[mercury-users] Re: Fergus' hack

[Bart Demoen]

> While this might be a bit more clumsy than just having two different
> predicates, it may save considerable code duplication (and numerous
> maintenance problems).


Several times already, misterious powers have been ascribed to Fergus'
extra argument which indicates the mode of use of a predicate, or
reflects the logic rather than the direction of use as Peter Schachte
prefers; now we read: "save considerable code duplication".

Can anyone show me an example where one saves considerable code
duplication with the extra argument while this is not possible with
the "two different predicates" approach ?

Bart Demoen