relation scan with enumerable and release

5 files changed, 19 insertions, 6 deletions

diff --git a/lib/protocols/Cursor.ml b/lib/protocols/Cursor.ml
index f9bd697..f53bfa1 100644
--- a/lib/protocols/Cursor.ml
+++ b/lib/protocols/Cursor.ml
@@ -39,3 +39,5 @@ let drain i ?(limit = 256) () =
     if batch.exhausted then Ok tuples else loop tuples
   in
   loop BatFingerTree.empty
+
+let consuming cursor f = Handle.releasing cursor (fun () -> Result.bind (require cursor) f)
diff --git a/lib/protocols/Cursor.mli b/lib/protocols/Cursor.mli
index ff6c027..deccf2a 100644
--- a/lib/protocols/Cursor.mli
+++ b/lib/protocols/Cursor.mli
@@ -19,3 +19,9 @@ val drain :
   ?limit:int ->
   unit ->
   (Concepts.Tuple.t BatFingerTree.t, Concepts.Condition.condition) result
+
+(** [f] over [cursor], which is released once [f] returns. *)
+val consuming :
+  Handle.t ->
+  (t Handle.interface -> ('a, Concepts.Condition.condition) result) ->
+  ('a, Concepts.Condition.condition) result
diff --git a/lib/protocols/Enumerable.ml b/lib/protocols/Enumerable.ml
index 53db834..76b4e86 100644
--- a/lib/protocols/Enumerable.ml
+++ b/lib/protocols/Enumerable.ml
@@ -19,3 +19,5 @@ let make impl = Enumerable (impl :> implementation)
 let from handle = Handle.into handle (function Enumerable impl -> Some impl | _ -> None)
 let require handle = from handle |> Option.to_result ~none:(Error.not_enumerable ())
 let enumerate i = Handle.invoke i (fun o -> o#enumerate)
+let cursor handle = Result.bind (require handle) enumerate
+let scan handle f = Result.bind (cursor handle) (fun cursor -> Cursor.consuming cursor f)
diff --git a/lib/protocols/Enumerable.mli b/lib/protocols/Enumerable.mli
index 2c0ee69..a0c1f1c 100644
--- a/lib/protocols/Enumerable.mli
+++ b/lib/protocols/Enumerable.mli
@@ -8,3 +8,10 @@ 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 enumerate : t Handle.interface -> (Handle.t, Concepts.Condition.condition) result
+val cursor : Handle.t -> (Handle.t, Concepts.Condition.condition) result
+
+(** [f] over a cursor on [handle], released once [f] returns. *)
+val scan :
+  Handle.t ->
+  (Cursor.t Handle.interface -> ('a, Concepts.Condition.condition) result) ->
+  ('a, Concepts.Condition.condition) result
diff --git a/lib/protocols/Relation.ml b/lib/protocols/Relation.ml
index c1cdfee..e475919 100644
--- a/lib/protocols/Relation.ml
+++ b/lib/protocols/Relation.ml
@@ -31,9 +31,5 @@ let heading 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) )
+  let* tuples = Enumerable.scan relation (fun scan -> Cursor.drain scan ()) in
+  Ok (heading, BatFingerTree.to_list tuples)