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Re: How to exclude a major mode from a hook

From: Nicolas Richard
Subject: Re: How to exclude a major mode from a hook
Date: Wed, 11 Feb 2015 11:15:01 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.0.50 (gnu/linux)


Cecil Westerhof <address@hidden> writes:
> I had the following in my .emacs:
>     (add-hook 'before-save-hook 'delete-trailing-whitespace)

IMO this is not the right thing to do, because one day you'll want to
edit a file in which trailing white spaces are important and you'll
wonder why it's all screwed up.

I would suggest to use a function that checks for trailing whitespaces
(with exceptions, such as the signature delimiter in message-mode) and
(interactievly) prompts if there is something to fix. I don't know if
such a function exists.

> So I rewrote it to:
>     (add-hook 'before-save-hook (lambda () (when (not (string= major-mode 
> "message-mode"))
>                                              'delete-trailing-whitespace)))

The condition
    (string= major-mode "message-mode")
can be written as
    (eq major-mode 'message-mode)
and would be better written as
    (derived-mode-p 'message-mode)


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