Re: [Scheme-reports] Formal Objection: Memoization is not possible in portable R7RS

[Alex Shinn <alexshinn@x>]

On Mon, Nov 26, 2012 at 9:53 AM, Per Bothner <per@x> wrote:

On 11/25/2012 04:07 PM, Mark H Weaver wrote:
> * Significant change: Fix the NaN problem by making sure that
>    two numbers can only be /substantially different/ if at
>    least one of them is numerically equal to itself.

IMO this does the wrong thing if you have two different NaN values,
as allowed by IEEE.  Neither is numerically equal to itself,
but they have different bit-patterns, and eqv? should compare
them as false.

The WG decided to make eqv? unspecified for NaNs

independently of the eqv? semantics.  Unless you are

doing so now, no member of the community has made

any objection to this decision.

We have no basis for re-opening the ticket regarding

NaNs, and changing it now would only break R5RS and

R6RS compatibility while alienating many members of

the community.  Even discussing it would likely take

valuable time away from the issue many people actually

are unhappy with, the (non-NaN) semantics of eqv?.

This is not to dismiss NaNs or say they are unimportant,

but that it is no longer useful to discuss the matter for

R7 small.  People who are interested in this should take

it up in future standards.

Regarding the general eqv? case, a private polling of the

WG members has so far shown that while every member

seems to want a re-vote, not a single member is interested

in changing his vote.  However, some members are flexible

about small variations within their broad semantics.  So I'm

going to re-open this ticket in a 9th ballot in the hopes that

we can at least get a same-bits variation that makes people

happier.

-- 

Alex

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