5 files changed, 91 insertions, 33 deletions

diff --git a/lib/evaluators/FOL.ml b/lib/evaluators/FOL.ml
new file mode 100644
index 0000000..70cf9de
--- /dev/null
+++ b/lib/evaluators/FOL.ml
@@ -0,0 +1,40 @@
+module Error = struct
+  open Concepts.Condition
+
+  let unknown_relation name =
+    condition "unknown-relation" "A plan named a relation that does not exist under this snapshot"
+      ("name" |=| Concepts.Value.String name)
+
+  let cancelled () =
+    condition "evaluation-cancelled" "An evaluation was stopped before it produced its result" empty
+end
+
+type plan = Base of string
+
+module Program = Protocols.Program.Make (struct
+  type t = plan
+end)
+
+let execute context = function
+  | Base name ->
+     let open Utilities.Result in
+     match context.Protocols.Context.status () with
+     | `Cancelled | `Exhausted -> Error (Error.cancelled ())
+     | `Live ->
+        let* found = Runtime.Context.resolve context name in
+        let* handle = Option.to_result ~none:(Error.unknown_relation name) found in
+        Fun.protect
+          ~finally:(fun () -> Protocols.Handle.release handle)
+          (fun () ->
+            let* enumerable = Protocols.Enumerable.require handle in
+            Protocols.Enumerable.enumerate enumerable context)
+
+class evaluator = object (self)
+  inherit Kernel.Lifecycle.null
+  inherit Kernel.Identity.of_id
+
+  method invoke ~program context = execute context program
+  method protocols : Protocols.Handle.protocol list = [Program.make self]
+end
+
+let make () = new evaluator |> Protocols.Handle.make
diff --git a/lib/kernel/Initialization.ml b/lib/kernel/Initialization.ml
index d213b66..ae041fc 100644
--- a/lib/kernel/Initialization.ml
+++ b/lib/kernel/Initialization.ml
@@ -1,12 +1,22 @@
 module Make (S : Abstract.Storage.STORAGE) = struct
   module BM = BranchManager.Make (S)
 
-  let initialize conn =
+  let initialize ?(evaluators = []) conn =
     let open Utilities.Result in
     let open Protocols in
     let root = Namespace.make () in
     let registry = Registry.from root |> Option.get in
     let* branch_manager = BM.make conn "rnt-head" in
     let* _ = Registry.update registry "branch" None (Some branch_manager) in
+    let evaluator_namespace = Namespace.make () in
+    let evaluator_registry = Registry.from evaluator_namespace |> Option.get in
+    let* _ =
+      List.fold_left
+        (fun acc (name, handle) ->
+          let* _ = acc in
+          Registry.update evaluator_registry name None (Some handle))
+        (Ok true) evaluators
+    in
+    let* _ = Registry.update registry "evaluator" None (Some evaluator_namespace) in
     Ok root
 end
diff --git a/lib/kernel/Initialization.mli b/lib/kernel/Initialization.mli
index 104d523..926bbd8 100644
--- a/lib/kernel/Initialization.mli
+++ b/lib/kernel/Initialization.mli
@@ -1,3 +1,6 @@
 module Make (S : Abstract.Storage.STORAGE) : sig
-  val initialize : S.connection -> (Protocols.Handle.t, Concepts.Condition.condition) result
+  val initialize :
+    ?evaluators:(string * Protocols.Handle.t) list ->
+    S.connection ->
+    (Protocols.Handle.t, Concepts.Condition.condition) result
 end
diff --git a/lib/protocols/Program.ml b/lib/protocols/Program.ml
index b82cafc..49e6e2d 100644
--- a/lib/protocols/Program.ml
+++ b/lib/protocols/Program.ml
@@ -1,17 +1,20 @@
-class type implementation = object
-  method entry_points : string BatFingerTree.t
-
-  method invoke :
-    entry:string ->
-    bindings:Concepts.Tuple.t ->
-    Context.t ->
-    (Handle.t, Concepts.Condition.condition) result
+module type PROGRAM = sig
+  type t
 end
 
-type Handle.protocol += Program of implementation
-type t = implementation
+module Make (P : PROGRAM) = struct
+  class type implementation = object
+    method invoke :
+      program:P.t ->
+      Context.t ->
+      (Handle.t, Concepts.Condition.condition) result
+  end
+
+  type Handle.protocol += Program of implementation
 
-let make impl = Program (impl :> implementation)
-let from handle = Handle.into handle (function Program impl -> Some impl | _ -> None)
-let entry_points i = Handle.invoke i (fun o -> o#entry_points)
-let invoke i ~entry ~bindings ctx = Handle.invoke i (fun o -> o#invoke ~entry ~bindings ctx)
+  type t = implementation
+
+  let make impl = Program (impl :> implementation)
+  let from handle = Handle.into handle (function Program impl -> Some impl | _ -> None)
+  let invoke i ~program ctx = Handle.invoke i (fun o -> o#invoke ~program ctx)
+end
diff --git a/lib/protocols/Program.mli b/lib/protocols/Program.mli
index a795f16..1d6c3ae 100644
--- a/lib/protocols/Program.mli
+++ b/lib/protocols/Program.mli
@@ -1,21 +1,23 @@
-type t
+module type PROGRAM = sig
+  type t
+end
+
+module Make (P : PROGRAM) : sig
+  type t
+
+  class type implementation = object
+    method invoke :
+      program:P.t ->
+      Context.t ->
+      (Handle.t, Concepts.Condition.condition) result
+  end
 
-class type implementation = object
-  method entry_points : string BatFingerTree.t
-  method invoke :
-    entry:string ->
-    bindings:Concepts.Tuple.t ->
+  val make : #implementation -> Handle.protocol
+  val from : Handle.t -> t Handle.interface option
+
+  val invoke :
+    t Handle.interface ->
+    program:P.t ->
     Context.t ->
     (Handle.t, Concepts.Condition.condition) result
 end
-
-val make : #implementation -> Handle.protocol
-val from : Handle.t -> t Handle.interface option
-val entry_points : t Handle.interface -> string BatFingerTree.t
-
-val invoke :
-  t Handle.interface ->
-  entry:string ->
-  bindings:Concepts.Tuple.t ->
-  Context.t ->
-  (Handle.t, Concepts.Condition.condition) result