On 2003-07-07 at 12:01+0200 Jerzy Karczmarczuk wrote:
Jon Fairbairn comments //Steffen Mazanek//:
Prelude> 0.1::Rational 13421773 % 134217728 Prelude> 13421773/134217728 0.1
I do not know how this fraction is calculated, but it does not fit my expectations :-)
Remember that internally arithmetic is binary, and that 0.1 can't be expressed exactly as a floating point number. I think that's the explanation.
I don't understand the remark that the internal arithmetic is binary. Sure, it is, so what?
My comment was perhaps too brief. As far as I am concerned, a constant with a decimal point in it should go like this: CCCCC.DD...DD \__d__/ becomes fromRational (CCCCCDD...DD % 100...00) and there's no problem in getting an accurate Rational (what you say about conversions applies if the desired result is some kind of float). However, if the conversion goes via float, and I think doing that is a bug, the fact that 1/5 has an infinite expansion in binary explains the peculiar numbers that Hugs produces in its Rational. It's an explanation of what happens, not what should be! During the revision of the report I said something to the effect that Int, Float and Double do not belong in the language proper. The suggestion was rejected for (I think) sociological reasons, but I still stand by it. While they should of course be provided in the standard libraries, they only serve to confuse things as far as the language design is concerned. Jón -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk 31 Chalmers Road jf@cl.cam.ac.uk Cambridge CB1 3SZ +44 1223 570179 (after 14:00 only, please!)