Reverse a linked list in perl - perl

Question

So I know that there are hundred examples on Stack overflow, and in fact i have used all the information from there - so this is what i have
use strict;
use warnings;
use Data::Dumper;
my $head= undef;
my $tail=\$head;
open FILE, "<datastored.txt" or die $!;
while (<FILE>){
my $node = {
"data" => $_ ,
"next" => undef
};
$$tail=$node;
$tail = \$node->{"next"};
};
print Dumper $head; #before reversing
$head = reverse_list($head);
print Dumper $head; #after reversing
sub reverse_list{
my ($list) =#_[0];
my $previous = undef;
while ($list->{next}){
$forward = $list->{next};
$list->{next}= $previous;
$previous = $list;
$list=$forward;
};
return $previous;
};
and this is the output I get
#this is the output before reversing (normal linked list)
$VAR1 = {
'next' => {
'next' => {
'next' => {
'next' => undef,
'data' => 'line 4
'
},
'data' => 'line 3
'
},
'data' => 'line 2
'
},
'data' => 'line 1
'
};
#this is the linked list after reversing (WITHOUT THE LAST DATA VARIABLE - "line 4")
$VAR1 = {
'next' => {
'next' => {
'next' => undef,
'data' => 'line 1
'
},
'data' => 'line 2
'
},
'data' => 'line 3
'
};
Note - the content of the file datastored.txt is simply
line 1
line 2
line 3
line 4
So my question is where is the data "line 4" gone and what should i change to ACTUALLY reverse the linked list without losing any value.

Answer 1

Your reversal sub-routine is almost correct. However, it misses the last entry (i.e. adding it in the final reversed list) because of the condition you are using. You have two options:
Change the while ($list->{next}) to while ($list) and make the code more idiomatic.
Add a $list->{next}= $previous; after the end of the while loop to add back the last remaining node to your reversed list. (Think of a list of two elements and see what your code does).