As promised yesterday, this is my code to create a linked list and count its nodes:

use strict;
use warnings;
use Data::Dumper;

my $pt = { value => "D", next => undef }; 
my $pt2 = {value => "C", next => $pt};
$pt = {value => "B", next => $pt2};
my $L = { value => "A", next => $pt};

sub solution {
    my $list = shift;
    my $length = 0;
    while (1) {
        return $length unless defined $list->{value}; # added for the 
+case of an empty list
        print $list->{value};
        $length++;
        return $length unless defined $list->{next};
        $list = $list->{next};
    }
}
    
my $len = solution($L);
print "\n$len \n";

print Dumper $L;
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Which finds 4 nodes and prints this:

ABCD
4
$VAR1 = {
          'next' => {
                      'next' => {
                                  'next' => {
                                              'next' => undef,
                                              'value' => 'D'
                                            },
                                  'value' => 'C'
                                },
                      'value' => 'B'
                    },
          'value' => 'A'
        };
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As I said yesterday, the initialization of the list could be simpler, but perhaps less easy to understand for a relative beginner. But this is how I would probably code the initialization of the linked list:

my $L = {
    value => "A", next => {
        value => "B", next => {
            value => "C", next => {
                value => "D", next => undef,
            }
        }
    }
};
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Or, better (especially if there are more nodes), I would construct it in a loop:

my $L;
for ( reverse qw / A B C D E F G/) {
    my $pt = { value => $_, next => $L };
    $L = $pt;
}
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Which prints:

$ perl linked_list.pl
ABCDEFG
7
$VAR1 = {
          'next' => {
                      'next' => {
                                  'next' => {
                                              'next' => {
                                                          'next' => {
                                                                      
+'next' => {
                                                                      
+            'next' => undef,
                                                                      
+            'value' => 'G'
                                                                      
+          },
                                                                      
+'value' => 'F'
                                                                    },
                                                          'value' => '
+E'
                                                        },
                                              'value' => 'D'
                                            },
                                  'value' => 'C'
                                },
                      'value' => 'B'
                    },
          'value' => 'A'
        };
[download]