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  ANSI Common Lisp   14 Conses   14.2 Dictionary of Conses

14.2.10 copy-tree Function

copy-tree tree    new-tree

Arguments and Values:
tree - a tree.

new-tree - a tree.

Creates a copy of a tree of conses.

If tree is not a cons, it is returned; otherwise, the result is a new cons of the results of calling copy-tree on the car and cdr of tree. In other words, all conses in the tree represented by tree are copied recursively, stopping only when non-conses are encountered.

copy-tree does not preserve circularities and the sharing of substructure.

 (setq object (list (cons 1 "one")
                    (cons 2 (list 'a 'b 'c))))
 ((1 . "one") (2 A B C))
 (setq object-too object)  ((1 . "one") (2 A B C))
 (setq copy-as-list (copy-list object))
 (setq copy-as-alist (copy-alist object))
 (setq copy-as-tree (copy-tree object))
 (eq object object-too)  true
 (eq copy-as-tree object)  false
 (eql copy-as-tree object)  false
 (equal copy-as-tree object)  true
 (setf (first (cdr (second object))) "a"
       (car (second object)) "two"
       (car object) '(one . 1))  (ONE . 1)
 object  ((ONE . 1) ("two" "a" B C))
 object-too  ((ONE . 1) ("two" "a" B C))
 copy-as-list  ((1 . "one") ("two" "a" B C))
 copy-as-alist  ((1 . "one") (2 "a" B C))
 copy-as-tree  ((1 . "one") (2 A B C)) 

See Also:

Allegro CL Implementation Details:

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