Вычисление факториала рекурсивным методом

unit Unit1; 
 
{$mode objfpc}{$H+}
 
interface
 
uses
  Classes, SysUtils, FileUtil, LResources, Forms, Controls, Graphics, Dialogs,
  StdCtrls;
 
type
 
  { TForm1 }
 
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Label1: TLabel;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end; 
 
type
  EFactorialError = class(Exception)
  end;
 
var
  Form1: TForm1;
 
implementation
 
//------------
function Factorial(n: integer): integer;
begin
  if n = 0 then Exit(1)
  else if n > 0 then Exit(n * Factorial(n - 1))
  else raise EFactorialError.Create('"n" must be non-negative');
end;
 
//------------
function FactorialFromStr(const n: AnsiString): AnsiString;
var
  val: integer;
begin
  val:= StrToInt(n);
  Exit( IntToStr(Factorial(val)) );
end;
 
{ TForm1 }
 
//------------
procedure TForm1.Button1Click(Sender: TObject);
begin
  try
    Label1.Caption:= 'Result: ' + FactorialFromStr(Edit1.Text);
  except
    on e: Exception do
      ShowMessage(e.Message);
  end;
end;
 
initialization
  {$I unit1.lrs}
 
end.