I thought hard before making this post, because I hate allowing material non-public information to affect a standards process, and especially when the information is about intentions rather than present facts -- life is short, and we all change our minds.
But I have been told by one Scheme implementer that he plans to add a second, non-floating-point, type of inexact numbers to his Scheme. Insofar as I understand the mathematics of them -- which is only slightly more than not at all -- there will be no negative zero or NaN(s), and perhaps no infinities either. But there will (I think) be more than one possible representation of a given number. For this sort of non-IEEE exact number, = is the Right Thing for `eqv?`. There are no special cases of numbers that should be distinguished even though they are not mathematically equal. However, there is (I think) more than one representation for a given mathematical number, so a "same-bits" standard will not work either: it will create unpredictable fluctuations in the use of `eqv?`, such that in principle (eqv? (+ 1.0 3.0) (+ 2.0 2.0)) might be #f, because the representation of a number depends on how it is computed. So there it is; make of it what you will. (The implementer is reading this, though not in advance; I would urge him not to reveal himself, as I think it will cause more difficulties for the WG than it solves.) -- Is a chair finely made tragic or comic? Is the John Cowan portrait of Mona Lisa good if I desire to see [email protected] it? Is the bust of Sir Philip Crampton lyrical, http://ccil.org/~cowan epical or dramatic? If a man hacking in fury at a block of wood make there an image of a cow, is that image a work of art? If not, why not? --Stephen Dedalus _______________________________________________ Scheme-reports mailing list [email protected] http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
