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Re: add-hook versus custom-set-variables

From: Bill Wohler
Subject: Re: add-hook versus custom-set-variables
Date: Thu, 29 Dec 2005 02:05:35 -0800

Stefan Monnier <address@hidden> wrote:

> >>> Two workarounds which aren't pretty are to insist that the user add a
> >>> defvar in .emacs for any hook he customizes
> >> 
> >> I don't understand what you're suggesting here.
> >> How could a defvar in .emacs help?
> > Please read Luc's article where he describes the technique and why.
> >   http://article.gmane.org/gmane.emacs.pretest.bugs/9993
> Oh, I see.  It's not specific to defvar: setq works just as well.
> >>> ;; MH-E hooks
> >>> (eval-after-load 'mh-customize
> >>> (progn
> >>> (message "Adding mailcrypt hooks to MH-E...")
> >>> (add-hook 'mh-folder-mode-hook 'mc-install-read-mode)
> >>> (add-hook 'mh-letter-mode-hook 'mc-install-write-mode)))
> >> 
> >> eval-after-load is a function, not a macro.  I know it's counter
> >> intuitive.
> > I don't know enough about the internals to know why this would be
> > counter-intuitive. I read your answer as: macros do what you expect,
> > functions don't. Please elaborate if this is not what you mean. Why
> > doesn't eval-after-load do what I expect?
> The evaluation of a form (A B C) can follow the following two paths:
> - if it's a macro:
>    (eval (macrocall A B C))
> - if it's a function
>    (funcall A (eval B) (eval C))
> Note how the function cannot delay the evaluation of its arguments.

Thanks for the explanation. There's a lot of strange things in
elisp--mostly around compilation and evaluation--that I don't understand
and every little bit helps. Maybe another reading of these sections in
the elisp manual will make more sense now.

In any event, I think I get it now. To keep eval-after-load from being
completely useless, the idiom is to quote the form. Right?

This works:

 (eval-after-load "mh-e"
     (add-hook 'mh-folder-mode-hook 'mc-install-read-mode)
     (add-hook 'mh-letter-mode-hook 'mc-install-write-mode)))


While coming up with a recipe to prove that the semantics had changed
between Emacs 21 and 22, I discovered I was inadvertently performing my
"site-init" *after* I ran custom-set-variables. (Recall that I'm
simulating the Debian site-init from my .emacs while using CVS Emacs.)
Normally, site-init is performed *before* one's .emacs is loaded. After
moving the site-init to the top of my .emacs file, I regained Emacs 21
semantics and all is well.

Sorry about the false alarm; at least I learned a few things.

Bill Wohler <address@hidden>  http://www.newt.com/wohler/  GnuPG ID:610BD9AD
Maintainer of comp.mail.mh FAQ and MH-E. Vote Libertarian!
If you're passed on the right, you're in the wrong lane.

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