refactor ephemeral and subs relations

2 files changed, 12 insertions, 8 deletions

diff --git a/lib/concepts/Mode.ml b/lib/concepts/Mode.ml
index 23abacf..6ac1704 100644
--- a/lib/concepts/Mode.ml
+++ b/lib/concepts/Mode.ml
@@ -21,15 +21,16 @@ let generation declaration bound =
     (fun tightest {bound= declared; affords} ->
       match affords with
       | Generates cardinality when BatSet.String.subset declared bound ->
-          Some
-            ( match tightest with
-            | None -> cardinality
-            | Some other -> Cardinality.meet cardinality other )
+          Some (Option.fold ~none:cardinality ~some:(Cardinality.meet cardinality) tightest)
       | Generates _ | Decides -> tightest )
     None declaration
 
+let exhaustible declaration bound =
+  Option.fold ~none:false ~some:Cardinality.exhaustible (generation declaration bound)
+
 let decision declaration bound =
-  List.exists
-    (fun {bound= declared; affords} ->
-      match affords with Decides -> BatSet.String.equal declared bound | Generates _ -> false )
-    declaration
+  exhaustible declaration bound
+  || List.exists
+       (fun {bound= declared; affords} ->
+         match affords with Decides -> BatSet.String.equal declared bound | Generates _ -> false )
+       declaration
diff --git a/lib/concepts/Mode.mli b/lib/concepts/Mode.mli
index 982518a..8d84093 100644
--- a/lib/concepts/Mode.mli
+++ b/lib/concepts/Mode.mli
@@ -24,4 +24,7 @@ val to_list : t -> mode list
     attributes left free are then fewer and no more numerous. *)
 val generation : t -> attributes -> Cardinality.t option
 
+val exhaustible : t -> attributes -> bool
+
+(** declared outright, or implied by a generation that can be exhausted. *)
 val decision : t -> attributes -> bool