Question

在Common Lisp代码中插入长多字符变量或常量的惯用方法是什么？在unix shell或其他语言中是否有类似HEREDOC的东西，以消除字符串文字中的缩进空格？

例如：

(defconstant +help-message+ 
             "Blah blah blah blah blah
              blah blah blah blah blah
              some more more text here")
; ^^^^^^^^^^^ this spaces will appear - not good

写这种方式有点难看：

(defconstant +help-message+ 
             "Blah blah blah blah blah
blah blah blah blah blah
some more more text here")

我们应该如何写它。如果有任何办法，当你不需要逃避报价时，它会更好。

Answer 1

我不知道惯用语，但format可以为你做这件事。（当然。format可以做任何事情。）

参见Hyperspec第22.3.9.3节，Tilde换行符。未修饰，它删除换行符和后续空格。如果要保留换行符，请使用@修饰符：

(defconstant +help-message+
   (format nil "Blah blah blah blah blah~@
                blah blah blah blah blah~@
                some more more text here"))

CL-USER> +help-message+
"Blah blah blah blah blah
blah blah blah blah blah
some more more text here"

Answer 2

没有这样的事情。

缩进通常是：

(defconstant +help-message+ 
  "Blah blah blah blah blah
blah blah blah blah blah
some more more text here")

也许使用阅读器宏或阅读时间评估。草图：

(defun remove-3-chars (string)
  (with-output-to-string (o)
    (with-input-from-string (s string)
      (write-line (read-line s nil nil) o)
      (loop for line = (read-line s nil nil)
            while line
            do (write-line (subseq line 3) o)))))

(defconstant +help-message+
  #.(remove-3-chars
  "Blah blah blah blah blah
   blah blah blah blah blah
   some more more text here"))

CL-USER 18 > +help-message+
"Blah blah blah blah blah
blah blah blah blah blah
some more more text here
"

需要更多抛光......你可以使用＆＃39; string-trim＆＃39;或类似的。

Answer 3

我有时会使用这种形式：

(concatenate 'string "Blah blah blah"
                     "Blah blah blah"
                     "Blah blah blah"
                     "Blah blah blah")

在Lisp代码中使用长多字符串常量（或变量）的惯用方法

3 个答案: