> From: "Drew Adams" <[EMAIL PROTECTED]> > Date: Fri, 24 Jun 2005 13:26:23 -0700 > > I didn't say above that (/0.0 0.0) should give `arith-error'.
Well, you seemed to: you complained that it did so in previous versions. > I suggested > that perhaps `numberp' should return nil for a NaN argument, since "NaN" > means "not a number" and "numberp" means "a number". NaN is a floating-point > value, but is it a number? Any floating-point value is a ``number'' as far as `numberp' is concerned. The fact that NaN is a short for not-a-number does not mean that Lisp should treat it like that. > As for a way to test for a NaN, try this: > (= (/ 0.0 0.0) (/ 0.0 0.0)) > It should evaluate to nil, since a NaN is defined to fail _any_ > arithmetic comparison, even a comparison to itself. > > That doesn't tell me how to test if `foobar' is a NaN. Exactly the same: (= foobar foobar). (Did you try that?) > See my previous > email: I knew I could test `(equal foo 0.0e+Nan)', but I thought I would > need to test against all of the possible NaN values. No need: the arithmetic equality trick takes care of all of the possible values. Note that you should use `=', not `equal' (nor `eql', btw). > BTW, here is something I didn't expect: > > `M-: 0.0e+NaN' returns -0.0e+NaN > `M-: -0.0e+NaN' returns 0.0e+NaN > > The reader seems to flip the (irrelevant) sign. I think it's not the reader, but the underlying library's printf family. _______________________________________________ Emacs-devel mailing list Emacs-devel@gnu.org http://lists.gnu.org/mailman/listinfo/emacs-devel
