sub recursiveFree {
    my $ref = shift;
    if( ref $ref eq 'ARRAY' ) {
        recursiveFree( $ref->[ $_ ] ) for 0 .. $#{ $ref };
    }
    elsif( ref $ref eq 'HASH' ) {
        recursiveFree( $ref->{ $_ } ) for keys %{ $ref };
    }
    elsif( ref $ref and ref $ref ne 'SCALAR' ) {
        warn "Unhandled reftype: ", ref( $ref );
    }
    undef $ref;
    return;
}

recursiveFree( $xls );