Elisp Variables

请大家认真看Elisp官方手册。

notes

ielm: elisp交互shell

example

;; global variables
;; 整个系统都能访问
;; C-h v 访问
(setq x '(a b))

;; variables never change
nil
t

;; local variables
;; let* local variables互相可以引用
(let* ((y 1)
       (z y)) 
  (list y z))
     ⇒ (1 1)

;; void variable
;; dynamic scoping
;; boundp: 测试当前变量在环境下有无值
(boundp 'abracadabra)          ; Still globally void.
     ⇒ nil
(setq abracadabra 5)           ; Make it globally nonvoid.
     ⇒ 5
(boundp 'abracadabra)
     ⇒ t

;; define global variables
;; defvar or defconst
;; 提供初始值、文档
;; C-h v
(defvar bar 23
  "The normal weight of a bar.")
     ⇒ bar

(defconst float-pi 3.141592653589793 "The value of Pi.")
     ⇒ float-pi

;; 定义一个复杂对象，实践
(defvar my-mode-map
  (let ((map (make-sparse-keymap)))
    (define-key map "\C-c\C-a" 'my-command)
    …
    map)
  docstring)

;; 访问变量
;; When a symbol is evaluated, it is treated as a variable. 
(setq x 1)
(symbol-value 'x)
(eval 'x)
(+ x 1) ; =>2

;; set value
;; setq
(setq x (1+ 2))
     ⇒ 3

(let ((x 5))
  (setq x 6)        ; The local binding of x is set.
  x)
     ⇒ 6     

(setq x 10          ; Notice that x is set before
      y (1+ x))     ;   the value of y is computed.
     ⇒ 11

;; set 比较绕，先不考虑

Buffer Local Variables

make-local-variable声明variable为local buffer variable。 之后在当前buffer里面怎么艹都和全局没关联了。

note：接在define-minor-mode定义中不错。

;; In buffer ‘b1’:
(setq foo 5)                ; Affects all buffers.
     ⇒ 5
(make-local-variable 'foo)  ; Now it is local in ‘b1’.
     ⇒ foo
foo                         ; That did not change
     ⇒ 5                   ;   the value.
(setq foo 6)                ; Change the value
     ⇒ 6                   ;   in ‘b1’.
foo
     ⇒ 6
;; In buffer ‘b2’, the value hasn’t changed.
(with-current-buffer "b2"
  foo)
     ⇒ 5

make-variable-buffer-local var让所有buffer内的var都成为buffer local。 warning：这个功能慎用，太猛了，容易误伤。