符号的含义

lisp中符号的类型是SYMBOL,一个符号就是这一类型的值.符号和整数其实差不多,只不过一个是数字表示的一个可以用字母表示.

* (type-of 'aaa)

SYMBOL
* 

相同的符号总是EQ的

* (eq 'a 'a)

T

符号绑定

一个符号可以同时绑定到变量 函数 类上,

CL-USER> (find "A" (map 'list #'symbol-name (loop for s being the symbol collect s)) :test #'string=)
NIL
CL-USER> (setf a "ddd")
; in: SETF A
;     (SETF A "ddd")
; ==>
;   (SETQ A "ddd")
; 
; caught WARNING:
;   undefined variable: A
; 
; compilation unit finished
;   Undefined variable:
;     A
;   caught 1 WARNING condition
"ddd"
CL-USER> (find "A" (map 'list #'symbol-name (loop for s being the symbol collect s)) :test #'string=)
"A"
CL-USER> (boundp 'a)
T
CL-USER> (defun a () ())
A
CL-USER> (fboundp 'a)
T
CL-USER> (defclass a () ())
#<STANDARD-CLASS COMMON-LISP-USER::A>
CL-USER> (find-class 'a)
#<STANDARD-CLASS COMMON-LISP-USER::A>

但结构和类不能绑定到同一个符号上

CL-USER> (defstruct a x y)
A
CL-USER> (defclass a () ())
; Evaluation aborted on #<SB-PCL::METAOBJECT-INITIALIZATION-VIOLATION "~@<Cannot ~S~@[ ~S~] objects into ~S metaobjects.~@:>" {1004D44943}>.
CL-USER>