From: Alan Mackenzie <acm@muc.de>
To: Stefan Monnier <monnier@iro.umontreal.ca>
Cc: emacs-devel@gnu.org
Subject: Re: Can't M-x compile-defun `edebug' because dynamic variables are falsely taken as lexical.
Date: Wed, 4 Jan 2017 20:04:58 +0000 [thread overview]
Message-ID: <20170104200458.GA2052@acm.fritz.box> (raw)
In-Reply-To: <jwv1swi6elk.fsf-monnier+gmane.emacs.devel@gnu.org>
Hello, Stefan
On Wed, Jan 04, 2017 at 10:23:16AM -0500, Stefan Monnier wrote:
> > Ouch! There seems to be a clash between symbols (which are global,
> > dynamic) and lexical variables (which are local and "invisible"): the
> > only way to mark a variable as lexical is at the global level.
> Yes, there are some subtleties there. The main issue is that every
> occurrence of an identifier, whether a binding occurrence or a "use" can
> be lexical or dynamic, but we don't want the coders to have to
> constantly specify which uses and which bindings are lexical and which
> are dynamic. So we offer ways to "mark" symbols are "this one uses
> dynamic scoping". There are 2 such ways:
> - *Evaluation* of (defvar VAR VAL . REST) marks this variable as being
> dynamically scoped in all the code that will be compiled in this session.
> - *Compilation* of (defvar VAR . REST) marks this variable as being
> dynamically scoped in the current compilation unit.
> > (vi) e (special-variable-p 'edebug-breakpoints).
> > This last returns nil. This suggests edebug-breakpoints has been bound
> > as a lexical variable, rather than a dynamic one. (There is a defvar
> > for it earlier in the file.) This is surely not right.
> special-variable-p only indicates if (defvar VAR VAL . REST) was evaluated.
So it would seem. There is a bug in the elisp manual, which says that a
variable being declared by defvar will cause special-variable-p to
return t for it. The doc string looks right, though far from helpful
for anybody who doesn't already know variable binding inside out, and
even a bit cryptic for those who do.
special-variable-p would appear to be a near useless function, since it
doesn't do what it's name says.
"Defining Variables" in the elisp manual states that "(defvar foo)" makes
foo a special variable; yet "(special-variable-p 'foo)" returns nil. This
has got to be a bug, of some sort.
There appears to be no way of checking whether a variable's binding is
(or will be) lexical.
I can foresee quite a bit of confusion happening over all this, if it
hasn't happened already.
Am I missing something, or is this all really as incoherent as it
appears to me?
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).
next prev parent reply other threads:[~2017-01-04 20:04 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-03 14:14 Can't M-x compile-defun `edebug' because dynamic variables are falsely taken as lexical Alan Mackenzie
2017-01-03 18:35 ` Stefan Monnier
2017-01-03 21:32 ` Alan Mackenzie
2017-01-03 21:48 ` Stefan Monnier
2017-01-04 13:39 ` Alan Mackenzie
2017-01-04 15:23 ` Stefan Monnier
2017-01-04 20:04 ` Alan Mackenzie [this message]
2017-01-04 21:49 ` Stefan Monnier
2017-01-04 22:02 ` Alan Mackenzie
2017-01-04 22:26 ` Stefan Monnier
2017-01-04 22:44 ` Drew Adams
2017-01-05 10:54 ` Alan Mackenzie
2020-02-13 16:42 ` Drew Adams
2020-02-13 20:02 ` Stefan Monnier
2020-02-13 20:43 ` Drew Adams
2020-02-13 22:09 ` Stefan Monnier
2020-02-14 1:07 ` Drew Adams
2020-02-14 2:24 ` Stefan Monnier
2020-02-14 17:25 ` Drew Adams
2020-02-14 19:19 ` Stefan Monnier
2020-02-17 18:23 ` Drew Adams
2020-02-13 22:11 ` Stefan Monnier
2020-02-14 1:13 ` Drew Adams
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