May 2024 - ghc-devs - Haskell.org

Reinstallable - base
by Simon Peyton Jones 07 Aug '24

07 Aug '24

Dear GHC devs Given the now-agreed split between ghc-internal and base <https://github.com/haskellfoundation/tech-proposals/pull/51>, what stands in the way of a "reinstallable base"? Specifically, suppose that - GHC 9.8 comes out with base-4.9 - The CLC decides to make some change to `base`, so we get base-4.10 - Then GHC 9.10 comes out with base-4.10 I think we'd all like it if someone could use GHC 9.10 to compile a library L that depends on base-4.9 and either L doesn't work at all with base-4.10, or L's dependency bounds have not yet been adjusted to allow base-4.10. We'd like to have a version of `base`, say `base-4.9.1` that has the exact same API as `base-4.9` but works with GHC 9.10. Today, GHC 9.10 comes with a specific version of base, *and you can't change it*. The original reason for that was, I recall, that GHC knows the precise place where (say) the type Int is declared, and it'll get very confused if that data type definition moves around. But now we have `ghc-internal`, all these "things that GHC magically knows" are in `ghc-internal`, not `base`. *Hence my question: what (now) stops us making `base` behave like any other library*? That would be a big step forward, because it would mean that a newer GHC could compile old libraries against their old dependencies. (Some changes would still be difficult. If, for example, we removed Monad and replaced it with classes Mo1 and Mo2, it might be hard to simulate the old `base` with a shim. But getting 99% of the way there would still be fantastic.) Simon

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Call for Talks: Haskell Implementors' Workshop 2024
by Matthew Pickering 08 Jul '24

08 Jul '24

``` ACM SIGPLAN Haskell Implementors' Workshop https://icfp24.sigplan.org/home/hiw-2024 Milan, Italy, September 2, 2024 Co-located with ICFP 2024 https://icfp24.sigplan.org/ ``` ## Important dates * Deadline: July 19, 2024 (AoE) * Notification: August 2, 2024 * Workshop: September 2, 2024 The 16th Haskell Implementors’ Workshop is to be held alongside ICFP 2024 this year in Milan. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure to share their work and to discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos, and lightning talks. ## Scope and Target Audience It is important to distinguish the Haskell Implementors’ Workshop from the Haskell Symposium which is also co-located with ICFP 2024. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors’ Workshop will have no proceedings – although we will aim to make talk videos, slides, and presented data available with the consent of the speakers. The Implementors’ Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community are encouraged to attend the workshop – we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are especially encouraged to share their work. The scope covers any of the following topics. There may be some topics that people feel we’ve missed, so by all means submit a proposal even if it doesn’t fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimization and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment ## Talks We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words. Submissions can be made via HotCRP at https://hiw2024.hotcrp.com until July 19 (anywhere on earth). We will also have a lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks should be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. ## Program Committee * Matthew Pickering (Well-Typed LLP) * David Binder (University of Tübingen) * Gabriella Gonzalez (Mercury) * Sylvain Henry (IOG) * Teofil Camarasu (Tracsis) ## Contact * Matthew Pickering

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RTS crashes
by Simon Peyton Jones 03 Jun '24

03 Jun '24

In my private build of !12492 I'm getting some assertion failures in CheckUnload (see below). This can't possibly be my fault! I don't know if CI perhaps has these assertion switched off, so only I am seeing them? I'd open a ticket but it may just be my bad, somehow Any ideas? Simon Stderr run ( MultiLayerModulesDefsGhci ): ghc: internal error: ASSERTION FAILED: file rts/CheckUnload.c, line 460 (GHC version 9.11.20240530 for x86_64_unknown_linux) Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug Aborted *** unexpected failure for MultiLayerModulesDefsGhci(ghci) ]0;MultiLayerModulesDefsGhciReload(ghci) 4776 of 10144 [0, 1, 0] ]0;InstanceMatching(normal) 4777 of 10144 [0, 1, 0] ]0;Running for 5m51s [35433/36451], predicted 1s (98%) Wrong exit code for MultiLayerModulesDefsGhciReload(ghci)(expected 0 , actual 134 ) Stderr run ( MultiLayerModulesDefsGhciReload ): ghc: internal error: ASSERTION FAILED: file rts/CheckUnload.c, line 460 (GHC version 9.11.20240530 for x86_64_unknown_linux) Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug Aborted *** unexpected failure for MultiLayerModulesDefsGhciReload(ghci) ]0;InstanceMatching1(normal) 4778 of 10144 [0, 2, 0] ]0;MultiLayerModulesNoCode(ghci) 4779 of 10144 [0, 2, 0] Wrong exit code for MultiLayerModulesNoCode(ghci)(expected 0 , actual 134 ) Stderr run ( MultiLayerModulesNoCode ): ghc: internal error: ASSERTION FAILED: file rts/CheckUnload.c, line 460 (GHC version 9.11.20240530 for x86_64_unknown_linux) Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug Aborted

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Haddock test suite failure -- can anyone guide me?
by Simon Peyton Jones 31 May '24

31 May '24

Dear Haddock experts I'm getting a failure on !12492 <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/12492> that I can't understand or debug. Can someone guide me? Failure is this: /builds/ghc/ghc/tmp/ghctest-2jo7oz8x/test spaces/testsuite/tests/haddock/haddock_testsuite/haddockHypsrcTest.run haddockHypsrcTest [bad exit code (2)] (normal) A snip of the log is at the end of this message. I want to - understand what it does - repro it locally. Trying the latter, I tried with my HEAD build and did bash$ cd testsuite/tests/haddock/haddock_testsuite bash$ make hypsrcTest but that failed on almost all the tests it does, even though HEAD is presumably OK. I'm stumped. Any ideas? The patch only changes the type checker! Thanks SImion This is the log from !12492 Wrong exit code for haddockHypsrcTest()(expected 0 , actual 2 ) Stdout ( haddockHypsrcTest ): [1 of 7] Compiling Test.Haddock.Process ( /builds/ghc/ghc/testsuite/../utils/haddock/haddock-test/src/Test/Haddock/Process.hs, Test/Haddock/Process.o ) [2 of 7] Compiling Test.Haddock.Utils ( /builds/ghc/ghc/testsuite/../utils/haddock/haddock-test/src/Test/Haddock/Utils.hs, Test/Haddock/Utils.o ) [3 of 7] Compiling Test.Haddock.Config ( /builds/ghc/ghc/testsuite/../utils/haddock/haddock-test/src/Test/Haddock/Config.hs, Test/Haddock/Config.o ) [4 of 7] Compiling Test.Haddock ( /builds/ghc/ghc/testsuite/../utils/haddock/haddock-test/src/Test/Haddock.hs, Test/Haddock.o ) [5 of 7] Compiling Test.Haddock.Xhtml ( /builds/ghc/ghc/testsuite/../utils/haddock/haddock-test/src/Test/Haddock/Xhtml.hs, Test/Haddock/Xhtml.o ) [6 of 7] Compiling Main ( /builds/ghc/ghc/testsuite/../utils/haddock/hypsrc-test/Main.hs, Main.o ) [7 of 7] Linking hypsrc-test Haddock version 2.30.0, (c) Simon Marlow 2006 Ported to use the GHC API by David Waern 2006-2008 9.11.20240530 Generating documentation... Testing output files... Checking "src/TemplateHaskellSplices.html"... PASS Checking "src/Bug1091.html"... PASS Checking "src/Polymorphism.html"... PASS Checking "src/UsingQuasiquotes.html"... PASS Checking "src/Records.html"... PASS Checking "src/Quasiquoter.html"... PASS Checking "src/CPP.html"... PASS Checking "src/Operators.html"... PASS Checking "src/Literals.html"... PASS Checking "src/LinkingIdentifiers.html"... PASS Checking "src/Classes.html"... FAIL Checking "src/PositionPragmas.html"... PASS Checking "src/Types.html"... PASS Checking "src/TemplateHaskellQuasiquotes.html"... PASS Checking "src/Constructors.html"... FAIL Checking "src/Identifiers.html"... FAIL Diffing failed cases... Diff for file "src/Classes.html": 1194c1194,1198 < > > >a -> b -> a > forall a b. a -> b -> a > > > >a -> b -> a > forall a b. a -> b -> a > > > >b -> a -> b > forall a b. a -> b -> a > > > >b -> a -> b > forall a b. a -> b -> a > > > >([Int] -> Int) -> (Norf -> [Int]) -> Norf -> Int > forall b c a. (b -> c) -> (a -> b) -> a -> c > > > >(String -> IO ()) -> (Int -> String) -> Int -> IO () > forall b c a. (b -> c) -> (a -> b) -> a -> c > ><a href="Identifiers.html#foo" < > > >Int -> Int -> Int > ><a href="Identifiers.html#foo" > > > >(String -> IO ()) -> (Int -> String) -> Int -> IO () > forall b c a. (b -> c) -> (a -> b) -> a -> c > ><a href="Identifiers.html#quux" < > > >Int -> Int > ><a href="Identifiers.html#quux" > > > >(String -> IO ()) -> (Int -> String) -> Int -> IO () > forall b c a. (b -> c) -> (a -> b) -> a -> c > ><a href="Identifiers.html#norf" < > > >Int -> Int -> Int -> Int > ><a href="Identifiers.html#norf" > ><span class="hs-identifier hs-var" Stderr run ( haddockHypsrcTest ): gmake: *** [Makefile:68: hypsrcTest] Error 1 *** unexpected failure for haddockHypsrcTest(normal)

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Documentation previews on Gitlab pipelines
by Teofil Camarasu 31 May '24

31 May '24

Hi folks, I just wanted to advertise that it is now possible to see rendered previews of documentation changes (haddocks/user guide/etc) on Gitlab pipelines. To access this you need to: 1. Wait for a pipeline to complete. 2. From the MR page, click on "Expand" under the pipeline widget, then "Documentation Preview" 3. This takes you to the job artefacts. Then open `docs/index.html`. 4. Gitlab will then redirect you to the hosted page. Alternatively instead of (2) you can open the "docs-tarball" job directly and click on "Browse" to go to the artefacts. I've also attached a screen recording to make it a bit clearer. I actually set this up a few weeks ago in !12415 <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/12415>. But I forgot to advertise this more widely at the time. And Gitlab isn't super helpful in directing users to it. So, I realised most folks probably don't know it exists. Cheers, Teo

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GHC release series adoption rates
by Clinton Mead 29 May '24

29 May '24

Hi All The recent GHC blog post: https://www.haskell.org/ghc/blog/20240521-ghc-release-priorities.html states: *"9.6.5 seems to be a relatively stable release so far and we plan to prioritise fixes given the relatively higher adoption of this branch"* I was wondering where this information came from? Is this based on a number of downloads or some other metric? Number of companies that have adopted the version? How many stack/ghcup pulls? Or just a vibe/what people seem to be talking about? If there are hard numbers, are they public? The current project I'm working on is still on GHC 9.2.2, so I was considering an upgrade to GHC 9.4.8, but this blog post has made me lean towards the 9.6 series instead. This is just an upgrade for stability not features and so we don't get too far behind. But it would be good to have this popularity info generally instead of having to wait for a blog post. Cheers, Clinton

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Looking for recent works on STG
by Rodrigo Mesquita 26 May '24

26 May '24

Dear all, Do you know of any recent works on the STG? In particular, I am looking for a result connecting STG's execution and Core’s call-by-need semantics when written in structural operational semantics style. Nonetheless, I’m also interested in possibly more recent formulations of STG (e.g. a mechanized one?) beyond the original paper. Cheers Rodrigo Mesquita

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Question about -G RTS flag
by chessai 23 May '24

23 May '24

The docs for -G state: ``` ... Anything larger than about 4 is probably not a good idea unless your program runs for a *long* time, because the oldest generation will hardly ever get collected. ``` What is a "*long*" time?

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Priorities for upcoming GHC releases
by Zubin Duggal 21 May '24

21 May '24

Hi all, We detail our plans for upcoming GHC releases in a new blog post: https://www.haskell.org/ghc/blog/20240521-ghc-release-priorities.html The summary is that we will prioritise work on the 9.10, 9.6 and master branches over work on the 9.8 branch for the coming few months due to time and resource constraints. This does not mean that we are dropping support for GHC 9.8, but that releases in this series might be made at a slower pace than usual. Cheers, Zubin.

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Haddock now lives full-time in the GHC repository
by Hécate 17 May '24

17 May '24

Hello devs, As of today, Haddock now lives in the GHC repository, and not anymore as a submodule from another Gitlab repository which itself was rebased on top of a Github repository. You are encouraged to migrate our currently opened PRs to the GHC repo. If you have any trouble, please do ping me on Matrix (@acidalia:matrix.org), on GitLab (@kleidukos), or by email directly. Read more here: https://discourse.haskell.org/t/haddock-now-lives-in-the-ghc-repository/9576 My thanks to Ben Gamari who was essential in making this migration happen! Cheers, Hécate -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW: https://glitchbra.in RUN: BSD

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