Doubly-linked list/Element definition

Define the data structure for a doubly-linked list element. The element should include a data member to hold its value and pointers to both the next element in the list and the previous element in the list. The pointers should be mutable.

Ada

type Link;
type Link_Access is access Link;
type Link is record
  Next : Link_Access := null;
  Prev : Link_Access := null;
  Data : Integer;
end record;

Ada's standard container library includes a generic doubly linked list. The structure of the link element is private.

C

struct link (
  struct link *next;
  struct link *prev;
  int data;
);

ALGOL 68

MODE LINK = STRUCT (
  REF LINK next,
  REF LINK prev,
  INT data
);
LINK example;
~

Perl

Just use an array. You can traverse and splice it any way. Linked lists are way too low level.

However, if all you got is a algorithm in a foreign language, you can use references to accomplish the translation.

my %node = (
    data => 'say what',
    next => \%foo_node,
    prev => \%bar_node,
);
$node{next} = \%quux_node;  # mutable

Pop11

uses objectclass;
define :class Link;
    slot next = [];
    slot prev = [];
    slot data = [];
enddefine;

Ruby

 class ListNode
   attr_accessor :val, :nxt, :prv
   def initialize(mval,mprv=nil,mnxt=nil)
     self.val=mval
     self.prv=mprv
     prv.nxt=self if prv
     self.nxt=mnxt
     nxt.prv=self if nxt
   end
   def each(&b)
     yield val
     nxt.each(&b) if nxt
     self
   end
   include Enumerable
 end

Python

class Node(object):
    def __init__(self, data = None, prev = None, next = None):
        self.prev = prev
        self.next = next
        self.data = data
    def __str__(self):
        return str(self.data)
    def __repr__(self):
        return repr(self.data)
    def iter_forward(self):
        c = self
        while c != None:
            yield c
            c = c.next
    def iter_backward(self):
        c = self
        while c != None:
            yield c
            c = c.prev