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Trying to speedup GHC compile times...Help!
by Young, Jeff 06 Jul '21

06 Jul '21

Hi ghc devs, I'm a long-time Haskeller but am just getting into GHC development. I started a 12 week internship at Tweag I/O under Richard Eisenberg this week with the singular goal to speedup GHC compile times. I'm specifically looking to contribute to ghc issues 18541 <https://gitlab.haskell.org/ghc/ghc/-/issues/18541> and 18535 <https://gitlab.haskell.org/ghc/ghc/-/issues/18535>. So I thought I would reach out to the community to get some direction on issues/features/problems to tackle in the pursuit of faster compilation times. This is a full time internship and so I think there is a real opportunity to nail down a deliverable for the community, but I want to get some guidance from the experts (you fine people!) before going down a rabbit hole. To be specific I'm looking for lingering items such as: 1. It would be great if we had <thing-here> but no one has time. 2. Primop foo is half complete but is the right type for <common-use-case-which-is-currently-just-a-list>. 3. Swap <some-type> to an array-like type *non-incrementally*, that is, establish a patch that rips out the previous type and replaces it with the array-like across the entire compiler, rather than module-by-module. Point 2 is a specific reference to MR 3571 <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/3571> but I'm unsure of the status and etiquette around MRs, and I'm unsure exactly how fulfilling the todos at the end of that MR would aid in faster compilation times (and if there is evidence to that effect somewhere). Thanks for the help! - Jeff

7 9

Breaking changes to the base library
by Harendra Kumar 03 Jul '21

03 Jul '21

I see the following errors when compiling with ghc head version: $ ghc-stage2 --version The Glorious Glasgow Haskell Compilation System, version 9.3.20210608 $ cabal build --with-compiler ghc-stage2 --allow-newer Data/Colour/CIE.hs:80:12: error: Ambiguous occurrence ‘sum’ It could refer to either ‘Prelude.sum’, imported from ‘Prelude’ at Data/Colour/CIE.hs:25:8-22 (and originally defined in ‘Data.Foldable’) or ‘Data.List.sum’, imported from ‘Data.List’ at Data/Colour/CIE.hs:41:1-16 (and originally defined in ‘GHC.List’) | 80 | total = sum $ map fst l | ^^^ Can someone briefly describe this change and what's the recommended way of fixing this? Just hide the Data.List definition? I do not see this mentioned in the release notes of 9.2/9.4 here: https://ghc.gitlab.haskell.org/ghc/doc/users_guide/9.2.1-notes.html -harendra

8 8

Writing GHC plugin to modify AST despite failure to type-check
by Evan Relf 01 Jul '21

01 Jul '21

Hi there, I would like to write a GHC plugin — initially as a learning exercise, and maybe real-world use if it works — that automatically applies `liftIO` to `IO` actions, to get the benefit that libraries like `lifted-base` or `relude` provide, but applied to all libraries, automatically. As a simple example, this program will not type-check by default, but it will if I can write my plugin: ``` program :: MonadIO m => m () program = putStrLn "Hello world!" ``` (That's `putStrLn :: String -> IO ()` from the regular `Prelude`) The idea is roughly, "if you see an `IO a` action where a `MonadIO m => m a` action is expected, add `liftIO` to make the `IO a` action type-check. But how to implement it? A type-checker plugin runs when type-checking fails, which is when I want to take action. But it doesn't seem to allow me to change the AST so I can add the `liftIO` function. So then I tried... A `typeCheckResultAction` plugin (for lack of a better name) does allow me to change the AST, and I can use the types to guide how I do it. But it doesn't seem to run if type-checking fails, which is exactly when I want to be adding the `liftIO`s. Am I missing something about GHC's plugin system that would allow me to do what I want? Whether that be AST manipulation in a type-checking plugin, or running the `typeCheckResultAction` despite type-checking failing. Or is AST manipulation with type information impossible if type-checking fails? This is my first foray into anything GHC-related, so I apologize if this doesn't make sense, or isn't the right place to ask. Thanks, - Evan

3 4

Re: Loading a typechecked module and then using it immediately as a package
by Erdi, Gergo 01 Jul '21

01 Jul '21

PUBLIC Unfortunately, that would take quite some extra effort. However, I think I have figured this out in the meantime: it seems it wasn't the FinderCache that needed invalidating, but the ModuleGraph. So now I have the following code for changing the home unit: ``` setHomeUnit :: (GhcMonad m) => UnitId -> m () setHomeUnit unitId = do modifySession $ \env -> env { hsc_dflags = (hsc_dflags env) { homeUnitId = unitId } } invalidateModSummaryCache invalidateModSummaryCache :: (GhcMonad m) => m () invalidateModSummaryCache = modifySession $ \env -> env { hsc_mod_graph = invalidateMG (hsc_mod_graph env) } where invalidateMG = mapMG invalidateMS invalidateMS ms = ms{ ms_hs_date = addUTCTime (-1) (ms_hs_date ms) } ``` Here, `invalidateModSummaryCache` is based on the one in the `GHC` module which doesn't export it. With the addition of `invalidateModSummaryCache` to `setHomeUnit`, I can now import `MyLib` from `Test` without using a package-qualified import. Adding or removing a `flushFinderCaches` call doesn’t seem to change anything. -----Original Message----- From: Matthew Pickering <matthewtpickering(a)gmail.com> Sent: Wednesday, June 30, 2021 6:11 PM To: Erdi, Gergo <Gergo.Erdi(a)sc.com> Subject: [External] Re: Loading a typechecked module and then using it immediately as a package ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients. Could you provide the code which is failing? Then it will be easier to fix. On Tue, Jun 29, 2021 at 12:00 PM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > PUBLIC > > Should I? OK, I just tried calling `flushFinderCaches` after I change the home unit to `mainUnitId`, but I still get exactly the same behaviour: `findInstalledHomeModule` returns `InstalledFound` and things go downhill from there. > > -----Original Message----- > From: Matthew Pickering <matthewtpickering(a)gmail.com> > Sent: Tuesday, June 29, 2021 6:34 PM > To: Erdi, Gergo <Gergo.Erdi(a)sc.com> > Cc: ghc-devs(a)haskell.org > Subject: [External] Re: Loading a typechecked module and then using it immediately as a package > > ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients. > > > Are you clearing the FinderCache? > > On Tue, Jun 29, 2021 at 11:14 AM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > > > PUBLIC > > > > I don't know yet what's going on, but one thing I did notice is that `findInstalledHomeModule` returns `InstalledFound` for `MyLib`, which doesn't sound right to me -- `MyLib` should come from the "fake-uid" unit, and `Test` is typechecked in the `mainUnitId`. > > > > -----Original Message----- > > From: Erdi, Gergo > > Sent: Tuesday, June 29, 2021 5:51 PM > > To: Matthew Pickering <matthewtpickering(a)gmail.com> > > Subject: Re: Loading a typechecked module and then using it immediately as a package > > > > PUBLIC > > > > I tried moving `MyLib.hs` into a directory different than `Test.sh`, but the error message still refers to its correct location! So this error is not guessing the file name of where `MyLib.hs` could be loaded from; instead, it seems to refer correctly to where the module (previously loaded) was. Hmm. > > > > -----Original Message----- > > From: Matthew Pickering <matthewtpickering(a)gmail.com> > > Sent: Tuesday, June 29, 2021 5:04 PM > > To: Erdi, Gergo <Gergo.Erdi(a)sc.com> > > Subject: [External] Re: Loading a typechecked module and then using it immediately as a package > > > > > > Do you have a `MyLib.hs` source file? If you move that somewhere else (another folder) then things might work? > > > > On Tue, Jun 29, 2021 at 9:41 AM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > > > > > PUBLIC > > > > > > What's weird about it is that if I print the `moduleNameProvidersMap`, I can see `MyLib` inside, and it looks no different than any other module from e.g. `ghc-prim` that I can import into `Test.hs` without any package qualification. Also, why does the error message refer to the file name `input/MyLib.hs`? Why does GHC even know that that is where it would have to be loaded from, if it weren't to be used from an already loaded package? > > > > > > > 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. > > 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. 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. 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1 0

Loading a typechecked module and then using it immediately as a package
by Erdi, Gergo 29 Jun '21

29 Jun '21

PUBLIC Hi, I have the following to .hs files: 1. MyLib.hs: module MyLib where ... 2. Test.hs: {-# LANGUAGE PackageImports #-} module Test where import "my-pkg" MyLib ... I would like to parse/typecheck/load MyLib.hs into some Unit "my-unit", then add that to the package "my-pkg", and then typecheck Test.hs, all in-proc using the GHC API, without putting any other files on disk. How do I do that? What I tried is loading MyLib.hs after setting the homeUnitId in the DynFlags to "my-unit", then editing the packageNameMap in the unitState of the DynFlags to may "my-pkg" to "my-unit": setHomeUnit :: (GhcMonad m) => UnitId -> m () setHomeUnit unitId = do dflags <- getSessionDynFlags modifySession $ \h -> h{ hsc_dflags = dflags{ homeUnitId = unitId } } registerUnit :: (GhcMonad m) => PackageName -> UnitId -> m () registerUnit pkg unitId = modifySession $ \h -> h{ hsc_dflags = addUnit $ hsc_dflags h } where addUnit dflags = dflags { unitState = let us = unitState dflags in us { packageNameMap = M.insert pkg (Indefinite unitId Nothing) $ packageNameMap us } } pipeline = do setHomeUnit myUnit loadModule =<< typecheckModule =<< parseModule =<< modSumarryFor "MyLib" registerUnit myPkg myUnit setHomeUnit mainUnitId typecheckModule =<< parseModule =<< modSumarryFor "Test" Alas, this doesn't work: the import of `MyLib` from `my-pkg` fails with: input/linking/Test.hs:5:1: error: Could not find module 'MyLib' It is not a module in the current program, or in any known package. TBH I'm not very surprised that it didn't work - that registerUnit function is doing some pretty deep surgery on the unitState that probably breaks several invariants. Still, I wasn't able to find a better way - all the functions in GHC.Unit.State seem to be for querying only. 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.

4 5

Re: Loading a typechecked module and then using it immediately as a package
by Erdi, Gergo 29 Jun '21

29 Jun '21

PUBLIC Should I? OK, I just tried calling `flushFinderCaches` after I change the home unit to `mainUnitId`, but I still get exactly the same behaviour: `findInstalledHomeModule` returns `InstalledFound` and things go downhill from there. -----Original Message----- From: Matthew Pickering <matthewtpickering(a)gmail.com> Sent: Tuesday, June 29, 2021 6:34 PM To: Erdi, Gergo <Gergo.Erdi(a)sc.com> Cc: ghc-devs(a)haskell.org Subject: [External] Re: Loading a typechecked module and then using it immediately as a package ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients. Are you clearing the FinderCache? On Tue, Jun 29, 2021 at 11:14 AM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > PUBLIC > > I don't know yet what's going on, but one thing I did notice is that `findInstalledHomeModule` returns `InstalledFound` for `MyLib`, which doesn't sound right to me -- `MyLib` should come from the "fake-uid" unit, and `Test` is typechecked in the `mainUnitId`. > > -----Original Message----- > From: Erdi, Gergo > Sent: Tuesday, June 29, 2021 5:51 PM > To: Matthew Pickering <matthewtpickering(a)gmail.com> > Subject: Re: Loading a typechecked module and then using it immediately as a package > > PUBLIC > > I tried moving `MyLib.hs` into a directory different than `Test.sh`, but the error message still refers to its correct location! So this error is not guessing the file name of where `MyLib.hs` could be loaded from; instead, it seems to refer correctly to where the module (previously loaded) was. Hmm. > > -----Original Message----- > From: Matthew Pickering <matthewtpickering(a)gmail.com> > Sent: Tuesday, June 29, 2021 5:04 PM > To: Erdi, Gergo <Gergo.Erdi(a)sc.com> > Subject: [External] Re: Loading a typechecked module and then using it immediately as a package > > > Do you have a `MyLib.hs` source file? If you move that somewhere else (another folder) then things might work? > > On Tue, Jun 29, 2021 at 9:41 AM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > > > PUBLIC > > > > What's weird about it is that if I print the `moduleNameProvidersMap`, I can see `MyLib` inside, and it looks no different than any other module from e.g. `ghc-prim` that I can import into `Test.hs` without any package qualification. Also, why does the error message refer to the file name `input/MyLib.hs`? Why does GHC even know that that is where it would have to be loaded from, if it weren't to be used from an already loaded package? > > > > 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. 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.

1 0

RE: Loading a typechecked module and then using it immediately as a package
by Erdi, Gergo 29 Jun '21

29 Jun '21

PUBLIC I don't know yet what's going on, but one thing I did notice is that `findInstalledHomeModule` returns `InstalledFound` for `MyLib`, which doesn't sound right to me -- `MyLib` should come from the "fake-uid" unit, and `Test` is typechecked in the `mainUnitId`. -----Original Message----- From: Erdi, Gergo Sent: Tuesday, June 29, 2021 5:51 PM To: Matthew Pickering <matthewtpickering(a)gmail.com> Subject: Re: Loading a typechecked module and then using it immediately as a package PUBLIC I tried moving `MyLib.hs` into a directory different than `Test.sh`, but the error message still refers to its correct location! So this error is not guessing the file name of where `MyLib.hs` could be loaded from; instead, it seems to refer correctly to where the module (previously loaded) was. Hmm. -----Original Message----- From: Matthew Pickering <matthewtpickering(a)gmail.com> Sent: Tuesday, June 29, 2021 5:04 PM To: Erdi, Gergo <Gergo.Erdi(a)sc.com> Subject: [External] Re: Loading a typechecked module and then using it immediately as a package Do you have a `MyLib.hs` source file? If you move that somewhere else (another folder) then things might work? On Tue, Jun 29, 2021 at 9:41 AM Erdi, Gergo <Gergo.Erdi(a)sc.com> wrote: > > PUBLIC > > What's weird about it is that if I print the `moduleNameProvidersMap`, I can see `MyLib` inside, and it looks no different than any other module from e.g. `ghc-prim` that I can import into `Test.hs` without any package qualification. Also, why does the error message refer to the file name `input/MyLib.hs`? Why does GHC even know that that is where it would have to be loaded from, if it weren't to be used from an already loaded package? > 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.

2 1

Re: Loading a typechecked module and then using it immediately as a package
by Erdi, Gergo 29 Jun '21

29 Jun '21

PUBLIC What's weird about it is that if I print the `moduleNameProvidersMap`, I can see `MyLib` inside, and it looks no different than any other module from e.g. `ghc-prim` that I can import into `Test.hs` without any package qualification. Also, why does the error message refer to the file name `input/MyLib.hs`? Why does GHC even know that that is where it would have to be loaded from, if it weren't to be used from an already loaded package? -----Original Message----- From: Erdi, Gergo Sent: Monday, June 28, 2021 3:04 PM To: 'Matthew Pickering' <matthewtpickering(a)gmail.com> Cc: 'ghc-devs(a)haskell.org' <ghc-devs(a)haskell.org> Subject: RE: [External] Re: Loading a typechecked module and then using it immediately as a package INTERNAL Oh, and one more question. This all works if in `Test.hs` I use a package import for `MyLib`. However, if I remove that, I get an error attempting to use module ‘main:MyLib’ (input/MyLib.hs) which is not loaded So I tried adding an ExposePackage to the DynFlags's packageFlags between loading the library and typechecking `Test.hs`, but I couldn't get that to work: 1. If I just set it in the `hsc_dflags`, it doesn't take. 2. If I use `initUnits` after setting it in `hsc_dflags`, I get a new error: cannot satisfy my-pkg -----Original Message----- From: Erdi, Gergo Sent: Monday, June 28, 2021 2:41 PM To: Matthew Pickering <matthewtpickering(a)gmail.com> Cc: ghc-devs(a)haskell.org Subject: RE: [External] Re: Loading a typechecked module and then using it immediately as a package INTERNAL Thanks, I got this working (after changing it slightly to use the GHC 9.0 API to the UnitState). However, I have some followup questions: 1. In the fakeUnitInfo, what is the relationship between unitLibraries and unitExposedModules? 2. In the fakeUnitInfo, what is the unitImportDirs used for? 3. What is the difference between a PackageId and a PackageName? Other than that, the code registers MyLib into the my-pkg package by letting `load` do the actual heavy lifting. For my purposes, I will need to control this loading myself: only `MyLib`'s typechecked interface should be used, with no actual compilation of definitions. So I wrote some code that makes a ModIface from a TcGblEnv. I seemingly got the whole thing working just by setting mi_exports from the TcGblEnv and leaving everything else with trivial values (fingerprint0 for fingerprints, empty lists for instances, etc.). If `MyLib` has no external dependencies and doesn't define any typeclasses, instances, or type families, is this enough? What is the role of `mi_globals`, should I set that from `tcg_rdr_env`, or should I leave it empty? Thanks, Gergo -----Original Message----- From: Matthew Pickering <matthewtpickering(a)gmail.com> Sent: Friday, June 25, 2021 6:54 PM To: Erdi, Gergo <Gergo.Erdi(a)sc.com> Cc: ghc-devs(a)haskell.org Subject: [External] Re: Loading a typechecked module and then using it immediately as a package ATTENTION: This email came from an external source. Do not open attachments or click on links from unknown senders or unexpected emails. Always report suspicious emails using the Report As Phishing button in Outlook to protect the Bank and our clients. Hi Gergo, Please see a minimal example in this gist. https://clicktime.symantec.com/3Eb2qXqu8Yp6VtdK9d5pNmL7Vc?u=https%3A%2F%2Fg… Cheers, Matt On Fri, Jun 25, 2021 at 10:20 AM Erdi, Gergo via ghc-devs <ghc-devs(a)haskell.org> wrote: > > PUBLIC > > > Hi, > > > > I have the following to .hs files: > > > > MyLib.hs: > > module MyLib where > … > > Test.hs: > > {-# LANGUAGE PackageImports #-} > module Test where > import “my-pkg” MyLib > … > > > > I would like to parse/typecheck/load MyLib.hs into some Unit “my-unit”, then add that to the package “my-pkg”, and then typecheck Test.hs, all in-proc using the GHC API, without putting any other files on disk. How do I do that? > > > > What I tried is loading MyLib.hs after setting the homeUnitId in the DynFlags to “my-unit”, then editing the packageNameMap in the unitState of the DynFlags to may “my-pkg” to “my-unit”: > > setHomeUnit :: (GhcMonad m) => UnitId -> m () > > setHomeUnit unitId = do > > dflags <- getSessionDynFlags > > modifySession $ \h -> h{ hsc_dflags = dflags{ homeUnitId = unitId > } } > > > > registerUnit :: (GhcMonad m) => PackageName -> UnitId -> m () > > registerUnit pkg unitId = modifySession $ \h -> h{ hsc_dflags = > addUnit $ hsc_dflags h } > > where > > addUnit dflags = dflags > > { unitState = let us = unitState dflags in us > > { packageNameMap = M.insert pkg (Indefinite unitId > Nothing) $ packageNameMap us > > } > > } > > > > pipeline = do > > setHomeUnit myUnit > > loadModule =<< typecheckModule =<< parseModule =<< modSumarryFor “MyLib” > > registerUnit myPkg myUnit > > > > setHomeUnit mainUnitId > > typecheckModule =<< parseModule =<< modSumarryFor “Test” > > > > > > Alas, this doesn’t work: the import of `MyLib` from `my-pkg` fails with: > > > > input/linking/Test.hs:5:1: error: > > Could not find module ‘MyLib’ > > It is not a module in the current program, or in any known package. > > > > TBH I’m not very surprised that it didn’t work – that registerUnit function is doing some pretty deep surgery on the unitState that probably breaks several invariants. Still, I wasn’t able to find a better way – all the functions in GHC.Unit.State seem to be for querying only. > > > > 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. > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > https://clicktime.symantec.com/3A3FModesGCHWyu3Lvr5tp57Vc?u=http%3A%2F > %2Fmail.haskell.org%2Fcgi-bin%2Fmailman%2Flistinfo%2Fghc-devs 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. 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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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