1 files changed, 25 insertions, 0 deletions
diff --git a/lib/protocols/Journal.ml b/lib/protocols/Journal.ml
new file mode 100644
index 0000000..392eb5a
--- /dev/null
+++ b/lib/protocols/Journal.ml
@@ -0,0 +1,25 @@
+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)