The Want module is quite interesting, but seems a little awkward in terms of implementation. Here's an example:

use Want;

sub fooz : lvalue
{
     defined ($foo_new)?
        $foo_new
        : (want('LVALUE','ASSIGN')?
              $foo_new = $foo
              : $foo);
}
[download]

Internally, there is a function from the Wait.xs component called 'want_lvalue', which is really all I need. If it were assigned a default parameter value (it relates to stack depth) then it could be used like so:

use Want;

sub fooz : lvalue
{
     defined ($foo_new)?
        $foo_new
        : want_lvalue?
              $foo_new = $foo
              : $foo);
}
[download]

This does seem to be a lot neater, though not currently implemented.

It just goes to show that CPAN has a module for every occasion. I wouldn't be surprised to see Cheese::Grater.

Thanks for the tip. It's exactly what I was looking for.