12/05/13 20:29:54.03
何か値を返さなきゃならないみたいなので、>>757を修正
nilと値じゃなくてoption型使ってるけど
type System.Int32 with
member x.Execute func = match x with 0 -> None | n -> func() |> Some
> (0).Execute (fun () -> "zero");;
val it : string option = None
> (1).Execute (fun () -> "one");;
val it : string option = Some "one"
> (1 - 1).Execute (fun () -> 1 - 1);;
val it : int option = None