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* The two-argument form of defvar
@ 2015-03-19 11:39 Philipp Stephani
  2015-03-19 15:03 ` Nicolas Richard
  0 siblings, 1 reply; 8+ messages in thread
From: Philipp Stephani @ 2015-03-19 11:39 UTC (permalink / raw)
  To: help-gnu-emacs@gnu.org

Hi,

when looking at the source code of defvar it becomes clear that the
two-argument form

(defvar foo)

is a no-op. It is often used as a signal to the byte compiler that a
certain variable will be available, similar to declare-function. Would it
be possible to clarify the docstring accordingly? Currently it has no
indication that the two-argument form doesn't do anything.


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
  2015-03-19 11:39 The two-argument form of defvar Philipp Stephani
@ 2015-03-19 15:03 ` Nicolas Richard
  2015-03-19 15:52   ` Tassilo Horn
  0 siblings, 1 reply; 8+ messages in thread
From: Nicolas Richard @ 2015-03-19 15:03 UTC (permalink / raw)
  To: Philipp Stephani; +Cc: help-gnu-emacs@gnu.org

Philipp Stephani <p.stephani2@gmail.com> writes:

> Hi,
>
> when looking at the source code of defvar it becomes clear that the
> two-argument form
>
> (defvar foo)
>
> is a no-op.

Not always a no-op. The source code has this comment :
    /* A simple (defvar foo) with lexical scoping does "nothing" except
       declare that var to be dynamically scoped *locally* (i.e. within
       the current file or let-block).  */

To reflect the above comment, the docstring has :
| The `defvar' form also declares the variable as "special",
| so that it is always dynamically bound even if `lexical-binding' is t.

-- 
Nicolas Richard



^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
  2015-03-19 15:03 ` Nicolas Richard
@ 2015-03-19 15:52   ` Tassilo Horn
  2015-04-18  9:25     ` Philipp Stephani
  0 siblings, 1 reply; 8+ messages in thread
From: Tassilo Horn @ 2015-03-19 15:52 UTC (permalink / raw)
  To: Nicolas Richard; +Cc: Philipp Stephani, help-gnu-emacs@gnu.org

Nicolas Richard <theonewiththeevillook@yahoo.fr> writes:

>> when looking at the source code of defvar it becomes clear that the
>> two-argument form
>>
>> (defvar foo)
>>
>> is a no-op.
>
> Not always a no-op. The source code has this comment :
>     /* A simple (defvar foo) with lexical scoping does "nothing" except
>        declare that var to be dynamically scoped *locally* (i.e. within
>        the current file or let-block).  */
>
> To reflect the above comment, the docstring has :
> | The `defvar' form also declares the variable as "special",
> | so that it is always dynamically bound even if `lexical-binding' is t.

But it doesn't *define* anything.

  (defvar xxx1 1) ;; C-h v xxx1 works
  (defvar xxx2)   ;; C-h v xxx2<tab> (No matches)

That behavior is a bit unexpected when the docstring says "Define SYMBOL
as a variable, and return SYMBOL."

Bye,
Tassilo



^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
  2015-03-19 15:52   ` Tassilo Horn
@ 2015-04-18  9:25     ` Philipp Stephani
  2015-04-18 13:27       ` Stefan Monnier
                         ` (2 more replies)
  0 siblings, 3 replies; 8+ messages in thread
From: Philipp Stephani @ 2015-04-18  9:25 UTC (permalink / raw)
  To: Nicolas Richard, help-gnu-emacs@gnu.org

Maybe there should be a declare-variable function to forward-declare
variables, parallel to declare-function.

Tassilo Horn <tsdh@gnu.org> schrieb am Do., 19. März 2015 um 16:52 Uhr:

> Nicolas Richard <theonewiththeevillook@yahoo.fr> writes:
>
> >> when looking at the source code of defvar it becomes clear that the
> >> two-argument form
> >>
> >> (defvar foo)
> >>
> >> is a no-op.
> >
> > Not always a no-op. The source code has this comment :
> >     /* A simple (defvar foo) with lexical scoping does "nothing" except
> >        declare that var to be dynamically scoped *locally* (i.e. within
> >        the current file or let-block).  */
> >
> > To reflect the above comment, the docstring has :
> > | The `defvar' form also declares the variable as "special",
> > | so that it is always dynamically bound even if `lexical-binding' is t.
>
> But it doesn't *define* anything.
>
>   (defvar xxx1 1) ;; C-h v xxx1 works
>   (defvar xxx2)   ;; C-h v xxx2<tab> (No matches)
>
> That behavior is a bit unexpected when the docstring says "Define SYMBOL
> as a variable, and return SYMBOL."
>
> Bye,
> Tassilo
>


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
  2015-04-18  9:25     ` Philipp Stephani
@ 2015-04-18 13:27       ` Stefan Monnier
  2015-04-18 14:14       ` Drew Adams
       [not found]       ` <mailman.1013.1429363810.904.help-gnu-emacs@gnu.org>
  2 siblings, 0 replies; 8+ messages in thread
From: Stefan Monnier @ 2015-04-18 13:27 UTC (permalink / raw)
  To: help-gnu-emacs

>> (defvar xxx2)   ;; C-h v xxx2<tab> (No matches)

What kind of info would you expect to get from C-h v xxx2 RET?
All Emacs knows about it at that point is that you intend to use it.
So C-h v wouldn't be able to tell you anything interesting about it.


        Stefan




^ permalink raw reply	[flat|nested] 8+ messages in thread

* RE: The two-argument form of defvar
  2015-04-18  9:25     ` Philipp Stephani
  2015-04-18 13:27       ` Stefan Monnier
@ 2015-04-18 14:14       ` Drew Adams
  2015-04-18 16:50         ` Philipp Stephani
       [not found]       ` <mailman.1013.1429363810.904.help-gnu-emacs@gnu.org>
  2 siblings, 1 reply; 8+ messages in thread
From: Drew Adams @ 2015-04-18 14:14 UTC (permalink / raw)
  To: Philipp Stephani, Nicolas Richard, help-gnu-emacs

(FWIW, this thread is about the one-argument form of defvar,
not a two-argument form.)



^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
  2015-04-18 14:14       ` Drew Adams
@ 2015-04-18 16:50         ` Philipp Stephani
  0 siblings, 0 replies; 8+ messages in thread
From: Philipp Stephani @ 2015-04-18 16:50 UTC (permalink / raw)
  To: Drew Adams, Nicolas Richard, help-gnu-emacs

Drew Adams <drew.adams@oracle.com> schrieb am Sa., 18. Apr. 2015 um
16:14 Uhr:

> (FWIW, this thread is about the one-argument form of defvar,
> not a two-argument form.)
>

I intended it to be about the one-argument form, but got the subject wrong.
Probably a habit from other programming languages where the number of
identifiers between ( and ) is the number of arguments.


^ permalink raw reply	[flat|nested] 8+ messages in thread

* Re: The two-argument form of defvar
       [not found]       ` <mailman.1013.1429363810.904.help-gnu-emacs@gnu.org>
@ 2015-04-19 21:48         ` Emanuel Berg
  0 siblings, 0 replies; 8+ messages in thread
From: Emanuel Berg @ 2015-04-19 21:48 UTC (permalink / raw)
  To: help-gnu-emacs

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> (defvar xxx2) ;; C-h v xxx2<tab> (No matches)
>
> What kind of info would you expect to get from C-h
> v xxx2 RET? All Emacs knows about it at that point
> is that you intend to use it. So C-h v wouldn't be
> able to tell you anything interesting about it.

It could say precisely that - no value, not documented,
only the intention: to use it. It doesn't, and I don't
suggest it should, but it isn't an obviously wrong
thing to do.

-- 
underground experts united
http://user.it.uu.se/~embe8573


^ permalink raw reply	[flat|nested] 8+ messages in thread

end of thread, other threads:[~2015-04-19 21:48 UTC | newest]

Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2015-03-19 11:39 The two-argument form of defvar Philipp Stephani
2015-03-19 15:03 ` Nicolas Richard
2015-03-19 15:52   ` Tassilo Horn
2015-04-18  9:25     ` Philipp Stephani
2015-04-18 13:27       ` Stefan Monnier
2015-04-18 14:14       ` Drew Adams
2015-04-18 16:50         ` Philipp Stephani
     [not found]       ` <mailman.1013.1429363810.904.help-gnu-emacs@gnu.org>
2015-04-19 21:48         ` Emanuel Berg

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