arithmetic issues Aubrey Jaffer (21 Oct 2005 14:53 UTC)
Re: arithmetic issues John.Cowan (21 Oct 2005 15:59 UTC)
Re: arithmetic issues bear (21 Oct 2005 16:39 UTC)
Re: arithmetic issues Aubrey Jaffer (22 Oct 2005 01:17 UTC)
Re: arithmetic issues Thomas Bushnell BSG (22 Oct 2005 01:22 UTC)
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Re: arithmetic issues Bradley Lucier (23 Oct 2005 19:46 UTC)
Re: arithmetic issues Aubrey Jaffer (23 Oct 2005 20:10 UTC)
Re: arithmetic issues Aubrey Jaffer (23 Oct 2005 19:54 UTC)
Re: arithmetic issues Jens Axel Søgaard (23 Oct 2005 20:01 UTC)
Re: arithmetic issues Aubrey Jaffer (23 Oct 2005 20:50 UTC)
Re: arithmetic issues Thomas Bushnell BSG (23 Oct 2005 21:12 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (23 Oct 2005 22:31 UTC)
Re: arithmetic issues Thomas Bushnell BSG (23 Oct 2005 22:33 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (23 Oct 2005 22:50 UTC)
Re: arithmetic issues Thomas Bushnell BSG (23 Oct 2005 22:57 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (24 Oct 2005 00:53 UTC)
Re: arithmetic issues Thomas Bushnell BSG (24 Oct 2005 01:05 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (24 Oct 2005 01:45 UTC)
Re: arithmetic issues Taylor Campbell (24 Oct 2005 02:00 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (24 Oct 2005 02:08 UTC)
Re: arithmetic issues Taylor Campbell (24 Oct 2005 02:14 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (24 Oct 2005 02:27 UTC)
Re: arithmetic issues Taylor Campbell (24 Oct 2005 02:45 UTC)
Re: arithmetic issues Alan Watson (24 Oct 2005 02:13 UTC)
Re: arithmetic issues Taylor Campbell (24 Oct 2005 02:22 UTC)
Re: arithmetic issues Alan Watson (24 Oct 2005 03:19 UTC)
Re: arithmetic issues Thomas Bushnell BSG (24 Oct 2005 02:01 UTC)
Re: arithmetic issues Aubrey Jaffer (24 Oct 2005 02:27 UTC)
Re: arithmetic issues Alan Watson (24 Oct 2005 03:14 UTC)
Re: arithmetic issues John.Cowan (24 Oct 2005 05:37 UTC)
Re: arithmetic issues Per Bothner (24 Oct 2005 07:05 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (24 Oct 2005 07:58 UTC)
Re: arithmetic issues Thomas Bushnell BSG (24 Oct 2005 08:05 UTC)
Re: arithmetic issues Alan Watson (24 Oct 2005 08:25 UTC)
reading NaNs Aubrey Jaffer (24 Oct 2005 15:35 UTC)
Re: reading NaNs Per Bothner (24 Oct 2005 17:35 UTC)
Re: reading NaNs bear (24 Oct 2005 19:23 UTC)
Re: reading NaNs Marcin 'Qrczak' Kowalczyk (24 Oct 2005 18:17 UTC)
Re: arithmetic issues bear (24 Oct 2005 06:13 UTC)
Re: arithmetic issues Taylor Campbell (24 Oct 2005 06:27 UTC)
Re: arithmetic issues Thomas Bushnell BSG (24 Oct 2005 07:49 UTC)
Re: arithmetic issues bear (24 Oct 2005 16:41 UTC)
Re: arithmetic issues Thomas Bushnell BSG (24 Oct 2005 07:49 UTC)
Re: arithmetic issues John.Cowan (22 Oct 2005 02:03 UTC)
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Re: +nan.0 problems bear (24 Oct 2005 06:04 UTC)
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Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (23 Oct 2005 20:24 UTC)
Re: arithmetic issues Thomas Bushnell BSG (23 Oct 2005 20:30 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (23 Oct 2005 22:25 UTC)
Re: arithmetic issues Thomas Bushnell BSG (23 Oct 2005 22:30 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (21 Oct 2005 17:15 UTC)
Re: arithmetic issues Taylor Campbell (21 Oct 2005 20:24 UTC)
Re: arithmetic issues Thomas Bushnell BSG (21 Oct 2005 20:32 UTC)
Re: arithmetic issues Alan Watson (22 Oct 2005 00:26 UTC)
Re: arithmetic issues Marcin 'Qrczak' Kowalczyk (22 Oct 2005 00:45 UTC)

reading NaNs Aubrey Jaffer 24 Oct 2005 15:35 UTC

 | Date: Mon, 24 Oct 2005 03:25:09 -0500
 | From: Alan Watson <xxxxxx@astrosmo.unam.mx>
 |
 | NaNs are atoms -- they have no context or stucture, just a single
 | value.

In an implementation which boxes flonums, NaNs aren't a single value;
EQ? and EQV? are *not* guaranteed to return #t given two NaNs.

 [Read-sytnax for singular objects is useful because it allows those
 objects to be put in CASE clauses.  But this works only for objects
 which match under EQV?.]

 | With the understandable exception of the eof object (and as has
 | been noted, this is exception is not universal), Lisps and Schemes
 | tranditionally provide read syntax for atoms.

Closures and continuations are atomic; R5RS provides no way to
deconstruct them.  Yet every implementation I have encountered has a
write syntax without a corresponding read syntax for them.

 | So, tradition suggests that we should have a read syntax for NaNs.

Are you suggesting a single NaN or multiple distinct NaNs?

To support existing IEEE-754 hardware, R6RS must not mandate multiple
distinct NaNs.  But specifying a singular NaN prevents implementations
from fully supporting IEEE-754 in the future.

Thus R6RS should declare that NaNs are numerical error-objects [or
condition-objects, whatever], and leave the rest to implementations.

We worked through this issue in SRFI-70.  I think SRFI-70's treatment
is Schemely, compatible with IEEE-754, and doesn't unnecessarily
constrain implementations:

  The notation 0/0 is used within this report to designate a numerical
  error-object.  A numerical function may return such an object when
  no other number (including real infinities) is the correct value.
  An implementation may report a violation of an implementation
  restriction in any calculation for which the result would be 0/0.