June 2021 - ghc-devs - Haskell.org

Is there a way to prevent reboxing in W/W (due to OPAQUE pragma proposal)
by Christiaan Baaij 24 Jun '21

24 Jun '21

Hi Ghc-Devs, I believe I've mostly finished the implementation of GHC proposal 0415 [1], the OPAQUE pragma, over at: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5562 The only remaining issue is that I'm unsure whether there's a way to prevent reboxing of worker arguments as witnessed here: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5562/diffs#29ad02619a9f… Note that the reboxing doesn't happen in the worker of the OPAQUE-annotated bindings, because OPAQUE-annotated bindings aren't W/W-transformed, but in a worker of a function that calls the OPAQUE-annotated binding. This reboxing was the reason behind the descision to W/W transform NOINLINE-annotated bindings in: https://gitlab.haskell.org/ghc/ghc/-/commit/b572aadb20c2e41e2f6d7b48401bd0b… But the whole idea behind OPAQUE is not to change calls to the annotated binding f by some call of a name-mangled version of f; so W/W transforming OPAQUE-annoted binders is not an option. Any hints on how to avoid the reboxing (if possible) would be appreciated, like: * Do I need to change something in GHC.Core.Opt.WorkWrap? or * Do I need to change the demand/strictness signature of OPAQUE-annoted bindings? * or something else? Thanks, Christiaan [1] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0415-o…

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Final Call for Talks: Haskell Implementors' Workshop @ ICFP'21
by Ningning Xie 23 Jun '21

23 Jun '21

Final Call for Talks ACM SIGPLAN Haskell Implementors' Workshop https://icfp21.sigplan.org/home/hiw-2021 Virtual, 22 Aug, 2021 Co-located with ICFP 2021 https://icfp21.sigplan.org/ New: Invited Speaker -------------------- Title: Haskell reinterpreted – large-scale real-world experience with the Mu compiler in Financial Markets Speaker: Bengt Marten Agren, Standard Chartered Bank Important dates --------------- Deadline: Wednesday, 30 June, 2021 (AoE) Notification: Wednesday, 14 July, 2021 Workshop: Sunday, 22 August, 2021 The 13th Haskell Implementors' Workshop is to be held alongside ICFP 2021 this year virtually. 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 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 short 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 2021. 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 encouraged to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are specially 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, optimisation 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 should be made via HotCRP. The website is: https://icfp-hiw21.hotcrp.com/ We will also have lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks 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. Logistics --------- Due to the on-going COVID-19 situation, ICFP (and, consequently, HIW) will be held remotely this year. However, the organizers are still working hard to provide for a great workshop experience. While we are sad that this year will lack the robust hallway track that is often the highlight of HIW, we believe that this remote workshop presents a unique opportunity to include more of the Haskell community in our discussion and explore new modes of communicating with our colleagues. We hope that you will join us in making this HIW as vibrant as any other. Program Committee ----------------- * Dominique Devriese (Vrije Universiteit Brussel) * Daan Leijen (Microsoft Research) * Andres Löh (Well-Typed LLP) * Julie Moronuki (Typeclass Consulting) * John Wiegley (DFINITY) * Ningning Xie (the University of Hong Kong) * Edward Z. Yang (Facebook AI Research) Contact ------- * Ningning Xie <xnning at hku.hk>

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An error occurred
by Simon Peyton Jones 22 Jun '21

22 Jun '21

Ben I'm getting this error "An error occurred while fetching the job log" a lot when trying to look at the result of CI. It seems to come and go. Refreshing the browser generally does not fix it. Coming back later sometimes does. It's frustrating. Do you have any idea what's happening or how I can avoid it? Thanks Simon [cid:image001.png@01D766EC.BBFC2D20]

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CI Status Update
by Ben Gamari 17 Jun '21

17 Jun '21

Hi all, As you may have realized, CI has been a bit of disaster over the last few days. It appears that this is just the most recent chapter in our on-going troubles with Docker image storage, being due to an outage of our upstream storage service [1]. Davean and I have started to implement a plan to migrate away from DreamObjects back to local storage. Unfortunately to complete this migration we need DreamObjects to come back online; I am currently waiting until this occurs. Further updates will come as the situation develops. Cheers, - Ben [1] https://www.dreamhoststatus.com/

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Error message degradation for (<= :: Nat -> Nat -> Constraint) in GHC 9.2+
by Christiaan Baaij 17 Jun '21

17 Jun '21

Hi Ghc-Devs, When upgrading one of our tc plugins https://hackage.haskell.org/package/ghc-typelits-natnormalise to GHC 9.2, one of our tests, repeated here: ``` {-# LANGUAGE DataKinds, TypeFamilies, TypeOperators #-} module TestInEq where import Data.Proxy import GHC.TypeLits proxyInEq :: (a <= b) => Proxy a -> Proxy b -> () proxyInEq _ _ = () proxyInEq1 :: Proxy a -> Proxy (a+1) -> () proxyInEq1 = proxyInEq ``` degraded quite badly in terms of the error message. Where in GHC 9.0.1 we get: ``` TestInEq.hs:11:14: error: • Couldn't match type ‘a <=? (a + 1)’ with ‘'True’ arising from a use of ‘proxyInEq’ • In the expression: proxyInEq In an equation for ‘proxyInEq1’: proxyInEq1 = proxyInEq • Relevant bindings include proxyInEq1 :: Proxy a -> Proxy (a + 1) -> () (bound at TestInEq.hs:11:1) | 11 | proxyInEq1 = proxyInEq | ``` with GHC 9.2.0.20210422 we get: ``` TestInEq.hs:11:14: error: • Couldn't match type ‘Data.Type.Ord.OrdCond (CmpNat a (a + 1)) 'True 'True 'False’ with ‘'True’ arising from a use of ‘proxyInEq’ • In the expression: proxyInEq In an equation for ‘proxyInEq1’: proxyInEq1 = proxyInEq • Relevant bindings include proxyInEq1 :: Proxy a -> Proxy (a + 1) -> () (bound at TestInEq.hs:11:1) | 11 | proxyInEq1 = proxyInEq | ``` Errors messages involving type-level naturals and their operations already weren't the poster-child of comprehensable GHC error messages, but this change has made the situation worse in my opinion. This change in error message is due to: https://gitlab.haskell.org/ghc/ghc/-/commit/eea96042f1e8682605ae68db10f2bcd… Is there a way we can get the nicer pre-9.2.0.2021 error message again before the proper 9.2.1 release? e.g. by doing one of the following: 1. Reinstate `(<=? :: Nat -> Nat -> Bool)` as a builtin type family 2. Somehow add a custom type-error to `Data.Type.Ord.OrdCond` 3. Don't expand type aliases in type errors What do you think? should this be fixed? should this be fixed before the 9.2.1 release? -- Christiaan

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Re[2]: GHC and the future of Freenode
by Sebastian Graf 16 Jun '21

16 Jun '21

Re: memory usage: I get that people don't like bloated Electron clients when they already run a browser instance, but fortunately, Element doesn't need to be run as a standalone app (*). Well, except when you want to search encrypted history. But then you're out of luck with irccloud, too... I run Element in a pinned Firefox tab, and according to its task manager it reports 27.4MB, which is about the same for my WhatsApp tab. It's a bit more than irccloud (about 20MB), but I also have quite a few chats in that one tab. It's also quite a lot less than every individual MR page of our GitLab instance (27-110MB), of which I have pinned about 5-10 at any time, so it really doesn't matter much. Since the Matrix<->Libera.chat bridge works now, I have next to no incentive to push for Matrix at the moment, although I still would prefer it. All arguments have been said, so I won't repeat them. It seems like this discussion will go stale in time without anyone stepping up to force a migration. Fine with me. Sebastian ------ Originalnachricht ------ Von: "Jakub Zalewski" <jakzale(a)gmail.com> An: "Janek Stolarek" <jwstolarek(a)gmail.com>; ghc-devs(a)haskell.org Gesendet: 16.06.2021 17:02:28 Betreff: Re: GHC and the future of Freenode >On Tue Jun 15, 2021 at 3:18 PM CEST, Janek Stolarek wrote: >> Apparently, Freenode deleted all registered users and channels several >> hours ago. > >I guess that should solve the problem of communities being split between >Freenode and Libera. > >If I may add towards using IRC, even though it may seem archaic towards >newcomers: > >- it allows them to join without registration (via web.libera.chat), and >- it allows them to use a client of their choosing (I am not aware of > any stable Matrix clients beside Element). > >From my own experience, Electron-based clients (Element included) >consume unreasonable amounts of RAM: Element is consuming ~700MiB of >RAM just to stay idle on my machine. To give a fair comparison, the tab >for irccloud tends to consume ~300MiB. > >-- >Jakub >_______________________________________________ >ghc-devs mailing list >ghc-devs(a)haskell.org >http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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GHC and the future of Freenode
by Ben Gamari 16 Jun '21

16 Jun '21

Hi all, As you may have heard the Freenode IRC network, long the home of #ghc and several other prominent Haskell channels, appears to be in the middle of a rather nasty hostile takeover [1,2,3,4]. As a consequence, it seems it will be necessary to migrate the #ghc community elsewhere. The next question is, of course, where will this be. One option is Liberachat, the spiritual successor of Freenode. However, in recent years I have also heard an increasingly loud choir of users, contributors, and potential-contributors note how archane IRC feels when compared to other modern chat platforms. Using IRC effectively in a collaborative environment essentially requires that all parties use a bouncer; however, this is (understandably) isn't something that most users are willing to do. Consequently, I think it would be wise to expand our search space to include other FOSS platforms. At the moment, I can see the following options: 1. Remain on IRC and move to Liberachat, the spiritual successor of Freenode 2. Remain on IRC and move to OFTC, another widely used network 3. Move to [Matrix] 4. Move to [Zulip] My sense is that of the non-IRC options Matrix is the truest successor to IRC, being a federated protocol with a wide array of (if somewhat immature) clients. I know some of our contributors already use it and in principle one could configure an IRC-to-Matrix bridge for those existing contributors who would rather continue using IRC. Zulip, while also being FOSS, is far more centralized than Matrix and appears to be more of a chat web application than an open protocol. Do you know of any other options? Thoughts? Cheers, - Ben [1]: https://gist.github.com/joepie91/df80d8d36cd9d1bde46ba018af497409 [2]: https://fuchsnet.ch/freenode-resign-letter.txt [3]: https://gist.github.com/aaronmdjones/1a9a93ded5b7d162c3f58bdd66b8f491 [4]: https://mniip.com/freenode.txt [Matrix]: https://www.matrix.org/ [Zulip]:

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abstract interpreter for GHC Core or STG
by Csaba Hruska 14 Jun '21

14 Jun '21

Hello, I wonder if there was an attempt in the past to create an abstract interpreter for GHC Core or STG to approximate the program runtime behaviour? I'm curious because I'd like to turn my external STG interterpreter to an abstract interpreter using the AAM (Abstracting Abstract Machines) method. This approach seems promising to me because a single Haskell code base (ext STG interpreter) could be the specification of the Haskell operational semantics and also be a detailed static analyzer that could help optimization transformations. I'm interested in any attempt that happened during GHC/Haskell evolution. Regards, Csaba Hruska

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Anyone ever wondered what our favourite merge bot is up to?
by Matthew Pickering 10 Jun '21

10 Jun '21

Hi all, I added a new dashboard on grafana which exposes some of the systemd logs from marge-bot. https://grafana.gitlab.haskell.org/d/iiCppweMz/marge-bot?orgId=2&refresh=5m You can use the logs to see why marge doesn't want to merge your MR or whether she is dead. Cheers, Matt

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[Haskell] [ANNOUNCE] GHC 8.10.5 released
by Zubin Duggal 06 Jun '21

06 Jun '21

The GHC team is very pleased to announce the availability of GHC 8.10.5. Source and binary distributions are available at the [usual place](https://downloads.haskell.org/ghc/8.10.5/). This release adds native ARM/Darwin support, as well as bringing performance improvements and fixing numerous bugs of varying severity present in the 8.10 series: - First-class support for Apple M1 hardware using GHC's LLVM ARM backend - Fix a bug resulting in segmentation faults where code may be unloaded prematurely when using the parallel garbage collector (#19417) along with other bugs in the GC and linker (#19147, #19287) - Improve code layout fixing certain performance regressions (#18053) and other code generation bug fixes (#19645) - Bug fixes for signal handling when using the pthread itimer implementation. - Improvements to the specializer and simplifier reducing code size and and memory usage (#17151, #18923,#18140, #10421, #18282, #13253). - Fix a bug where typechecker plugins could be run with an inconsistent typechecker environment (#19191). - Fix a simplifier bug which lead to an exponential blow up and excessive memory usage in certain cases A complete list of bug fixes and improvements can be found in the release notes: [release notes](https://downloads.haskell.org/~ghc/8.10.5/docs/html/users_guide/8.10… As always, feel free to report any issues you encounter via [gitlab.haskell.org](https://gitlab.haskell.org/ghc/ghc/-/issues/new).

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