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From: Kai.Grossjohann@CS.Uni-Dortmund.DE (Kai =?iso-8859-1?q?Gro=DFjoha?=  =?iso-8859-1?q?nn?=)
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Subject: Re: (concat "/dir/name/" "foo") --> (expand-file-name "foo" "/dir/name/")
Date: 22 Oct 2000 20:51:04 +0200
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I have tried hard to come up with a reason why expand-file-name could
fail to be idempotent, but I can't come up with a reason.  The only
possibility I can come up with is that file name expansion might be a
multi-step operation, and expand-file-name might only make one of
those steps.  But I think that expand-file-name should be doing all of
the steps right at the first call.

But I agree that functions which expect file names might need to
document whether or not expand-file-name is called on those file
names.  OTOH, it's just an efficiency issue if expand-file-name is
idempotent.

But in any case, using concat to create a file name from a directory
and a relative path name is not a good thing, I think.

kai
-- 
I like BOTH kinds of music.