Re: why are there [v e c t o r s] in Lisp?

[Random832]

"Pascal J. Bourguignon" <pjb@informatimago.com> writes:
> Random832 <random832@fastmail.com> writes:
>> Well, what happens if you cdr that list? Does it make a
>> copy? 
>
> cdr'ing is no problem you just increment your pointer.
>
>> The thing is, if you can car a string people will wonder why
>> you can't cdr it. And with mutable objects it's hard to make
>> cdr work right. (fsvo "right")
>
> It's rplacd which becomes much more complex.

You didn't mention my issue with "list of 5000 elements, cdr
4000 times" - does the garbage collector know to discard the
first 4000 elements which are no longer reachable?

> Also, when you program with such a system, you might be afraid that
> rplacd leads to fragmented chains, and will have a tendency to call
> copy-list to compact them.

Hmm... can the garbage collector compact them?

>  But indeed, copy-list means that less
> structure is shared, and therefore would waste time and memory.  This is
> what they do in C++ and why they believe lists are costly.

Also with this kind of list I think you still lose the
ability to have constant-time indexing, since you have to
check every cell for the cdr bit.