Re: Typo in 'org-without-partial-completion'

[David Maus <dmaus@ictsoc.de>]

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At Thu, 30 Jun 2011 21:28:08 +0200,
David Maus wrote:
> 
> At Thu, 30 Jun 2011 11:12:15 +0200,
> Bastien wrote:
> > 
> > Hi Paul,
> > 
> > Paul Sexton <psexton@xnet.co.nz> 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.
> 
> http://www.gnu.org/software/emacs/elisp/html_node/Compiling-Macros.html#Compiling-Macros
> 
> #+begin_quote
> 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.
> #+end_quote
> 
> 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
>          (unwind-protect
>              (progn
>                (partial-completion-mode -1)
>                ,@body)
>            (partial-completion-mode 1)))))
> #+end_src
> 
> This will turn off partial-completion-mode if the symbol is non-nil
> and callable.


Or even better:

#+begin_src emacs-lisp
  (defmacro org-without-partial-completion (&rest body)
    `(when (and (boundp 'partial-completion-mode)
                (fboundp 'partial-completion-mode))
       (unwind-protect
           (progn
             (partial-completion-mode -1)
             ,@body)
         (partial-completion-mode 1))))
#+end_src

This avoids leaking if 'body happens to uses a symbol 'pc-mode-p in a
different context.

Best,
  -- David
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