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Re: Defadvice use
From: |
Barry Margolin |
Subject: |
Re: Defadvice use |
Date: |
Tue, 19 Apr 2005 01:07:49 -0400 |
User-agent: |
MT-NewsWatcher/3.4 (PPC Mac OS X) |
In article <1113869741.838603.250620@o13g2000cwo.googlegroups.com>,
"rgb" <rbielaws@i1.net> wrote:
> Stefan Monnier wrote:
> > > Doesn't (let (bookmark-bmenu-other-window) ...) have limited life.
> >
> > (let (bookmark-bmenu-other-window) ...)
> >
> > only affects the bookmark-bmenu-other-window *variable*, not the
> > bookmark-bmenu-other-window function.
> >
>
> If that isn't a bug waiting to happen I don't know what is.
> You appear to be asserting that it's documented to work that
> way but I'd counter with 2 arguments.
>
> 1. The `feature' is only _implied_, not documented. There is
> no mention in any Elisp manual section that covers plists
> or symbol function cells about this behavior.
The Elisp manual specifically says that 'let' binds variables. That's
all it does. Does it have to explicitly say all the things it *doesn't*
do, like binding functions and property lists? Function and variable
bindings of symbols are totally independent.
If you want to bind a function, you can (require 'cl) and then use
'flet'.
>
> 2. The `feature' invalidates much of the documented behavior of
> symbols unless you know how the symbol was created.
>
> Look at this:
>
> (defun test1 ()
> (let (a01)
> (put 'a01 'hold "this")
> (symbol-plist 'a01)))
>
> (put 'a01 'hold "that") ; insure symbol already exists
> (symbol-plist 'a01)
> => (hold "that") ; value is there as expected
>
> (test1)
> => (hold "this")
>
> (symbol-plist 'a01)
> => (hold "this") ; external value unexpectedly changed
>
> (unintern "a01") ; insure it doesn't exist
> (symbol-plist 'a01)
> => nil ; no error.
>
> (test1)
> => (hold "this")
>
> (symbol-plist 'a01) ; Given the external value should change
> => nil ; it now unexpectedly doesn't
You're looking at the plist of a different symbol. test1 is still
referencing the symbol that you uninterned. When you then type 'a01
later, you intern a new symbol, which is not the one whose plist is
modified when you call test1.
> It's obviously impossible to easily create any function or
> macro that manipulates function or property cells unless you
> can guarantee none of the symbols are ever created by let.
>
> Since it appears to be by design, I'd be terribly curious to
> see any archive of discussions concerning why this is
> appropriate behavior.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
- Re: Mis-features of let, (continued)
- Re: Mis-features of let, rgb, 2005/04/19
- Re: Mis-features of let, Kevin Rodgers, 2005/04/19
- Re: Mis-features of let, David Kastrup, 2005/04/19
- Re: Mis-features of let, rgb, 2005/04/19
- Re: Mis-features of let, David Kastrup, 2005/04/20
- Re: Mis-features of let, Stefan Monnier, 2005/04/20
- Re: Mis-features of let, Thien-Thi Nguyen, 2005/04/20
- Re: Mis-features of let, Thien-Thi Nguyen, 2005/04/19
- Re: Defadvice use,
Barry Margolin <=
Re: Defadvice use, Stefan Monnier, 2005/04/18
Re: Defadvice use, Kevin Rodgers, 2005/04/18