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From: Richard Stallman <rms@gnu.org>
Newsgroups: gmane.emacs.devel
Subject: Re: Missing `with' macro?
Date: Mon, 24 Jul 2006 23:09:11 -0400
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    (defmacro with-file (file &rest body)
      "Run BODY in a buffer visiting FILE.
    If the buffer was not open before calling this macro, it's killed
    afterwards."
      (let ((file-sym (make-symbol "file"))
	    (existsp-sym (make-symbol "existsp"))
	    (buf-sym (make-symbol "buf")))
	`(let* ((,file-sym ,file)
		(,existsp-sym (get-file-buffer ,file-sym))
		(,buf-sym (find-file-noselect ,file-sym)))

Using find-file-noselect could be the right thing in some cases,
but there are many cases (especially where you just read the file
or scan it quickly) where that is much too heavy.