relation scan with enumerable and release

8 files changed, 25 insertions, 26 deletions

diff --git a/lib/evaluators/FOL.ml b/lib/evaluators/FOL.ml
index 92b1c38..050e528 100644
--- a/lib/evaluators/FOL.ml
+++ b/lib/evaluators/FOL.ml
@@ -118,14 +118,9 @@ let rec modes =
       |> Result.map
            (Concepts.Mode.project (BatSet.String.of_list (BatFingerTree.to_list attributes)))
 
-let enumerate relation =
-  let open Utilities.Result in
-  let* enumerable = Protocols.Enumerable.require relation in
-  Protocols.Enumerable.enumerate enumerable
-
 let project description relation =
   let open Utilities.Result in
-  let* cursor = enumerate relation in
+  let* cursor = Protocols.Enumerable.cursor relation in
   let produce ~yield =
     let* scan = Protocols.Cursor.require cursor in
     let rec distinct seen =
@@ -168,7 +163,7 @@ let rec execute plan =
   match plan with
   | Base relation ->
       let relation = Protocols.Handle.move relation in
-      Ok (derive ~decide:(contains relation) relation description modes enumerate)
+      Ok (derive ~decide:(contains relation) relation description modes Protocols.Enumerable.cursor)
   | Project (plan, _) ->
       let* relation = execute plan in
       Ok (derive relation description modes (project description))
diff --git a/lib/kernel/EphemeralRelation.ml b/lib/kernel/EphemeralRelation.ml
index fd40aff..250aacc 100644
--- a/lib/kernel/EphemeralRelation.ml
+++ b/lib/kernel/EphemeralRelation.ml
@@ -84,8 +84,7 @@ class ephemeral_relation ?program ?decide description value modes enumerate inpu
             Error (Error.undecidable_membership ())
           else
             let* cursor = self#enumerate in
-            Protocols.Handle.releasing cursor (fun () ->
-                let* scan = Protocols.Cursor.require cursor in
+            Protocols.Cursor.consuming cursor (fun scan ->
                 Protocols.Cursor.exists scan (fun member ->
                     Concepts.Hash.hash_equals (Concepts.Tuple.hash member)
                       (Concepts.Tuple.hash tuple) ) )
@@ -119,7 +118,6 @@ type binding = {root: Protocols.Handle.t; within: Protocols.Handle.t}
 
 (* The relation a program produced has to outlive the cursor over it. *)
 let enumerate_owned relation =
-  let open Utilities.Result in
   let owner =
     object
       method reference = true
@@ -127,10 +125,7 @@ let enumerate_owned relation =
       method is_managed = true
     end
   in
-  match
-    let* enumerable = Protocols.Enumerable.require relation in
-    Protocols.Enumerable.enumerate enumerable
-  with
+  match Protocols.Enumerable.cursor relation with
   | Error c -> Protocols.Handle.release relation; Error c
   | Ok cursor ->
       Ok
diff --git a/lib/kernel/Multigroup.ml b/lib/kernel/Multigroup.ml
index 9fbd386..669babb 100644
--- a/lib/kernel/Multigroup.ml
+++ b/lib/kernel/Multigroup.ml
@@ -192,12 +192,8 @@ module Make (S : Abstract.Storage.STORAGE) = struct
             if not (Concepts.Mode.exhaustible modes BatSet.String.empty) then
               Error (Error.unjudgeable name)
             else
-              let* enumerable = Protocols.Enumerable.require relation in
-              let* cursor = Protocols.Enumerable.enumerate enumerable in
-              Protocols.Handle.releasing cursor (fun () ->
-                  let* scan = Protocols.Cursor.require cursor in
-                  let* first = Protocols.Cursor.next scan in
-                  Ok (Option.to_list (Option.map (fun witness -> name, witness) first)) ) ) )
+              let* first = Protocols.Enumerable.scan relation Protocols.Cursor.next in
+              Ok (Option.to_list (Option.map (fun witness -> name, witness) first)) ) )
 
   class multigroup ?bind conn value schema_tree denial_tree =
     object (self)
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)