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Re: How to use a symbol and its value to create alist?
From: |
Pascal J. Bourguignon |
Subject: |
Re: How to use a symbol and its value to create alist? |
Date: |
Wed, 12 Aug 2015 04:12:47 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) |
Navy Cheng <navych@126.com> writes:
> On Tue, Aug 11, 2015 at 08:21:53AM -0700, Ian Zimmerman wrote:
>> On 2015-08-11 21:52 +0800, Navy Cheng wrote:
>>
>> > (setq a 1)
>> > (setq b 2)
>> > (setq c 3)
>> >
>> > How can I a alist, like:
>> > ((a . 1) (b . 2) (c .3))
>> >
>> > The value of a, b and c may change, so don't do this like
>> > (setq tree ((a . 1) (b . 2) (c .3)))
>>
>> That's a strange question. Why would you want such a list, how would
>> it be useful? To look up the value a a symbol, you just use it, for
>> example:
>
> I need to push some global variable to a "stack" and pop them later. If
> I don't do like this, the global variables will be changed by program
(defvar a 1)
(defvar b 2)
(defvar cc 3)
(defun do-something ()
(print (list 'before a b cc))
(setf a 0 b 0 cc 0)
(print (list 'after a b cc)))
(progn
(let ((a a)
(b b)
(cc cc))
(do-something))
(list 'finally a b cc))
prints:
(before 1 2 3)
(after 0 0 0)
--> (finally 1 2 3)
--
__Pascal Bourguignon__ http://www.informatimago.com/
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