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authorAndrew Martin <andrew.thaddeus@gmail.com>2019-05-12 09:23:25 -0400
committerMarge Bot <ben+marge-bot@smart-cactus.org>2019-06-14 10:48:13 -0400
commiteffdd948056923f3bc03688c24d7e0339d6272f5 (patch)
tree02a3cb68ce1680db89c8440ba8beea808cbf4a11 /libraries/ghc-boot-th
parent3bc6df3223f62a8366e2e4267bac23aa08e6a939 (diff)
downloadhaskell-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 'libraries/ghc-boot-th')
-rw-r--r--libraries/ghc-boot-th/GHC/LanguageExtensions/Type.hs1
1 files changed, 1 insertions, 0 deletions
diff --git a/libraries/ghc-boot-th/GHC/LanguageExtensions/Type.hs b/libraries/ghc-boot-th/GHC/LanguageExtensions/Type.hs
index ac47e165ff..ef1d5c9f9f 100644
--- a/libraries/ghc-boot-th/GHC/LanguageExtensions/Type.hs
+++ b/libraries/ghc-boot-th/GHC/LanguageExtensions/Type.hs
@@ -49,6 +49,7 @@ data Extension
| AllowAmbiguousTypes
| UnboxedTuples
| UnboxedSums
+ | UnliftedNewtypes
| BangPatterns
| TypeFamilies
| TypeFamilyDependencies