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module Error = struct
open Concepts.Condition
let not_a_relation () =
condition "not-a-relation" "A handle was expected to carry the relation protocol and did not"
empty
end
class type implementation = object
method contains : Concepts.Tuple.t -> (bool, Concepts.Condition.condition) result
end
type Handle.protocol += Relation of implementation
type t = implementation
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 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
Fun.protect
~finally:(fun () -> Handle.release cursor)
(fun () ->
let* scan = Cursor.require cursor in
let* tuples = Cursor.drain scan () in
Ok (heading, BatFingerTree.to_list tuples) )
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