It looks like I'll increasingly be writing code like this, to support multiple platforms:

      BB4W% = (INKEY(-256) = &57)

      IF BB4W% THEN
        SYS "SetWindowText", @hwnd%, Title$
        ON ERROR SYS "MessageBox", @hwnd%, REPORT$, "Error", 0 : QUIT
      ELSE
        SYS "SDL_SetWindowTitle", @hwnd%, Title$
        ON ERROR SYS "SDL_ShowSimpleMessageBox", 0, "Error", REPORT$, @hwnd% : QUIT
      ENDIF

Richard.