Reason · Reason lets you write simple, fast and quality type safe code while leveraging both the JavaScript & OCaml ecosystems.

sig
 val copy : (< .. > as 'a) -> 'a
 external id : < .. > -> int = "%field1"
 val new_method : string -> CamlinternalOO.tag
 val public_method_label : string -> CamlinternalOO.tag
end