Re: How to make a copy of a list

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.
.

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