[ANNOUNCE] Glasgow Haskell Compiler 9.0.1-rc1 released

Ben Gamari ben at well-typed.com
Wed Dec 30 15:16:33 UTC 2020

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:


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

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

 * 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


- 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-linear-types.rst
[3] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-simplify-subsumption.rst
[4] https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-qualified-do.rst 
[5] https://downloads.haskell.org/ghc/9.0.1-rc1/docs/html/users_guide/9.0.1-notes.html
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