I recently discovered a CPAN module called WhatIf (http://search.cpan.org/author/SIMONW/Whatif-1.01/). This module has the ability to provide rollback functionality for arbitrary code.
I don't really understand continuations yet (although I'm reading up on them), so perhaps they would allow this to be done trivially. However, I think it would be very cool to roll this module into the core language and provide the keyword support in core. Is this feasible? What would the overhead costs be? --Dks
