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| author | Andrew Martin <andrew.thaddeus@gmail.com> | 2019-05-12 09:23:25 -0400 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-06-14 10:48:13 -0400 |
| commit | effdd948056923f3bc03688c24d7e0339d6272f5 (patch) | |
| tree | 02a3cb68ce1680db89c8440ba8beea808cbf4a11 /docs/users_guide/8.10.1-notes.rst | |
| parent | 3bc6df3223f62a8366e2e4267bac23aa08e6a939 (diff) | |
| download | haskell-effdd948056923f3bc03688c24d7e0339d6272f5.tar.gz | |
Implement the -XUnliftedNewtypes extension.
GHC Proposal: 0013-unlifted-newtypes.rst
Discussion: https://github.com/ghc-proposals/ghc-proposals/pull/98
Issues: #15219, #1311, #13595, #15883
Implementation Details:
Note [Implementation of UnliftedNewtypes]
Note [Unifying data family kinds]
Note [Compulsory newtype unfolding]
This patch introduces the -XUnliftedNewtypes extension. When this
extension is enabled, GHC drops the restriction that the field in
a newtype must be of kind (TYPE 'LiftedRep). This allows types
like Int# and ByteArray# to be used in a newtype. Additionally,
coerce is made levity-polymorphic so that it can be used with
newtypes over unlifted types.
The bulk of the changes are in TcTyClsDecls.hs. With -XUnliftedNewtypes,
getInitialKind is more liberal, introducing a unification variable to
return the kind (TYPE r0) rather than just returning (TYPE 'LiftedRep).
When kind-checking a data constructor with kcConDecl, we attempt to
unify the kind of a newtype with the kind of its field's type. When
typechecking a data declaration with tcTyClDecl, we again perform a
unification. See the implementation note for more on this.
Co-authored-by: Richard Eisenberg <rae@richarde.dev>
Diffstat (limited to 'docs/users_guide/8.10.1-notes.rst')
| -rw-r--r-- | docs/users_guide/8.10.1-notes.rst | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/docs/users_guide/8.10.1-notes.rst b/docs/users_guide/8.10.1-notes.rst index fde1451250..dfbb8f9224 100644 --- a/docs/users_guide/8.10.1-notes.rst +++ b/docs/users_guide/8.10.1-notes.rst @@ -10,6 +10,8 @@ following sections. Highlights ---------- +- The `UnliftedNewtypes` extension. + Full details ------------ @@ -83,6 +85,11 @@ Language type forall a (f :: forall k. k -> Type). T a f = f Int +- A new extension :extension:`UnliftedNewtypes` that relaxes restrictions + around what kinds of types can appear inside of the data constructor + for a `newtype`. This was proposed in + `GHC proposal #13 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0013-unlifted-newtypes.rst>`__. + Compiler ~~~~~~~~ |