Преобразовать заданную строку, заменив в ней каждое сочетание символов

var 
  Str : string = 'строка';
 
begin
   while Pos('<–>', Str) <> 0 do 
      Str.Replace('<–>','–+–');
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  Str : string; 
begin
str:=Edit1.Text;
  while Pos('<–>', Str) <> 0 do 
Str.Repaint('<–>','–+–');
end;

  after  := StringReplace(before, ' a ', ' THE ',  [rfReplaceAll, rfIgnoreCase]);

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
procedure TForm1.Button1Click(Sender: TObject);
var
  Str : string;
begin
str:=Edit1.Text;
  while Pos('<–>', Str) <> 0 do
 Str := StringReplace(Str, '<–>', '–+–',[rfReplaceAll]);
 Edit1.Text:=str;
end;
 
end.

procedure TForm1.Button1Click(Sender: TObject);
begin
Edit1.Text := StringReplace(Edit1.Text, '<–>', '–+–',[rfReplaceAll]);
end;