my $half_life = 5; # seconds
my $foo;

tie $foo, 'Radioactive::Decay::Analytical', $half_life;

$foo = 100;
for (1..10) {print $foo,"\n"; sleep(2)}

tie $foo, 'Radioactive::Decay::Discreet', $half_life;
$foo = 100;
for (1..10) {print $foo,"\n"; sleep(2)}

package Radioactive::Decay::Analytical;
sub TIESCALAR { bless [0,log(2)/$_[1],0], $_[0]; }
sub STORE     { $_[0]->[2] = time; $_[0]->[0] = $_[1] }
sub FETCH     { $_[0]->[0] * exp(-$_[0]->[1] * (time - $_[0]->[2])) }

package Radioactive::Decay::Discreet;
sub TIESCALAR { bless [0,log(2)/$_[1],0], $_[0]}
sub STORE     {$_[0]->[2] = time; $_[0]->[0] = $_[1]}
sub FETCH     { if (rand() < (1-exp(-$_[0]->[1] * (time-$_[0]->[2])))) 
		  {$_[0]->[0] = 0} 
		else {$_[0]->[2] = time}
		$_[0]->[0];}