How can I execute a given function on every element of a complicated data structure in Perl?

sub _html_decode {
    my $self = shift;
    my $ref = shift;

    if (ref($ref) eq "HASH") {
        $self->_html_decode_hash($ref)
    }
    if (ref($ref) eq "ARRAY") {
        $self->_html_decode_array($ref);
    }

}

sub _html_decode_array {
    my $self = shift;
    my $ref = shift;

    unless (@$ref) {return;}

    foreach (0 .. (scalar(@$ref) - 1)) {
        if (ref($ref->[$_]) eq "HASH") {
            $self->_html_decode_hash($ref->[$_]);
        }
        if (ref($ref->[$_]) eq "ARRAY") {
            $self->_html_decode_array($ref->[$_]);
        }
        else {
            $ref->[$_] = decode_entities($ref->[$_]);
        }
    }
}

sub _html_decode_hash {
    my $self = shift;
    my $ref = shift;

    unless (%$ref) {return;}

    while (my ($k, $v) = each %$ref) {
        if (ref($v) eq "HASH") {
            $self->_html_decode_hash($v);
        }
        if (ref($v) eq "ARRAY") {
            $self->_html_decode_array($v)
        }
        else {
            $ref->{$k} = decode_entities($v);
        }
    }
}

sub _html_decode {
    my ($self, $ref) = @_;

    if (ref($ref) eq "HASH") {
        for my $value (values %{$ref}) {
            $self->_html_decode($value);
        }
    }
    elsif (ref($ref) eq "ARRAY") {
        for my $value (@{$ref}) {
            $self->_html_decode($value);
        }
    }
    else {
        $_[1] = decode_entities($_[1]);
    }
}