Re: How to make a copy of a list

På Tue, 29 Apr 2008 22:26:55 +0200, skrev John Thingstad <jpthing@xxxxxxxxx>:


You write your own. copy-seq works like copy-list but works on arrays as well.
sequencep sais whether it is a sequence. Since a list is also a sequence you just need a
depth first traversal to duplicate the structure.


Lot of nonsence here. (subtypep (type-of sequence) 'sequence) determines if it is a sequence.
Traversal is breath first. (Next time I will write the code FIRST.)

Something like:

(defun deep-copy-sequence (sequence)
"Recursivly copy all array's and list's."
(when (subtypep (type-of sequence) 'sequence)
(setf sequence (copy-seq sequence))
(loop for i from 0 below (length sequence) do
(setf (elt sequence i) (deep-copy-sequence (elt sequence i)))))
sequence)


Using the iterate package this is a more efficient version.

(defun deep-copy-sequence (sequence)
"Recursivly copy all array's and list's."
(when (subtypep (type-of sequence) 'sequence)
(setf sequence (copy-seq sequence))
(iter (for element in-sequence sequence)
(when (subtypep (type-of element) 'sequence)
(setf element (deep-copy-sequence element)))))
sequence)

1. No need recursivly go down the structure for atoms.
2. elt and length are not needed. Both have order n complexity for list's.

This works for characters, numbers, vectors, strings, arrays

You get in trouble with structures and classes.
They can in themself have substructure.

For your own classes define a method deep-copy.

For library classes/structure all bets are off. You could hack something together I suppose using introspection..

--------------
John Thingstad
.

Relevant Pages

  • Re: How to make a copy of a list
    ... > (defun deep-copy-sequence (sequence) ... > John Thingstad ... macro covering the original storage place within the sequence. ...
    (comp.lang.lisp)
  • Re: How to make a copy of a list
    ... (setf sequence (copy-seq sequence)) ... (loop for i from 0 below (length sequence) ... do (setf element (deep-copy-sequence element)))) ...
    (comp.lang.lisp)
  • Re: How to make a copy of a list
    ... (setf sequence (copy-seq sequence)) ... (loop for i from 0 below (length sequence) ...
    (comp.lang.lisp)