GNU bug report logs - #5371
Priority of different kind of local variable bindings

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Lennart Borgman <lennart.borgman <at> gmail.com>
To: emacs-pretest-bug <at> gnu.org
Subject: Priority of different kind of local variable bindings
Date: Wed, 13 Jan 2010 10:20:12 +0100

I can't find a description in the manual of the priority of different
kind of local variables. Can that please be added to the manual?

Message #8 received at 5371 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Lennart Borgman <lennart.borgman <at> gmail.com>
Cc: 5371 <at> debbugs.gnu.org
Subject: Re: bug#5371: Priority of different kind of local variable bindings
Date: Wed, 13 Jan 2010 09:41:01 -0500

> I can't find a description in the manual of the priority of different
> kind of local variables.  Can that please be added to the manual?

What do you mean by "priority of different kind of local variables"?


        Stefan

Message #11 received at 5371 <at> debbugs.gnu.org (full text, mbox):

From: Lennart Borgman <lennart.borgman <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 5371 <at> debbugs.gnu.org
Subject: Re: bug#5371: Priority of different kind of local variable bindings
Date: Wed, 13 Jan 2010 16:50:25 +0100

On Wed, Jan 13, 2010 at 3:41 PM, Stefan Monnier
<monnier <at> iro.umontreal.ca> wrote:
>> I can't find a description in the manual of the priority of different
>> kind of local variables.  Can that please be added to the manual?
>
> What do you mean by "priority of different kind of local variables"?


I just meant which value is active at a certain point.

I saw a strange thing working with mumamo and the js.el problem, but I
have not understod yet. I have kind of solved it, but I don't know
why. Here is some code that perhaps is related. Look at the value at
"ff". Is not that a bit surprising?

(defun temp-var-display (where)
  (message "%s temp-var: u=%s, b=%s d=%s" where
           temp-var
           (buffer-local-value 'temp-var (current-buffer))
           (default-value 'temp-var)))

(defvar temp-var "global")

(set (make-local-variable 'temp-var) "buffer-1")
(temp-var-display "bb")

(with-temp-buffer
  (set (make-local-variable 'temp-var) "buffer-2")
  (temp-var-display "cc")

  (let ((temp-var "let"))
    (temp-var-display "dd")

    (kill-local-variable 'temp-var)
    (temp-var-display "ff"))

  (temp-var-display "gg"))

(temp-var-display "hh")

(kill-local-variable 'temp-var)
(temp-var-display "ii")

bb temp-var: u=buffer-1, b=buffer-1 d=global
cc temp-var: u=buffer-2, b=buffer-2 d=global
dd temp-var: u=let, b=let d=global
ff temp-var: u=global, b=global d=global
gg temp-var: u=global, b=global d=global
hh temp-var: u=buffer-1, b=buffer-1 d=global
ii temp-var: u=global, b=global d=global

Message #14 received at 5371 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Lennart Borgman <lennart.borgman <at> gmail.com>
Cc: 5371 <at> debbugs.gnu.org
Subject: Re: bug#5371: Priority of different kind of local variable bindings
Date: Wed, 13 Jan 2010 13:45:47 -0500

>> What do you mean by "priority of different kind of local variables"?
> I just meant which value is active at a certain point.

It's not based on priorities.

> (with-temp-buffer
>   (set (make-local-variable 'temp-var) "buffer-2")
>   (temp-var-display "cc")

>   (let ((temp-var "let"))
>     (temp-var-display "dd")

>     (kill-local-variable 'temp-var)
>     (temp-var-display "ff"))

The `let' binding affects the currently "active" slot, so in this case
it affects the buffer-local slot.  So after kill-local-variable, this
binding is lost.

Note that mixing let-binding and buffer-local bindings is generally
discouraged.  The only known reasonably sane semantics for such a mix is
when the variable is always buffer-local.  If you mix `let' with
make-local-variable and kill-local-variable you're really asking
for trouble.


        Stefan

Message #17 received at 5371 <at> debbugs.gnu.org (full text, mbox):

From: Lennart Borgman <lennart.borgman <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 5371 <at> debbugs.gnu.org
Subject: Re: bug#5371: Priority of different kind of local variable bindings
Date: Wed, 13 Jan 2010 19:50:11 +0100

On Wed, Jan 13, 2010 at 7:45 PM, Stefan Monnier
<monnier <at> iro.umontreal.ca> wrote:
>>> What do you mean by "priority of different kind of local variables"?
>> I just meant which value is active at a certain point.
>
> It's not based on priorities.
>
>> (with-temp-buffer
>>   (set (make-local-variable 'temp-var) "buffer-2")
>>   (temp-var-display "cc")
>
>>   (let ((temp-var "let"))
>>     (temp-var-display "dd")
>
>>     (kill-local-variable 'temp-var)
>>     (temp-var-display "ff"))
>
> The `let' binding affects the currently "active" slot, so in this case
> it affects the buffer-local slot.  So after kill-local-variable, this
> binding is lost.


Ok, I see.


> Note that mixing let-binding and buffer-local bindings is generally
> discouraged.  The only known reasonably sane semantics for such a mix is
> when the variable is always buffer-local.  If you mix `let' with
> make-local-variable and kill-local-variable you're really asking
> for trouble.


I know ;-)

Is this explained somewhere (except for the code)?

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