the visitor lifted into the search monad.

For example, the following code will find the first pointer:

module Search = C.Type.Mapper.Search

let find_pointer t = Search.result @@ (object
    inherit [C.Type.t] C.Type.Mapper.Finder.base
    method! enter_pointer = Search.finished
  end)#run t
type ('a, 'e) m = ('a, 'e) Search.t
class 'e base : object ... end