计算字符串中单词个数的函数word-count

wc.lisp

(defun same-kind-chars (c1 c2)
  (or (and (alpha-char-p c1)
	   (alpha-char-p c2))
      (and (not (alpha-char-p c1))
	   (not (alpha-char-p c2)))))

(defun singleton-list (list)
  (and list (null (cdr list))))

;;; 普通递归版本
(defun word-count (str)
  (labels ((aux (s)
	     (cond ((null s) 0)
		   ((and (singleton-list s)
			 (not (alpha-char-p (car s)))) 0)
		   ((and (singleton-list s)
			 (alpha-char-p (car s))) 1)
		   (t (+ (aux (cdr s))
			 (if (and (not (same-kind-char (car s) (cadr s)))
				  (char/= (car s) #\Space))
			     1 0))))))
    (aux (coerce str 'list))))

;;; 尾递归版本
(defun word-count (str)
  (labels ((aux (cnt s)
	     (cond ((null s) cnt)
		   ((and (singleton-list s)
			 (not (alpha-char-p (car s)))) cnt)
		   ((and (singleton-list s)
			 (alpha-char-p (car s))) (1+ cnt))
		   (t (aux (+ cnt
			      (if (and (not (same-kind-char (car s) (cadr s)))
				       (char/= (car s) #\Space))
				  1 0))
			   (cdr s))))))
    (aux 0 (coerce str 'list))))