常见Lisp中的set，setq和setf之间的区别？ [英] Difference between `set`, `setq`, and `setf` in Common Lisp?

问题描述

Common Lisp中 set， setq和 setf之间有什么区别？

What is the difference between "set", "setq", and "setf" in Common Lisp?

推荐答案

在Lisp中，没有词法变量-只有动态变量。
没有SETQ或SETF，只有SET函数。

Originally, in Lisp, there were no lexical variables -- only dynamic ones. And there was no SETQ or SETF, just the SET function.

现在写成：

(setf (symbol-value '*foo*) 42)

的写法是：

(set (quote *foo*) 42)

最终缩写为SETQ（用SET引用）：

which was eventually abbreviavated to SETQ (SET Quoted):

(setq *foo* 42)

然后出现了词法变量，SETQ出现了

Then lexical variables happened, and SETQ came to be used for assignment to them too -- so it was no longer a simple wrapper around SET.

后来，有人发明了SETF（SET字段）作为通用方法为数据结构分配值，以反映其他语言的l值：

Later, someone invented SETF (SET Field) as a generic way of assigning values to data structures, to mirror the l-values of other languages:

x.car := 42;

将写为

(setf (car x) 42)

对于对称性和通用性，SETF还提供了SETQ的功能。在这一点上，说SETQ是一个低级原语，而SETF是一个高级操作，是正确的。

For symmetry and generality, SETF also provided the functionality of SETQ. At this point it would have been correct to say that SETQ was a Low-level primitive, and SETF a high-level operation.

然后发生了符号宏。为了使符号宏能够透明地工作，人们意识到，如果分配给变量的确是符号宏，则SETQ必须像SETF一样工作：

Then symbol macros happened. So that symbol macros could work transparently, it was realized that SETQ would have to act like SETF if the "variable" being assigned to was really a symbol macro:

(defvar *hidden* (cons 42 42))
(define-symbol-macro foo (car *hidden*))

foo => 42

(setq foo 13)

foo => 13

*hidden* => (13 . 42)

所以我们到了今天：SET和SETQ是萎缩的残骸的方言，并且很可能会从Common Lisp的最终继承者那里引来。

So we arrive in the present day: SET and SETQ are atrophied remains of older dialects, and will probably be booted from eventual successors of Common Lisp.

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