functional programming - How do you copy an array in common lisp?

Question

I'd like to make copies of my 2D array, which feels like the nice, functional, nondestructive way of handling arrays. What is the lispy way of doing this?

Answer 1

UPDATE: Nowadays, alexandria has a copy-array very similar to the implementation given below. Use that.

OBSOLETE ANSWER: I used the following, which I believed was better than the alexandria version at the time:

(defun copy-array (array &key
                   (element-type (array-element-type array))
                   (fill-pointer (and (array-has-fill-pointer-p array)
                                      (fill-pointer array)))
                   (adjustable (adjustable-array-p array)))
  "Returns an undisplaced copy of ARRAY, with same fill-pointer and
adjustability (if any) as the original, unless overridden by the keyword
arguments."
  (let* ((dimensions (array-dimensions array))
         (new-array (make-array dimensions
                                :element-type element-type
                                :adjustable adjustable
                                :fill-pointer fill-pointer)))
    (dotimes (i (array-total-size array))
      (setf (row-major-aref new-array i)
            (row-major-aref array i)))
    new-array))

The problem with the alexandria version was that the adjust-array hack causes the result (at least on SBCL) to never be a simple-array, which some other libraries (e.g. opticl) expect. The above version also was faster for me.

Someone else has published a very similar version in a different library, but I forgot the names of both person and library.