foo() + bar() + baz()
  1      2
     3           4
              5

##</code><code>##

#! /usr/bin/perl
use strict;

package Foo;
use overload
  '+' => sub {
           my ($self, $other) = @_;
           print "Evaluating $self + $other\n";
           return Foo->new($$self + $$other);
         },
  '0+' => sub {my $self = shift; $$self},
  '""' => sub {my $self = shift; $$self};

sub new {
  my $class = shift;
  my $obj = \shift;
  print "Creating $$obj\n";
  bless $obj, $class;
}

package main;
Foo->new(1) + Foo->new(2) + Foo->new(4);
__END__
Creating 1
Creating 2
Evaluating 1 + 2
Creating 3
Creating 4
Evaluating 3 + 4
Creating 7

##</code><code>##

my $foo = 0;
print ++$foo + $foo++;