符号表达式流 I/O

Question

在 Common Lisp 中，如何读写符号表达式 from/to 流？例如，我可能想将一个匿名函数写入文件，然后读取并调用它：

;;; sexp-io.lisp
;;; Try writing a sexp to file and reading it back in

(with-open-file (file "~/Documents/Lisp/Concurrency/sexp.lisp"
                  :direction :output :if-exists :supersede)
  (print #'(lambda () (+ 1 1)) file))

(with-open-file (file "~/Documents/Lisp/Concurrency/sexp.lisp"
                  :direction :input)
  (read file))

但是，该代码会导致可疑输出

 #<Anonymous Function #x3020018F950F>

当我尝试读回它时确实会导致错误：

> Error: Reader error on #<BASIC-FILE-CHARACTER-INPUT-STREAM ("/Users/frank/Documents/Lisp/Concurrency/sexp.lisp"/7 UTF-8) #x3020018F559D>, near position 3, within "
>        #<Anonymous ":
>        "#<" encountered.
> While executing: CCL::SIGNAL-READER-ERROR, in process Listener(4).

Answer 1

您正在做 TRT, except for #' which turns the list (lambda () (+ 1 1)) into a function object. Just replace the sharp-quote (which is read as function) with a simple quote (which is read as quote)，应该可以。

您可能想要进行的另一项更改是将 print with write 替换为参数 :readably t:

(write my-object :stream out :readably t)

:readably 的好处是，如果它不能以保持打印-读取一致性的方式写入，它就会失败。

符号表达式流 I/O

symbolic expression stream I/O

lisp

common-lisp

s-expression