🚀 go-pugleaf

There is a discussion here (if I understand it correctly) about how
one can constrain two variables in such a way that a change to one
will effect a change in the other.  In particular, if a is set to
a list, and b is set to the cdr of that list, then a change in b
ought to cause a change in a.  [This is my interpretation of the
discussion between Jeff Dalton and Peter da Silva re:

>>(setq a '(foo (bar baz)))
>>(setq b (cdr a))
>>(rplaca b 'bog)                       ].

Since this sort of thing only makes sense in a temporal context,
would it not be reasonable to view pointers/aliasing as the
introduction of a temporal constraint, along the lines of:
        From time_current to time_end_of_scope Ensure b = cdr a
together with the assumption that everything remains the same
over time unless explicitly changed, or unless a change is needed
to maintain the constraints?

That is, rather than view b as a pointer into a, view it as a
distinct variable that is constrained with respect to a?

I find the semantics of the latter easier to understand (but what
do I know? :-)
-----------------------------------------------------------------------------
 Chris.Holt@newcastle.ac.uk      Computing Lab, U of Newcastle upon Tyne, UK
-----------------------------------------------------------------------------
 "He either fears his fate too much, or his programming tools are small..."