Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!cwjcc!gatech!hubcap!ncrcae!ece-csc!ncsuvx!mcnc!rti!xyzzy!biesack
From: biesack@xyzzy.UUCP (Dave Biesack)
Newsgroups: comp.emacs
Subject: call-interactively crashes emacs
Message-ID: <1456@xyzzy.UUCP>
Date: 12 Oct 88 19:59:22 GMT
Reply-To: biesack@dg-rtp.UUCP ()
Organization: Data General Corporation, Research Triangle Park, NC
Lines: 44

A couple weeks ago, John Sturdy (jcgs@harlqn.UUCP) posted some elisp for
doing completion based on a tags file. I tried it and it crashed my
emacs:

(emacs-version) GNU Emacs 18.51.2 of Tue Jun  7 1988 on godel (berkeley-unix)
(running under X11, but I doubt that matters)

I traced it down to the following expression:

      (call-interactively (symbol-function 'visit-tags-table)))

which causes emacs to crash when 
(symbol-function 'visit-tags-table) is '(autoload "tags" 184745 t nil)

The big question is: why does this crash emacs? Is this a bug? I can
understand this being an error because an autoload form is not really a
function, but the error should be caught.

The quick fix is to load tags first:
  (cond ((null tags-file-name)
	 (load-library "tags") ; this defines visit-tags-table
	 (call-interactively (symbol-function 'visit-tags-table))))

Another problem I encountered was an apparent byte-trashing due to
a DEL character in the posting. The copy I received contained a line
in the make-tags-name-list function:
      (while (search-forward "" (point-max) t)
Of course, the test always fails so the loop is void. The string
should really contain a DEL (^?, 0xff) character. Change this to:

      (while (search-forward del-string (point-max) t)

where del-string is defined:

(defconst del-string (char-to-string 127) "String containing DEL character")

After these fixes, things work well. Sorry they're not 'diff' format.

djb
-- 
		    David J. Biesack  (919) 248-5989
		Data General, Research Triangle Park, NC
	      {ihnp4, seismo, ...}!mcnc!rti!dg-rtp!biesack
			 biesack@dg-rtp.dg.com