Re: How to make a copy of a list

On Apr 29, 5:54 pm, "John Thingstad" <jpth...@xxxxxxxxx> wrote:
På Tue, 29 Apr 2008 23:24:00 +0200, skrev John Thingstad
<jpth...@xxxxxxxxx>:



(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)

Third and final version.. Trades succinctness for efficiency.
Lisp needs a efficient generic iterator over a sequence..
(Looking at the macroexpansion of iter it was just length and elt under
the hood)

(defun deep-copy-sequence (sequence)
"Recursivly copy all array's and list's."
(cond
((arrayp sequence)
(setf sequence (copy-seq sequence))
(loop for element across sequence
when (subtypep (type-of element) 'sequence)
do (setf element (deep-copy-sequence element))))
((listp sequence)
(setf sequence (copy-list sequence))
(loop for element in sequence
when (subtypep (type-of element) 'sequence)
do (setf element (deep-copy-sequence element)))))
sequence)

--------------
John Thingstad

John, your original version of deep-copy-sequence works, but the
latest doesn't (the original list gets changed).
I can't put my finger on it, the simple copy-list should work, but the
tree is so complicated so I can't make a simple test and show why the
original list gets mutilated.
Thank you!

Andrew
.

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