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Re: Customizing the VC backend order

From: Vinicius Jose Latorre
Subject: Re: Customizing the VC backend order
Date: Fri, 10 Aug 2007 11:59:51 -0300
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.6) Gecko/20070802 SeaMonkey/1.1.4 
David Kastrup wrote:

[...]
Well, at least when you actually _read_ the line once.  So try the
following example.  Can you figure out what happens?

(setq xxx (copy-sequence vc-handled-backends))
(dotimes (i 3)
  (setq xxx (nconc '(Hg) (delq 'Hg xxx))))
xxx




Hummm, interesting, see:

;; 1 time
M-:
(progn
  (setq xxx (copy-sequence vc-handled-backends))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  xxx)
RET
==> (Hg RCS CVS SCCS Bzr Git Arch MCVS)


;; 2 times
M-:
(progn
  (setq xxx (copy-sequence vc-handled-backends))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  xxx)
RET
==> (Hg RCS CVS SCCS Bzr Git Arch MCVS)


;; 3 times
M-:
(progn
  (setq xxx (copy-sequence vc-handled-backends))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  (setq xxx (nconc '(Hg) (delq 'Hg xxx)))
  xxx)
RET
==> (Hg RCS CVS SCCS Bzr Git Arch MCVS)


;; dotimes
M-:
(progn
  (setq xxx (copy-sequence vc-handled-backends))
  (dotimes (i 3)
    (setq xxx (nconc '(Hg) (delq 'Hg xxx))))
  xxx)
RET
==> INFINITE LOOP!!!! ?
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