the new ED has been found. Until 22 September, I have time reserved to meet with people who are interested, but unsure about whether the role is a good fit. I myself have had these concerns - it was my first job not doing research or software development since I was 23 years old, after all. I'm happy to have an honest discussion about the job, how I did it, how someone else with different strengths might do it, what my daily life is like and the constraints that give rise to that, and so forth. Just let me know if you're interested. My canonical farewell post is here: https://discourse.haskell.org/t/an-opportunity-that-i-couldnt-pass-up/7485 Thanks for your support! I'll see you around. David

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Call for Papers: JFP Special Issue on Program Calculation (papers due 1st Dec)
by Graham Hutton 04 Sep '23

04 Sep '23

================================================================== JFP Special Issue on Program Calculation https://tinyurl.com/prog-calc We invite submissions to the Journal of Functional Programming Special Issue on Program Calculation. Notification of intent : 20 October 2023 Submission deadline : 1 December 2023 *** If you are attending the ICFP conference in Seattle this week, please feel free to speak with Nicolas Wu if you have any questions about submitting for the special issue *** SCOPE The idea of program calculation, in which programs are derived from specifications using equational reasoning techniques, has been a topic of interest in functional programming since its earliest days. In particular, the approach allows us to systematically discover how programs can be defined, while at the same time obtaining proofs that they are correct. The aim of this special issue is to document advances that have been made in the field of program calculation in recent years. TOPICS Full-length, archival-quality submissions are solicited on all aspects of program calculation and related topics. Specific topics of interest include but are not limited to: - Program derivation and transformation; - Inductive and co-inductive methods; - Recursion and co-recursion schemes; - Categorical and graphical methods; - Tool support and proof assistants; - Efficiency and resource usage; - Functional algorithm design; - Calculation case studies. The special issue will also consider papers on program calculation that are not traditional research papers. This may include pearls, surveys, tutorials or educational papers, which will be judged by the usual JFP standards for such submissions. Papers will be reviewed as regular JFP submissions, and acceptance in the special issue will be based on both JFP's quality standards and relevance to the theme. NOTIFICATION OF INTENT Authors must notify the special issue editors of their intent to submit by 20 October 2023. The notification of intent should be submitted by filling out the following form, which asks for data to help identify suitable reviewers: tinyurl.com/intent-to-submit If you miss the notification of intent deadline, but still wish to submit, please contact the special-issue editors. SUBMISSIONS Papers must be submitted by 1 December 2023. Submissions should be typeset in LaTeX using the JFP style file, and submitted through the JFP Manuscript Central system. Choose "Program Calculation" as the paper type, so it gets assigned to the special issue. Further author instructions are available from: tinyurl.com/JFP-instructions We welcome extended versions of conference or workshop papers. Such submissions must clearly describe the relationship with the initial publication, and must differ sufficiently that the author can assign copyright to Cambridge University Press. Prospective authors are welcome to discuss submissions with the editors to ensure compliance. SPECIAL-ISSUE EDITORS Graham Hutton <graham.hutton(a)nottingham.ac.uk> Nicolas Wu <n.wu(a)imperial.ac.uk> IMPORTANT DATES We anticipate the following schedule: 20 October 2023 : Notification-of-intent deadline 1 December 2023 : Submission deadline 22 March 2024 : First round of reviews 12 July 2024 : Revision deadline 4 October 2024 : Second round of reviews, if applicable 29 November 2024 : Final versions due ================================================================== 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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ANN: hledger 1.31
by Simon Michael 03 Sep '23

03 Sep '23

I'm pleased to announce hledger 1.31 ! Highlights: - In conversion transactions, costs and equity postings are matched more tolerantly. - The `print` command now more closely replicates the original journal amount styles, which is helpful when round-tripping / cleaning up journal files. - Multi-pivot - the --pivot option can now construct account names from multiple fields. Thank you release contributors Dmitry Astapov, Eric Mertens, Jay Neubrand, and Jonathan Dowland. - https://github.com/simonmichael/hledger/releases/1.31 - https://hledger.org/release-notes.html#hledger-1-31 - https://hledger.org/install What is hledger ? - Fast, reliable, free, multicurrency, double-entry, plain text accounting software for unix, mac, windows, and the web - Built around human-readable, version-controllable plain text files - Inspired by and largely compatible with Ledger CLI, convertible to and from Beancount - Written in Haskell for reliability and longevity. For help getting started or more info, see https://hledger.org and join our Matrix/IRC chat or mail list: https://hledger.org/support . Newcomers, experts, contributors, sponsors, feedback are welcome! For more about plain text accounting, see https://plaintextaccounting.org . Live well and prosper, -Simon

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OAuth on gitlab.haskell.org
by Julian Brunner 28 Aug '23

28 Aug '23

Hello, I last used gitlab.haskell.org in 2022 via OAuth on my GitHub account. However, this seems to no longer be an option. The account itself (https://gitlab.haskell.org/julianbrunner) seems to still exist, but I am unable to log in or request a password reset. I could not find any way to contact anyone on gitlab.haskell.org or any information on the removal of the OAuth option. Does anyone know how I can get my account back or who I should contact to get this sorted out? Cheers, Julian

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debugging <<loop>> exception
by Dennis Raddle 27 Aug '23

27 Aug '23

I'm getting Exception: <<loop>>. It doesn't print the line number. When I load the program into ghci, it still doesn't print the line number. When I trace the program in ghci it never gets to the point of emitting the exception. I set up my program in stack. I tried both "stack ghci" and just "ghci".. the latter to make sure it wasn't using any compiled code (at least in my own code). If it doesn't print a line number does this mean it's happening in compiled code? Any ideas how I can go about debugging this?

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Munich Haskell Meeting, 2023-08-30 @ 19:30
by Leah Neukirchen 26 Aug '23

26 Aug '23

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, August 30 at Augustiner-Kurgarten (De-la-Paz-Straße 10, 80639 München) at 19h30. Different location as Rumpler is on summer holidays! For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this nuudel so we can reserve enough seats! It is OK to add yourself to the nuudel anonymously or pseudonymously. https://nuudel.digitalcourage.de/xYna3xETL2UACtzT Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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IOSim on Hackage
by coot＠coot.me 26 Aug '23

26 Aug '23

Hello dear Haskell-Cafe, I realised that I haven't shared here that we (the networking team of IOG) released io-sim on Hackage. We found and fixed countless bugs thanks to it, including some concurrent ones. Here's a blog post which I wrote some time ago: https://engineering.iog.io/2023-04-14-io-sim-annoucement https://hackage.haskell.org/package/io-sim https://hackage.haskell.org/package/io-classes Cheers, Marcin Szamotulski

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[ANNOUNCE] GHC 9.4.7 is now available
by Zubin Duggal 26 Aug '23

26 Aug '23

The GHC developers are happy to announce the availability of GHC 9.4.7. Binary distributions, source distributions, and documentation are available at https://downloads.haskell.org/ghc/9.4.7 The GHC developers are happy to announce the availability of GHC 9.4.7. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org](https://downloads.haskell.org/ghc/9.4.7). This release is primarily a bugfix release addressing some issues found in 9.4.6. These include: * A bump to bytestring-0.11.5.2 allowing GHC to be bootstrapped on systems where the bootstrap compiler is built with the `pthread_condattr_setclock` symbol available (#23789). * A number of bug fixes for scoping bugs in the specialiser, preventing simplifier panics (#21391, #21689, #21828, #23762). * Distributing dynamically linked alpine bindists (#23349, #23828). * A bug fix for the release notes syntax, allowing them to built on systems with older python and sphinx versions (#23807, #23818). * ... and a few more. See the [release notes] for a full accounting. 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 compiling, - Zubin [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.4.7/docs/users_guide/9.4.7-notes.html

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[ANNOUNCE] GHC 9.4.6 is now available
by Ben Gamari 25 Aug '23

25 Aug '23

The GHC developers are happy to announce the availability of GHC 9.4.6. Binary distributions, source distributions, and documentation are available at https://downloads.haskell.org/ghc/9.4.6 This release is primarily a bugfix release addressing some issues found in 9.4.6. These include: * Many bug fixes for the simplifier, preventing compiler panics, loops and incorrect code generation (#22761, #22549, #23208, #22761, #22272, #23146, #23012, #22547). * Bug fixes for the typechecker involving newtype family instances, making type equalities more robust and bugs having to do with defaulting representation polymorphic type variables (#23329, #23333, #23143, #23154, #23176). * Some bug fixes for code generation, particularly on the aarch64 backend, including adding more memory barriers for array read operations (#23541, #23749). * Some bug fixes for windows builds, ensuring the reliablility of IO manager shutdown and a bug fix for the RTS linker on windows (#23691, #22941). * A bug fix for the non-moving GC ensuring mutator allocations are properly accounted for (#23312). * A bug fix preventing some segfaults by ensuring that pinned allocations respect block size (#23400). * Many bug fixes for the bytecode interpreter, allowing a greater subset of the language to be interpreted (#22376, #22840, #22051, #21945, #23068, #22958). * ... and a few more. See the [release notes] for a full accounting. 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 compiling, - Zubin & Ben [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.4.6/docs/users_guide/9.4.6-notes.html

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