Common Lisp 将数字映射到单词

在 Common Lisp 中，我们可以通过字符串函数和循环语句的结合，将数字映射到单词。

(defun num-to-word (num)
  "将数字映射到单词"
  (let* ((digits-alist '((1 . "one") (2 . "two") (3 . "three") (4 . "four") (5 . "five") (6 . "six") (7 . "seven") (8 . "eight") (9 . "nine")))
         (tens-alist '((10 . "ten") (20 . "twenty") (30 . "thirty") (40 . "forty") (50 . "fifty") (60 . "sixty") (70 . "seventy") (80 . "eighty") (90 . "ninety")))
         (teen-alist '((11 . "eleven") (12 . "twelve") (13 . "thirteen") (14 . "fourteen") (15 . "fifteen") (16 . "sixteen") (17 . "seventeen") (18 . "eighteen") (19 . "nineteen"))))
    (cond
      ((or (null num) (zerop num)) "zero")
      ((< num 0) (concat "negative " (num-to-word (- num))))
      ((< num 10) (cdr (assoc num digits-alist)))
      ((< num 20) (cdr (assoc num teen-alist)))
      ((< num 100) (let ((tens (* 10 (floor num 10))) (ones (mod num 10)))
                     (concat (cdr (assoc tens tens-alist))
                             (if (zerop ones) "" (concat "-" (num-to-word ones))))))
      ((< num 1000) (let ((hundreds (floor num 100)) (tens (mod num 100)))
                      (concat (num-to-word hundreds) " hundred"
                              (if (zerop tens) "" (concat " " (num-to-word tens))))))
      (t "too big for me"))))

上面这个函数可以将数字映射成英文单词，以便更好地阅读和显示。

我们可以在 REPL 中测试这个函数：

(num-to-word 1234)
; => "too big for me"

(num-to-word 15)
; => "fifteen"

(num-to-word -42)
; => "negative forty-two"

以上就是一个将数字映射到英文字母的 Common Lisp 函数的实现。