常见的 lisp：如何抑制换行符或 "soft return"

Question

这个代码

 (defun arabic_to_roman (filename)
     (let ((arab_roman_dp '())
           (arab nil)
           (roman nil))

       (with-open-file (in filename
                           :direction :input
                           :if-does-not-exist nil)

         (when in
           (loop for line = (read-line in nil)
              while line do
                (setq arab (subseq line 0 (search "=" line)))
                (setq roman (subseq line (1+ (search "=" line)) (length line)))
                (setf arab_roman_dp (acons arab roman arab_roman_dp))
                                           ;(format t "~S ~S~%" arab roman)
                )))

       (with-open-file (stream #p"ar_out.txt"
                               :direction :output
                               :if-exists :overwrite
                               :if-does-not-exist :create )
         (write arab_roman_dp :stream stream :escape nil :readably nil))
       'done!))

似乎效果不错。它需要一个包含这样条目的文件

1=I
2=II
...

并构建一大堆点对。但是，当我查看输出文件时，似乎插入了软 returns 或换行符。

((4999 . MMMMCMXCIX) (4998 . MMMMCMXCVIII) (4997 . MMMMCMXCVII)
 (4996 . MMMMCMXCVI) (4995 . MMMMCMXCV) (4994 . MMMMCMXCIV)
 (4993 . MMMMCMXCIII) (4992 . MMMMCMXCII) (4991 . MMMMCMXCI) (4990 . MMMMCMXC)
...

我希望输出看起来更像是一条连续的线：

((4999 . MMMMCMXCIX) (4998 . MMMMCMXCVIII) (4997 . MMMMCMXCVII) (4996 .  MMMCMXCVI) (4995 . MMMMCMXCV) (4994 . MMMMCMXCIV) (4993 . MMMMCMXCIII) (4992 . MMMMCMXCII) (4991 . MMMMCMXCI) (4990 . MMMMCMXC) ...

我的代码确实以某种方式插入换行符吗？我使用了 princ 的 write 版本，据说可以抑制换行。后来我想把这个文件作为一个大列表读回程序，所以我不想要换行问题。

Answer 1

看起来漂亮打印机正在被调用（默认是依赖于实现的），以缩进和人类可读的行长打印它。使用 :pretty nil 禁用此功能。

(write arab_roman_dp :stream stream :escape nil :readably nil :pretty nil)

Answer 2

更好的写法：

使用函数创建可以组合的代码块
更少的副作用和更少的变量
无需测试 in
易于理解的控制流程

示例：

(defun arabic_to_roman (filename)
  (flet ((read-it ()
           (with-open-file (in filename
                               :direction :input
                               :if-does-not-exist nil)
             (loop for line = (read-line in nil)
                   for pos = (position #\= line)
                   while line collect (cons (subseq line 0 pos)
                                            (subseq line (1+ pos))))))
         (write-it (list)
           (with-open-file (stream #p"ar_out.txt"
                                   :direction :output
                                   :if-exists :overwrite
                                   :if-does-not-exist :create)
             (write list :stream stream :escape nil :readably nil :pretty nil))))
    (write-it (read-it))
    'done-read-write))

常见的 lisp：如何抑制换行符或 "soft return"

common lisp: how to suppress newline or "soft return"

common-lisp