Common Lisp：列表和數組之間的轉換

Question

我們如何在任意嵌套的列表和數組之間進行優雅轉換？

例如

((1 2 3) (4 5 6)) 

變得

#2A((1 2 3) (4 5 6)) 

反之亦然

Answer 1

列表以二維數組：

(defun list-to-2d-array (list) 
    (make-array (list (length list) 
        (length (first list))) 
       :initial-contents list)) 

2D陣列以列出：

(defun 2d-array-to-list (array) 
    (loop for i below (array-dimension array 0) 
     collect (loop for j below (array-dimension array 1) 
         collect (aref array i j)))) 

列表到2d的多維表單很容易。

(defun list-dimensions (list depth) 
    (loop repeat depth 
     collect (length list) 
     do (setf list (car list)))) 

(defun list-to-array (list depth) 
    (make-array (list-dimensions list depth) 
       :initial-contents list)) 

要列出的數組更復雜。

也許是這樣的：

(defun array-to-list (array) 
    (let* ((dimensions (array-dimensions array)) 
     (depth  (1- (length dimensions))) 
     (indices (make-list (1+ depth) :initial-element 0))) 
    (labels ((recurse (n) 
       (loop for j below (nth n dimensions) 
        do (setf (nth n indices) j) 
        collect (if (= n depth) 
           (apply #'aref array indices) 
           (recurse (1+ n)))))) 
     (recurse 0)))) 

Answer 2

另一個二維數組列出的解決方案：

(defun 2d-array-to-list (array) 
    (map 'list #'identity array)) 

和列表，以二維數組（但也許不是一樣有效，最後回覆的解決方案）：

(defun list-to-2d-array (list) 
    (map 'array #'identity list))