#!/usr/bin/perl -l

use strict;
use warnings;
{
    package Number;

    use overload 
      '+'      => \&plus,
      '""'     => \&value, 
      fallback => 1;

    use Scalar::Util qw(blessed looks_like_number);
    use Carp qw(carp croak);

    sub new {
        my ( $class, $number ) = @_;
        unless ( looks_like_number($number) ) {
            croak("($number) is not a valid number");
        }
        return bless { number => $number } => $class;
    }

    sub value { shift->{number} }

    sub plus {
        my ( $num1, $num2, $reversed ) = @_;
        if ($reversed) {
            carp("$num1 and $num2 are reversed");
        }
        return __PACKAGE__->new(
            $num1->value 
            + 
            ( blessed $num2 ? $num2->value : $num2 ) 
        );
    }
}

my $seven = Number->new(7);
my $pi    = Number->new(3.14);

# overloading stringification ('""') allows the following to work
print $seven + $pi;

# 'blessed' in &plus allows this to work
print $seven + $pi + 1 + $pi;

# without overloading, the above is:
print $seven->plus($pi)->plus(1)->plus($pi)->value;

# perl's smart enough to reverse these
print 3 + $seven;