[m-rev.] diff: mention NaN issues in BUGS file

[Fergus Henderson]

Estimated hours taken: 0.25
Branches: main, release

BUGS:
	Mention the issues with NaN reported by Peter Moulder.

Workspace: /home/mars/fjh/ws1/mercury
Index: BUGS
===================================================================
RCS file: /home/mercury1/repository/mercury/BUGS,v
retrieving revision 1.15
diff -u -d -r1.15 BUGS
--- BUGS	14 Oct 2002 07:07:57 -0000	1.15
+++ BUGS	22 Nov 2002 19:10:37 -0000
@@ -86,6 +86,22 @@
 	io__write_string("\n").
 
 -----------------------------------------------------------------------------
+Subject: NaN behaviour
+Date: Mon, 21 Oct 2002 21:02:00 +1000
+
+The mercury standard library tends to avoid producing NaN (e.g. throwing
+an exception in many places where libc would return NaN), but it's still
+possible from arithmetic functions (e.g. 0.0*Inf, Inf - Inf, Inf + -Inf,
+Inf / Inf), sin,cos,tan when passed infinity, and perhaps other things (I
+haven't done a full search).  Presumably it can also arise from using the
+foreign language interface.
+
+When NaN does arise, we have a problem that `=' (and unification) aren't
+reflexive.  From a logical point of view, this is a fairly serious problem.
+
+A lesser problem is that `<' doesn't induce a total order on floats.
+
+-----------------------------------------------------------------------------
 Subject: nit in error msg
 Date: Thu, 16 May 1996 10:25:42 +1000 (EST)
 

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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