Add kind equalities to GHC.

This implements the ideas originally put forward in
"System FC with Explicit Kind Equality" (ICFP'13).

There are several noteworthy changes with this patch:
 * We now have casts in types. These change the kind
   of a type. See new constructor `CastTy`.

 * All types and all constructors can be promoted.
   This includes GADT constructors. GADT pattern matches
   take place in type family equations. In Core,
   types can now be applied to coercions via the
   `CoercionTy` constructor.

 * Coercions can now be heterogeneous, relating types
   of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2`
   proves both that `t1` and `t2` are the same and also that
   `k1` and `k2` are the same.

 * The `Coercion` type has been significantly enhanced.
   The documentation in `docs/core-spec/core-spec.pdf` reflects
   the new reality.

 * The type of `*` is now `*`. No more `BOX`.

 * Users can write explicit kind variables in their code,
   anywhere they can write type variables. For backward compatibility,
   automatic inference of kind-variable binding is still permitted.

 * The new extension `TypeInType` turns on the new user-facing
   features.

 * Type families and synonyms are now promoted to kinds. This causes
   trouble with parsing `*`, leading to the somewhat awkward new
   `HsAppsTy` constructor for `HsType`. This is dispatched with in
   the renamer, where the kind `*` can be told apart from a
   type-level multiplication operator. Without `-XTypeInType` the
   old behavior persists. With `-XTypeInType`, you need to import
   `Data.Kind` to get `*`, also known as `Type`.

 * The kind-checking algorithms in TcHsType have been significantly
   rewritten to allow for enhanced kinds.

 * The new features are still quite experimental and may be in flux.

 * TODO: Several open tickets: #11195, #11196, #11197, #11198, #11203.

 * TODO: Update user manual.

Tickets addressed: #9017, #9173, #7961, #10524, #8566, #11142.
Updates Haddock submodule.

1 files changed, 16 insertions, 8 deletions

diff --git a/testsuite/tests/ghci/scripts/T9181.stdout b/testsuite/tests/ghci/scripts/T9181.stdout
index 15504ec324..0e9913966f 100644
--- a/testsuite/tests/ghci/scripts/T9181.stdout
+++ b/testsuite/tests/ghci/scripts/T9181.stdout
@@ -1,10 +1,16 @@
-type family (*) (a :: Nat) (b :: Nat) :: Nat
-type family (+) (a :: Nat) (b :: Nat) :: Nat
-type family (-) (a :: Nat) (b :: Nat) :: Nat
+type family (*) (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Nat
+type family (+) (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Nat
+type family (-) (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Nat
 type (<=) (x :: Nat) (y :: Nat) = (x <=? y) ~ 'True
-type family (<=?) (a :: Nat) (b :: Nat) :: Bool
-type family CmpNat (a :: Nat) (b :: Nat) :: Ordering
-type family CmpSymbol (a :: Symbol) (b :: Symbol) :: Ordering
+type family (<=?) (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Bool
+type family CmpNat (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Ordering
+type family CmpSymbol (a :: Symbol) (b :: Symbol)
+  Kind: Symbol -> Symbol -> Ordering
 data ErrorMessage where
   Text :: Symbol -> ErrorMessage
   ShowType :: t -> ErrorMessage
@@ -20,8 +26,10 @@ data SomeNat where
   SomeNat :: KnownNat n => (Proxy n) -> SomeNat
 data SomeSymbol where
   SomeSymbol :: KnownSymbol n => (Proxy n) -> SomeSymbol
-type family TypeError (a :: ErrorMessage) :: b where
-type family (^) (a :: Nat) (b :: Nat) :: Nat
+type family TypeError (a :: ErrorMessage)
+  Kind: forall b1. ErrorMessage -> b1
+type family (^) (a :: Nat) (b :: Nat)
+  Kind: Nat -> Nat -> Nat
 natVal :: KnownNat n => proxy n -> Integer
 natVal' :: KnownNat n => Proxy# n -> Integer
 sameNat ::