I must say I've still not read all apocalypses, and OTOH I suspect that
this could be done more or less easily with a custom function (provided
that variables will have a method to keep track of their history, or, more
reasonably, will be *allowed* to have it), but I wonder if Perl6 may
include a builtin undo() function to recover values prior, say, to the
last assignement (or push() or, etc. etc.[*])

For optimization reasons track of a variable's "history" may be kept only
upon explicit appearance of undo()...

[*] To be definite, any atomic value-changing expression or statement, for
a choice of "atomic" to be decided upon.

Just my 2 cents,
Michele
--
: I've actually fixed the security glitches now
Bullshit.  Security is designed into a product.  Your design is inherently
insecure.  This is not something you can fix by pecking in a few more lines
of code.
- Jay Tilton in clpmisc, "Re: free source for bbs"