Make_access.1-T
type ('a, 'b) t
val mapper : ('at -> f:('a -> 'b) -> 'bt) -> ('a, 'b) t -> ('at, 'bt) t
A legal implementation of this function must satisfy the following properties:
mapper (fun a ~f -> f a) = Fn.id
Fn.compose (mapper f) (mapper g) = mapper (fun a ~f:h -> f a ~f:(g ~f:h))