Let me make a tiny change so that I can talk about this more easily. The problem is that one $list is being changed while the other $list isn't. So lets rename one of them: 

use strict;

my $list        = { head=>undef, tail=>undef };

while (1)
{
    print '<i>nput, <o>utput : ';
    chomp (my $input = <STDIN>);
    
    if ($input eq  'i')
    {
        add($list);
        next;
    }        

    if ($input eq 'o')
    {
        show($list);
        next;
    }
}

sub add
{
    my ($list) = @_;
    chomp (my $input = <STDIN>);

    my $newnode = [undef, $input];
    $list{tail}[0]= $newnode;
    $list{tail}= $newnode;
}

[download]
The problem is that $list is updated when you modify $$lastnode, but my ($root, $lastnode) = @_; makes $root a copy of $list and so $root is not changed. Then add() returns $root and, in effect, you end up doing $list= $root, which restores $list to its previous value.

You could change the last line of add() to be return ($_[0], $lastnode); since $_[0] is an alias to $list and not a copy of $list.

But better would be to encapsulate the $list and $lastnode variables into a single item that is passed to add() and show().

        - tye (but my friends call me "Tye")

In reply to (tye)Re: Linked List Strangeness by tye
in thread Linked List Strangeness by Mandor

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