formatting - 如何使用格式指令生成列表索引

Question

有没有办法获得与此相同的输出:
(手牌是一张牌列表)

(loop for card in hand
           with i = 1
           do
             (format t "~&~a. ~a~%" i card)
             (incf i))

1. (5 . HEARTS)
2. (5 . CLUBS)
3. (10 . DIAMONDS)
4. (JACK . DIAMONDS)
5. (8 . CLUBS)

但只使用一次调用格式化？到目前为止我有这个，但我不知道如何增加索引。

(format nil "~{~%1. ~a~}~%" hand)

1. (5 . HEARTS)
1. (5 . CLUBS)
1. (10 . DIAMONDS)
1. (JACK . DIAMONDS)
1. (8 . CLUBS)

我还尝试在 Call Function 指令旁边使用闭包，但是您必须为每次调用重置计数器，而且感觉非常笨拙。

(let ((counter 0))
  (defun increment (output-stream format-argument colonp at-sign-p &rest directive-parameters)
    (declare (ignore colonp at-sign-p directive-parameters))
    (incf counter)
    (format output-stream "~a. ~a" counter format-argument))
  (defun reset-counter ()
    (setf counter 0)))

(format t "~&~{~&~/increment/~}" '(a c b d))

1. A
2. C
3. B
4. D

Answer 1

你的循环形式:

(loop for card in hand
           with i = 1
           do
             (format t "~&~a. ~a~%" i card)
             (incf i))

人们通常会这样写:

(loop for card in hand and i from 1
      do (format t "~&~a. ~a~%" i card))

简单处理该问题的一种方法是提供一个带有数字的列表:

(defun numbering (list &key (i0 1))
  (loop for i from i0 and element in list
        collect i collect element))

CL-USER > (format t "~{~%~a. ~a~}~%" (numbering hand))

1. (5 . HEARTS)
2. (5 . CLUBS)
3. (10 . DIAMONDS)
4. (JACK . DIAMONDS)
5. (8 . CLUBS)
NIL