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Re: Need help with macros


From: Cecil Westerhof
Subject: Re: Need help with macros
Date: Wed, 06 Jan 2010 20:25:13 +0100
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.3 (gnu/linux)

address@hidden (Pascal J. Bourguignon) writes:

>> I am trying to make some useful functionality for Gnus. I think that I
>> should use a macro for that. I made the following macro (the two message
>> statements are just for debugging):
>>     (defmacro gnus-group-jump-bind (key-binding group-to-jump-to)
>>       (message "#%s#%s#" key-binding      (type-of key-binding))
>
> I would avoid using the character # in lisp output, since it is
> meaningful (readable).
>
> (let ((print-circle t))
>   (let* ((a "hello")
>          (b (list a a)))
>     (print b)))
> prints:
> (#1="hello" #1#)
>
> (read-from-string "(#1=\"hello\" #1#)")
> --> ((#1="hello" #1#) . 16)

I do not really understand what happens here -but I am a newbie with
lisp, so that is not that strange-, but I will not use the '#' anymore.


> In a preceding message, I used "%S" instead.  You should try it!

I find the '#' termination more clear, but I can get used to this.
Better safe as sorry.


>>       (message "#%s#%s#" group-to-jump-to (type-of group-to-jump-to))
>>       (define-key gnus-group-mode-map key-binding
>>         (lambda ()
>>           (interactive)
>>           (gnus-group-jump-to-group group-to-jump-to))))
>
> gnus-group-jump-bind has no need to be a macro.  As a macro it is
> wrong.  Use defun!

I could not get the defun working, that is why I thought it had to be
done with a macro. The macro first also did not work. The macro works
now. I'll rewrite the macro to a defun.

I do have a lot of questions. I am glad that you and others are so
helpful. ;-)

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof


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