alists

[David Roderick]

Elisp 5.8
 -- Function: copy-alist alist
     This function returns a two-level deep copy of ALIST: it creates a
     new copy of each association, so that you can alter the
     associations of the new alist without changing the old one.

          (setq needles-per-cluster
                '((2 . ("Austrian Pine" "Red Pine"))
                  (3 . ("Pitch Pine"))
                  (5 . ("White Pine"))))
          =>
          ((2 "Austrian Pine" "Red Pine")
           (3 "Pitch Pine")
           (5 "White Pine"))

          (setq copy (copy-alist needles-per-cluster))
          =>
          ((2 "Austrian Pine" "Red Pine")
           (3 "Pitch Pine")
           (5 "White Pine"))

          (eq needles-per-cluster copy)
               => nil
          (equal needles-per-cluster copy)
               => t
          (eq (car needles-per-cluster) (car copy))
               => nil
          (cdr (car (cdr needles-per-cluster)))
               => ("Pitch Pine")

I don't understand how the cdr of one element in the alist in connected
with the next cons cell.
The first cons cell has a CDR of "Austrian Pine" "Red Pine".
In what way does this contain a reference to the next list (3.("Pitch
Pine"))?
Is there an outer level of a sequence happening?
Yes, an outer list.
So (2 . ("Austrian Pine" "Red Pine")) is actually the CAR of an outer
cons cell which has (3 . ("Pitch Pine")) as its CDR.
Is this correct?

2.3.6.2 Dotted Pair Notation
............................
 In dotted pair
notation, the list `(1 2 3)' is written as `(1 .  (2 . (3 . nil)))'

(car (cdr needles-per-cluster))
is (3 . ("Pitch Pine"))

ELISP can be HEAVY GOING

Elisp 5.3
-- Function: cdr cons-cell
     This function returns the value referred to by the second slot of
     the cons cell CONS-CELL.  Expressed another way, this function
     returns the CDR of CONS-CELL.

     As a special case, if CONS-CELL is `nil', then `cdr' is defined to
     return `nil'; therefore, any list is a valid argument for `cdr'.
     An error is signaled if the argument is not a cons cell or `nil'.

          (cdr '(a b c))
               => (b c)
          (cdr '())
               => nil


-- 
from 
David Roderick