Re: GHC 9.14.1-alpha2 is now available

[George Colpitts]

Tahoe , the new MacOS, is out today. Should GHC users not upgrade to it? I am concerned about https://gitlab.haskell.org/ghc/ghc/-/issues/26166

On Fri, Sep 12, 2025 at 10:26 AM Ben Gamari <b...@well-typed.com> wrote:

The GHC developers are very pleased to announce the availability of the
second alpha prerelease of GHC 9.14.1. Binary distributions, source
distributions, and documentation are available at [downloads.haskell.org].

GHC 9.14 will bring a number of new features and improvements, including:

* Significant improvements in specialisation:

   * The `SPECIALISE` pragma now allows use of type application syntax

   * The `SPECIALISE` pragma can be used to specialise for expression arguments
     as well as type arguments.

   * Specialisation is now considerably more reliable in the presence of
     `newtype`s

* Significant improvements in the GHCi debugger

* Record fields can be defined to be non-linear when `LinearTypes` is enabled.

* `RequiredTypeArgments` can now be used in more contexts

* SSE/AVX2 support in the x86 native code generator backend

* A major update of the Windows toolchain

* ... and many more

A full accounting of changes can be found in the [release notes]. Given the
many specialisation improvements and their potential for regression, we would
very much appreciate testing and performance characterisation on downstream
workloads.

Observant readers of these prerelease announcements will note that polymorphic
specialisation has been dropped from alpha 2. This measure was taken out of an
abundance of caution after finding a miscompilation during testing of alpha 1.
While this bug will be fixed in the next alpha, we expect to keep polymorphic
specialisation disabled by default in the final release. Users needing more
aggressive specialisation can explicitly enable this feature with the
`-fpolymorphic-specialisation` flag. Depending upon our experience with 9.14.1,
we may enable this feature by default in a later minor release.

This is the second of three expected alpha prereleases. We expect the next
(third) alpha will come 23 Sept. 2025, with the release candidate coming 7 Oct.
2025.

We would like to thank the Zw3rk stake pool, Well-Typed, Mercury, Channable,
Tweag I/O, Serokell, SimSpace, the Haskell Foundation, and other anonymous
contributors whose on-going financial and in-kind support has facilitated GHC
maintenance and release management over the years. Finally, this release would
not have been possible without the hundreds of open-source contributors whose
work have made the Haskell ecosystem what it is today.

As always, do give this release a try and open a [ticket] if you see
anything amiss.


[downloads.haskell.org]: https://downloads.haskell.org/ghc/9.14.1-alpha2
[release notes]: https://downloads.haskell.org/ghc/9.14.1-alpha2/docs/users_guide/9.14.1-notes.html
[ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new
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