- Glasgow-haskell-users

Re: Pattern synonym 'Required' constraints === Datatype Contexts(?)
by Anthony Clayden 12 Mar '21

12 Mar '21

Thank you Richard, Lennart, *Gergő* >* pattern Positive :: (Ord a, Num a) => a* >* pattern Positive <- ((>0) -> True)* *Heh heh, there's another surprise/undocumented 'feature'.* *It's not necessary to give a signature for pattern `Positive`, GHC will infer that from the decl.* *I was surprised to see `True`, and even more surprised there wasn't a `Bool` in the signature. I guess that's so `Positive` can appear as a pattern in a case expr. To dig out the positive value in a lambda expr, it seems I go* *> (\p@Positive -> p) 5 -- returns 5* *Seems I can't use any trick like that to turn `Positive` into explicitly bidirectional. I also tried* >* pattern Positive' <- ((>0) -> ())* *But that's rejected '"** Couldn't match expected type `Bool' with actual type `()'". Is the hidden `Bool` documented somewhere? (Doesn't seem to be in the User Guide nor the wiki nor the paper, on a quick scan.)

2 1

Pattern synonym 'Required' constraints === Datatype Contexts(?)
by Anthony Clayden 12 Mar '21

12 Mar '21

I must be slow on the uptake. I've just grokked this equivalence -- or is it? Consider > data Eq a => Set a = NilSet | ConsSet a (Set a) -- from the Language report > > -- ConsSet :: forall a. Eq a => a -> Set a => Set a -- inferred/per report > > -- equiv with Pattern syn 'Required' constraint > data Set' a = NilSet' | ConsSet' a (Set' a) -- no DT context > > pattern ConsSetP :: (Eq a) => () => a -> (Set' a) -> (Set' a) > pattern ConsSetP x xs = ConsSet' x xs > > ffP ((ConsSet x xs), (ConsSetP y ys)) = (x, y) > > -- ffP :: forall {a} {b}. (Eq a, Eq b) => (Set a, Set' b) -> (a, b) -- inferred The signature decl for `ConsSetP` explicitly gives both the Required `(Eq a) =>` and Provided `() =>` constraints, but the Provided could be omitted, because it's empty. I get the same signature for both `ConsSetP` as `ConsSet` with the DT Context. Or is there some subtle difference? This typing effect is what got DT Contexts called 'stupid theta' and deprecated/removed from the language standard. ("widely considered a mis-feature", as GHC is keen to tell me.) If there's no difference, why re-introduce the feature for Patterns? That is, why go to the bother of the double-context business, which looks weird, and behaves counter to usual signatures: > foo :: (Eq a) => (Show a) => a -> a > -- foo :: forall {a}. (Eq a, Show a) => a -> a -- inferred There is a slight difference possible with Pattern synonyms, compare: > pattern NilSetP :: (Eq a) => () => (Set' a) > pattern NilSetP = NilSet' > > -- NilSetP :: forall {a}. Eq a => Set' a -- inferred > -- NilSet :: forall {a}. => Set a -- inferred/per report Using `NilSetP` somewhere needs giving an explicit signature/otherwise your types are ambiguous; but arguably that's a better discipline than using `NilSet` and allowing a Set with non-comparable element types. AntC

4 3

[ANN] cabal-install-3.4.0.0
by Emily Pillmore 23 Feb '21

23 Feb '21

The Cabal team is excited to announce the release of cabal-install 3.4. This is the third release of the 3.0 release series, bringing a support for the `Cabal-Version: 3.4` `.cabal` file format. This introduces a number of user-facing features including: - Support for GHC 9.0 - Package sublibrary dependency syntax - Allowing omission of the `default-language` declaration - A mixins field allowing the user to specify a sublibrary - [Many other features]( https://cabal.readthedocs.io/en/latest/file-format-changelog.html#cabal-ver… ) In addition, the `cabal-install` frontend itself has gained a number of new features including: - New `active-repositories` `cabal.project` fields allowing users to specify an order and various ways of combining package repositories - Improvements to `cabal init` - A rework of the `cabal v2-sdist` command. `cabal v1-sdist` is removed as of this version - `source-repository-package` directories are no longer local - A new `list-bin` command - `cabal sandbox` is now removed in favor of default nix-style builds - `cabal list` now accepts regular expressions - More rich `index-state` syntax. `v2-freeze` saves `index-state` I'd also like to thank the many contributors who offered patches, tickets, and other help in the preparation of this release. We appreciate all of your help! For a full set of release notes, see https://github.com/haskell/cabal/blob/master/release-notes/cabal-install-3.…. If you have issues, we'd love to hear about there here: https://github.com/haskell/cabal/issues. Happy hacking! Emily

1 0

[ANNOUNCE] GHC 8.10.4 released
by Ben Gamari 10 Feb '21

10 Feb '21

The GHC team is very pleased to announce the availability of GHC 8.10.4. Source and binary distributions are available at the usual place: https://downloads.haskell.org/ghc/8.10.4/ This is a small bug-fix release, fixing two bugs present in 8.10.3: * Fix a linker hang triggered by dynamic code loading on Windows (#19155) * Fix a crash caused by inappropriate garbage of heap-allocated data reachable from foreign exports (#19149) As always, feel free to report any issues you encounter via [gitlab.haskell.org](https://gitlab.haskell.org/ghc/ghc/-/issues/new). Cheers, - Ben

2 1

[ANNOUNCE] GHC 9.0.1 released
by Ben Gamari 08 Feb '21

08 Feb '21

The GHC team is very pleased to announce the availability of GHC 9.0.1. Source and binary distributions are available at the usual place: https://downloads.haskell.org/ghc/9.0.1/ In addition to numerous bug fixes, GHC 9.0.1 will bring a number of new features: * A first cut of the new LinearTypes language extension [2], allowing use of linear function syntax and linear record fields. * A new bignum library, ghc-bignum, improving portability and allowing GHC to be more easily used with integer libraries other than GMP. * Improvements in code generation, resulting in considerable runtime performance improvements in some programs. * Improvements in pattern-match checking, allowing more precise detection of redundant cases and reduced compilation time. * Implementation of the "simplified subsumption" proposal [3] simplifying the type system and paving the way for QuickLook impredicativity in GHC 9.2. * Implementation of the QualifiedDo extension [4], allowing more convenient overloading of `do` syntax. * An experimental new IO manager implementation for Windows platforms, both improving performance and fixing many of the quirks with the old manager built on POSIX-emulation. * Improvements in compilation time. And many more. See the release notes [5] for a full accounting of the changes in this release. As always, feel free to report any issues you encounter via gitlab.haskell.org. Cheers, - Ben [1]: https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.0#ghc-prim-07 [2]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0111-l… [3]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-s… [4]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-q… [5]: https://downloads.haskell.org/ghc/9.0.1/docs/html/users_guide/9.0.1-notes.h…

2 1

[ANNOUNCE] Glasgow Haskell Compiler 9.0.1-rc1 released
by Ben Gamari 26 Jan '21

26 Jan '21

Hello all, The GHC team is very pleased to announce the availability of the first release candidate of GHC 9.0.1 series. Source and binary distributions are available at the usual place: https://downloads.haskell.org/ghc/9.0.1-rc1/ This release candidate comes quite a bit later than expected after difficulty finding a performance neutral fix for a critical soundness bug, #17760. See [1] for details on the solution, particularly if you are a library maintainer currently using the touch# primop or withForeignPtr. Nevertheless, this release has nevertheless seen a considerable amount of testing and consequently we hope that this should be the last pre-release before the final release. In addition to numerous bug fixes, GHC 9.0.1 will bring a number of new features: * A first cut of the new LinearTypes language extension [2], allowing use of linear function syntax and linear record fields. * A new bignum library (ghc-bignum), allowing GHC to be more easily used with integer libraries other than GMP. * Improvements in code generation, resulting in considerable performance improvements in some programs. * Improvements in pattern-match checking, allowing more precise detection of redundant cases and reduced compilation time. * Implementation of the "simplified subsumption" proposal [3] simplifying the type system and paving the way for QuickLook impredicativity in GHC 9.2. * Implementation of the QualifiedDo extension [4], allowing more convenient overloading of `do` syntax. * Improvements in compilation time. And many more. See the release notes [5] for a full accounting of the changes in this release. As always, do test this release and open tickets for whatever issues you encounter. Cheers, - Ben [1] https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.0#ghc-prim-07 [2] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0111-l… [3] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-s… [4] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-q… [5] https://downloads.haskell.org/ghc/9.0.1-rc1/docs/html/users_guide/9.0.1-not…

2 1

Linking only some libraries dynamically
by Volker Wysk 09 Jan '21

09 Jan '21

Hi! When you have to link an specific library dynamically, then all libraries, as well as all parts of the program must be compiled and linked dynamically. Is this correct? Is it possible to link only one library dynamically and the rest statically? Regards, Volker

1 0

Re: [ANNOUNCE] Glasgow Haskell Compiler 8.10.3 released
by Ben Gamari 20 Dec '20

20 Dec '20

Shayne Fletcher <shayne.fletcher.50(a)gmail.com> writes: > On Sat, Dec 19, 2020 at 7:23 PM Ben Gamari <ben(a)well-typed.com> wrote: > >> Hello all, >> >> The GHC team is happy to announce the release of GHC 8.10.3. Source >> and binary distributions are available at the usual place: >> >> https://downloads.haskell.org/ghc/8.10.3/ > > > Thanks! > > There doesn't seem to be a ghc-8.10.3-release tag in > the git@gitlab.haskell.org:ghc/ghc.git repository. Shouldn't there be? > Indeed. Fixed! Cheers, - Ben

1 0

[ANNOUNCE] Glasgow Haskell Compiler 8.10.3 released
by Ben Gamari 20 Dec '20

20 Dec '20

Hello all, The GHC team is happy to announce the release of GHC 8.10.3. Source and binary distributions are available at the usual place: https://downloads.haskell.org/ghc/8.10.3/ GHC 8.10.3 fixes a number of issues in present in GHC 8.10.2 including: * Numerous stability improves on Windows * More robust support for architectures with weak memory ordering guarantees (e.g. modern ARM hardware). * GHC can now split dynamic objects to accomodate macOS' RPATH size limitation when building large projects (#14444) * Several correctness bugs in the new low-latency garbage collector * Many, many other bug-fixes Note that at the moment we still require that macOS Catalina users exempt the binary distribution from the notarization requirement by running `xattr -cr .` on the unpacked tree before running `make install`. This situation will hopefully be improved for GHC 9.0.1 with the resolution of #17418 [1]. Cheers, - Ben [1] https://gitlab.haskell.org/ghc/ghc/issues/17418

1 0

[ANNOUNCE] Glasgow Haskell Compiler 9.0.1-alpha1 released
by Ben Gamari 07 Dec '20

07 Dec '20

Hello all, The GHC team is very pleased to announce the availability of the first alpha release in the GHC 9.0 series. Source and binary distributions are available at the usual place: https://downloads.haskell.org/ghc/9.0.1-alpha1/ This first alpha comes quite a bit later than expected. However, we have done a significant amount of testing on this pre-release and therefore hope to be able to move forward quickly with a release candidate next week and with a final release in mid-October. GHC 9.0.1 will bring a number of new features: * A first cut of the new LinearTypes language extension [1], allowing use of linear function syntax and linear record fields. * A new bignum library (ghc-bignum), allowing GHC to be more easily used with integer libraries other than GMP. * Improvements in code generation, resulting in considerable performance improvements in some programs. * Improvements in pattern-match checking, allowing more precise detection of redundant cases and reduced compilation time. * Implementation of the "simplified subsumption" proposal [2] simplifying the type system and paving the way for QuickLook impredicativity in GHC 9.2. * Implementation of the QualifiedDo extension [3], allowing more convenient overloading of `do` syntax. * Improvements in compilation time. And many more. See the release notes [4] for a full accounting of the changes in this release. Do note that there are a few things that we expect will change before the final release: * We expect to sort out a notarization workflow for Apple Darwin, allowing our binary distributions to be used on macOS Catalina without hassle. Until this has been sorted out Catalina users can exempt the current macOS binary distribution from the notarization requirement themselves by running `xattr -cr .` on the unpacked tree before running `make install`. * We will likely transition the Alpine binary distribution to be fully statically-linked, providing a convenient, distribution-independent packaging option for Linux users. * We will be merging a robust solution for #17760 which will introduce a new primitive, `keepAlive#`, to the `base` library, subsuming most uses of `touch#`. As always, do test this release and open tickets for whatever issues you encounter. To help with this, we will be publishing a blog post describing use of our new `head.hackage` infrastructure to ease testing of larger projects with Hackage dependencies later this week. Cheers, - Ben [1] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0111-l… [2] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-s… [3] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-q… [4] https://downloads.haskell.org/ghc/9.0.1-alpha1/docs/html/users_guide/9.0.1-…

4 4