Re: How to make a copy of a list

På Wed, 30 Apr 2008 05:19:59 +0200, skrev Kaz Kylheku <kkylheku@xxxxxxxxx>:

On Apr 29, 4:46 pm, Trastabuga <lisper...@xxxxxxxxx> wrote:
On Apr 29, 5:54 pm, "John Thingstad" <jpth...@xxxxxxxxx> wrote:
> (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).

The problem is that the (SETF ELEMENT ...) expressions in the LOOP-s
don't do what is intended. ELEMENT is a local variable, not a symbol
macro covering the original storage place within the sequence.

DUH! right..

(loop for rest over sequence do (setf (car rest) (deep-copy-sequence (car rest)))

might fare better.

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