As a refugee from C++ on Windows I will say that, in MS Visual Studio, it is possible to "move execution point to here". This isn't exactly the same as rewinding execution--it doesn't play well with leaving the current stack frame, for example--but it comes pretty close; you can generally reconstruct the program state you care about by hand. The primary use case (IME) for "backing up" in a debugger is to make a change in a variable and then repeat the last few lines. This should be well within perl's, and Parrot's, abilities.