Janilabo | function ReplaceEx() [Simba]

function ReplaceEx(Text, FindStr, ReplaceStr: string; Offset: Integer): string;
var
  fsL, tL: Integer;
begin
  fsL := Length(FindStr);
  tL := Length(Text);
  if ((fsL > tL) or (Offset > tL)) then
    Exit;
  if (Offset < 1) then
    Offset := 1;
  Result := (Copy(Text, 1, (Offset - 1)) + Replace(Copy(Text, Offset, ((tL - Offset) + 1)), FindStr, ReplaceStr, [rfReplaceAll]));
end;

var
  str: string;

begin
  str := 'Janilabo is naab';
  WriteLn(ReplaceEx(str, 'a', 'o', (Pos('abo ', str) + 1)));
end.