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