val laws : int ‑> 'a gen ‑> ('a ‑> bool) ‑> 'a optionlaws iter gen func applies func repeatedly (iter times) on output
of gen, and if func ever returns false, then the input that caused
the failure is returned optionally.
val laws_exn : string ‑> int ‑> 'a gen ‑> ('a ‑> bool) ‑> unitLike laws, but throws an exception instead of returning an option.
val repeat : int ‑> ('a ‑> unit) ‑> 'a gen ‑> unit