Code:

unit Unit1;

interface

uses

Windows, Messages, SysUtils, Classes, Graphics, Controls,

Forms, Dialogs, StdCtrls, ComCtrls;

type

TForm1 = class(TForm)

   Button1: TButton;

   Button2: TButton;

   RichEdit1: TRichEdit;

   procedure RichEdit1KeyPress(Sender: TObject; var Key: Char);

private

   { Private declarations }

public

   { Public declarations }

end;

var

Form1: TForm1;

implementation

{$R *.DFM}

uses

richedit;

procedure TForm1.RichEdit1KeyPress(Sender: TObject; var Key: Char);

var

line, col, indent: integer;

S: string;

begin

if key = #13 then

begin

   key := #0;

   with sender as TRichEdit do

   begin

     {figure out line and column position of caret}

     line := PerForm( EM_EXLINEFROMCHAR, 0, SelStart );

     Col := SelStart - Perform( EM_LINEINDEX, line, 0 );

     {get part of current line in front of caret}

     S:= Copy( lines[ line ], 1, col );

     {count blanks and tabs in this string}

     indent := 0;

     while (indent < length( S )) and (S[indent + 1] in [' ', #9]) do

       Inc( indent );

     {insert a linebreak followed by the substring of blanks and tabs}

     SelText := #13#10 + Copy(S, 1, indent);

   end;

end;

end;

end.