GHC 9.4.1-alpha3 now available

The GHC developers are happy to announce the availability of the third
alpha release of the GHC 9.4 series. Binary distributions, source
distributions, and documentation are available at

This major release will include:

  • A new profiling mode, -fprof-late, which adds automatic cost-center
    annotations to all top-level functions after Core optimisation has
    run. This incurs significantly less performance cost while still
    providing informative profiles.

  • A variety of plugin improvements including the introduction of a new
    plugin type, defaulting plugins, and the ability for typechecking
    plugins to rewrite type-families.

  • An improved constructed product result analysis, allowing unboxing of
    nested structures, and a new boxity analysis, leading to less reboxing.

  • Introduction of a tag-check elision optimisation, bringing
    significant performance improvements in strict programs.

  • Generalisation of a variety of primitive types to be levity
    polymorphic. Consequently, the ArrayArray# type can at long last be
    retired, replaced by standard Array#.

  • Introduction of the \cases syntax from GHC proposal 0302

  • A complete overhaul of GHC’s Windows support. This includes a
    migration to a fully Clang-based C toolchain, a deep refactoring of
    the linker, and many fixes in WinIO.

  • Support for multiple home packages, significantly improving support
    in IDEs and other tools for multi-package projects.

  • A refactoring of GHC’s error message infrastructure, allowing GHC to
    provide diagnostic information to downstream consumers as structured
    data, greatly easing IDE support.

  • Significant compile-time improvements to runtime and memory consumption.

  • On overhaul of our packaging infrastructure, allowing full
    traceability of release artifacts and more reliable binary

  • … and much more. See the release notes for a full accounting.

Note that, as 9.4.1 is the first release for which the released
artifacts will all be generated by our Hadrian build system, it’s possible that there
will be packaging issues. If you enounter trouble while using a binary
distribution, please open a ticket. Likewise, if you are a downstream
packager, do consider migrating to Hadrian to run your build; the
Hadrian build system can be built using cabal-install, stack, or the
in-tree bootstrap script.

We would like to thank Microsoft Azure, GitHub, IOG, the Zw3rk
stake pool, Tweag I/O, Serokell, Equinix, SimSpace, 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 comprise this release.

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

Happy testing,

  • Ben