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Re: [Scheme-reports] multiple NaN values
| 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?.
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