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*To*: Aubrey Jaffer <agj@xxxxxxxxxxxx>*Subject*: Re: reading NaNs*From*: Alan Watson <a.watson@xxxxxxxxxxxxxxxx>*Date*: Sat, 29 Oct 2005 14:21:38 -0700*Cc*: tb@xxxxxxxxxx, srfi-77@xxxxxxxxxxxxxxxxx*Delivered-to*: srfi-77@xxxxxxxxxxxxxxxxx*In-reply-to*: <20051029191005.043221B77BD@xxxxxxxxxxxxxxxxxxxxx>*Organization*: Centro de Radioastronomía y Astrofísica UNAM*References*: <20051021145326.816C11B77BB@xxxxxxxxxxxxxxxxxxxxx> <20051023181854.4E7DD1B77BB@xxxxxxxxxxxxxxxxxxxxx> <871x2cowe8.fsf@xxxxxxxxxxxxxxxxx> <20051023195403.A50AF1B77BB@xxxxxxxxxxxxxxxxxxxxx> <435BEC21.60509@xxxxxxxxxxxx> <20051023205012.BFD241B77BB@xxxxxxxxxxxxxxxxxxxxx> <87zmoz27dg.fsf@xxxxxxxxxxxxx> <87hdb7kgmk.fsf@xxxxxxxxxxxxxxxxx> <87k6g3zw34.fsf@xxxxxxxxxxxxx> <871x2bkfj7.fsf@xxxxxxxxxxxxxxxxx> <8764rnu45b.fsf@xxxxxxxxxxxxx> <87br1fiv26.fsf@xxxxxxxxxxxxxxxxx> <87ll0jpu0q.fsf@xxxxxxxxxxxxx> <20051024022744.6CA581B77BB@xxxxxxxxxxxxxxxxxxxxx> <87veznbb37.fsf@xxxxxxxxxxxxx> <8764rnbaqr.fsf@xxxxxxxxxxxxxxxxx> <435C9A65.7060106@xxxxxxxxxxxxxxxx> <20051024153539.D98031B77BB@xxxxxxxxxxxxxxxxxxxxx> <435D49E3.2010001 @astrosmo.unam.mx> <20051025224529.2760C1B77BB@xxxxxxxxxxxxxxxxxxxxx> <435EBC32.801020 3@xxxxxxxxxxxxxxxx> <20051027164540.2B79C1B77BB@xxxxxxxxxxxxxxxxxxxxx> <436131C2.8070 003@xxxxxxxxxxxxxxxx> <20051029191005.043221B77BD@xxxxxxxxxxxxxxxxxxxxx>*User-agent*: Mozilla Thunderbird 1.0 (X11/20050317)

Aubrey Jaffer wrote:

I think there is a practical problem with "designer-NaNs" in that, unlike all other IEEE-754 number objects, they cannot be constructed by IEEE-754 floating-point operations alone.

Yes, you have to twiddle bits, but that isn't difficult.

IEEE-754:1985 section 6.2: ... Quiet NaNs should, by means left to the implementor's discretion, afford retrospective diagnostic information inherited from invalid or unavailable data and results.

Notice that using NaNs for unavailable data is explicitly mentioned.

| That's a valid opinion, but I do not share it. I use them quite | usefully to flag possible and planned-for events for which there is | no other good answer. Such reasonable disagreement is why R6RS should *not* specify a read or write syntax for NaNs. Implementations should be free to have read/write syntax for NaNs or not.

Can you give me a real example that satisfies these constraints? Regards, Alan -- Dr Alan Watson Centro de Radioastronomía y Astrofísica Universidad Astronómico Nacional de México

**Follow-Ups**:**Re: reading NaNs***From:*Aubrey Jaffer

**References**:**arithmetic issues***From:*Aubrey Jaffer

**Re: arithmetic issues***From:*Aubrey Jaffer

**Re: arithmetic issues***From:*Thomas Bushnell BSG

**Re: arithmetic issues***From:*Aubrey Jaffer

**Re: arithmetic issues***From:*Jens Axel Søgaard

**Re: arithmetic issues***From:*Aubrey Jaffer

**Re: arithmetic issues***From:*Marcin 'Qrczak' Kowalczyk

**Re: arithmetic issues***From:*Thomas Bushnell BSG

**Re: arithmetic issues***From:*Marcin 'Qrczak' Kowalczyk

**Re: arithmetic issues***From:*Thomas Bushnell BSG

**Re: arithmetic issues***From:*Marcin 'Qrczak' Kowalczyk

**Re: arithmetic issues***From:*Thomas Bushnell BSG

**Re: arithmetic issues***From:*Marcin 'Qrczak' Kowalczyk

**Re: arithmetic issues***From:*Aubrey Jaffer

**Re: arithmetic issues***From:*Marcin 'Qrczak' Kowalczyk

**Re: arithmetic issues***From:*Thomas Bushnell BSG

**Re: arithmetic issues***From:*Alan Watson

**reading NaNs***From:*Aubrey Jaffer

**Re: reading NaNs***From:*Aubrey Jaffer

**Re: reading NaNs***From:*Aubrey Jaffer

**Re: reading NaNs***From:*Aubrey Jaffer

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