I copy & paste Hervert's reddit answer here [1], for ones who don't follow it: As the suffix "alpha" implies, this is a very bleeding edge release with very little guarantees regarding API stability (c.f. new GHC schedule [2] https://ghc.haskell.org/trac/ghc/wiki/WorkingConventions/Releases/NewSchedul...). Put differently, a package that works now with GHC 8.4.1-alpha1 may not necessarily work with the final GHC 8.4.1 release. In order to support early adopters in testing GHC 8.4.1-alpha, there's a new Overlay Hackage Package Index https://github.com/hvr/head.hackage [3] which provides packages patched for unreleased GHCs (currently GHC 8.4.1-alpha1 & GHC 8.5/HEAD). See its README https://github.com/hvr/head.hackage#README [4] for instructions on how to use it; there's also a shell script included which automates common workflows; finally there's also support for HEAD.hackage in themake-travis-yml Travis CI script generator https://github.com/haskell-hvr/multi-ghc-travis. [5] Don't hesitate to ask if you have questions! As usual, there's already an (incomplete & work-in-progress) GHC 8.4.x Migration Guide https://ghc.haskell.org/trac/ghc/wiki/Migration/8.4 [6] you can consult and maybe even help complete. Links: - [1]: https://www.reddit.com/r/haskell/comments/7l4b19/announce_ghc_841alpha1_avai... - [2]: https://ghc.haskell.org/trac/ghc/wiki/WorkingConventions/Releases/NewSchedul... - [3]: https://github.com/hvr/head.hackage - [4]: https://github.com/hvr/head.hackage#README - [5]: https://github.com/haskell-hvr/multi-ghc-travis - [6]: https://ghc.haskell.org/trac/ghc/wiki/Migration/8.4 Cheers, Oleg On 21.12.2017 22:16, George Colpitts wrote:

Thanks Ben. I installed the Mac binaries.

For others who are wondering, you need llvm 5 if you want to use llvm with this.

Needless to say, many libraries, e.g. haskell-src-exts, primitive, and intero won't compile with this even with --allow-newer

I'll notify those libraries about that in case they want to get started on 8.4.1

Cheers George

On Wed, Dec 20, 2017 at 4:48 PM Ben Gamari mailto:ben@well-typed.com> wrote:

The GHC development team is pleased to announce the first alpha release of the 8.4.1 release. The usual release artifacts are available from

    https://downloads.haskell.org/~ghc/8.4.1-alpha1 https://downloads.haskell.org/%7Eghc/8.4.1-alpha1

Note that this release drops compatibility with GCC 4.6 and earlier. While we generally try to place as few constraints on system toolchain as possible, this release depends upon the __atomic__ builtins provided by GCC 4.7 and later (see #14244).

=== Notes on release scheduling ===

The 8.4.1 release marks the first release where GHC will be adhering to its new, higher-cadence release schedule [1]. Under this new scheme, major releases will be made in 6-month intervals with interstitial minor releases as necessary.

In order to minimize the likelihood of schedule slippage and to ensure adequate testing, each major release will be preceeded by a number of regular alpha releases. We will begin issuing these releases roughly three months before the final date of the major release and will issue roughly one every two weeks during this period. This high release cadence will allow us to quickly get fixes in to users hands and allow better feedback on the status of the release.

GHC 8.4 is slated to be released in mid-February but, due to technical constraints, we are starting the alpha-release cycle a bit later than planned under the above schedule. For this reason, it would be greatly appreciated if users could put this alpha through its paces to make up for lost time.

As always, do let us know if you encounter any trouble in the course of testing. Thanks for your help!

Cheers,

- Ben

[1] https://ghc.haskell.org/trac/ghc/blog/2017-release-schedule _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org mailto:Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users

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Probably stating what is obvious and well-know but anyways: - On the status page https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-8.4.1 it would be good to have a link for "Phase 2 of the Semigroup-Monoid Proposal (Herbert Riedel)" - Also IIRC we normally have a page on porting to the new release. It would be good to have that also when we have a chance. It's great that we are getting started early. On Thu, Dec 21, 2017 at 4:16 PM George Colpitts wrote:

Thanks Ben. I installed the Mac binaries.

For others who are wondering, you need llvm 5 if you want to use llvm with this.

Needless to say, many libraries, e.g. haskell-src-exts, primitive, and intero won't compile with this even with --allow-newer

I'll notify those libraries about that in case they want to get started on 8.4.1

Cheers George

On Wed, Dec 20, 2017 at 4:48 PM Ben Gamari wrote:

...

The GHC development team is pleased to announce the first alpha release of the 8.4.1 release. The usual release artifacts are available from

https://downloads.haskell.org/~ghc/8.4.1-alpha1

Note that this release drops compatibility with GCC 4.6 and earlier. While we generally try to place as few constraints on system toolchain as possible, this release depends upon the __atomic__ builtins provided by GCC 4.7 and later (see #14244).

=== Notes on release scheduling ===

The 8.4.1 release marks the first release where GHC will be adhering to its new, higher-cadence release schedule [1]. Under this new scheme, major releases will be made in 6-month intervals with interstitial minor releases as necessary.

In order to minimize the likelihood of schedule slippage and to ensure adequate testing, each major release will be preceeded by a number of regular alpha releases. We will begin issuing these releases roughly three months before the final date of the major release and will issue roughly one every two weeks during this period. This high release cadence will allow us to quickly get fixes in to users hands and allow better feedback on the status of the release.

GHC 8.4 is slated to be released in mid-February but, due to technical constraints, we are starting the alpha-release cycle a bit later than planned under the above schedule. For this reason, it would be greatly appreciated if users could put this alpha through its paces to make up for lost time.

As always, do let us know if you encounter any trouble in the course of testing. Thanks for your help!

Cheers,

- Ben

[1] https://ghc.haskell.org/trac/ghc/blog/2017-release-schedule _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users