+1 from me. I'd happy hack up 'nats/semigroups' to use a standard version if it was available.

On Tue, Nov 11, 2014 at 8:51 AM, Herbert Valerio Riedel <hvr@gnu.org> wrote:

On 2014-11-11 at 14:32:47 +0100, Richard Eisenberg wrote:
> What would the semantics of subtraction be for this? I'm assuming
> there would be a `Num` instance for `Natural`.

It wouldn't be total, and 'throw (Underflow :: ArithException)' if the
result would fall outside the non-negative domain.

This is similiar to how e.g.

 http://hackage.haskell.org/package/nats-0.2/docs/Numeric-Natural.html

handles out-of-domain subtraction results.

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