lisp - 宣布，宣布，宣布

Question

能否解释一下proclaim、declaim和declare这三个符号的区别？

Answer 1

它们是 symbols , 不是 keywords .

1. proclaim命名为function使全局化 declarations .你应该使用 declaim而是尽可能。

2. declaim命名为macro使全局化 declarations (如 proclaim )在编译时也有效。

3. declare只是一个symbol (即，它没有命名 function 、 macro 或 special operator )用于制作 local declarations在一些形式的开头(您可以将其视为这些形式的语法的一个元素)。

因此，前两个影响 global environment最后一个是local .

declaim优于 proclaim因为它在 compilation environment 中立即生效:

Although the execution of a proclaim form has effects that might affect compilation, the compiler does not make any attempt to recognize and specially process proclaim forms. A proclamation such as the following, even if a top level form, does not have any effect until it is executed:

(proclaim '(special *x*))

If compile time side effects are desired, eval-when may be useful. For example:

(eval-when (:execute :compile-toplevel :load-toplevel)
(proclaim '(special *x*)))

In most such cases, however, it is preferrable to use declaim for this purpose.

即，如果您的代码是

(proclaim '(special *x*))
(defun foo () (print *x*))

编译器会提示foo读取了一个未知的特殊变量*x*，而

(declaim (special *x*))
(defun foo () (print *x*))

不会引起警告。

附言。如果你想知道为什么 CL 甚至有 proclaim : 首先，历史上它在那之前 declaim ，和，第二，proclaim在宏中更简单、更有用。