[m-dev.] diff: rat - rational numbers module.

[Thomas Charles CONWAY]

Fergus Henderson, you write:
> Also you don't really need to explicitly check for Gcd0 = 0,
> because `//' will, on almost all current hardware, raise a runtime
> exception.
> 

However, if you call error instead, you get told where the /0 occured
(at the cost of the test - I guess it's an efficiency/ease-of-debugging
trade-off).

-- 
Thomas Conway    || conway at cs.mu.oz.au
AD DEUM ET VINUM || Nail here [] for new monitor.