为什么在Common Lisp中将未隔离的符号用于程序包名称和导出? [英] Why are uninterned symbols used for package names and exports in Common Lisp?

问题描述

在常见清单"上的屏幕投射中，作者使用的是未实习生包裹名称和出口的符号.

In a screen cast on Common List the author uses uninterned symbols for package names and exports.

(defpackage #:foo
  (:use :cl)
  (:export #:bar
           #:baz))

(in-package #:foo)

他还在匿名函数前面使用了尖号.

He also uses the sharp sign in front of anonymous functions.

(defun transposed (m)
  (make-instance 'matrix
                 :rows (matrix-cols m)
                 :cols (matrix-rows m)
                 :generator #'(lambda (i j) (matrix-at m j i))))

在 Practical Common Lisp 一书中，尖锐符号不用于包装名称，也不能用于导出据我所读.

In the book Practical Common Lisp the sharp sign isn't used for package names and exports as far as I have read.

在这种情况下使用未使用的符号(尖锐符号)的原因是什么?

What's the reason for using the uninterned symbols (the sharp sign) in these cases?

推荐答案

使用插入符号会反正以仅用于其名称的符号污染您当前所在的包裹:

Using an interned symbol pollutes the package you're currently in with symbols that are only used for their names anyway:

[1]> *package*
#<PACKAGE COMMON-LISP-USER>
[2]> (defpackage bar)
#<PACKAGE BAR>
[3]> (find-symbol "BAR")
BAR ;
:INTERNAL

未互连的符号不能这样做:

Uninterned symbols don't do that:

;; Uninterned symbols don't cause symbol pollution:
[4]> (defpackage #:foo)
#<PACKAGE FOO>
[5]> (find-symbol "FOO")
NIL ;
NIL

您也可以直接使用字符串，但是由于您通常要处理大写的符号名称，因此编写起来不太方便:

You can also use strings directly, but since you're usually dealing with uppercase symbol names, they are less convenient to write:

[6]> (defpackage "BARFOO")
#<PACKAGE BARFOO>
[7]> (find-symbol "BARFOO")
NIL ;
NIL

示例

为说明此问题，请考虑以下交互作用:

Example

To illustrate the problem, consider the following interaction:

[1]> (defpackage hello (:use cl) (:export hello))
#<PACKAGE HELLO>

;; Let's write some FOO stuff...
[2]> (defpackage foo (:use cl))
#<PACKAGE FOO>
[3]> (in-package foo)
#<PACKAGE FOO>

;; Oh, I forgot to import HELLO!
;; Let's fix that.
FOO[4]> (defpackage foo (:use cl hello))
*** - (COMMON-LISP:USE-PACKAGE (#<PACKAGE HELLO> #<PACKAGE COMMON-LISP>)
      #<PACKAGE FOO>): 1 name conflicts remain
      Which symbol with name "HELLO" should be accessible in #<PACKAGE FOO>?

;; Oops.

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