You can search for identifiers within the package.
in-package search v0.2.0
type ('a, 'a_t, 'result, 'is_empty) t =
| O : ('a, 'a_t, 'a_t, [ `Empty ]) t
| S : ('a, 'a_t, 'result, _) t -> ('a, 'a_t, 'a -> 'result, [ `Not_empty ]) t