- Glasgow-haskell-users

GHC 10.0.1-alpha1 is now available
by Zubin Duggal 19 Sep '26

19 Sep '26

The GHC developers are very pleased to announce the availability of the first alpha prerelease of GHC 10.0.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 10.0 will bring a number of new features and improvements, including: * The default language edition is now `GHC2024` ([GHC Proposal #632][ghc2024], #26039). * `Type` and `Constraint` are now completely distinct types, just as much as `Int` and `Bool` (#24279). * The new [QualifiedStrings][] language extension ([GHC Proposal #723][qualified-strings]) allows string literals to be qualified using module qualification syntax, so that `M."my string"` desugars to`M.fromString "my string"`. * The treatment of static forms has been simplified, implementing [GHC Proposal #732][static-forms] (#26556). The free term variables of `(static e)` must now be bound at top level. * `-fpolymorphic-specialisation` is now (re)enabled by default (#23559), * Bytecode can now be written to disk with `-fwrite-byte-code` and packaged into bytecode libraries with `-bytecodelib`, which the interpreter can use to satisfy package dependencies (#26298). * Executables can now be properly statically linked with the new `-fully-static` and `-static-external` flags (#26434). * SIMD support in the AArch64 native code generator (#26536). * A new `poll` I/O manager, which is now the default in the single-threaded RTS on all POSIX platforms except macOS (!9677). * Version 2 of the [GHC Jobserver Protocol][jsem] for GHC's `-jsem` jobserver on Linux and other POSIX platforms (#25087, #27253). This is sadly a necessary breaking change. `-jsem` requires cabal-install 3.18 or later, and is otherwise ignored with a warning, falling back to sequential compilation. * Changes to `base`: * `GHC.Num.{BigNat,Integer,Natural}` are no longer exposed ([CLC #359][clc-359]) and GHC internals in `GHC.Num` are deprecated ([CLC #360][clc-360]). * `Data.List.init` and `Data.List.last` now carry an `x-partial` warning ([CLC #292][clc-292]). * The minimum bootstrap compiler is now GHC 9.10, LLVM versions up to 23 are supported (#26813, #27764), and the Debian 9, Debian 10, Ubuntu 18.04 and Ubuntu 20.04 bindists have been dropped in favour of a new Debian 13 bindist (#25876). * ... and many more A full accounting of changes can be found in the [release notes][]. See the [migration guide][] for guidance on migrating programs to this release. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. Given the many changes in this major release, we would very much appreciate testing on downstream workloads. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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. [downloads.haskell.org] https://downloads.haskell.org/ghc/10.0.1-alpha1 [release notes]: https://downloads.haskell.org/ghc/10.0.1-alpha1/docs/users_guide/10.0.1-not… [migration guide]: https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/10.0 [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [ghc2024]: https://github.com/ghc-proposals/ghc-proposals/pull/632 [static-forms]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0732-s… [QualifiedStrings]: https://downloads.haskell.org/ghc/10.0.1-alpha1/docs/users_guide/exts/quali… [qualified-strings]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0723-q… [jsem]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0540-j… [clc-292]: https://github.com/haskell/core-libraries-committee/issues/292 [clc-359]: https://github.com/haskell/core-libraries-committee/issues/359 [clc-360]: https://github.com/haskell/core-libraries-committee/issues/360

2 1

GHC 9.14.2-rc2 is now available
by Zubin Duggal 17 Sep '26

17 Sep '26

The GHC developers are very pleased to announce the availability of the second release candidate for GHC 9.14.2. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). See also the [previous announcement of 9.14.2-rc1][rc1]. The changes since the first release candidate are: * Several fixes to the specialiser and demand analyser for miscompilations causing incorrect runtime results, crashes, or hangs (#27626, #27627, #27629, #27703, #27704, #27705, #27717). * Fixes for a number of runtime system bugs: * a missing memory barrier in the parallel garbage collector, which could crash or silently corrupt the heap on weakly-ordered architectures such as AArch64 (#27477). * a use-after-free with TSOs (#26716, #26717). * an "unknown/strange object" crash in the compacting collector when collecting the large data constructors that the bytecode interpreter allocates (#27649). * a segfault when querying the label of an unlabelled thread (#27618). * a crash when capturing or resuming a delimited continuation that adjusts the asynchronous exception masking state (#27651). * stack corruption when returning large unboxed tuples in GHCi (#27633). * Further fixes to the AArch64 native code generator, addressing bugs that caused incorrect runtime results from subword operations (#27430, #27533, #27537, #27538, #27539, #27550). * `toException` for `SomeException` no longer drops the attached `ExceptionContext`, and a `catchSTM` handler no longer breaks `retry` or asynchronous exception delivery (#27455, #27657). * Reduced memory usage with multiple home units (#26423, #27308, #27500, #27748). * Fixes for panics and spurious out-of-scope errors involving type arguments in pattern synonym right-hand sides (#27440, #27583, #27586). * The pattern-match checker now recognises `considerAccessible` under ticks, and no longer emits a spurious `-Wincomplete-uni-patterns` warning under `-finfo-table-map` (#27314, #27360). * The deprecation warning for static forms, added in rc1, no longer fires on free type variables (#27664). * A fix for a regression preventing modules from being loaded into GHCi after startup (#27202, #27640). * A fix for representation-polymorphism checks producing a coercion that fails Core Lint (#27639). * Support for LLVM up to version 23 (#27764). * Updates for libffi (3.8.0), `directory` (1.3.11.0), `file-io` (0.1.6), `haskeline` (0.8.5.0) and `os-string` (2.0.10). GHC 9.14.2 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Version 2 of the [GHC Jobserver Protocol][jsem] for GHC's `-jsem` jobserver on Linux and other POSIX platforms (#25087, #27253). This is sadly a necessary breaking change: `-jsem` requires cabal-install 3.18 or later, and is otherwise ignored with a [warning][jsem-warning], falling back to sequential compilation. * A new deprecation warning for static forms that mention nested let-bound variables. This will become an error in GHC 10.0 ([GHC Proposal #732][static-forms], #26718). * A fix for a CorePrep miscompilation that could project a field out of an absent dictionary, resulting in a segfault (#25924). * A fix for demand analysis giving an absent demand to an argument that was still used by the function's stable unfolding, which could cause a runtime crash (#26416). * Numerous fixes for register allocation and Cmm register-conflict analysis bugs, preventing incorrect code generation and corruption of vector registers when spilling and reloading (#26411, #26526, #26537, #26542, #26550, #26668). * Many NCG fixes on AArch64: `MOVK` clobbering live values (#26980), register clobbering and an incorrect overflow bit in `MUL2` (#27046, #27047), and incorrect sign extension (#26978) and unsigned right shift (#26979) at subword widths. * A fix for a stack alignment bug on x86 that could cause segfaults or corrupted registers when using AVX/AVX-512 vector code (#26595, #26822). * Fixes for several black hole handling bugs that could lead to deadlocks or crashes in multithreaded programs, showing up as hangs or "END_TSO_QUEUE object entered" errors (#26922, #26936). * Fixes for many other runtime system crashes and races (#26341, #26573, #26640, #27007, #27008, #27009, #27082). * A fix for an "unknown/strange object" crash in the compacting garbage collector (#27434). * Fixes for split sections on Windows (#26696, #26494) and the LLVM backend (#26770). * Fixes for the Wasm backend (#26916, #27257), and the RISC-V (#27300, #27303, #27306) and PowerPC (#23969, #24145, #26828) native code generators. * The JavaScript backend now supports more than 128 registers, fixing runtime `ReferenceError` failures for functions taking very many arguments (#26558). * Correctness and performance improvements in the bytecode interpreter (#12953, #26287, #26946, #26995, #27001). * Fixes for several compiler panics, including issues with SetLevels (#26681), the type-class specialiser (#26682), `mkTick` (#26772, #27121), CoreToStg (#27182, #27386), the pattern-match checker (#25926, #27124), module graph reachability (#26568), and continuation trimming for bottoming functions (#27261). * Fixes for several cases where the compiler could hang or loop, including with negative type literals (#26861), deep subsumption (#26823), and when simplifying the right-hand sides of rewrite rules (#26323, #26826). * A fix for cast worker/wrapper incorrectly firing on INLINE functions (#26903). * A fix for exponential-time desugaring of nested `case` expressions (#27383, #20251). * A fix for a regression that caused overloaded functions to no longer be specialised as effectively as in previous releases, hurting runtime performance (#26831). * A fix for associated type family and data family instance changes not triggering recompilation (#26183, #26705). * Fixes for Explicit Level Imports and Template Haskell staging (#26088, #26098, #26099, #26616, #27385). * Improvements to determinism of compiler output, including the order in which `:info` lists instances (#26846, #26858, #26877, #27532). * Additions for GHCi and GHC API users: the `-fimport-loaded-targets` flag (#26866), custom external interpreter commands (#26652), `decodeStackWithIpe` and related stack-decoding helpers (#27065), an optional `SrcLoc` on `StackAnnotation` (#26806), and a `gc_sync_elapsed_ns` counter in `RTSStats` (#26944). * ... and many more. A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 1 October 2026. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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. [release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.14/docs/users_guide/9.14.2-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.14.2-rc2 [jsem]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0540-j… [static-forms]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0732-s… [jsem-warning]: https://downloads.haskell.org/ghc/9.14.2-rc2/docs/users_guide/using-warning… [rc1]: https://www.haskell.org/ghc/blog/20260730-ghc-9.14.2-rc1-released.html [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

1 0

GHC 9.12.5 RC3 is now available
by Magnus Viernickel 31 Jul '26

31 Jul '26

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.12.5. Binary distributions, source distributions, and documentation are available at downloads.haskell.org and via GHCup. GHC 9.12.5 is a bug fix release. For a long form announcement, check out https://discourse.haskell.org/t/ghc-9-12-5-rc3-is-now-available/14491. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 13 August 2026. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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, please give this release a try and open a ticket if you see anything amiss. Best Magnus

1 0

GHC 9.14.2-rc1 is now available
by Zubin Duggal 31 Jul '26

31 Jul '26

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.14.2. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.14.2 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fixed a CorePrep miscompilation that could project a field out of an absent dictionary, resulting in a segfault (#25924) * Fixed demand analysis giving an absent demand to an argument that was still used by the function's stable unfolding, which could cause a run-time crash (#26416) * Numerous fixes for register allocation and Cmm register-conflict analysis bugs, preventing incorrect code generation and corruption of vector registers when spilling and reloading (#26411, #26526, #26537, #26542, #26550, #26668) * Many NGG fixes on AArch64: `MOVK` clobbering live values (#26980), register clobbering and an incorrect overflow bit in `MUL2` (#27046, #27047), and incorrect sign extension (#26978) and unsigned right shift (#26979) at sub-word widths * Fixed several black hole handling bugs that could lead to deadlocks or crashes in multithreaded programs, showing up as hangs or "END_TSO_QUEUE object entered" errors (#26922, #26936) * Fixed a stack alignment bug on x86 that could cause segfaults or corrupted registers when using AVX/AVX-512 vector code (#26595, #26822) * Fixed an "unknown/strange object" crash in the compacting garbage collector (#27434) * Fixed a regression that caused overloaded functions to no longer be specialised as effectively as in previous releases, hurting runtime performance (#26831) * Fixed exponential-time desugaring of nested `case` expressions (#27383, #20251) * Fixes for several compiler panics, including issues with SetLevels (#26681), the type-class specialiser (#26682), `mkTick` (#26772, #27121) and CoreToStg (#27182, #27386) * Fixed cast worker/wrapper incorrectly firing on INLINE functions (#26903) * Fixed negative type literals causing the compiler to hang (#26861) * Fixed associated type family and data family instance changes not triggering recompilation (#26183, #26705) * Improvements to determinism of compiler output, including the order in which `:info` lists instances (#26846, #26858, #26877, #27532) * Fixed split sections support on Windows (#26696, #26494) and the LLVM backend (#26770) * The JavaScript backend now supports more than 128 registers, fixing runtime `ReferenceError` failures for functions taking very many arguments (#26558) * Fixes for the Wasm backend, and the RISC-V and PowerPC native code generators * ... and many more A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 13 August 2026. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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. [release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.14/docs/users_guide/9.14.2-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.14.2-rc1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

1 0

GHC 9.12.5 RC2 is now available
by Magnus Viernickel 24 Jun '26

24 Jun '26

Dear GHC users, distributors and devs, I'm pleased to announce that the second release candidate for GHC 9.12.5 is now available from downloads.haskell.org and on GHCup. GHC 9.12.5 is a bug fix release. For a long form announcement, check out https://discourse.haskell.org/t/ghc-9-12-5-rc2-is-now-available/14313/1. Mind that the very important overhaul of the semaphore-compat library to v2 is included in this release and that the semaphore feature will only start working with cabal-install 3.18 again, which is sadly a breaking but necessary change. Your testing of the release is much appreciated. Many thanks to the nixpkgs and stackage package set distributors for testing the first release candidate. If you find any issues with the candidate, please open an issue on the ghc issue tracker. If there are no critical regressions are discovered within this release candidate, it will be published in about 2 weeks of time (the week of 8 July 2026). Best Magnus

2 2

release progress GHC 9.12.5
by Magnus Viernickel 26 May '26

26 May '26

Dear GHC release stakeholders, We are approaching a release candidate for GHC 9.12.5. Currently there's only one blocking patch (https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15640) that still needs to be backported and the test-suite seems to be doing well. Here are some important notes for this release of GHC 9.12. 1. Our Darwin CI is now running on MacOS version 26 for the aarch64 runners and on MacOS version 15 for the x86_64 runner. The SDK version on the MacOS 15 runner is 26.2, the SDK version on the aarch64 runners is 26.4. Note that this may affect bindists. 2. See https://gitlab.haskell.org/ghc/ghc/-/issues/27286 for an exhaustive list of MRs that have been backported. 3. If you are a distributor of haskell packages like stackage or nixpkgs, I would appreciate testing an RC with you, as soon as it's there. Please reach out if that's the case. 4. In ncoordinatio with the cabal developers, the GHC team has decided to stop maintaining the V1 ghc semaphore protocol that had some fundamental architectural flaws. While this is technically a (performance) regression (cabal versions that only support v1 will fall back to -j1 even when passed -jsem with 9.12.5) and adds a significant feature, it is the most pragmatic approach to fixing the glaring issues with the previous semaphore implementation without having to maintain a fundamentally broken design. Please check out https://gitlab.haskell.org/ghc/ghc/-/merge_requests/15729 for further information. We expect that `-jsem` will work out of the box with the next released cabal version and 9.12.5. I expect a release candidate to appear this week, depending on progress of the blocking patch. Please don't hesitate to reach out if you have any questions or remarks. Best Magnus

1 0

GHC 9.12.4 is now available
by Zubin Duggal 27 Mar '26

27 Mar '26

The GHC developers are very pleased to announce the release of GHC 9.12.4. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.4 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fixed a critical code generation regression where sub-word division produced incorrect results (#26711, #26668), similar to the bug fixed in 9.12.2 * Numerous fixes for register allocation bugs, preventing data corruption when spilling and reloading registers (#26411, #26526, #26537, #26542, #26550) * Fixes for several compiler crashes, including issues with CSE (#25468), and the simplifier(#26681), implicit parameters (#26451), and the type-class specialiser (#26682) * Fixed cast worker/wrapper incorrectly firing on INLINE functions (#26903) * Fixed LLVM backend miscompilation of bit manipulation operations (#20645, #26065, #26109) * Fixed associated type family and data family instance changes not triggering recompilation (#26183, #26705) * Fixed negative type literals causing the compiler to hang (#26861) * Improvements to determinism of compiler output (#26846, #26858) * Fixes for eventlog shutdown deadlocks (#26573) and lost wakeups in the RTS (#26324) * Fixed split sections support on Windows (#26696, #26494) and the LLVM backend (#26770) * Fixes for the bytecode compiler, PPC native code generator, and Wasm backend * The runtime linker now supports COMMON symbols (#6107) * Improved backtrace support: backtraces for `error` exceptions are now evaluated at throw time * `NamedDefaults` now correctly requires the class to be standard or have an in-scope default declaration, and handles poly-kinded classes (#25775, #25778, #25882) * ... and many more A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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. [release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.4-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.4 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

1 0

GHC 9.12.4-rc1 is now available
by Zubin Duggal 18 Mar '26

18 Mar '26

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.12.4. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][] and via [GHCup](https://www.haskell.org/ghcup/). GHC 9.12.4 is a bug-fix release fixing many issues of a variety of severities and scopes, including: * Fixed a critical code generation regression where sub-word division produced incorrect results (#26711, #26668), similar to the bug fixed in 9.12.2 * Numerous fixes for register allocation bugs, preventing data corruption when spilling and reloading registers (#26411, #26526, #26537, #26542, #26550) * Fixes for several compiler crashes, including issues with CSE (#25468), SetLevels (#26681), implicit parameters (#26451), and the type-class specialiser (#26682) * Fixed cast worker/wrapper incorrectly firing on INLINE functions (#26903) * Fixed LLVM backend miscompilation of bit manipulation operations (#20645, #26065, #26109) * Fixed associated type family and data family instance changes not triggering recompilation (#26183, #26705) * Fixed negative type literals causing the compiler to hang (#26861) * Improvements to determinism of compiler output (#26846, #26858) * Fixes for eventlog shutdown deadlocks (#26573) and lost wakeups in the RTS (#26324) * Fixed split sections support on Windows (#26696, #26494) and the LLVM backend (#26770) * Fixes for the bytecode compiler, PPC native code generator, and Wasm backend * The runtime linker now supports COMMON symbols (#6107) * Improved backtrace support: backtraces for `error` exceptions are now evaluated at throw time * `NamedDefaults` now correctly requires the class to be standard or have an in-scope default declaration, and handles poly-kinded classes (#25775, #25778, #25882) * ... and many more A full accounting of these fixes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. This release candidate will have a two-week testing period. If all goes well the final release will be available the week of 26 March 2026. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) * [Mercury](https://mercury.com) We would like to thank these sponsors 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. [release notes]: https://gitlab.haskell.org/ghc/ghc/-/blob/ghc-9.12/docs/users_guide/9.12.4-… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.4-rc1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

2 4

Critical code generation bug with GHC 9.12.3
by Zubin Duggal 08 Jan '26

08 Jan '26

Hello all, Unfortunately we discovered a major code generation regression in GHC 9.12.3 that results in incorrect runtime results for certain operations involving sub-word divisions. We recommend avoiding upgrading to this minor release at this time. See https://gitlab.haskell.org/ghc/ghc/-/issues/26711 for more details. This is the same bug that affected GHC 9.12.1. A patch re-introducing this bug was accidently backported onto the 9.12.3 branch and went unnoticed throughout the testing period. We are taking steps to ensure similar situations are less likely to occur again, including looking at ways to improve our testing procedure for minor GHC release, potentially using the Stackage infrastructure to run the testsuites of a broad range of packages to detect such issues. We are also starting to prepare GHC 9.12.4 with a fix, which we hope to release soon. However, a significant amount of time has passed since the initial set of backports to GHC 9.12.3 were completed, which means that a number of merge requests addressing issues of various severities has been marked for backporting to the GHC 9.12 branch. We are in the process of triaging this list and preparing a robust and reliable GHC 9.12.4 release. Thanks, Zubin.

1 0

GHC 9.14.1 is now available
by Zubin Duggal 27 Dec '25

27 Dec '25

The GHC developers are very pleased to announce the release of GHC 9.14.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. GHC 9.14 brings 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 GHCi improvements including: * Correctness and performance improvements in the bytecode interpreter * Features in the GHCi debugger * Support for multiple home units in GHCi * Implementation of the [Explicit Level Imports proposal][levels] * `RequiredTypeArguments` can now be used in more contexts * Greatly improved [SSE/AVX2 support][sse] in the x86 native code generator backend * Initial native code generator support for LoongArch * The WebAssembly backend now supports [evaluation via the interpreter][wasm-ghci], allowing GHCi and TemplateHaskell evaluation, including `foreign import javascript` usage from within the browser * A new primop [`annotateStack#`][annotate-stack] for pushing arbitrary data onto the call stack for later extraction when decoding stack traces * [`-Wincomplete-record-selectors`][incomplete-selectors] is now part of `-Wall`. Libraries compiled with `-Werror` may need adjustment. * A major update of the Windows toolchain * Improved compatibility with [macOS Tahoe][macos] * ... and many more A full accounting of changes can be found in the [release notes][]. See the [migration guide][] for guidance on migrating programs to this release. Note that while this release makes many improvements in the specialisation optimisation, polymorphic specialisation remains disabled by default in the release due to concern over regressions of the sort identified in [#26329][T26329]. 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. GHC development is sponsored by: * [Juspay](https://juspay.com/) * [QBayLogic](https://qbaylogic.com/) * [Channable](https://www.channable.com/) * [Haskell Foundation](https://haskell.foundation/) * [Serokell](https://serokell.io/) * [Well-Typed](https://well-typed.com/) * [Tweag](https://www.tweag.io/) * [Dotcom-Monitor](https://www.dotcom-monitor.com/) * [LoadView](https://www.loadview-testing.com/) * [Web Hosting Buddy](https://webhostingbuddy.com/) * [Find My Electric](https://www.findmyelectric.com/) * [Standard Chartered](https://www.sc.com) * [UpCloud](https://upcloud.com) We would like to thank these sponsors 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 comprises this release. 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 [release notes]: https://downloads.haskell.org/ghc/9.14.1/docs/users_guide/9.14.1-notes.html [ticket]: https://gitlab.haskell.org/ghc/homepage/-/issues/new [macos]: https://gitlab.haskell.org/ghc/ghc/-/issues/26166 [T26329]: https://gitlab.haskell.org/ghc/ghc/-/issues/26329 [levels]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0682-e… [wasm-ghci]: https://www.tweag.io/blog/2025-04-17-wasm-ghci-browser/ [incomplete-selectors]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0516-i… [annotate-stack]: https://gitlab.haskell.org/ghc/ghc/-/issues/26218 [migration guide]: https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.14 [sse]: https://gitlab.haskell.org/ghc/ghc/-/issues/25030

2 1