On 2013-09-21, at 4:46 AM, Stijn van Drongelen <rhymoid@gmail.com> wrote:

I do have to agree with Damodar Kulkarni that different laws imply different classes. However, this will break **a lot** of existing software.

You could argue that the existing software is already broken.

If we would do this, only Eq and Ord need to be duplicated, as they cause most of the problems. Qualified imports should suffice to differentiate between the two.

import qualified Data.Eq.Approximate as A
import qualified Data.Ord.Approximate as A

main = print $ 3.16227766016837956 A.== 3.16227766016837955

As soon as you start doing computations with fp numbers things get much worse. Something like Edward Kmett's Numeric.Interval package would likely be helpful, a start at least (and the comments in the Numeric.Interval documentation are amusing) In the distant past when I was worried about maintaining accuracy in a solids modeller we went with an interval arithmetic library that we *carefully* implemented. It worked. Unpleasant in C, but it worked. And this link might be interesting:

http://lambda-the-ultimate.org/node/1301

Cheers,

Bob