2 files changed, 30 insertions, 0 deletions
diff --git a/lib/protocols/Relation.ml b/lib/protocols/Relation.ml
index 3962c9c..c1cdfee 100644
--- a/lib/protocols/Relation.ml
+++ b/lib/protocols/Relation.ml
@@ -8,6 +8,7 @@ end
 
 class type implementation = object
   method contains : Concepts.Tuple.t -> (bool, Concepts.Condition.condition) result
+  method modes : (Concepts.Mode.t, Concepts.Condition.condition) result
 end
 
 type Handle.protocol += Relation of implementation
@@ -17,3 +18,22 @@ let make impl = Relation (impl :> implementation)
 let from handle = Handle.into handle (function Relation impl -> Some impl | _ -> None)
 let require handle = from handle |> Option.to_result ~none:(Error.not_a_relation ())
 let contains i tuple = Handle.invoke i (fun o -> o#contains tuple)
+let modes i = Handle.invoke i (fun o -> o#modes)
+
+let heading relation =
+  let open Utilities.Result in
+  let* schematics = Handle.require Schematics.from relation in
+  let* description = Schematics.describe schematics in
+  match description with
+  | Schematics.Relation heading -> Ok heading
+  | _ -> Error (Error.not_a_relation ())
+
+let read relation =
+  let open Utilities.Result in
+  let* heading = heading relation in
+  let* enumerable = Enumerable.require relation in
+  let* cursor = Enumerable.enumerate enumerable in
+  Handle.releasing cursor (fun () ->
+      let* scan = Cursor.require cursor in
+      let* tuples = Cursor.drain scan () in
+      Ok (heading, BatFingerTree.to_list tuples) )
diff --git a/lib/protocols/Relation.mli b/lib/protocols/Relation.mli
index be11cc1..28dfdff 100644
--- a/lib/protocols/Relation.mli
+++ b/lib/protocols/Relation.mli
@@ -2,9 +2,19 @@ type t
 
 class type implementation = object
   method contains : Concepts.Tuple.t -> (bool, Concepts.Condition.condition) result
+  method modes : (Concepts.Mode.t, Concepts.Condition.condition) result
 end
 
 val make : #implementation -> Handle.protocol
 val from : Handle.t -> t Handle.interface option
 val require : Handle.t -> (t Handle.interface, Concepts.Condition.condition) result
 val contains : t Handle.interface -> Concepts.Tuple.t -> (bool, Concepts.Condition.condition) result
+val modes : t Handle.interface -> (Concepts.Mode.t, Concepts.Condition.condition) result
+
+(** the heading a relation describes itself with. *)
+val heading : Handle.t -> (Schematics.relation_description, Concepts.Condition.condition) result
+
+(** the heading and tuples of a relation, read whole. *)
+val read :
+  Handle.t ->
+  (Schematics.relation_description * Concepts.Tuple.t list, Concepts.Condition.condition) result