File "b_bad.ml", lines 13-14, characters 29-28:
13 | .............................function
14 |     A.X s -> print_endline s
Error (warning 8 [partial-match]): this pattern-matching is not exhaustive.
  Here is an example of a case that is not matched: Y

File "b_bad.ml", line 18, characters 11-14:
18 | let () = f A.y
                ^^^
Error: Unbound value A.y