Callback

type
  TCallback = function(Value: string): Boolean;

function Call(Value: string): Boolean;
begin
  ShowMessage(Value);
  Result := Boolean(Random(2));
end;

procedure Proc(Callback: TCallback);
begin
  if Assigned(Callback) then
    ShowMessage('Callback вернул ' +BoolToStr(Callback('Внутри callback'), True));
  ShowMessage('Внутри процедуры');
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Proc(Call);
  Halt;
end;