It would take a compelling argument to make me accept that "Yes, I shouldn't do that", but I don't assume that such a compelling argument doesn't exist.

Probably not what you want to hear, but IMO Math modules should treat NaN in accordance with the following paragraphs:

Floating point operations other than comparisons normally propagate a quiet NaN (qNaN). Floating point operations on a signaling NaN (sNaN) signal an invalid operation exception, the default exception action is then the same as for qNaN operands and they produce a qNaN if producing a floating point result.

A comparison with a NaN always returns an unordered result even when comparing with itself. The comparison predicates are either signaling or non-signaling, the signaling versions signal an invalid exception for such comparisons. The equality and inequality predicates are non-signaling so x = x returning false can be used to test if x is a quiet NaN. The other standard comparison predicates all signal if they receive a NaN operand, the standard also provides non-signaling versions of these other predicates. The predicate isNaN(x) determines if a value is a NaN and never signals an exception.

Which I interprete to mean that: given one or more NaN values to compare, equality operators should return false if they are of the non-signalling variety and raise an exception if the are signalling.

As (TTBOMK), there is no concept of non-signalling/signalling NaNs anywhere else in Perl, I think there are 3 possibilities for Math modules:

  1. Opt to implement non-signalling NaNs.

    Any equality operator involving a NaN value, and any other value including NaN, +/-inf or an numeric value returns false.

    To allow the programmer to detect when they are dealing with NaN value, you either a) provide an isNaN( $x ) function; or b) allow the (somewhat bemusing) suggestion above of using die "We got a NaN\n" unless $x == $x;

  2. Opt to implement signalling NaNs.

    Any operation involving (being passed, rather than resulting in) a NaN value raises an exception.

    This at least forces the programmer to deal with the possibility.

  3. Make it configurable.

    Offer both modes of operation and let the programmer choose.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^3: NaNs are true by BrowserUk
in thread NaNs are true by syphilis

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