2 files changed, 65 insertions, 0 deletions
diff --git a/lib/concepts/Mode.ml b/lib/concepts/Mode.ml
new file mode 100644
index 0000000..4d7501c
--- /dev/null
+++ b/lib/concepts/Mode.ml
@@ -0,0 +1,39 @@
+type attribute = string
+type attributes = BatSet.String.t
+type affordance = Decides | Generates of Cardinality.t
+type mode = {bound: attributes; affords: affordance}
+type t = mode list
+
+let attributes_of_list = BatSet.String.of_list
+
+let decides_when bound = {bound= attributes_of_list bound; affords= Decides}
+
+let generates_when bound cardinality =
+  {bound= attributes_of_list bound; affords= Generates cardinality}
+
+let enumerable cardinality = {bound= BatSet.String.empty; affords= Generates cardinality}
+
+let empty = []
+let declare mode declaration = mode :: declaration
+let of_list modes = modes
+let to_list declaration = declaration
+
+let generation declaration bound =
+  List.fold_left
+    (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 )
+      | Generates _ | Decides -> tightest )
+    None declaration
+
+let decision 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
new file mode 100644
index 0000000..57b079f
--- /dev/null
+++ b/lib/concepts/Mode.mli
@@ -0,0 +1,26 @@
+type attribute = string
+type attributes = BatSet.String.t
+
+(** what asking a relation under a given set of bound attributes
+    affords. The answer is to whether anything satisfies the binding,
+    or the bindings of the attributes left free together with the
+    class of what is produced. *)
+type affordance = Decides | Generates of Cardinality.t
+
+type mode = {bound: attributes; affords: affordance}
+type t
+
+val attributes_of_list : attribute list -> attributes
+val decides_when : attribute list -> mode
+val generates_when : attribute list -> Cardinality.t -> mode
+val enumerable : Cardinality.t -> mode
+val empty : t
+val declare : mode -> t -> t
+val of_list : mode list -> t
+val to_list : t -> mode list
+
+(** the tightest class declared for generating under [bound]. A mode
+    declared for fewer bound attributes applies to more, since the
+    attributes left free are then fewer and no more numerous. *)
+val generation : t -> attributes -> Cardinality.t option
+val decision : t -> attributes -> bool