Re: [Scheme-reports] multiple NaN values

[Per Bothner <per@x>]

On 02/20/2012 09:12 AM, Aubrey Jaffer wrote:
>   | Date: Mon, 20 Feb 2012 01:07:09 -0800
>   | From: Per Bothner<per@x>
>   |
>   | IEEE allows multiple NaN values.  They're unlikely to matter for
>   | Scheme implementations or code, but I think a note is in order.
>   |
>   | I suggest something like the following:
>   |
>   | IEEE 754 specifies multiple NaN values.  A Scheme implementation
>   | may collapse all NaN values to a single "representative NaN", or
>   | there may be multiple NaN values.  In the latter case, the +nan.0
>   | is the "canonical NaN" value.  Scheme functions in general must
>   | treat all NaN values as equivalent. This specifically includes the
>   | nan? functions, which must be true for all NaN values.  The only
>   | standard Scheme function which can distingish different NaN values
>   | is eqv?, though it is also permitted to treat all NaN values as
>   | eqv?
>
> EQ? is allowed to distinguish different NaN values.  It is better to
> let EQ? make this distinction than EQV?.

EQ? can distinguish the "same" values as being different:
    (eq? 2.0 2.0) => unspecified.
Thus it is uninteresting in this context.
-- 
	--Per Bothner
per@x   http://per.bothner.com/

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