Explicit Specificity

Implementation for Ticket #16393.
Explicit specificity allows users to manually create inferred type variables,
by marking them with braces.
This way, the user determines which variables can be instantiated through
visible type application.

The additional syntax is included in the parser, allowing users to write
braces in type variable binders (type signatures, data constructors etc).
This information is passed along through the renamer and verified in the
type checker.
The AST for type variable binders, data constructors, pattern synonyms,
partial signatures and Template Haskell has been updated to include the
specificity of type variables.

Minor notes:
- Bumps haddock submodule
- Disables pattern match checking in GHC.Iface.Type with GHC 8.8

1 files changed, 6 insertions, 0 deletions

diff --git a/libraries/template-haskell/changelog.md b/libraries/template-haskell/changelog.md
index 4a522837af..55aab10c0d 100644
--- a/libraries/template-haskell/changelog.md
+++ b/libraries/template-haskell/changelog.md
@@ -9,6 +9,12 @@
     written in terms of `Q` are now disallowed. The types of `unsafeTExpCoerce`
     and `unTypeQ` are also generalised in terms of `Quote` rather than specific
     to `Q`.
+    
+  * Implement Explicit specificity in type variable binders (GHC Proposal #99).
+    In `Language.Haskell.TH.Syntax`, `TyVarBndr` is now annotated with a `flag`,
+    denoting the additional argument to its constructors `PlainTV` and `KindedTV`.
+    `flag` is either the `Specificity` of the type variable (`SpecifiedSpec` or
+    `InferredSpec`) or `()`.
 
   * Fix Eq/Ord instances for `Bytes`: we were comparing pointers while we should
     compare the actual bytes (#16457).