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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/glasgow_exts.rst | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst index 5fef204831..bce2bf8370 100644 --- a/docs/users_guide/glasgow_exts.rst +++ b/docs/users_guide/glasgow_exts.rst @@ -9012,6 +9012,11 @@ do so. Complete user-supplied kind signatures and polymorphic recursion ---------------------------------------------------------------- +.. extension:: CUSKs + :shortdesc: Enable detection of complete user-supplied kind signatures. + + :since: 8.10.1 + Just as in type inference, kind inference for recursive types can only use *monomorphic* recursion. Consider this (contrived) example: :: @@ -9110,6 +9115,13 @@ example, consider :: According to the rules above ``X`` has a CUSK. Yet, the kind of ``k`` is undetermined. It is thus quantified over, giving ``X`` the kind ``forall k1 (k :: k1). Proxy k -> Type``. +The detection of CUSKs is enabled by the :extension:`CUSKs` flag, which is +switched on by default. When :extension:`CUSKs` is switched off, there is +currently no way to enable polymorphic recursion in types. In the future, the +notion of a CUSK will be replaced by top-level kind signatures +(`GHC Proposal #36 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0036-kind-signatures.rst>`__), +then, after a transition period, this extension will be turned off by default, and eventually removed. + Kind inference in closed type families -------------------------------------- |