Larry Wall wrote:
Another note, it's likely that numeric literals such as 1.23 will turn
into Rats rather than Nums, at least up to some precision that is
pragmatically determined.
Doing these as Rat would avoid a lot of the precision issues that floating point arithmetic has all the time. It will actually work perfectly well with addition, because the denominator is always a small power of 10, so that is true for the sum as well. Multiplying might be an issue, because the denominator becomes a large power of 10, but I think that that can be handled pretty well, unless the multiplication is really performed
to an extent that the result uses significant amounts of memory.
But as soon as division is occuring, these rational numbers tend to develop denominators that are not powers of 10 any more. Combining this with some multiplications and additions this may result in huge numerators and denominators that are somewhat expensive to handle.

So what would happen after such a long calculation:

- would the Rats somehow know that they are all derived from Rats that were just used instead of floats because of being within a pragmatically determined precision? Then the result of * or / could just as pragmatically become a floating point number? - would the Rats grow really huge numerators and denominators, making it expensive to work with them? - would the first division have to deal with the conversion from Rat to floating point? - or should there be a new numeric type similar to Rat that is always having powers of 10 as denominator (like BigDecimal in Java or LongDecimal for Ruby or decimal in C# or so)? Even in this last case the division is not really easy to define, because the exact result cannot generelly be expressed with a denomonator that is a power of 10.
This can be resolved by:
- requires additional rounding information (so writing something like a.divide(b, 10, ROUND_UP) or so instead of a/b - implicitely find the number of significant digits by using partial derivatives of f(x,y)=x/y
- express the result as some kind of rational number
- express the result as some kind of floating point number.



Reply via email to