Doubly-Linked List (element)
This is much like inserting into a Singly-Linked List, but with added assignments so that the backwards-pointing links remain correct.

See also

 Array
 Associative array: Creation, Iteration
 Collections
 Compound data type
 Doubly-linked list: Definition, Element definition, Element insertion, List Traversal, Element Removal
 Linked list
 Queue: Definition, Usage
 Set
 Singly-linked list: Element definition, Element insertion, List Traversal, Element Removal
 Stack
role DLElem[::T] {
    has DLElem[T] $.prev is rw;
    has DLElem[T] $.next is rw;
    has T $.payload = T;
 
    method pre-insert(T $payload) {
        die "Can't insert before beginning" unless $!prev;
        my $elem = ::?CLASS.new(:$payload);
        $!prev.next = $elem;
        $elem.prev = $!prev;
        $elem.next = self;
        $!prev = $elem;
        $elem;
    }
 
    method post-insert(T $payload) {
        die "Can't insert after end" unless $!next;
        my $elem = ::?CLASS.new(:$payload);
        $!next.prev = $elem;
        $elem.next = $!next;
        $elem.prev = self;
        $!next = $elem;
        $elem;
    }
 
    method delete {
        die "Can't delete a sentinel" unless $!prev and $!next;
        $!next.prev = $!prev;
        $!prev.next = $!next;   # conveniently returns next element
    }
}
 
role DLList[::DLE] {
    has DLE $.first;
    has DLE $.last;
 
    submethod BUILD {
	$!first = DLE.new;
	$!last = DLE.new;
	$!first.next = $!last;
	$!last.prev = $!first;
    }
 
    method list { ($!first.next, *.next ...^ !*.next).map: *.payload }
    method reverse { ($!last.prev, *.prev ...^ !*.prev).map: *.payload }
}
 
class DLElem_Str does DLElem[Str] {}
class DLList_Str does DLList[DLElem_Str] {}
 
my $sdll = DLList_Str.new;
my $b = $sdll.first.post-insert('A').post-insert('B');
$b.pre-insert('C');
say $sdll.list;  # A C B