#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

package BinTree;

sub new {
    my $class = shift;
    my $val = shift;
    my $self = { val => $val, l => undef, r => undef };
    bless $self, ref($class) || $class;
    return $self;
}

sub set_l {
    my $self = shift;
    my $val  = shift;
    
    if (ref $self->{l}) {
        $self->{l}->append($val);
    } else {
        $self->{l} = $self->new($val);
    }
}

sub set_r {
    my $self = shift;
    my $val  = shift;
    
    if (ref $self->{r}) {
        $self->{r}->append($val);
    } else {
        $self->{r} = $self->new($val);
    }
}

sub to_s {
    my $self = shift;
    my $v = $self->{val};
    my $l = ref $self->{l} ? $self->{l}->to_s : undef;
    my $r = ref $self->{r} ? $self->{r}->to_s : undef;
    return join ', ',  grep defined, ($l, $v, $r);
}

sub append {
    my $self = shift;
    my @vals = @_;
    while ( my $n = shift @vals ) {
        if ($n < $self->{val}) { $self->set_l($n) }
        elsif ($n > $self->{val}) { $self->set_r($n) }           
    }
}

package main;

my @list = (20, 4, 28, 9, 100, 12, 84, 10, 11);
my $tree = BinTree->new(shift @list);
$tree->append(@list);

print $tree->to_s . "\n" x 2;
print Dumper $tree;