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, 22 insertions, 3 deletions

diff --git a/compiler/iface/IfaceEnv.hs b/compiler/iface/IfaceEnv.hs
index 645ceda5c0..43094f94aa 100644
--- a/compiler/iface/IfaceEnv.hs
+++ b/compiler/iface/IfaceEnv.hs
@@ -9,7 +9,8 @@ module IfaceEnv (
         lookupOrig, lookupOrigNameCache, extendNameCache,
         newIfaceName, newIfaceNames,
         extendIfaceIdEnv, extendIfaceTyVarEnv,
-        tcIfaceLclId, tcIfaceTyVar, lookupIfaceTyVar,
+        tcIfaceLclId, tcIfaceTyVar, lookupIfaceVar,
+        lookupIfaceTyVar, extendIfaceEnvs,
 
         ifaceExportNames,
 
@@ -31,11 +32,13 @@ import Avail
 import Module
 import UniqFM
 import FastString
+import IfaceType
 import UniqSupply
 import SrcLoc
 import Util
 
 import Outputable
+import Data.List     ( partition )
 
 {-
 *********************************************************
@@ -277,8 +280,16 @@ tcIfaceTyVar occ
             Nothing     -> failIfM (text "Iface type variable out of scope: " <+> ppr occ)
         }
 
-lookupIfaceTyVar :: FastString -> IfL (Maybe TyVar)
-lookupIfaceTyVar occ
+lookupIfaceTyVar :: IfaceTvBndr -> IfL (Maybe TyVar)
+lookupIfaceTyVar (occ, _)
+  = do  { lcl <- getLclEnv
+        ; return (lookupUFM (if_tv_env lcl) occ) }
+
+lookupIfaceVar :: IfaceBndr -> IfL (Maybe TyCoVar)
+lookupIfaceVar (IfaceIdBndr (occ, _))
+  = do  { lcl <- getLclEnv
+        ; return (lookupUFM (if_id_env lcl) occ) }
+lookupIfaceVar (IfaceTvBndr (occ, _))
   = do  { lcl <- getLclEnv
         ; return (lookupUFM (if_tv_env lcl) occ) }
 
@@ -289,6 +300,14 @@ extendIfaceTyVarEnv tyvars thing_inside
               ; pairs   = [(occNameFS (getOccName tv), tv) | tv <- tyvars] }
         ; setLclEnv (env { if_tv_env = tv_env' }) thing_inside }
 
+extendIfaceEnvs :: [TyCoVar] -> IfL a -> IfL a
+extendIfaceEnvs tcvs thing_inside
+  = extendIfaceTyVarEnv tvs $
+    extendIfaceIdEnv    cvs $
+    thing_inside
+  where
+    (tvs, cvs) = partition isTyVar tcvs
+
 {-
 ************************************************************************
 *                                                                      *