[求助]添加文件怎么不行??

代码如下:
private

{ Private declarations }
public
procedure assignfile(var f;filename:string);
{ Public declarations }
end;

var
Form1: TForm1;
f:textfile;

implementation

{$R *.dfm}

procedure assignfile(var f;filename:string);
var
f:textfile;
begin
if opendialog1.execute then
begin
assignfile(f,opendialog1.filename);
try
append(f);
wrintln(f);
finally
closefile(f);
end;
end;