Two-sided references in a list - perl

Question

I'm just starting to learn Perl and I have to do an exercise containing references.
I have to create a program, that constructs a list with two sided references, that are are received as command line arguments. At the beginning of the program, there is only one element in the list - 0. To go through the list, reference is being used, that references to the only element of the list at the moment - 0. The arguments of the command line are being read one by one and added right behind the element, that is being referenced to. When one argument is added, the reference slides one element to the right(it references to the newly added element). There are also two special elements - + and -. + allows the reference to move one element to the right, and - one element to the left. Also, it is important that the reference would not go beyond the list limit.
The output is all the arguments in the correct order of the list.
Additional requirements are that the list must be created by using hashes, that contain links to neighbouring elements. Also, I cannot use arrays to store the whole list.
There are a few examples to make it easier to grasp the concept, this is the most useful one:
./3.pl A D - B C + E
0 A B C D E
All I've got now is just the start of the program, it is nowhere near done and doesn't compile, but I can't figure out where to go from there. I've tried looking for some information about two-sided references(I'm not sure if I'm translating it correctly), but I can't seem to find anything. Any information about two-sided references or any tips how to start writing this program properly would be very appreciated.
My code:
#!/usr/bin/perl
use strict;
use warnings;
my $A= {
value=>'0',
prev=>'undef',
next=>'$B'
};
my $B= {
value=>'0',
prev=>'$A',
next=>'$C'
};
my $C= {
value=>'0',
prev=>'$B',
next=>'undef'
};
for my $smbl(0..#$ARGV) {
$A-> {value} = $ARGV[$smbl];
$Α-> {next} = $ARGV[$smbl+1];
}

Answer 1

First of all, what you are building is called a doubly linked list.
Let me tell you the biggest trick for working with linked lists: Create a dummy "head" node and a dummy "tail" node. You won't print their values, but having them will greatly reduce the number of special cases in your code, making it so much simpler!
At the core, you will have three "pointers" (references).
$head points to the first node of the list.
$tail points to the last node of the list.
$cursor initially points to the node in $tail. New nodes will be inserted before this node.
When processing +, two different situations you need to handle:
$cursor == $tail: Error! Cursor moved beyond end of list.
$cursor != $tail: Point $cursor to the node following the one it references.
When processing -, there are two different situations you need to handle:
$cursor->{prev} == $head: Error! Cursor moved beyond start of list.
$cursor->{prev} != $head: Point $cursor to the node preceding the one it references.
When processing inserting nodes, no checks need to be performed because of the dummy nodes!