8 files changed, 35 insertions, 100 deletions
diff --git a/lib/protocols/Derived.ml b/lib/protocols/Derived.ml
deleted file mode 100644
index 1968ffc..0000000
--- a/lib/protocols/Derived.ml
+++ /dev/null
@@ -1,10 +0,0 @@
-class type implementation = object
-  method within : Handle.t -> (Handle.t, Concepts.Condition.condition) result
-end
-
-type Handle.protocol += Derived of implementation
-type t = implementation
-
-let make impl = Derived (impl :> implementation)
-let from handle = Handle.into handle (function Derived impl -> Some impl | _ -> None)
-let within i directory = Handle.invoke i (fun o -> o#within directory)
diff --git a/lib/protocols/Derived.mli b/lib/protocols/Derived.mli
deleted file mode 100644
index b3dce96..0000000
--- a/lib/protocols/Derived.mli
+++ /dev/null
@@ -1,13 +0,0 @@
-(** a relation computed from other relations. [within] gives the same
-    relation read against another directory of relations, so a snapshot
-    of the tree can hand out its derived relations as they were, or as
-    they would be, at that moment. *)
-type t
-
-class type implementation = object
-  method within : Handle.t -> (Handle.t, Concepts.Condition.condition) result
-end
-
-val make : #implementation -> Handle.protocol
-val from : Handle.t -> t Handle.interface option
-val within : t Handle.interface -> Handle.t -> (Handle.t, Concepts.Condition.condition) result
diff --git a/lib/protocols/Evaluator.ml b/lib/protocols/Evaluator.ml
index 789fb9d..9f4f5c6 100644
--- a/lib/protocols/Evaluator.ml
+++ b/lib/protocols/Evaluator.ml
@@ -1,5 +1,5 @@
 class type implementation = object
-  method invoke : Handle.t -> (Handle.t, Concepts.Condition.condition) result
+  method invoke : Handle.t -> within:Handle.t -> (Handle.t, Concepts.Condition.condition) result
 end
 
 type Handle.protocol += Evaluator of implementation
@@ -8,4 +8,4 @@ type t = implementation
 let make impl = Evaluator (impl :> implementation)
 let from handle = Handle.into handle (function Evaluator impl -> Some impl | _ -> None)
 let require = Handle.require from
-let invoke i program = Handle.invoke i (fun o -> o#invoke program)
+let invoke i program ~within = Handle.invoke i (fun o -> o#invoke program ~within)
diff --git a/lib/protocols/Evaluator.mli b/lib/protocols/Evaluator.mli
index 3d42b5c..04b3612 100644
--- a/lib/protocols/Evaluator.mli
+++ b/lib/protocols/Evaluator.mli
@@ -1,10 +1,18 @@
 type t
 
+(** [within] is the directory the program's paths resolve against: the
+    branch state a stored program was read through, or whatever part of
+    the tree a caller hands over. *)
 class type implementation = object
-  method invoke : Handle.t -> (Handle.t, Concepts.Condition.condition) result
+  method invoke : Handle.t -> within:Handle.t -> (Handle.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 invoke : t Handle.interface -> Handle.t -> (Handle.t, Concepts.Condition.condition) result
+
+val invoke :
+  t Handle.interface ->
+  Handle.t ->
+  within:Handle.t ->
+  (Handle.t, Concepts.Condition.condition) result
diff --git a/lib/protocols/Journal.ml b/lib/protocols/Journal.ml
deleted file mode 100644
index 392eb5a..0000000
--- a/lib/protocols/Journal.ml
+++ /dev/null
@@ -1,25 +0,0 @@
-type change = {name: string; expected: Handle.t option; replacement: Handle.t option}
-type commit = {number: int; snapshot: Handle.t; changed: string list}
-type proposal = {previous: commit; proposed: commit}
-type guard = proposal -> (unit, Concepts.Condition.condition) result
-type observer = commit -> unit
-
-class type implementation = object
-  method commit : change list -> (commit option, Concepts.Condition.condition) result
-  method head : commit
-  method history : commit list
-  method guard : string -> guard option -> unit
-  method observe : string -> observer option -> unit
-end
-
-type Handle.protocol += Journal of implementation
-type t = implementation
-
-let make impl = Journal (impl :> implementation)
-let from handle = Handle.into handle (function Journal impl -> Some impl | _ -> None)
-let require = Handle.require from
-let commit i changes = Handle.invoke i (fun o -> o#commit changes)
-let head i = Handle.invoke i (fun o -> o#head)
-let history i = Handle.invoke i (fun o -> o#history)
-let guard i name g = Handle.invoke i (fun o -> o#guard name g)
-let observe i name f = Handle.invoke i (fun o -> o#observe name f)
diff --git a/lib/protocols/Journal.mli b/lib/protocols/Journal.mli
deleted file mode 100644
index 5f2e760..0000000
--- a/lib/protocols/Journal.mli
+++ /dev/null
@@ -1,48 +0,0 @@
-(** a directory that keeps its history. Every change to its bindings is
-    a commit: one or more names bound again together, numbered, with a
-    snapshot of every binding as it stood afterwards. Guards are shown a
-    commit before it lands and may refuse it; observers are told of it
-    after. *)
-type t
-
-(** bind [name] to [replacement], or unbind it when [None], provided it
-    is still bound to [expected]. *)
-type change = {name: string; expected: Handle.t option; replacement: Handle.t option}
-
-(** [snapshot] is a directory of the bindings as of the commit. *)
-type commit = {number: int; snapshot: Handle.t; changed: string list}
-
-(** what a guard is shown: the commit the proposal would follow and the
-    commit it would be. *)
-type proposal = {previous: commit; proposed: commit}
-
-type guard = proposal -> (unit, Concepts.Condition.condition) result
-type observer = commit -> unit
-
-class type implementation = object
-  (** [Ok None] when a name was no longer bound to what was expected;
-      [Error] when a guard refused. Either way nothing changes. *)
-  method commit : change list -> (commit option, Concepts.Condition.condition) result
-
-  method head : commit
-
-  (** every commit, the oldest first. *)
-  method history : commit list
-
-  (** install, replace or remove the guard or observer of that name. *)
-  method guard : string -> guard option -> unit
-
-  method observe : string -> observer option -> unit
-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 commit :
-  t Handle.interface -> change list -> (commit option, Concepts.Condition.condition) result
-
-val head : t Handle.interface -> commit
-val history : t Handle.interface -> commit list
-val guard : t Handle.interface -> string -> guard option -> unit
-val observe : t Handle.interface -> string -> observer option -> unit
diff --git a/lib/protocols/Relation.ml b/lib/protocols/Relation.ml
index 3962c9c..b4cc4ec 100644
--- a/lib/protocols/Relation.ml
+++ b/lib/protocols/Relation.ml
@@ -17,3 +17,21 @@ 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 read relation =
+  let open Utilities.Result in
+  let* schematics = Handle.require Schematics.from relation in
+  let* description = Schematics.describe schematics in
+  let* heading =
+    match description with
+    | Schematics.Relation heading -> Ok heading
+    | _ -> Error (Error.not_a_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) )
diff --git a/lib/protocols/Relation.mli b/lib/protocols/Relation.mli
index be11cc1..87e6ab2 100644
--- a/lib/protocols/Relation.mli
+++ b/lib/protocols/Relation.mli
@@ -8,3 +8,8 @@ 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
+
+(** the heading and tuples of a relation, read whole. *)
+val read :
+  Handle.t ->
+  (Schematics.relation_description * Concepts.Tuple.t list, Concepts.Condition.condition) result