1 files changed, 46 insertions, 0 deletions
diff --git a/lib/concepts/Tuple.ml b/lib/concepts/Tuple.ml
new file mode 100644
index 0000000..3050c13
--- /dev/null
+++ b/lib/concepts/Tuple.ml
@@ -0,0 +1,46 @@
+module AttributeMap = BatMap.String
+
+(** A tuple: a finite map from attribute name to attribute. *)
+type t = Value.value AttributeMap.t
+
+(** [empty] The tuple with no attributes. *)
+let empty : t = AttributeMap.empty
+
+(** [access name t] Looks up the attribute bound to [name] in [t].
+    @param name attribute name to look up.
+    @param t tuple to search.
+    @return the attribute, or [None] when [name] is unbound. *)
+let access (name : string) (t : t) : Value.value option = AttributeMap.find_opt name t
+
+(** [merge left right] Unions two tuples. Shared attributes take the
+    [left] value; one-sided attributes are kept. Precondition: shared
+    attributes agree (the natural-join matcher guarantees this), so the
+    [left] bias is never observable.
+    @param left first tuple.
+    @param right second tuple.
+    @return the merged tuple. *)
+let merge (left : t) (right : t) : t =
+  let merger _ (left : Value.value option) (right : Value.value option) : Value.value option =
+    match left, right with (Some _ as v), _ | None, (Some _ as v) -> v | None, None -> None
+  in
+  AttributeMap.merge merger left right
+
+(** [project keep t] Keeps only the attributes of [t] whose names are
+    in [keep].
+    @param keep set of attribute names to retain.
+    @param t tuple to project.
+    @return the projected tuple. *)
+let project (keep : BatSet.String.t) (t : t) : t =
+  AttributeMap.filter (fun name _ -> BatSet.String.mem name keep) t
+
+(** [rename mapping t] Renames the attributes of [t] through
+    [mapping]; names absent from [mapping] are left unchanged.
+    @param mapping map from old name to new name.
+    @param t tuple to rename.
+    @return the renamed tuple. *)
+let rename (mapping : string BatMap.String.t) (t : t) : t =
+  AttributeMap.fold
+    (fun name attr acc ->
+      let name = BatMap.String.find_default name name mapping in
+      AttributeMap.add name attr acc )
+    t AttributeMap.empty