A quick test ... shows that multiple closures made from the same anonymous sub have different states

Nice one! That's what I wanted to hear.

It is likely to be possible to save (and with 5.8.1, restore) a flipflop's state using the B module.

I don't think my internals knowledge is up to it. A CPAN module that did this would be nice though :).

In the mean time I am looking at preserving the input file position (with tell), together with the line counter and flipflop state using the return value from .. (in combination with $. when .. returns false). When I restore, I will need to short circuit the left operand if the flipflop state was on.

Anyone see any issues with this?