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| author | Sebastian Graf <sgraf1337@gmail.com> | 2019-11-03 19:42:52 +0000 |
|---|---|---|
| committer | Sebastian Graf <sebastian.graf@kit.edu> | 2021-03-12 11:01:09 +0100 |
| commit | 27abfd0023589cb6ee3363512d160df2d1016275 (patch) | |
| tree | e7a45b9557f6c4086cfe3197875454a6bf654889 /docs/users_guide/9.2.1-notes.rst | |
| parent | df8e8ba267ffd7b8be0702bd64b8c39532359461 (diff) | |
| download | haskell-wip/unlifted-data.tar.gz | |
Implement the UnliftedDatatypes extensionwip/unlifted-data
GHC Proposal: 0265-unlifted-datatypes.rst
Discussion: https://github.com/ghc-proposals/ghc-proposals/pull/265
Issues: https://gitlab.haskell.org/ghc/ghc/-/issues/19523
Implementation Details: Note [Implementation of UnliftedDatatypes]
This patch introduces the `UnliftedDatatypes` extension. When this extension is
enabled, GHC relaxes the restrictions around what result kinds are allowed in
data declarations. This allows data types for which an unlifted or
levity-polymorphic result kind is inferred.
The most significant changes are in `GHC.Tc.TyCl`, where
`Note [Implementation of UnliftedDatatypes]` describes the details of the
implementation.
Fixes #19523.
Diffstat (limited to 'docs/users_guide/9.2.1-notes.rst')
| -rw-r--r-- | docs/users_guide/9.2.1-notes.rst | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/docs/users_guide/9.2.1-notes.rst b/docs/users_guide/9.2.1-notes.rst index de4a983001..b0f80e93c3 100644 --- a/docs/users_guide/9.2.1-notes.rst +++ b/docs/users_guide/9.2.1-notes.rst @@ -13,6 +13,7 @@ Language <https://www.microsoft.com/en-us/research/publication/a-quick-look-at-impredicativity/>`__ (Serrano et al, ICFP 2020). More information here: :ref:`impredicative-polymorphism`. This replaces the old (undefined, flaky) behaviour of the :extension:`ImpredicativeTypes` extension. + * The first stage of the `Pointer Rep Proposal`_ has been implemented. All boxed types, both lifted and unlifted, now have representation kinds of the shape ``BoxedRep r``. Code that references ``LiftedRep`` and ``UnliftedRep`` @@ -20,6 +21,24 @@ Language .. _Pointer Rep Proposal: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0203-pointer-rep.rst +* :extension:`UnliftedDatatypes`: The `Unlifted Datatypes Proposal`_ has been + implemented. That means GHC Haskell now offers a way to define algebraic + data types with strict semantics like in OCaml or Idris! The distinction to + ordinary lifted data types is made in the kind system: Unlifted data types + live in kind ``TYPE (BoxedRep Unlifted)``. :extension:`UnliftedDatatypes` + allows giving data declarations such result kinds, such as in the following + example with the help of :extension:`StandaloneKindSignatures`: :: + + type IntSet :: UnliftedType -- type UnliftedType = TYPE (BoxedRep Unlifted) + data IntSet = Branch IntSet !Int IntSet | Leaf + + See :extension:`UnliftedDatatypes` for what other declarations are + possible. Slight caveat: Most functions in ``base`` (including ``$``) + are not levity-polymorphic (yet) and hence won't work with unlifted + data types. + +.. _Unlifted Datatypes Proposal: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0265-unlifted-datatypes.rst + * Kind inference for data/newtype instance declarations is slightly more restrictive than before. See the user manual :ref:`kind-inference-data-family-instances`. This is a breaking change, albeit a fairly obscure one that corrects a specification bug. |