my $excel_obj;
if ($ext eq ".xls") {
    $excel_obj = Spreadsheet::ParseExcel->new();
} elsif ($ext eq ".xlsx") {
    $excel_obj = Spreadsheet::ParseXLSX->new();
} elsif ($ext eq ".ods") {
    $excel_obj = Spreadsheet::ReadSXC->new();
} else {
    die "Extension $ext not (yet) supported...";
}
my $workbook = $excel_obj->Parse( ... );