在lua的iup包中'iup.config'有什么问题

Question

我开始学习lua（版本5.1）和iup（版本3.5）库，但这个问题让我失望:( 所以，iup教程http://webserver2.tecgraf.puc-rio.br/iup/en/tutorial/tutorial3.html#Recent_Config

中最明显的例子

require("iuplua")
require("iupluaimglib")


--********************************** Utilities *****************************************


function str_find(str, str_to_find, casesensitive, start)
  if (not casesensitive) then
    return str_find(string.lower(str), string.lower(str_to_find), true, start)
  end

  return string.find(str, str_to_find, start, true)
end

function read_file(filename)
  local ifile = io.open(filename, "r")
  if (not ifile) then
    iup.Message("Error", "Can't open file: " .. filename)
    return nil
  end

  local str = ifile:read("*a")
  if (not str) then
    iup.Message("Error", "Fail when reading from file: " .. filename)
    return nil
  end

  ifile:close()
  return str
end

function write_file(filename, str)
  local ifile = io.open(filename, "w")
  if (not ifile) then
    iup.Message("Error", "Can't open file: " .. filename)
    return false
  end

  if (not ifile:write(str)) then
    iup.Message("Error", "Fail when writing to file: " .. filename)
  end

  ifile:close()
  return true
end


--********************************** Main (Part 1/2) *****************************************

-- it`s there:

config = iup.config{}    ------ here it is, first error
config.app_name = "simple_notepad"
config:Load()

lbl_statusbar = iup.label{title = "Lin 1, Col 1", expand = "HORIZONTAL", padding = "10x5"}

multitext = iup.text{
  multiline = "YES",
  expand = "YES"
}

font = config:GetVariable("MainWindow", "Font")
if (font) then
  multitext.font = font
end

item_open = iup.item{title = "&Open...\tCtrl+O"}
item_saveas = iup.item{title="Save &As...\tCtrl+S"}
item_font = iup.item{title="&Font..."}
item_about = iup.item{title="&About..."}
item_find = iup.item{title="&Find...\tCtrl+F"}
item_goto = iup.item{title="&Go To..."}
item_exit = iup.item{title="E&xit"}


--********************************** Callbacks *****************************************


function config:recent_cb()
  local filename = self.title
  local str = read_file(filename)
  if (str) then
    multitext.value = str
  end
end

function multitext:caret_cb(lin, col)
  lbl_statusbar.title = "Lin "..lin..", Col "..col
end

function item_open:action()
  local filedlg = iup.filedlg{
    dialogtype = "OPEN",
    filter = "*.txt",
    filterinfo = "Text Files",
    parentdialog=iup.GetDialog(self)
    }

  filedlg:popup(iup.CENTERPARENT, iup.CENTERPARENT)

  if (tonumber(filedlg.status) ~= -1) then
    local filename = filedlg.value
    local str = read_file(filename)
    if (str) then
      config:RecentUpdate(filename)
      multitext.value = str
    end
  end
  filedlg:destroy()
end

function item_saveas:action()
  local filedlg = iup.filedlg{
    dialogtype = "SAVE",
    filter = "*.txt",
    filterinfo = "Text Files",
    parentdialog=iup.GetDialog(self)
    }

  filedlg:popup(iup.CENTERPARENT, iup.CENTERPARENT)

  if (tonumber(filedlg.status) ~= -1) then
    local filename = filedlg.value
    if (write_file(filename, multitext.value)) then
      config:RecentUpdate(filename)
    end
  end
  filedlg:destroy()
end

function item_exit:action()
  config:DialogClosed(iup.GetDialog(self), "MainWindow")
  config:Save()
  config:destroy()
  return iup.CLOSE
end

function item_goto:action()
  local line_count = multitext.linecount
  local lbl_goto = iup.label{title = "Line Number [1-"..line_count.."]:"}
  local txt_goto = iup.text{mask = iup.MASK_UINT, visiblecolumns = 20} --unsigned integer numbers only

  local bt_goto_ok = iup.button{title = "OK", text_linecount = 0, padding = "10x2"}
  bt_goto_ok.text_linecount = line_count
  function bt_goto_ok:action()
    local line_count = tonumber(self.text_linecount)
    local line = tonumber(txt_goto.value)
    if (line < 1 or line >= line_count) then
      iup.Message("Error", "Invalid line number.")
      return
    end
    goto_dlg.status = 1
    return iup.CLOSE
  end

  local bt_goto_cancel = iup.button{title = "Cancel", padding = "10x2"}
  function bt_goto_cancel:action()
    goto_dlg.status = 0
    return iup.CLOSE
  end

  local box = iup.vbox{
    lbl_goto,
    txt_goto,
    iup.hbox{
      iup.fill{},
      bt_goto_ok,
      bt_goto_cancel,
      normalizesize="HORIZONTAL",
    },
    margin = "10x10",
    gap = "5",
  }
  goto_dlg = iup.dialog{
    box,
    title = "Go To Line",
    dialogframe = "Yes",
    defaultenter = bt_goto_ok,
    defaultesc = bt_goto_cancel,
    parentdialog = iup.GetDialog(self)
  }

  goto_dlg:popup(iup.CENTERPARENT, iup.CENTERPARENT)

  if (tonumber(goto_dlg.status) == 1) then
    local line = txt_goto.value
    local pos = iup.TextConvertLinColToPos(multitext, line, 0)
    multitext.caretpos = pos
    multitext.scrolltopos = pos
  end

  goto_dlg:destroy()
end

function item_find:action()
  local find_dlg = self.find_dialog
  if (not find_dlg) then
    local find_txt = iup.text{visiblecolumns = "20"}
    local find_case = iup.toggle{title = "Case Sensitive"}
    local bt_find_next = iup.button{title = "Find Next", padding = "10x2"}
    local bt_find_close = iup.button{title = "Close", padding = "10x2"}

    function bt_find_next:action()
      local find_pos = tonumber(find_dlg.find_pos)
      local str_to_find = find_txt.value

      local casesensitive = (find_case.value == "ON")

      -- test again, because it can be called from the hot key
      if (not str_to_find or str_to_find:len()==0) then
        return
      end

      if (not find_pos) then
        find_pos = 1
      end

      local str = multitext.value

      local pos, end_pos = str_find(str, str_to_find, casesensitive, find_pos)
      if (not pos) then
        pos, end_pos = str_find(str, str_to_find, casesensitive, 1)  -- try again from the start
      end

      if (pos) and (pos > 0) then
        pos = pos - 1
        find_dlg.find_pos = end_pos

        iup.SetFocus(multitext)
        multitext.selectionpos = pos..":"..end_pos

        local lin, col = iup.TextConvertPosToLinCol(multitext, pos)
        local pos = iup.TextConvertLinColToPos(multitext, lin, 0)  -- position at col=0, just scroll lines
        multitext.scrolltopos = pos
      else
        find_dlg.find_pos = nil
        iup.Message("Warning", "Text not found.")
      end
    end

    function bt_find_close:action()
      iup.Hide(iup.GetDialog(self))  -- do not destroy, just hide
    end

    box = iup.vbox{
      iup.label{title = "Find What:"},
      find_txt,
      find_case,
      iup.hbox{
        iup.fill{},
        bt_find_next,
        bt_find_close,
        normalizesize="HORIZONTAL",
      },
      margin = "10x10",
      gap = "5",
    }

    find_dlg = iup.dialog{
      box,
      title = "Find",
      dialogframe = "Yes",
      defaultenter = bt_next,
      defaultesc = bt_close,
      parentdialog = iup.GetDialog(self)
      }

    -- Save the dialog to reuse it
    self.find_dialog = find_dlg -- from the main dialog */
  end

  -- centerparent first time, next time reuse the last position
  find_dlg:showxy(iup.CURRENT, iup.CURRENT)
end

function item_font:action()
  local font = multitext.font
  local fontdlg = iup.fontdlg{value = font, parentdialog=iup.GetDialog(self)}

  fontdlg:popup(iup.CENTERPARENT, iup.CENTERPARENT)

  if (tonumber(fontdlg.status) == 1) then
    multitext.font = fontdlg.value
    config:SetVariable("MainWindow", "Font", fontdlg.value)
  end

  fontdlg:destroy()
end

function item_about:action()
  iup.Message("About", "   Simple Notepad\n\nAutors:\n   Gustavo Lyrio\n   Antonio Scuri")
end


--********************************** Main (Part 2/2) *****************************************


recent_menu = iup.menu{}

file_menu = iup.menu{
  item_open,
  item_saveas,
  iup.separator{},
  iup.submenu{title="Recent &Files", recent_menu},
  item_exit
  }
edit_menu = iup.menu{item_find, item_goto}
format_menu = iup.menu{item_font}
help_menu = iup.menu{item_about}
sub_menu_file = iup.submenu{file_menu, title = "&File"}
sub_menu_edit = iup.submenu{edit_menu, title = "&Edit"}
sub_menu_format = iup.submenu{format_menu, title = "F&ormat"}
sub_menu_help = iup.submenu{help_menu, title = "&Help"}

menu = iup.menu{
  sub_menu_file,
  sub_menu_edit,
  sub_menu_format,
  sub_menu_help,
  }

btn_open = iup.button{image = "IUP_FileOpen", flat = "Yes", action = item_open.action, canfocus="No", tip = "Open (Ctrl+O)"}
btn_save = iup.button{image = "IUP_FileSave", flat = "Yes", action = item_saveas.action, canfocus="No", tip = "Save (Ctrl+S)"}
btn_find = iup.button{image = "IUP_EditFind", flat = "Yes", action = item_find.action, canfocus="No", tip = "Find (Ctrl+F)"}

toolbar_hb = iup.hbox{
  btn_open,
  btn_save,
  iup.label{separator="VERTICAL"},
  btn_find,
  margin = "5x5",
  gap = 2,
  }

vbox = iup.vbox{
  toolbar_hb,
  multitext,
  lbl_statusbar,
}

dlg = iup.dialog{
  vbox,
  title = "Simple Notepad",
  size = "HALFxHALF",
  menu = menu,
  close_cb = item_exit.action,
}

function dlg:k_any(c)
  if (c == iup.K_cO) then
    item_open:action()
  elseif (c == iup.K_cS) then
    item_saveas:action()
  elseif (c == iup.K_cF) then
    item_find:action()
  elseif (c == iup.K_cG) then
    item_goto:action()
  end
end

config:RecentInit(recent_menu, 10)

-- parent for pre-defined dialogs in closed functions (IupMessage)
iup.SetGlobal("PARENTDIALOG", iup.SetHandleName(dlg))

config:DialogShow(dlg, "MainWindow")

-- to be able to run this script inside another context
if (iup.MainLoopLevel()==0) then
  iup.MainLoop()
  iup.Close()
end

不工作： 错误输出：  wlua：source.wlua：52：尝试调用字段'config'（零值）

那么，为什么它不起作用？