🚀 go-pugleaf

In article <5P57P18@xds13.ferranti.com> peter@ficc.ferranti.com (Peter da Silva) writes:
>In article <3808@skye.ed.ac.uk> jeff@aiai.UUCP (Jeff Dalton) writes:

>> What you can't do is:
>
>>   (setq a '(some list))
>>   (setq b (pointer-to (cdr a)))
>
>But "a" is already a "pointer" to "cdr a". In this case the "reference"
>operation is simply "cdr".

And in that sense of "pointer to" it's also a pointer to (cadr a)
and to (car (symbol-value (intern (elt (string (car a)) 0)))) [ie,
the car of s]; it's just that the dereference operation is cadr or
(lambda (x) (car (symbol-value (elt (string (car x)) 0)))).

>You want to factor the pointer out of the cons. I don't care if you can
>or not: the cons already has the same semantics as a pair of pointers, and
>everything that can be said "about" pointers can be said "about" a cons.

Then why do some Lisps add locatives?  They can do things that can't
be done with cons and cdr, that's why.

Common Lisp simulations of locatives were posted in comp.lang.lisp not
too long ago, if anyone wants to see what it involves.

-- JD