Re: Dude where is my car ?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

On Sat, May 26 2012, Philippe M. Coatmeur wrote:

> Hi everyone ;
>
> I have this function that loops trough a list of lists of email
> elements to extract them. The list looks like this :
>
> (("<test@adamweb.net>" "Fri, 25 May 2012 23:49:58 +0200" "Re: plopz" "1648")
>  ("contact <plop@gmail.com>" "Fri, 25 May 2012 22:21:49 +0000" "tst" "1647"))
>
> (This is what you get if you C-h v with point over mail-bug-unseen-mails-one)
>
> (defun mail-bug-desktop-notify-one ()
>   (mapcar
>    (lambda (x)
>      (if (not (member x mail-bug-advertised-mails-one))
> 	 (progn
> 	   (mail-bug-desktop-notification
> 	    "Mew mail!"
> 	    (format "%s %s %s"           ;; Produces the values below
> 		    (car (nthcdr 1 x))   ;; Fri, 25 May 2012 23:49:58 +0200
> 		    (car (nthcdr 2 x))   ;; Re: plopz
> 		    (car (nthcdr 3 x)))  ;; 1648
> 	    "500000" mail-bug-new-mail-icon-one)
> 	   (add-to-list 'mail-bug-advertised-mails-one x))))
>    mail-bug-unseen-mails-one))
>
> And this works fine, so it follows that (car (car x)) is the first
> element of each atomic list, right ? but when I try to extract it
> emacs (24.1.50 cvs) insults me!? I spent more than a good hour trying
> to figure this out
>
> (format "%s %s %s"
>  (car (car x))        ;; Should produce <test@adamweb.net>
>  (car (nthcdr 2 x))   ;; Re: encor un autre
>  (car (nthcdr 3 x)))  ;; 1643
>
> error in process sentinel: format: Wrong type argument: listp, "<test@adamweb.net>"
> error in process sentinel: Wrong type argument: listp, "<test@adamweb.net>"

Since x equals ("<test@adamweb.net>" "Fri, 25 May 2012 23:49:58 +0200"
"Re: plopz" "1648") in your second example, the car of that is
"<test@adamweb.net>", and you can't take the car of that again, because
it fails to pass the listp test. I think where you're going wrong is
that nthcdr returns a list, so you can car it. Car itself returns an
atom, so you can't.

Have I got that right?

Also, the whole thing might be easier to read/debug if you use "first"
"second" "third" "fourth" to extract the list elements. Or, if that
seems too unscientific, then "nth", that also pulls a single element out
of a list.

Eric

-- 
GNU Emacs 24.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.24.10)
 of 2012-05-25 on pellet