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| ANSI Common Lisp 14 Conses 14.2 Dictionary of Conses
14.2.10 copy-tree | Function
  Syntax: copy-tree tree new-tree Arguments and Values: tree - a tree. new-tree - a tree. Description: 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. Examples:
       (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: tree-equal Allegro CL Implementation Details: None.

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