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, 9 insertions, 11 deletions

diff --git a/compiler/deSugar/DsArrows.hs b/compiler/deSugar/DsArrows.hs
index 7735aa8e50..56c44c59d5 100644
--- a/compiler/deSugar/DsArrows.hs
+++ b/compiler/deSugar/DsArrows.hs
@@ -275,7 +275,7 @@ dsProcExpr pat (L _ (HsCmdTop cmd _unitTy cmd_ty ids)) = do
     var <- selectSimpleMatchVarL pat
     match_code <- matchSimply (Var var) ProcExpr pat env_stk_expr fail_expr
     let pat_ty = hsLPatType pat
-        proc_code = do_premap meth_ids pat_ty env_stk_ty cmd_ty
+    let proc_code = do_premap meth_ids pat_ty env_stk_ty cmd_ty
                     (Lam var match_code)
                     core_cmd
     return (mkLets meth_binds proc_code)
@@ -403,8 +403,8 @@ dsCmd ids local_vars stack_ty res_ty
         (HsCmdLam (MG { mg_alts = L _ [L _ (Match _ pats _
                                            (GRHSs [L _ (GRHS [] body)] _ ))] }))
         env_ids = do
+    let pat_vars = mkVarSet (collectPatsBinders pats)
     let
-        pat_vars = mkVarSet (collectPatsBinders pats)
         local_vars' = pat_vars `unionVarSet` local_vars
         (pat_tys, stack_ty') = splitTypeAt (length pats) stack_ty
     (core_body, free_vars, env_ids') <- dsfixCmd ids local_vars' stack_ty' res_ty body
@@ -711,9 +711,8 @@ dsCmdDo ids local_vars res_ty [L _ (LastStmt body _ _)] env_ids = do
         env_ids')
 
 dsCmdDo ids local_vars res_ty (stmt:stmts) env_ids = do
-    let
-        bound_vars = mkVarSet (collectLStmtBinders stmt)
-        local_vars' = bound_vars `unionVarSet` local_vars
+    let bound_vars  = mkVarSet (collectLStmtBinders stmt)
+    let local_vars' = bound_vars `unionVarSet` local_vars
     (core_stmts, _, env_ids') <- trimInput (dsCmdDo ids local_vars' res_ty stmts)
     (core_stmt, fv_stmt) <- dsCmdLStmt ids local_vars env_ids' stmt env_ids
     return (do_compose ids
@@ -785,10 +784,10 @@ dsCmdStmt ids local_vars out_ids (BodyStmt cmd _ _ c_ty) env_ids = do
 -- but that's likely to be defined in terms of first.
 
 dsCmdStmt ids local_vars out_ids (BindStmt pat cmd _ _) env_ids = do
-    (core_cmd, fv_cmd, env_ids1) <- dsfixCmd ids local_vars unitTy (hsLPatType pat) cmd
+    let pat_ty = hsLPatType pat
+    (core_cmd, fv_cmd, env_ids1) <- dsfixCmd ids local_vars unitTy pat_ty cmd
+    let pat_vars = mkVarSet (collectPatBinders pat)
     let
-        pat_ty = hsLPatType pat
-        pat_vars = mkVarSet (collectPatBinders pat)
         env_ids2 = varSetElems (mkVarSet out_ids `minusVarSet` pat_vars)
         env_ty2 = mkBigCoreVarTupTy env_ids2
 
@@ -1018,9 +1017,8 @@ dsCmdStmts ids local_vars out_ids [stmt] env_ids
   = dsCmdLStmt ids local_vars out_ids stmt env_ids
 
 dsCmdStmts ids local_vars out_ids (stmt:stmts) env_ids = do
-    let
-        bound_vars = mkVarSet (collectLStmtBinders stmt)
-        local_vars' = bound_vars `unionVarSet` local_vars
+    let bound_vars  = mkVarSet (collectLStmtBinders stmt)
+    let local_vars' = bound_vars `unionVarSet` local_vars
     (core_stmts, _fv_stmts, env_ids') <- dsfixCmdStmts ids local_vars' out_ids stmts
     (core_stmt, fv_stmt) <- dsCmdLStmt ids local_vars env_ids' stmt env_ids
     return (do_compose ids