I tried implementing a binary tree in Perl without using any external library. My code follows. The problem is, it says:

"Use of uninitialized value in numeric eq (==) at Tree.pl line 42.
Use of uninitialized value in numeric eq (==) at Tree.pl line 42."
[download]

in the traverse() function. I took help from algorithms in Perl book.

use strict;
use warnings;

sub search {
    my ($tree, $element) = @_; # we pass the root node and the element
+ to be found
    my $node;
    
    while($node = $$tree) { # $tree is a reference so we dereference i
+t using $$.
        if($element == $node->{val}) {
            return($tree, $node); # return the subtree where the node 
+was found.
        } else {
            if($element < $node->{val}) {
                # go left
                $tree = \$node->{left}; # note that $tree is a referen
+ce so we assign it a reference with '\'
            } else {
                $tree = \$node->{right};
            }
        }
    } # we reach here iff there is no $element to be found
    # we politely suggest user that they may add the element at the gi
+ven position.
    return ($tree, undef);
}

sub insert {
    my ($tree, $element) = @_;
    my $found;
    ($tree, $found) = search($tree, $element);
    
    unless($found) {
        $found = {
            left => undef,
            right => undef,
            val => $element,
        };
        $$tree = $found;
    }
    return $found;
}

sub traverse {
    my $tree = shift;
    if($$tree->{left} == undef || $$tree->{right} == undef) {
        return;
    }
    traverse(\$tree->{left});
    print $$tree->{val};
    print "\n";
    traverse(\$tree->{right});
}

my @ele = [1, 2, 3, 4, 5];

my ($tree, $stat, $link);

for my $ele (@ele) {
    ($stat, $link) = insert(\$tree, $ele);
}

traverse(\$tree);
[download]

As per my (limited) knowledge of Perl, I guess the search() and insert() function are correct, but I'm not sure.

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