# infinite (fractional) precision

**Ashley Yakeley
**
ashley@semantic.org

*Thu, 10 Oct 2002 02:25:59 -0700*

At 2002-10-10 01:29, Ketil Z. Malde wrote:
>*I realize it's probably far from trivial, e.g. comparing two equal
*>*numbers could easily not terminate, and memory exhaustion would
*>*probably arise in many other cases.
*
I considered doing something very like this for real (computable)
numbers, but because I couldn't properly make the type an instance of Eq,
I left it. Actually it was worse than that. Suppose I'm adding two
numbers, both of which are actually 1, but I don't know that:
1.000000000.... +
0.999999999....
The trouble is, as far as I know with a finite number of digits, the
answer might be
1.9999999999937425
or it might be
2.0000000000013565
...so I can't actually generate any digits at all. So I can't even make
the type an instance of my Additive class. Not very useful...
--
Ashley Yakeley, Seattle WA