sub traverse {
    my ($hash, $callback, $mode) = @_;
    traverse($hash->[0], $callback, $mode) if ref($hash) eq "ARRAY";    # <---
    return unless ref($hash) eq "HASH";
    for my $key (keys %$hash) {
        my $val = $hash->{$key};
        if (ref($val)) {
            traverse($val, $callback, $mode);
            if ($mode eq "collect") {
                if (exists $val->{repval}) {
                    $callback->($key, $val->{repval});
                }
            }
        }
        if ($mode eq "replace") {
            $callback->($key, $val, $hash);
        }
    }
}