type hwnd

type message_box_option =
    MB_ABORTRETRYIGNORE
  | MB_APPLMODAL
  | MB_DEFAULT_DESKTOP_ONLY
  | MB_DEFBUTTON1
  | MB_DEFBUTTON2
  | MB_DEFBUTTON3
  | MB_DEFBUTTON4
  | MB_HELP
  | MB_ICONASTERISK
  | MB_ICONERROR
  | MB_ICONEXCLAMATION
  | MB_ICONHAND
  | MB_ICONINFORMATION
  | MB_ICONQUESTION
  | MB_ICONSTOP
  | MB_ICONWARNING
  | MB_OK
  | MB_OKCANCEL
  | MB_RETRYCANCEL
  | MB_RIGHT
  | MB_RTLREADING
  | MB_SETFOREGROUND
  | MB_SYSTEMMODAL
  | MB_TASKMODAL
  | MB_TOPMOST
  | MB_YESNO
  | MB_YESNOCANCEL

type standard_control_id =
    IDABORT
  | IDCANCEL
  | IDCLOSE
  | IDHELP
  | IDIGNORE
  | IDNO
  | IDOK
  | IDRETRY
  | IDYES

external get_null_hwnd : unit -> hwnd = "get_null_hwnd"
let null_hwnd = get_null_hwnd ()

external message_box :
    wnd:hwnd ->
    text:string ->
    caption:string ->
    options:message_box_option list ->
    standard_control_id = "message_box"

let () =
  ignore ( message_box ~wnd:null_hwnd ~text:"Hello, Win32 API World!" ~caption:"Hello, World!" ~options:[MB_OK] );