macros - 初始内容由函数确定的数组

Question

我正在尝试创建一个多维数组，其初始内容由一个函数确定。对于数组的任何指定维数，这很容易做到。

例如 2x2 数组:

(defmacro array-generation (fun &rest size-dimensions)
 (let ((a (gensym)) 
       (b (gensym))) 
    `(make-array ',size-dimensions
       :initial-contents 
          (loop for ,a from 0 below (first ',size-dimensions) by 1           
       collect 
          (loop for ,b from 0 below (second ',size-dimensions) by 1
       collect (,fun  ,a ,b))))))

(defparameter bla (array-generation + 2 3))

给我 #2A((0 1 2) (1 2 3)).

我如何概括任何维度的宏？例如对于 2x3x5x6x7x8

(defparameter bla (array-generation + 2 3 5 6 7 8))

Answer 1

(defmacro array-generation (fun &rest dims)
  (let ((syms (loop :repeat (length dims) :collect (gensym))))
    (reduce (lambda (x y) (append x (list y)))
            (mapcar (lambda (sym dim)
                      `(loop for ,sym from 0 below ,dim by 1 collect))
                    syms dims)
            :initial-value (cons fun syms)
            :from-end t)))