OCaml中分号和`let _ = ... in`的区别

Question

On this site 它说分号在语义上与

let _ = ... in

相同，但在以下代码中并非如此。此代码打印

None

和

End

:

let m = None

let () =
  let () = match m with
    | None -> print_endline "None"
    | Some file -> print_endline "Some"
  in
  print_endline "End";

但是这段代码只打印

None

.

let m = None

let () =
  match m with
    | None -> print_endline "None"
    | Some file -> print_endline "Some"
  ;
  print_endline "End";

为什么？分号和

let in

有什么区别？