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

解決方案

Originally, in Lisp, there were no lexical variables -- only dynamic ones. And

there was no SETQ or SETF, just the SET function.

What is now written as:

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

was written as:

(set (quote *foo*) 42)

which was eventually abbreviavated to SETQ (SET Quoted):

(setq *foo* 42)

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.

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;

would be written as

(setf (car x) 42)

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.

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)

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.

總結

以上是生活随笔為你收集整理的setq 常驻内存lisp_常见Lisp中的set，setq和setf之间的区别？的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。