FWIW, about a year ago I submitted rational module.  Here are the links:

source:  https://github.com/Arlen/phobos/blob/units/std/rational.d
docs:  http://arlen.github.com/phobos/std_rational.html
discussion:
http://forum.dlang.org/thread/mailman.579.1349545483.5162.digitalmars-d@puremagic.com

I think we discussed the issue of BigInt and BigFloat.  Personally, I'm not a big fan of BigInt, and rational supporting it.

Anyway, I hope you find it useful.

Arlen


On Wed, Sep 25, 2013 at 11:57 AM, H. S. Teoh <hsteoh@quickfur.ath.cx> wrote:

> Does anybody happen to have a working rational number library in D? Any plans to add that to Phobos at some point?
>
> Just wondering, because I'm working on some numerical code that would benefit from a custom number type that could be implemented in terms of rational numbers. I just don't feel like reinventing a rational library if one already exists. :)
>
>
> T
>
> --
> GEEK = Gatherer of Extremely Enlightening Knowledge
>

On 05/10/13 10:12, Arlen wrote:
> I think we discussed the issue of BigInt and BigFloat.  Personally, I'm not a
> big fan of BigInt, and rational supporting it.

Can you explain your reasoning here?  A rational type should support arbitrary-precision integers, even if you don't like std.bigint.BigInt.