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(** 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
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