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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. |