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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.lang.lisp,comp.lang.scheme,comp.lang.smalltalk,comp.object
Subject: Re: IEEE FP NaNs = everything else?
Message-ID: <34725@news.Think.COM>
Date: 16 Mar 90 05:41:07 GMT
References: <1990Mar15.211150.19338@Neon.Stanford.EDU>
Sender: news@Think.COM
Reply-To: barmar@nugodot.think.com.UUCP (Barry Margolin)
Followup-To: comp.lang.lisp
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 19

In article <1990Mar15.211150.19338@Neon.Stanford.EDU> max@Neon.Stanford.EDU (Max Hailperin) writes:
>Has anyone explored the possibility of useing IEEE floating-point as a
>general representation in a manifestly-typed language, with everything
>other than flonums being NaNs (Not-A-Numbers)?

The IEEE rule is that any arithmetic involving NaNs must result in a NaN.
But if fixnums are implemented as NaNs then this means that (+ 3.0 1) must
evaluate to a NaN rather than 4.0, since this would be (+ 3.0 NaN).

Perhaps, instead of using NaNs for all non-fixnums you should use NaNs for
all non-numbers (NaN *does* stand for Not a Number, so this makes sense).
You could then use signalling NaNs, which would cause ordinary IEEE FP
hardware to trap on things like (+ 3.0 'a).

--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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