November 2023 - Haskell-Cafe

A question about type families conflicting instances
by Darryn 21 Nov '23

21 Nov '23

Sir/Madam, I have familiarity with Haskell and have recently returned to using it on a small project, and have just taken a crack at using type families for the first time. I've used functional dependencies more in the past. My example below is a greatly simplified version of what I'm trying to do; for context, the overall purpose is a clean representation of logical forms across languages for abstract case analysis for theorem-proving for certain multimodal logics. The idea represented here is a unified representation for sentential forms and labelled sentential forms. The instance for the latter would be defined in terms of the instance for the former, but to keep it as simple as possible, the snippet here just has a separate (nonsense) implementation of three functions f1,f2,f3 that represent the pattern. I understand that that I'm running into overlapping instances but am unsure about how to correct it, and I couldn't find anything to address this in a search of the haskell-cafe archive (which is not to say that it isn't there, just that I couldn't find and/or recognise it). I'm sure it will be a simple matter to point me in the right direction here for people with more experience. Thank you to anyone in advance who can help; I do really appreciate it. ------------------------------------------------------------------------------- {-# LANGUAGE TypeFamilies, TypeFamilyDependencies, MultiParamTypeClasses, FlexibleInstances #-} -- A simplified model for sentences. data S a = SA a (S a) | SB a (S a) | SC String deriving (Eq, Show) -- A simplified model for what will be abstract case analysis: data Form a b = FA a b | FB deriving (Eq, Show) -- A simplified a model for the case analysis class: class (F a ~ b) => Formable a b where type F a = t | t -> a f1 :: b -> Form a b f2 :: b -> b f3 :: b -> Bool -- Simple test instance of Formable for S: instance Formable a (S a) where type F a = S a f1 (SA a y) = FA a y f1 (SB a y) = FA a y f1 (SC x) = FB f2 (SA a y) = SA a y f2 (SB a y) = SA a y f2 (SC x) = SC "nothing" f3 (SA a y) = False f3 (SB a y) = False f3 (SC _) = True -- Some test instances all work fine: -- > f1 (SA "a" (SB "b" (SC "c"))) -- > f2 (SA "a" (SB "b" (SC "c"))) -- > f3 (SA "a" (SB "b" (SC "c"))) -- A model of a wrapper for sentences to iadd integer labels: data W a = W Int (S a) deriving (Eq, Show) -- Test instance modelling an instance for labelled sentences: instance Formable a (W a) where type F a = W a f1 (W k (SA a y)) = FA a (W k y) f1 (W k (SB a y)) = FA a (W k y) f1 (W k (SC x)) = FB f2 (W k x) = W (1+k) x f3 (W k (SA a y)) = False f3 (W k (SB a y)) = False f3 (W k (SC _)) = True -- Intend to re-implement f1,f2,f3 in terms of the instance for S once -- I can convince GHC to let both instances stand. ------------------------------------------------------------------------------- Everything is dandy if either of the two instances, for S and for W, are provided, but GHC is not at all impressed with the idea of having both. GHCi reports the following error. Test.hs:29:10: error: Conflicting family instance declarations: F a = S a -- Defined at Test.hs:29:10 F a = W a -- Defined at Test.hs:51:10 Regards, D.

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Re: [Haskell-cafe] Haskell Usage
by Adrian Cochrane 15 Nov '23

15 Nov '23

Hi from New Zealand! My Haskell usage is more hobbyist than academic or industrial, but I've got a massive personal project written in Haskell (a browser engine). And I'm actively for one of my upcoming contracts (a converter between metadata formats) to use Haskell! I find I'm more productive in Haskell, and that my code is of generally higher quality. Its certainly not a popular language (neither is Erlang) though, which I have to actively plan for when suggesting it for a project. But given the dominance of C/C++, does that count for much? On 16/11/2023 1:00 am, haskell-cafe-request(a)haskell.org wrote: > Send Haskell-Cafe mailing list submissions to > haskell-cafe(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > or, via email, send a message with subject or body 'help' to > haskell-cafe-request(a)haskell.org > > You can reach the person managing the list at > haskell-cafe-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Haskell-Cafe digest..." > > > Today's Topics: > > 1. Haskell Usage (Henrique Caldeira) > 2. Re: Haskell Usage (Brandon Allbery) > 3. Re: Haskell Usage (Henning Thielemann) > 4. Re: Haskell Usage (Jo Durchholz) > 5. Re: Haskell Usage (MigMit) > 6. Re: Haskell Usage (Ivan Perez) > 7. Re: Haskell Usage (Jared Tobin) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 14 Nov 2023 21:27:57 +0000 (GMT+00:00) > From: Henrique Caldeira <h.caldeira(a)ua.pt> > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Haskell Usage > Message-ID: <aae4e8e1-bf10-4bd5-bf58-9566b2a0be04(a)ua.pt> > Content-Type: text/plain; charset="utf-8" > > Good Evening from Portugal, > > I write to you about the usage of Haskell because I had a professor recommending me Erlang instead because Haskell was "more for academic purposes", which left me wondering if all my time spent was spent only for curiosity sake. > > I want to know how true my professor's statement is. > > I am very passionate about Haskell, although I admit the ecosystem can be confusing sometimes (for example, when to use cabal or stack, which versions of packages to use in order to avoid conflicts, or simply installing them through nixos or arch can be a learning process). > > Would love to hear your thoughts about all of this and thank you with all my heart. > > Lastly, all these wonderings are asked in a curious, "wanting to learn more" mindset. > > Kind regards, > Henrique Caldeira >

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How to use the GPU in Apple M2 from Haskell?
by David Banas 15 Nov '23

15 Nov '23

Does anyone have a good reference for explicitly accessing the GPU in the new Apple M2 chip from a user Haskell program?

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Re. Haskell Usage
by Rishiyur Nikhil 15 Nov '23

15 Nov '23

> Haskell was "more for academic purposes", The Bluespec Hardware Design Languages BSV (Bluespec SystemVerilog) and BH (Bluespec Haskell) digital hardware circuit design have been in industrial production and commercial use for over 20 years now. They have been used inside ST Micro, Texas Instruments, IBM, Qualcomm, Google, Galois and other companies, for ASIC and FPGA products and for high-level hardware prototyping and architecture exploration. The BSV and BH languages are themselves heavily inspired by Haskell. The 'bsc' compiler for BSV and BH is written entirely in Haskell, and has been in continuous use/development/maintenance/improvement for 20 years, and constitutes about 125K lines of Haskell. The 'bsc' compiler was open-sourced a few years ago and continues to be actively used and maintained: https://github.com/B-Lang-org/bsc The Haskell code for the compiler is in the src/ directory. Nikhil

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Haskell Usage
by Henrique Caldeira 14 Nov '23

14 Nov '23

Good Evening from Portugal, I write to you about the usage of Haskell because I had a professor recommending me Erlang instead because Haskell was "more for academic purposes", which left me wondering if all my time spent was spent only for curiosity sake. I want to know how true my professor's statement is. I am very passionate about Haskell, although I admit the ecosystem can be confusing sometimes (for example, when to use cabal or stack, which versions of packages to use in order to avoid conflicts, or simply installing them through nixos or arch can be a learning process). Would love to hear your thoughts about all of this and thank you with all my heart. Lastly, all these wonderings are asked in a curious, "wanting to learn more" mindset. Kind regards, Henrique Caldeira

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Journal of Functional Programming - Call for PhD Abstracts
by Graham Hutton 13 Nov '23

13 Nov '23

Dear all, If you or one of your students recently completed a PhD (or Habilitation) in the area of functional programming, please submit the dissertation abstract for publication in JFP: simple process, no refereeing, open access, 200+ published to date, deadline 30th November 2023. Please share! Best wishes, Graham Hutton ============================================================ CALL FOR PHD ABSTRACTS Journal of Functional Programming Deadline: 30th November 2023 http://tinyurl.com/jfp-phd-abstracts ============================================================ PREAMBLE: Many students complete PhDs in functional programming each year. As a service to the community, twice per year the Journal of Functional Programming publishes the abstracts from PhD dissertations completed during the previous year. The abstracts are made freely available on the JFP website, i.e. not behind any paywall. They do not require any transfer of copyright, merely a license from the author. A dissertation is eligible for inclusion if parts of it have or could have appeared in JFP, that is, if it is in the general area of functional programming. The abstracts are not reviewed. Please submit dissertation abstracts according to the instructions below. We welcome submissions from both the student and the advisor/supervisor although we encourage them to coordinate. Habilitation dissertations are also eligible for inclusion. ============================================================ SUBMISSION: Please submit the following information to Graham Hutton <graham.hutton(a)nottingham.ac.uk> by 30th November 2023. o Dissertation title: (including any subtitle) o Student: (full name) o Awarding institution: (full name and country) o Date of award: (month and year; depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise) o Advisor/supervisor: (full names) o Dissertation URL: (please provide a permanently accessible link to the dissertation if you have one, such as to an institutional repository or other public archive; links to personal web pages should be considered a last resort) o Dissertation abstract: (plain text, maximum 350 words; you may use \emph{...} for emphasis, but we prefer no other markup or formatting; if your original abstract exceeds the word limit, please submit an abridged version within the limit) Please do not submit a copy of the dissertation itself, as this is not required. JFP reserves the right to decline to publish abstracts that are not deemed appropriate. ============================================================ PHD ABSTRACT EDITOR: Graham Hutton School of Computer Science University of Nottingham Nottingham NG8 1BB United Kingdom ============================================================ 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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Trouble installing example code for Parallel and Concurrent Programming in Haskell
by David Banas 12 Nov '23

12 Nov '23

I just picked up a copy of “Parallel and Concurrent Programming in Haskell”. And I’m trying to follow the instructions on p.4 for getting the examples installed, but having trouble: [23-11-10 9:49] dbanas@Davids-Air-M2:~/prj % cabal unpack parconc-examples Downloading parconc-examples-0.4.8 Downloaded parconc-examples-0.4.8 Unpacking to parconc-examples-0.4.8/ [23-11-10 9:50] dbanas@Davids-Air-M2:~/prj % pushd parconc-examples-0.4.8 ~/prj/parconc-examples-0.4.8 ~/prj ~ [23-11-10 9:50] dbanas@Davids-Air-M2:~/prj/parconc-examples-0.4.8 % cabal install --only-dependencies cabal: Could not resolve dependencies: [__0] trying: parconc-examples-0.4.8 (user goal) [__1] next goal: base (dependency of parconc-examples) [__1] rejecting: base-4.17.2.0/installed-4.17.2.0 (conflict: parconc-examples => base>=4.5 && <4.14) [__1] skipping: base-4.19.0.0, base-4.18.1.0, base-4.18.0.0, base-4.17.2.0, base-4.17.1.0, base-4.17.0.0, base-4.16.4.0, base-4.16.3.0, base-4.16.2.0, base-4.16.1.0, base-4.16.0.0, base-4.15.1.0, base-4.15.0.0, base-4.14.3.0, base-4.14.2.0, base-4.14.1.0, base-4.14.0.0 (has the same characteristics that caused the previous version to fail: excluded by constraint '>=4.5 && <4.14' from 'parconc-examples') [__1] rejecting: base-4.13.0.0, base-4.12.0.0, base-4.11.1.0, base-4.11.0.0, base-4.10.1.0, base-4.10.0.0, base-4.9.1.0, base-4.9.0.0, base-4.8.2.0, base-4.8.1.0, base-4.8.0.0, base-4.7.0.2, base-4.7.0.1, base-4.7.0.0, base-4.6.0.1, base-4.6.0.0, base-4.5.1.0, base-4.5.0.0, base-4.4.1.0, base-4.4.0.0, base-4.3.1.0, base-4.3.0.0, base-4.2.0.2, base-4.2.0.1, base-4.2.0.0, base-4.1.0.0, base-4.0.0.0, base-3.0.3.2, base-3.0.3.1 (constraint from non-upgradeable package requires installed instance) [__1] fail (backjumping, conflict set: base, parconc-examples) After searching the rest of the dependency tree exhaustively, these were the goals I've had most trouble fulfilling: base, parconc-examples Thanks, -db

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[ANNOUNCE] GHC 9.4.8 is now available
by Zubin Duggal 10 Nov '23

10 Nov '23

The GHC developers are happy to announce the availability of GHC 9.4.8. Binary distributions, source distributions, and documentation are available on the [release page](/download_ghc_9_4_8.html). This release is primarily a bugfix release addressing a few issues found in the 9.4 series. These include: * A fix for a recompilation checking bug where GHC may miss changes in transitive dependencies when deciding to relink a program (#23724). * A fix for a code generator bug on AArch64 platforms resulting in invalid conditional jumps (#23746). * Support for `-split-sections` on Windows. * Enabling `-split-sections` for various Linux and Windows binary distributions, enabling GHC to produce smaller binaries on these platforms. * 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 compiling! -Zubin [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.4.8/docs/users_guide/9.4.8-notes.html

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[ANN] mig-0.2 library to build servers and clients
by Anton Kholomiov 09 Nov '23

09 Nov '23

I’m happy to announce the latest release of mig-0.2 <https://github.com/anton-k/mig> library. It is a library to write composable servers for simple / boring haskell. The main focus of this release is the ability to serve Swagger UI from the server with ease and ability to create clients from the same code as servers. I’m happy to confirm that both goals are reached with this release. The tutorial for the library <https://anton-k.github.io/mig/> was created. Also there are many other improvements: - OpenApi schema for servers - swagger servers support (we can add swagger to server with one line of code: withSwagger def server ) - clients from the same code as servers - redesign of internal types - redesign of DSL for routes - many ergonomic improvements - packages for extra utils - split of mig package to several packages: - mig <https://hackage.haskell.org/package/mig> - core - mig-wai <https://hackage.haskell.org/package/mig-wai> - rendering servers to wai apps - mig-client <https://hackage.haskell.org/package/mig-client> - clients - mig-extra <https://hackage.haskell.org/package/mig-extra> - extra utils - mig-server <https://hackage.haskell.org/package/mig-server> - mig servers with batteries - mig-swagger-ui <https://hackage.haskell.org/package/mig-swagger-ui> - swagger ui server - tutorial and quickstart guide <https://anton-k.github.io/mig/> on github pages - CI for repo with formatter, build and tests and update of docs on github pages The internal type for Servers was redesigned so that we assemble the handler function with API description at the same time. In the first release it was just a handler function under the hood. As a refresher mig <https://github.com/anton-k/mig> is a family of libraries to write lightweight, simple, type-safe and composable servers. It strives to be in the middle ground between scotty and servant. To be composable, flexible and type-safe as servant and simple and lightweight in concepts as scotty. One thing that interesting to think about as Server is a first-class value and all servers have the same type and we have just a small number of functions to compose them (they are link server to path and make alternative routes with Monoid) it’s interesting to explore the possibility of creation small grain-like servers for typical tasks. For example, a server can be a function from interfaces (logging, DB or something else) to server value and we can join them together on various paths. This idea is interesting to consider. Thanks to Ambros for contribution. Also I’d like to thank the authors of packages servant, servant-swagger-ui and servant-openapi3 packages for inspiration for my work in this release. Many lines of code are influenced by those packages. Links: - github <https://github.com/anton-k/mig> - tutorial <https://anton-k.github.io/mig/> - mig on hackage <https://hackage.haskell.org/package/mig> also see packages mig-server <https://hackage.haskell.org/package/mig-server> and mig-client <https://hackage.haskell.org/package/mig-client>. - examples <https://github.com/anton-k/mig/tree/main/examples/mig-example-apps> Cheers, Anton

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[ANN] Copilot 3.17
by Ivan Perez 09 Nov '23

09 Nov '23

Hi everyone!! We are very excited to announce Copilot 3.17 [2]. Copilot is a stream-based EDSL in Haskell for writing and monitoring embedded C programs, 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. Copilotis being used at NASA in drone test flights. Through the NASA tool Ogma [1] (also written in Haskell), Copilot also serves as a runtime monitoring backend for NASA's Core Flight System, Robot Operating System (ROS2), and FPrime (the software framework used in the Mars Helicopter) applications. This release introduces compatibility with what4 versions up to 1.5.1, and replaces several functions in copilot-core. The second change is a breaking change: the functions replaced have been deprecated and new alternatives introduced instead. As always, we're releasing exactly 2 months since the last release. Our next release is scheduled for Jan 7th, 2024. In our last announcement, we mentioned that Copilot has received full approval for release as NASA Class D open-source software. Current emphasis is on increasing test coverage for the two remaining libraries without tests (copilot-libraries and copilot-theorem), removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our new coding standards. Users are encouraged to participate by opening issues and asking questions via our github repo [3]. There have been many updates on the Copilot front in the last few months. We'll be able to announce more soon. Stay tuned. Happy Haskelling! Ivan [1] https://github.com/nasa/ogma [2] https://github.com/Copilot-Language/copilot/releases/tag/v3.17 [3] https://github.com/Copilot-Language/copilot [4] https://hackage.haskell.org/package/copilot

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