From: "Aurélien Aptel" <aurelien.aptel+emacs@gmail.com>
To: Emanuel Berg <embe8573@student.uu.se>
Cc: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
Subject: Re: Lexical and Dynamic Scope
Date: Thu, 24 Jul 2014 10:50:35 +0200 [thread overview]
Message-ID: <CA+5B0FPo63V8jrGwFhMasC9DM=rNO0c0Jd_5wsdjB-gUJxFWBQ@mail.gmail.com> (raw)
In-Reply-To: <87ha2bstgt.fsf@debian.uxu>
On Sun, Jul 20, 2014 at 9:47 PM, Emanuel Berg <embe8573@student.uu.se> wrote:
> But: is the stack of names global? Howcome all the Lisp
> don't get crazy from other Lisp changing "its"
> variables? But come to think of it, I very seldom use
> variables - I use `let's, and perhaps that is both a
> shield from interference and doesn't change the global
> name stack?
In dynamic scoping, each time you nest a let binding to same symbol
you add to this variable stack. When you take the value of a symbol
the value comes from the top of the stack of this symbol.
(defvar a 1)
(defun my-a ()
"Return current value of a (top top the stack)"
a)
(my-a)
=> 1
(let ((a 2)) ;; push 2 in the `a' stack
;; we usually say: a is shadowed in this scope
(my-a))
=> 2
;; at the end of let scope, 2 is popped from the stack
(my-a)
=> 1
(list
(my-a)
(let ((a 2))
(my-a))
(let ((a 3))
(let ((a 4))
(my-a)))
(my-a))
=> (1 2 4 1)
next prev parent reply other threads:[~2014-07-24 8:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.5712.1405800439.1147.help-gnu-emacs@gnu.org>
2014-07-20 19:47 ` Lexical and Dynamic Scope Emanuel Berg
2014-07-24 8:50 ` Aurélien Aptel [this message]
[not found] ` <mailman.5948.1406191841.1147.help-gnu-emacs@gnu.org>
2014-07-24 22:16 ` Emanuel Berg
2014-07-24 22:28 ` Stefan Monnier
[not found] ` <mailman.5974.1406240948.1147.help-gnu-emacs@gnu.org>
2014-07-24 22:44 ` Emanuel Berg
2014-07-19 18:12 run-with-timer does not display message Stefan Monnier
2014-07-19 20:06 ` Lexical and Dynamic Scope Robert Thorpe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CA+5B0FPo63V8jrGwFhMasC9DM=rNO0c0Jd_5wsdjB-gUJxFWBQ@mail.gmail.com' \
--to=aurelien.aptel+emacs@gmail.com \
--cc=embe8573@student.uu.se \
--cc=help-gnu-emacs@gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.