Re: copy-sequence no longer copies rings

[David Kastrup]

"Stephen J. Turnbull" <address@hidden> writes:

> David Kastrup writes:
>
>  > If `copy-sequence' allows for dotted lists, so should `length'.  I am
>  > not sure I like the implications since every list implicitly is also a
>  > dotted list.
>  > 
>  > To wit:
>  > (copy-sequence '(2 3 . (4 5))) creates an element-wise copy of (4 5)
>  > while (copy-sequence '(2 3 . [4 5])) would not create an element-wise
>  > copy of [4 5].
>  > 
>  > (length '(2 3 . (4 5))) is 4, while (length '(2 3 . [4 5])) should
>  > presumably be 3.
>
> I don't see the problem.  `(2 3 . (4 5))' is just notation; the
> structure is `(2 . (3 . (4 . (5 . nil))))'.

Yes, that is the point.  It's just notation.  So what is the principal
difference between a cdr that is a list, and a cdr that is a non-list
cons cell?  Or should every cons cell be called a list?

(copy-sequence '(2 . (3 . (4 . (5 . nil))))) copies every dotted pair
recursing on the cdr, to a total of 4 dotted pairs.

So what should (copy-sequence '(2 . (3 . (4 . 5)))) copy?  3 dotted
pairs?  Probably.  But then it would appear logical if the "length"
were 3, too.

> The two cases above surely have lengths 4 and 3 respectively, while
> the interesting case is `(2 3 4 . 5)' which I suppose should have
> length 4, but I'm not massively invested in it.

That's good since I have convinced myself by now that any such
investment should be lost.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum