type 'a t =
| Initialized of 'a
| Changed of 'a * 'a(*

Changed (old_value, new_value)

*)
| Invalidated
val compare : ( 'a -> 'a -> int ) -> 'a t -> 'a t -> int
val sexp_of_t : ( 'a -> Ppx_sexp_conv_lib.Sexp.t ) -> 'a t -> Ppx_sexp_conv_lib.Sexp.t