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Re: [O] Typo in 'org-without-partial-completion'

From: David Maus
Subject: Re: [O] Typo in 'org-without-partial-completion'
Date: Thu, 30 Jun 2011 21:28:08 +0200
User-agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (Gojō) APEL/10.8 Emacs/23.2 (i486-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO)

At Thu, 30 Jun 2011 11:12:15 +0200,
Bastien wrote:
> Hi Paul,
> Paul Sexton <address@hidden> writes:
> > I think there's an error in 'org-without-partial-completion' in org-macs.el.
> > The variable pc-mode gets bound to the value of partial-completion-mode - 
> > but 
> > this is a VARIABLE (t if that mode is enabled). Funcalling the value of 
> > the variable produces an error, unsurprisingly. This breaks insertion of 
> > properties with 'org-set-property'. 
> >
> > Fixing it involves quoting the the symbol as shown below:
> >
> >
> > (defmacro org-without-partial-completion (&rest body)
> >    `(let ((pc-mode (and (boundp 'partial-completion-mode)
> >                         'partial-completion-mode)))   ; <-- quote added
> >       (unwind-protect
> >           (progn
> >             (when pc-mode (funcall pc-mode -1))
> >             ,@body)
> >         (when pc-mode (funcall pc-mode 1)))))
> I've just reverted this modification, per Sebastian report.
> Can you be more precise about the problem it creates with
> org-set-property?
> Can you check if this version fixes the problems, if any?
> #+begin_src emacs-lisp
> (defmacro org-without-partial-completion (&rest body)
>   `(let ((pc-mode ,(and (boundp 'partial-completion-mode)
>                       'partial-completion-mode)))
>      (unwind-protect
>        (progn
>          (when pc-mode (funcall pc-mode -1))
>          ,@body)
>        (when pc-mode (funcall pc-mode 1)))))
> #+end_src emacs-lisp

No, I think this won't work. On compile time the byte compiler will
expand the macro and place the expansion in the byte compiled
lisp. Thus it will evaluate the ,(and ...) condition at compile time.


When a macro call appears in a Lisp program being compiled, the Lisp
compiler calls the macro definition just as the interpreter would, and
receives an expansion. But instead of evaluating this expansion, it
compiles the expansion as if it had appeared directly in the
program. As a result, the compiled code produces the value and side
effects intended for the macro, but executes at full compiled
speed. This would not work if the macro body computed the value and
side effects itself—they would be computed at compile time, which is
not useful.

What about this:

#+begin_src emacs-lisp
  (defmacro org-without-partial-completion (&rest body)
    `(let ((pc-mode-p (and (boundp 'partial-completion-mode)
                           (fboundp 'partial-completion-mode))))
       (when pc-mode-p
               (partial-completion-mode -1)
           (partial-completion-mode 1)))))

This will turn off partial-completion-mode if the symbol is non-nil
and callable.

For Sebastien's problem: Strange thing. Looks like the symbol
partial-completion-mode is non-nil but not callable. 

Maybe an Emacs 24 development version issue?

  -- David
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