On Mon, Jul 07, 2003 at 12:01:09PM +0200, Jerzy Karczmarczuk wrote:
This is less a bug than a Nessie monster which haunts Hugs some centuries already, and on Internet the issue has been discussed at least 4 times. The old, experimental Gofer Prelude numeric functions were sometimes abominable, since Mark Jones concentrated on other things, and nobody really complained, people were busy with other stuff as well.
But I can't understand why this continues until now. The obvious technique to convert floats to rationals is the continued fraction expansion which gives the simplified answer fast.
That would be because resources for Hugs maintenance are extremely limited, and expertise in numerical methods even more lacking. (e.g.: which approximant in the series should be chosen?) I think that if someone who knows about these things submitted a patch, and it didn't increase the size of the Prelude (by much), it would be gratefully accepted. (That's probably true of all of Hugs.) However, as far as I know, the outstanding numeric bugs in the Prelude are - floating point literals of type Ratio t (mostly fixed in CVS), and - the show instances for Float and Double (because the correct Numeric.showFloat would make the Prelude too large)
I don't understand the remark that the internal arithmetic is binary. Sure, it is, so what?
In the case of 0.1::Rational, it shouldn't be using floating point. The Report says this means fromRational (1%10), i.e. 1%10. If Hugs implemented the Haskell definition directly, the question of approximation wouldn't arise. GHC does it that way, and usually removes the fromRational at compile time, but Hugs isn't that clever.