package Variable;

sub new{
  my ($class) = @_;
  my $self = {value => 0};
  bless $self,$class;
  return $self;
}

sub setValueAdderVar{
  my ($self,$val) = @_;
  $self->{old}   = $self->{value};
  $self->{value} = $val * $val;
  $self->{Adder}->refresh($self->{old},$self->{value});
}

sub connectAdder{
  my ($self,$var) = @_;
  $self->{Adder} = $var;
}

sub connectSqrt{
  my ($self,$var) = @_;
  $self->{Sqrt} = $var;
}

sub setValueSqrtVar{
  my ($self,$val) = @_;
  $self->setValue($val);
  $self->{Sqrt}->refresh($self->getValue());
}

sub setValue{
  my ($self,$val) = @_;
  $self->{value} = $val;
}

sub getValue{
  my ($self) = @_;
  return $self->{value};
}

1;

package Adder;

sub new{
  my ($class) = @_;
  my $self = {sum => 0};
  bless $self,$class;
  return $self;
}

sub connectSum{
  my ($self,$var) = @_;
  $self->{SumVar} = $var;
}

sub refresh{
  my ($self,$old,$new) = @_;
  $self->{sum} += ($new - $old);
  $self->{SumVar}->setValueSqrtVar($self->{sum});
}

1;

package Sqrt;

sub new{
  my ($class) = @_;
  my $self = {};
  bless $self,$class;
  return $self;
}

sub connectRes{
  my ($self,$var) = @_;
  $self->{Result} = $var;
}

sub refresh{
  my ($self,$val) = @_;
  $self->{Result}->setValue(sqrt($val));
}

1;

#! /usr/bin/perl

use strict;
use warnings;
use lib qw(.);
use Variable;
use Adder;
use Sqrt;

my $alpha = Variable->new();
my $beta  = Variable->new();
my $gamma = Variable->new();
my $delta = Variable->new();

my $adder = Adder->new();
my $sqrt  = Sqrt->new();

$alpha->connectAdder($adder);
$beta->connectAdder($adder);

$adder->connectSum($gamma);
$gamma->connectSqrt($sqrt);

$sqrt->connectRes($delta);

$alpha->setValueAdderVar(3);
$beta->setValueAdderVar(4);

print $delta->getValue(),"\n";