type (!'a, !'a_diff) t = (Key.t, 'a, 'a_diff) Diffable.Map_diff.tval get :
(from:'a -> to_:'a -> 'a_diff Diffable__.Optional_diff.t) ->
from:'a derived_on ->
to_:'a derived_on ->
('a, 'a_diff) t Diffable__.Optional_diff.tval of_list_exn :
('a_diff list -> 'a_diff Diffable__.Optional_diff.t) ->
('a -> 'a_diff -> 'a) ->
('a, 'a_diff) t list ->
('a, 'a_diff) t Diffable__.Optional_diff.t