Make explicit that UGraph lower bounds are only of two kinds.

This makes the invariants in the code clearer, and also highlight this is
only required to implement template polymorphic inductive types.

1 files changed, 9 insertions, 5 deletions

diff --git a/engine/uState.ml b/engine/uState.ml
index 00649ce042..99ac5f2ce8 100644
--- a/engine/uState.ml
+++ b/engine/uState.ml
@@ -34,7 +34,7 @@ type t =
    (** The subset of unification variables that can be instantiated with
         algebraic universes as they appear in inferred types only. *)
    uctx_universes : UGraph.t; (** The current graph extended with the local constraints *)
-   uctx_universes_lbound : Univ.Level.t; (** The lower bound on universes (e.g. Set or Prop) *)
+   uctx_universes_lbound : UGraph.Bound.t; (** The lower bound on universes (e.g. Set or Prop) *)
    uctx_initial_universes : UGraph.t; (** The graph at the creation of the evar_map *)
    uctx_weak_constraints : UPairSet.t
  }
@@ -48,7 +48,7 @@ let empty =
     uctx_univ_variables = LMap.empty;
     uctx_univ_algebraic = LSet.empty;
     uctx_universes = initial_sprop_cumulative;
-    uctx_universes_lbound = Univ.Level.set;
+    uctx_universes_lbound = UGraph.Bound.Set;
     uctx_initial_universes = initial_sprop_cumulative;
     uctx_weak_constraints = UPairSet.empty; }
 
@@ -443,6 +443,10 @@ let check_univ_decl ~poly uctx decl =
       (ContextSet.constraints uctx.uctx_local);
   ctx
 
+let is_bound l lbound = match lbound with
+| UGraph.Bound.Prop -> Level.is_prop l
+| UGraph.Bound.Set -> Level.is_set l
+
 let restrict_universe_context ~lbound (univs, csts) keep =
   let removed = LSet.diff univs keep in
   if LSet.is_empty removed then univs, csts
@@ -455,7 +459,7 @@ let restrict_universe_context ~lbound (univs, csts) keep =
   let allkept = LSet.union (UGraph.domain UGraph.initial_universes) (LSet.diff allunivs removed) in
   let csts = UGraph.constraints_for ~kept:allkept g in
   let csts = Constraint.filter (fun (l,d,r) ->
-      not ((Level.equal l lbound && d == Le) || (Level.is_prop l && d == Lt && Level.is_set r))) csts in
+      not ((is_bound l lbound && d == Le) || (Level.is_prop l && d == Lt && Level.is_set r))) csts in
   (LSet.inter univs keep, csts)
 
 let restrict ctx vars =
@@ -600,10 +604,10 @@ let make_with_initial_binders ~lbound e us =
 
 let add_global_univ uctx u =
   let initial =
-    UGraph.add_universe ~lbound:Univ.Level.set ~strict:true u uctx.uctx_initial_universes
+    UGraph.add_universe ~lbound:UGraph.Bound.Set ~strict:true u uctx.uctx_initial_universes
   in
   let univs =
-    UGraph.add_universe ~lbound:Univ.Level.set ~strict:true u uctx.uctx_universes
+    UGraph.add_universe ~lbound:UGraph.Bound.Set ~strict:true u uctx.uctx_universes
   in
   { uctx with uctx_local = ContextSet.add_universe u uctx.uctx_local;
                                      uctx_initial_universes = initial;