- ghc-devs - Haskell.org

Losing (parallel) sleep over module dependencies
by Matthew Pickering 09 Apr '19

09 Apr '19

Hi all, I get worried quite often about the interaction of two facts 1. Adding a new dependency to a module is easy. 2. Adding a new dependency changes the build graph and potentially reduces the amount of parallelism which the build is capable of. Has anyone thought of any strategies to analyse the dependency graph of GHC so that a linter can be created to warn against any changes which create dependencies which affect the parallelism? hs-boot files make this issue even worse I think but I'm not sure of the precise recompilation semantics. It would be quite straight forward to index ghc as it is being built to create a dependency graph (at the identifier) level but it's unclear to me whether it is possible to do anything productive with this information. Cheers, Matt

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Validation Failures on aarch64
by Travis Whitaker 09 Apr '19

09 Apr '19

Hello GHC devs, When attempting to validate a patch on aarch64, it seems there are a large number of validation failures: SUMMARY for test run started at Mon Apr 8 07:19:05 2019 UTC 0:15:35 spent to go through 6890 total tests, which gave rise to 17169 test cases, of which 10018 were skipped 41 had missing libraries 3151 expected passes 150 expected failures 11 caused framework failures 0 caused framework warnings 0 unexpected passes 3798 unexpected failures 0 unexpected stat failures The failures seem consistent on recent-ish master, specifically the neighborhood of 6113d0d4540af7853c71e9f42a41c3b0bab386fd. Is this to be expected? Thanks, Travis Whitaker

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Merge Request Submission Confusion
by Ara Adkins 08 Apr '19

08 Apr '19

Hey all, I'm trying to submit a minor MR as described on the wiki [0]. I can't seem to find the mentioned 'New Merge Request' button, however. Do I need a specific set of permissions to open MRs? Any pointers would be appreciated. Best, _ara [0] https://gitlab.haskell.org/ghc/ghc/wikis/home#opening-a-merge-request

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CI execution
by Sylvain Henry 08 Apr '19

08 Apr '19

Hi devs, It seems that the CI doesn't check branches in GHC forks on Gitlab anymore. Is is intentional? Is there a way to trigger a CI execution manually on a specific branch? Thanks, Sylvain

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Proposal: Don't read environment files by default
by Matthew Pickering 08 Apr '19

08 Apr '19

Hi all, Environment files have caused a large amount of pain for users because they are read by default by GHC. For example: https://github.com/haskell/cabal/issues/4542 Cabal developers have indicated that they are not going to stop generating them by default despite the overwhelming user pressure. Therefore I propose that users should opt-in to using environment files by having to explicitly pass a flag to enable the search behavior. This will provide a much better user experience overall and will stop tooling having to isolate itself from their existence. Cheers, Matt

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Re: Recover role of a type variable in source Haskell
by Ryan Scott 07 Apr '19

07 Apr '19

It depends on what you mean by "source Haskell". If you're willing to consider including Template Haskell in your definition of "source", then the answer is yes, since there is a reifyRoles function [1] which gives you this information. I'm not aware of another way to accomplish this (without resorting to something like the GHC API). Ryan S. ----- [1] https://hackage.haskell.org/package/template-haskell-2.14.0.0/docs/Language…

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Recover role of a type variable in source Haskell
by chessai . 07 Apr '19

07 Apr '19

Hi devs, Is it possible to programmatically recover the role of a type variable? Or, possibly, a list of the roles of the type variables from left to right? For example, if i have: data Foo a = Foo (1) newtype Bar a b = Bar (a -> b) (1) Getting the role list of (1) would give me [Phantom], and (2) would give me [Representational, Representational]. I know in compiler/types/TyCon.hs that TyCon has a list of Roles in it, but there doesn't seem to be any machinery available to do this in source haskell. Thanks

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Re: Debug printing inside the typechecker knot
by Ryan Scott 05 Apr '19

05 Apr '19

> Did you mean "What is the TcHsSyn counterpart to TcMType.zonkTcTyVar"? D'oh. Yes, I did. > But it's never a bad idea to document more. I've documented all the wisdom from here in this wiki page [1]! Feel free to edit it if there are any corrections to be made. Ryan S. ----- [1] https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/tying-the-knot…

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Can Gitlab's "issue was closed by ..." mails be improved?
by Ömer Sinan Ağacan 05 Apr '19

05 Apr '19

Hi, Currently Gitlab doesn't give any details of why an issue was closed, it just says "Issue was closed by ...". You have to go to the issue page to see that it was closed because of a closing merge request was merged. I'm wondering if this could be improved so that in the email it says "issue was closed by ... via commit ..." or something like that. Anyone know if there's already a ticket for this in Gitlab issue tracker? Ömer

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Defining a wired-in type of a different kind
by Jan van Brügge 05 Apr '19

05 Apr '19

Hi, when trying to get familiar with the GHC code base for my Bachelor's thesis. I followed the GHC Wiki, especially the case study about the bool type. Now I wanted to add a new kind and a new type inhabiting this kind (without having to expose a data constructor, so without datatype promotion). So in TysWiredIn.hs I added the new TyCons and added them to the list of wired-in types: -- data Row a b rowKindCon :: TyCon rowKindCon = pcTyCon rowKindConName Nothing [alphaTyVar, betaTyVar] [] rowKind :: Kind rowKind = mkTyConTy rowKindCon -- data RNil :: Row a b rnilTyCon :: TyCon rnilTyCon = mkAlgTyCon rnilTyConName [] rowKind [] Nothing [] (mkDataTyConRhs []) (VanillaAlgTyCon (mkPrelTyConRepName rnilTyConName)) False rnilTy :: Type rnilTy = mkTyConTy rnilTyCon I also added two new empty data decls to ghc-prim, but if I inspect the kind of RNil it is not Row, but Type. So I think I am either understanding res_kind wrong or I have to do something completely different. I am also not sure how to verify that the code in TysWiredIn.hs is working at all, from all what I can tell it could just be the declarations in ghc-prim that result in what I see in ghci. Thank you and sorry for my beginner question Jan

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