struct node {
    int data;
    struct node *next;
    struct node *prev;
};

struct node *start = NULL; // pointer to start of list.
struct node *end = NULL; // pointer to end of list

struct node * create (data)
    int data;
{
    struct node *temp = (struct node *)malloc(sizeof(struct node));
    temp->data = data;
    temp->next = temp->prev = NULL;
    return temp;
}

struct node * push(start, temp)
    struct node *start;
    struct node *temp;
{
    if(start == NULL) {
        // this node is the first node, assign it as is.
        start = temp;
    } else {
        temp->next = start;
        start->prev = temp;
        start = temp;
    }
    return start;
}

##</code><code>##

package doublyLinkedList;

sub new {
    my ($class, @elements) = @_;	

    my $self = bless {
	start => undef,
    }, $class;
	
    $self->push(@elements);
    return $self;
}

sub push {
    my ($self, @elements) = @_;
    for my $element (@elements) {
	my $newNode = {
		element => $element,
		next => undef,
		prev => undef,
	}; # newNode becomes an anonymous hash ref.
        if(not defined $self->{start}) {
            $self->{start} = $newNode; # the list is empty, assign to start as is
        } else {
            $newNode->{next} = $self->{start};
            $self->{start}{prev} = $newNode;
            $self->{start} = $newNode; # else make the new node point to start and then assign new node as the new start of the list.
        }
    }
    return;
}

##</code><code>##

void pop(start)
    struct node *start;
{
    if(start == NULL) {
        printf("The list is empty!\n");
        return;
    }
    struct node *temp = start;
    start = temp->next;
    temp->next = start->prev = NULL;
    free(temp);
    return; # or maybe we can return the element popped before freeing temp or whatever.
}

##</code><code>##

sub pop {
    my $self = shift;
    my $ret = $self->{start};
    return if not defined $ret; # return if the list is empty.
    $self->{start} = $ret->{next};
    $self->{start}{prev} = $ret->{next} = undef;
    return $ret->{element};
}