val find : empty_is_none:bool -> string -> string option
val find' :
empty_is_none:bool ->
(string -> ('a, string) result) ->
string ->
('a option, string) result
val override : t -> by:t -> t
val add : string -> string -> t -> t
val current : unit -> (t, string) result
type assignments = string list
val of_assignments : ?init:t -> string list -> (t, string) result