[Gcl-devel] Re: printing IEEE 754 special values (inf, nan)

[Robert Dodier]

Hi Paul, thanks for your interest in this topic. You wrote:

> One property that is important: if *PRINT-READABLY* is true,
> then either NaN should print in a readable form (that is,
> in a form that, when read back in with the other reader/printer
> variables bound to the same values, produces a 'similar' value,
> similarity meaning = on numbers), or it should signal
> a PRINT-NOT-READABLE error.

Well, the hyperspec says (3.2.4.2.2) that two numbers are
similiar if they "represent the same mathematical value".
Since all NaN's act the same, it is plausible that this
means it's not necessary to distinguish one NaN from another.

That said, I'd be happy enough if a NaN were printed as
NaN or NAN or some such when *PRINT-READABLY* is false,
and NAN-XXXXXXXXXXXXXXX or something (with X's representing
hex digits here) when it's true.

For what it's worth,
Robert Dodier

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