- ghc-devs - Haskell.org

Fwd: GHC Module change database
by Ari Fordsham 08 Aug '21

08 Aug '21

I've made a database of GHC API module changes. https://github.com/AriFordsham/ghc-module-renames This might be useful for automatic tooling. It would be nice if this would be moved into the GHC Gitlab, and kept up-to-date. Ari Fordsham

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How to Collect Type Errors?
by Guanda Yuan 06 Aug '21

06 Aug '21

Hello all, I want to write a plugin for Haskell Language Server, to collect type errors in the code. I'm new to GHC API, so I need some help. My current thought is, I can collect diagnostics or the error messages and extract the type error infos. I have tried to referred to the Haddock documentation for GHC API, but I'm still not sure which function should I use. Thanks, Guanda

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Call for Lightning Talks: Haskell Implementors' Workshop @ ICFP'21
by Ningning Xie 06 Aug '21

06 Aug '21

Call for Lightning 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/ Important dates --------------- Deadline: Thursday, 19 Aug, 2021 (or when slots are full, whichever is sooner) Workshop: Sunday, 22 Aug, 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. We will have a number of slots for lightning talks. Lightning talks will be ~7 minutes 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. Lightning talks are proposed by submitting a title and an abstract. Submissions will not be part of the peer-review process. Notification of acceptance will be continuous until slots are full. Submissions should be made via Google form: https://forms.gle/BmUSyWWTXt1AMTec8 Accepted lightning talks will be posted on the workshop’s website. Scope and target audience ------------------------- 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 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. Contact ------- * Ningning Xie <xnningxie(a)gmail.com>

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Email Threading (finally fixed)
by Matthew Pickering 02 Aug '21

02 Aug '21

Hi all, If anyone received emails from gitlab you may have noticed that the comments to issues ended up in different threads to the original issue description. This was because of a custom patch on our gitlab instance which I think I have now fixed. For example issue #20192 now has the correct threading, the original issue and comment now appear in the same email thread (at least in my client). Cheers, Matt

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Install WIP app in haskell org
by Phyx 31 Jul '21

31 Jul '21

Hi Ben, Is it possible to install the WIP app into the github Haskell org? https://github.com/apps/wip It's quite handy to mark things as in progress. Regards, Tamar

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CI build failures
by ÉRDI Gergő 27 Jul '21

27 Jul '21

Hi, I'm seeing three build failures in CI: 1. On perf-nofib, it fails with: == make boot -j --jobserver-fds=3,4 --no-print-directory; in /builds/cactus/ghc/nofib/real/smallpt ------------------------------------------------------------------------ /builds/cactus/ghc/ghc/bin/ghc -M -dep-suffix "" -dep-makefile .depend -osuf o -O2 -Wno-tabs -Rghc-timing -H32m -hisuf hi -packageunboxed-ref -rtsopts smallpt.hs <command line>: cannot satisfy -package unboxed-ref (use -v for more information) (e.g. https://gitlab.haskell.org/cactus/ghc/-/jobs/743141#L1465) 2. On validate-x86_64-darwin, pretty much every test fails because of the following extra stderr output: + +<no location info>: + warning: Couldn't figure out C compiler information! + Make sure you're using GNU gcc, or clang (e.g. https://gitlab.haskell.org/cactus/ghc/-/jobs/743129#L3655) 3. On validate-x86_64-linux-deb9-integer-simple, T11545 fails on memory consumption: Unexpected stat failures: perf/compiler/T11545.run T11545 [stat decreased from x86_64-linux-deb9-integer-simple-validate baseline @ 5f3991c7cab8ccc9ab8daeebbfce57afbd9acc33] (normal) This one is interesting because there is already a commit that is supposed to fix this: commit efaad7add092c88eab46e00a9f349d4675bbee06 Author: Matthew Pickering <matthewtpickering(a)gmail.com> Date: Wed Jul 21 10:03:42 2021 +0100 Stop ug_boring_info retaining a chain of old CoreExpr [...] ------------------------- Metric Decrease: T11545 ------------------------- But still, it's failing. Can someone kick these build setups please? -- .--= ULLA! =-----------------. \ http://gergo.erdi.hu \ `---= gergo(a)erdi.hu =-------'

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Where else do I need to register fixity declarations?
by Erdi, Gergo 27 Jul '21

27 Jul '21

PUBLIC Hi, In the attached program, I am typechecking two Haskell modules with GHC 9.0.1: `Imported.hs` defines some infix operators, and `Importer.hs` uses them. After typechecking the first one, I put it in the moduleNameProvidersMap and the HPT. However, when I am typechecking the second one, the fixity declarations of the infix operators aren't picked up correctly. I know they aren't because I have defined operators that only typecheck if they are parsed right-associatively. In contrast, if I put both the definitions and the usage into the same file (`Standalone.hs`), typechecking succeeds (as I would expect it to). What am I doing wrong? Is filling the `mi_fixities` field of the `ModIface` not enough to let importers see the correct fixities? 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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Is simplified subsumption really necessary?
by Chris Smith 23 Jul '21

23 Jul '21

This might be in the "ship has sailed" territory, but I'd like to bring it up anyway. https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-s… says: Suppose GHC lacked all four features, and someone proposed adding them. > That proposal would never leave the launchpad. > Let's test that hypothesis. I've been spending increasing amounts of time fighting against simplified subsumption while porting Haskell code to GHC 9.0. It's not that any specific instance of this problem is hard to fix; rather, it's that it completely screws up my intuition about what should be valid Haskell. It doesn't help that HLS still requires 8.10.4, so I usually don't find out I've broken my libraries for GHC 9.0 until continuous integration kicks in. At this point, it's become fairly routine that my code that works fine with 8.10.4 is broken with 9.0, and this makes me sad. Understandably, eta expansion reducing the strictness of terms is bad. But wouldn't it be possible to choose a desugaring with seq that doesn't do so?

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Using overloaded syntax to avoid `base` dependency (RE: Marking ParsedModule fragments as non-user-originating)
by Erdi, Gergo 23 Jul '21

23 Jul '21

PUBLIC OK so I tried out OverloadedStrings and it basically went as bad as I expected. The documentation on `HsOverLit` is very promising: it points to the Note [Overloaded literal witnesses], which states: Note [Overloaded literal witnesses] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *Before* type checking, the HsExpr in an HsOverLit is the name of the coercion function, 'fromInteger' or 'fromRational'. So that sounds great, right? It sounds like just before renaming, I should be able to replace `HsLit _ (HsString _ fs)` with `HsOverLit _ (OverLit _ (HsIsString _ fs) unpack` with my own `unpack` function coming from my own package, and everything would work out. Unfortunately, this is not what happens: if I try getting this through the renamer, I get this error: Failed to load interface for 'Data.String' no unit id matching 'base' was found Can't find interface-file declaration for variable fromString Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error So even though I am specifying my own coercion function, it is still looking for `Data.String.fromString` which is not going to work, since I don't have `base`. So either I am misunderstanding that Note, or it is simply out of date, but in either case, this isn't going to be a viable route to going base-less. Gergo From: Erdi, Gergo Sent: Tuesday, July 6, 2021 5:39 PM To: Simon Peyton Jones <simonpj(a)microsoft.com> Cc: GHC <ghc-devs(a)haskell.org> Subject: RE: Marking ParsedModule fragments as non-user-originating PUBLIC Thanks Simon! Of course, you're right, it's the renamer, not the typechecker - I didn't really check, just saw that "it happens during `typecheckModule`. I'll look at the rebindable syntax stuff in detail, but at least for OverloadedStrings, I already know that the problem will be that ultimately they do go through the `String` type from `base`, and I need to use GHC baselessly. This is a problem for two reasons: * I can't implement `IsString` for `MyString`, because `IsString` is in `base` * Even if I made my own fake `base` with a fake `IsString` class, there is nothing to put in the codomain of `fromString`: I *only* have `MyString`, not `String`. And renaming `MyString to `String` in my fake `base` is not going to cut it, since `String` is wired into GHC to be a type synonym for `[Char]` (which `MyString` is not). I foresee similar problems for OverloadedLists :/ Thanks, Gergo From: Simon Peyton Jones <simonpj(a)microsoft.com<mailto:simonpj@microsoft.com>> Sent: Tuesday, July 6, 2021 5:08 PM To: Erdi, Gergo <Gergo.Erdi(a)sc.com<mailto:Gergo.Erdi@sc.com>> Cc: GHC <ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org>> Subject: [External] RE: Marking ParsedModule fragments as non-user-originating The typechecker now complains that the `ViewPatterns` language extension is not turned on I think it's the renamer: rnPatAndThen mk p@(ViewPat _ expr pat) = do { liftCps $ do { vp_flag <- xoptM LangExt.ViewPatterns ; checkErr vp_flag (badViewPat p) } More generally, don't you just want OverloadedStrings or OverloadedLists? You might want to read Note [Handling overloaded and rebindable constructs] in GHC.Rename.Expr, and Note [Rebindable syntax and HsExpansion] in GCH.Hs.Expr. These Notes describe how GHC already does something similar to what you want. Maybe you can use the same mechanism in your plugin. Simon From: ghc-devs <ghc-devs-bounces(a)haskell.org<mailto:ghc-devs-bounces@haskell.org>> On Behalf Of Erdi, Gergo via ghc-devs Sent: 06 July 2021 09:08 To: ghc-devs(a)haskell.org<mailto:ghc-devs@haskell.org> Subject: Marking ParsedModule fragments as non-user-originating PUBLIC Hi, I'd like to hijack some syntax (like string literals or list patterns) for my own use, and I thought a low-tech way of doing that is to transform the ParsedModule before typechecking. For example, if I have a function `uncons :: Array a -> Maybe (a, Array a)`, I can rewrite the pattern `[x1, x2, x3]` into the view pattern `(uncons -> Just (x1, (uncons -> Just (x2, (uncons -> Just (x3, (uncons -> Nothing)))))))` and let the normal GHC type checker take over from here. This is working for me so far, except for one problem: the typechecker now complains that the `ViewPatterns` language extension is not turned on. I would like to make the view patterns coming from my ParsedModule rewriter to be exempt from this check (but of course still require the `ViewPatterns` extension for user-originating code). Is there a way to do that? Or would I be better off checking for user-originating view patterns myself before the rewrite and then changing the `DynFlags` to always enable view patterns for typechecking? 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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Rewriting plugins: request for feedback
by Sam Derbyshire 22 Jul '21

22 Jul '21

Hi everyone, Recent refactors to the constraint solver have complicated the story for authors of type-checking plugins. Following a suggestion by Christiaan Baaij, and aided by Richard Eisenberg, I'm working on adding the ability for type-checking plugins to rewrite type family applications directly (hooking straight into GHC's type-family rewriting code). The goal is to ease migration for the plugin authors, hopefully simplifying the common operation of rewriting type family applications. Let me now describe the current API for this new functionality, for which I would like feedback. -------------------------------------------------------------------------- A new field is added to the TcPlugin data type, namely tcPluginRewrite :: s -> UniqFM TyCon TcPluginRewriter Here s is the existential plugin state that users can choose as they wish for their own plugin. Plugins thus register which type family TyCons they are interested in rewriting, like so: myTcPluginRewrite :: MyPluginState -> UniqFM TyCon TcPluginRewriter myTcPluginRewrite s@(MyPluginState {myFam1TyCon, myFam2TyCon}) = listToUFM [ (myFam1TyCon, myFam1Rewriter s), (myFam2TyCon, myFam2Rewriter s) ] For each type family TyCon, the plugin should provide a rewriting function (corresponding to myFam1Rewriter and myFam2Rewriter above), of type type TcPluginRewriter = [Ct] -> [TcType] -> TcPluginM TcPluginRewriteResult This means that a rewriting function is supplied with the current Given constraints and the arguments of the (guaranteed to be saturated) type-family application, and should return a result of type: data TcPluginRewriteResult where TcPluginRewriteError :: (Diagnostic a, Typeable a) => a -> TcPluginRewriteResult TcPluginNoRewrite :: TcPluginRewriteResult TcPluginRewriteTo :: { rewriteTo :: TcType , rewriteEvidence :: TcCoercion } -> TcPluginRewriteResult That is, the plugin can specify what the type-family application should be rewritten to, throw an error, or do nothing. -------------------------------------------------------------------------- I'm hoping that the components of existing type-checking plugins concerned with type-family applications can instead use this mechanism and achieve more robust results by doing so, with less effort. I would like to hear from plugin authors whether this API suits their needs. If you know of someone not on this list that might be interested, please invite them to join the conversation. The current state of this patch can be found in the GHC MR 5909: https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5909 Thanks, Sam

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