- ghc-devs - Haskell.org

GHC and type-family rewriting?
by Benjamin Redelings 17 Dec '22

17 Dec '22

Hi, I've managed to code up implications and GADTs, and am now working on adding type families. I've been following the OutsideIn paper, but it seems that GHC is not really following the same plan for the solver. For example, instead of replacing every type family with a metavariable, it only does this for occur-check failures. It talks about "cycle breakers" instead of "flattening substitutions". It creates flatting substitutions for both givens and wanteds (I think). And I see this note: > -- | A 'Xi'-type is one that has been fully rewritten with respect > -- to the inert set; that is, it has been rewritten by the algorithm > -- in GHC.Tc.Solver.Rewrite. (Historical note: 'Xi', for years and years, > -- meant that a type was type-family-free. It does *not* mean this > -- any more.) > type Xi = TcType If I'm understanding correctly, the inert set is now thought of as a "generalized substitution" that replaces either an LHS (untouchable type variables or type family applications) with an RHS. I guess what I'm wondering is: (Q1) Did GHC evolve to this point starting from something fairly close to the OutsideIn paper? (Q2) Is the new approach (i.e. eager type family rewriting) mostly to making rewriting faster? (Q3) Does it sound reasonable to implement the approach from the OutsideIn paper, and than gradually transform it to look more like GHC? -BenRI

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9.4.4 release
by Matthew Pickering 15 Dec '22

15 Dec '22

Hi all, We are going to release the latest release in the 9.4.* series before Christmas. The release fixes a number of small bugs which have surfaced to do with 9.4. For the current full list of backports see: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/9523 I am preparing the release branch and then Ben will perform the final steps necessary for the release. Cheers, Matt

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Re: 9.4.4 release
by Matthew Pickering 15 Dec '22

15 Dec '22

That issue has not been resolved for 9.4.4 but we will still provide CentOS7 builds (which link against the older glibc). On Thu, Dec 15, 2022 at 1:19 AM Julian Ospald <hasufell(a)posteo.de> wrote: > > Has there been any changes to the bindists? Does https://gitlab.haskell.org/ghc/ghc/-/issues/22268 still exist? > > On December 14, 2022 12:51:00 PM UTC, Matthew Pickering <matthewtpickering(a)gmail.com> wrote: >> >> Hi all, >> >> We are going to release the latest release in the 9.4.* series before Christmas. >> >> The release fixes a number of small bugs which have surfaced to do with 9.4. >> >> For the current full list of backports see: >> >> https://gitlab.haskell.org/ghc/ghc/-/merge_requests/9523 >> >> I am preparing the release branch and then Ben will perform the final >> steps necessary for the release. >> >> Cheers, >> >> Matt

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Merge failures due to stats increase
by Bryan Richter 30 Nov '22

30 Nov '22

Last night, Marge's merge requests failed several times because of a stats increase. compile_time/bytes allocated increased from x86_64-linux-fedora33-release baseline @ def47dd32491311289bff26230b664c895f178cc: Expected T9872a (normal) compile_time/bytes allocated: 1655471856.0 +/-1% Lower bound T9872a (normal) compile_time/bytes allocated: 1638917137 Upper bound T9872a (normal) compile_time/bytes allocated: 1672026575 Actual T9872a (normal) compile_time/bytes allocated: 1674083264 Deviation T9872a (normal) compile_time/bytes allocated: 1.1 % *** unexpected stat test failure for T9872a(normal) This happened on three separate attempts, each with a deviation of 1.1%: * https://gitlab.haskell.org/ghc/ghc/-/jobs/1247176 * https://gitlab.haskell.org/ghc/ghc/-/jobs/1247312 * https://gitlab.haskell.org/ghc/ghc/-/jobs/1247512 The reason I'm making an email out of this is that none of the individual patches that Marge is merging have this problem, but it seems to happen consistently when they are combined. You can see a list of patches by looking at the list of mentions on https://gitlab.haskell.org/ghc/ghc/-/merge_requests/9439. There were other problems with Marge's merges last night that I DO understand and have fixed. But this one, of course, is over my head. :) Maybe somebody can look at the list of patches and deduce something useful. Otherwise, I will continue monitoring Marge's progress, and try to find a smaller set of patches that can make it through. I'll prioritize getting the Javascript backend through. -Bryan

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Implementors for deprecated exports?
by David Christiansen 29 Nov '22

29 Nov '22

Dear GHC developers, The HF's Stability Working Group ( https://github.com/haskellfoundation/stability) has been looking into ways to help Haskell developers maintain their code in the face of changes to the language and libraries. Out of the ideas we found, one is already an accepted GHC proposal, just waiting for implementation! This is adding the ability to deprecate an export, rather than just a definition, which would allow a function to be moved to a new home, with the old location re-exporting it under a deprecation warning for a few releases. We're wondering: do any of you feel inspired to implement this? If you did, we'd do our best to make sure that you are supported with design advice and code review. This is probably not a good first contribution to GHC; you'll need some familiarity with GHC and how to build it. The accepted proposal is here: https://github.com/ghc-proposals/ghc-proposals/pull/134 The GHC ticket that it emerged from is here: https://gitlab.haskell.org/ghc/ghc/-/issues/4879 All the best, David and Simon

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Almost all tests fail after 08bf28819b
by Erdi, Gergo 24 Nov '22

24 Nov '22

PUBLIC Hi, Even though I've rebuilt everything from scratch, I'm unable to run most tests on `master` from (including) 08bf28819b78e740550a73a90eda62cce8d21c90. The error message is the same for all tests: ghc: /home/mi/prog/ghc/_build/stage1/lib/x86_64-linux-ghc-9.5.20221122/base-4.17.0.0/HSbase-4.17.0.0.o: unknown symbol `newArena' ghc: Could not load Object Code /home/mi/prog/ghc/_build/stage1/lib/x86_64-linux-ghc-9.5.20221122/base-4.17.0.0/HSbase-4.17.0.0.o. ghc: unable to load unit `base-4.17.0.0' Am I doing something wrong locally, or did something that breaks tests sneak through during the Gitlab outage yesterday? Thanks, Gergo This email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please delete all copies and notify the sender immediately. You may wish to refer to the incorporation details of Standard Chartered PLC, Standard Chartered Bank and their subsidiaries at https: //www.sc.com/en/our-locations Where you have a Financial Markets relationship with Standard Chartered PLC, Standard Chartered Bank and their subsidiaries (the "Group"), information on the regulatory standards we adhere to and how it may affect you can be found in our Regulatory Compliance Statement at https: //www.sc.com/rcs/ and Regulatory Compliance Disclosures at http: //www.sc.com/rcs/fm Insofar as this communication is not sent by the Global Research team and contains any market commentary, the market commentary has been prepared by the sales and/or trading desk of Standard Chartered Bank or its affiliate. It is not and does not constitute research material, independent research, recommendation or financial advice. Any market commentary is for information purpose only and shall not be relied on for any other purpose and is subject to the relevant disclaimers available at https: //www.sc.com/en/regulatory-disclosures/#market-disclaimer. Insofar as this communication is sent by the Global Research team and contains any research materials prepared by members of the team, the research material is for information purpose only and shall not be relied on for any other purpose, and is subject to the relevant disclaimers available at https: //research.sc.com/research/api/application/static/terms-and-conditions. Insofar as this e-mail contains the term sheet for a proposed transaction, by responding affirmatively to this e-mail, you agree that you have understood the terms and conditions in the attached term sheet and evaluated the merits and risks of the transaction. We may at times also request you to sign the term sheet to acknowledge the same. Please visit https: //www.sc.com/en/regulatory-disclosures/dodd-frank/ for important information with respect to derivative products.

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GitLab maintenance has started
by Bryan Richter 24 Nov '22

24 Nov '22

Hi all, I've started the migration, so the maintenance period has officially started. GitLab itself will go read-only soon. As a reminder, I scheduled 4 hours for the maintenance window. I'll send updates at major points of the migration. -Bryan

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'Caching' of results of default instance definitions
by Clinton Mead 22 Nov '22

22 Nov '22

Hi All My apologies if this is the wrong place to post questions about GHC internals from a non-GHC dev, I thought about using GHC Users but it seems quiet on that mailing list and I think my question relates closely to how GHC implements things, so I suspect only a dev could answer anyway. I have posted the following StackOverflow question: https://stackoverflow.com/questions/74540639/when-are-the-results-of-defaul… I won't repeat the full contents here, but basically my question is that if I have a class with a "method" which has a default definition, and that default definition has no arguments on the LHS, will a separate "instance" of that default definition be created for each instance of that class that inherits that default definition? The important consequence of that being that the default definition is only computed once per type. Or is the default definition treated as a definition generalised over a typeclass, and hence having a hidden typeclass variable and therefore treated as a function, so it needs to be recomputed every time it's referenced? Any feedback or references will be appreciated. Thanks, Clinton

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Upcoming maintenance on Haskell services
by Bryan Richter 22 Nov '22

22 Nov '22

Hello folks, On Thursday 24 November at 6 AM UTC, I will start a 4-hour maintenance window for the following Haskell services: 1. downloads.haskell.org 2. gitlab.haskell.org In particular, I expect the following outages: 1. downloads.haskell.org will be read-only for the duration of the window. * No uploads 2. gitlab.haskell.org will be read-only for the duration of the window. * No CI pipelines(!) * No git pushes * No commenting on issues or merge requests 3. gitlab.haskell.org will furthermore be entirely inaccessible very briefly. * There will be 1-2 outages. * Each outage will last a few seconds. The reason for the maintenance is that our hosting sponsor, Equinix Metal, is performing a facilities migration. One of our servers, gitlab-storage, is slated for retirement. All data and services that run on that server must be moved to a new server. I'm sending this first notification to a wide audience as an extra precaution in case something goes wrong. :) In reality, I expect this maintenance to only affect GHC developers and a small group of ecosystem maintainers. In particular, web access of https://downloads.haskell.org should *not* be affected by this maintenance. I will send further updates to a smaller audience. Note: The actual migration will be quick. Most of the maintenance window will be spent waiting for DNS propagation. -Bryan Haskell Foundation DevOps

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How do you build GHC 9.2.4 cross compilers for windows?
by Moritz Angermann 16 Nov '22

16 Nov '22

Hi, Does anyone know how to build a 9.2.4 windows cross compiler? Hadrian seems to get in the way a lot? This is the essence of what we tried to get working: ./configure --enable-bootstrap-with-devel-snapshot --build=x86_64-apple-darwin --host=x86_64-apple-darwin --target=x86_64-w64-mingw32 hadrian --flavour=default+no_dynamic_ghc --docs=no-sphinx -j Can someone please advise how this is supposed to be built now? Cheers, Moritz

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